General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.

Users may download and print one copy of any publication from the public portal for the purpose of private study or research.

You may not further distribute the material or use it for any profit-making activity or commercial gain

You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Downloaded from orbit.dtu.dk on: Nov 13, 2020

Novel biomimetic membrane technologies for the application in water treatment andenergy production

Schneider, Carina

Publication date:2019

Document VersionPublisher's PDF, also known as Version of record

Link back to DTU Orbit

Citation (APA):Schneider, C. (2019). Novel biomimetic membrane technologies for the application in water treatment andenergy production. Technical University of Denmark.

Novel biomimetic membrane technologies for the application in water treatment and energy production

Carina Schneider

Phd thesis

2019

i

Novel biomimetic membrane technologies

for the application in water treatment and

energy production

Carina Schneider

PhD Thesis

May 2019

DTU Environment

Department of Environmental Engineering

Technical University of Denmark

ii

Novel biomimetic membrane technologies for the application in water

treatment and energy production

Carina Schneider

PhD Thesis, May 2019 The synopsis part of this thesis is available as a pdf-file for download from the DTU research database ORBIT: http://www.orbit.dtu.dk. Address: DTU Environment

Department of Environmental Engineering Technical University of Denmark Miljoevej, building 113 2800 Kgs. Lyngby Denmark

Phone reception: +45 4525 1600 Fax: +45 4593 2850 Homepage: http://www.env.dtu.dk E-mail: reception@env.dtu.dk Cover: GraphicCo and Beatrice Schneider

iii

Preface

This thesis is submitted in partial fulfilment of the requirements for obtaining the Ph.D. degree from the Technical University of Denmark (DTU). The work was carried from September 2015 to March 2019. This thesis is part of the Membrane energy technology operations (MEMENTO) project

The thesis is organized in two parts: the first part puts into context the findings of the PhD in an introductive review; the second part consists of the papers listed below. These will be referred to in the text by their paper number written with the Roman numerals I-IV.

I Schneider, C., Rajmohan, R. S., Zarebska, A., Tsapekos, P., & Hélix-Nielsen, C. (2019). Treating anaerobic effluents using forward osmosis for combined water purification and biogas production. Science of the Total Environment, 647, 1021-1030

II Schneider, C., Oñoro A. E., Hélix-Nielsen C., Fotidis, I. Start-up of for-ward-osmosis anaerobic-membrane bioreactors for brewery wastewater remediation. Manuscript draft

III Pape, M. L., Valverde-Pérez, B., Astrid F. Kjeldgaard, August A. Zacha-riae, Schneider, C., Hélix-Nielsen C., Zarebska, A., Smets, B. F. Evalua-tion of forward osmosis to harvest methane oxidizing bacteria cultivated for single cell protein production. Manuscript under submission

IV Schneider, C., Zarebska, A., Wakefield, E., Yangali-Quintanilla, V., Hé-lix-Nielsen, C. Combined forward osmosis-reverse osmosis for the treat-ment of brewery wastewater. Manuscript draft

In this online version of the thesis, paper I-IV are not included but can be obtained from electronic article databases e.g. via www.orbit.dtu.dk or on request from DTU Environment, Technical University of Denmark, Miljoevej, Building 113, 2800 Kgs. Lyngby, Denmark, info@env.dtu.dk.

iv

Contributions to each paper

Paper I

I made the initial plans for the design of the experiments and the selection of anaerobic digestion effluents. I conducted the membrane autopsies, analysed and interpreted the results. I created all figures and tables, put the results into context and, wrote the arti-cle and handled the submission.

Paper II

I took decisive part in the designing and building of the lab-scale setup and designed the experiments. I conducted part of the experiments, including reactor maintenance, wastewater analysis and optical microscopy. I created all figures and tables, put the results into context and, wrote the art i-cle and handled the submission.

Paper III

I contributed to the design of the experiments and selection of methods as well as the relevant literature review. I helped to build the setup and contributed to the interpretation of the forward osmosis results and the calculation of the osmotic pressure. I assisted with writing the manuscript

Paper IV

I designed the experiments and selected the methods. I conducted all the ex-periments, literature review and analyses. I analysed the data, interpreted the results and put the results into context I created all figures and tables, put the results into context and wrote the arti-cle.

v

In addition, the following publications in conference proceedings, not included in this thesis, were also concluded during this PhD study

Schneider, Carina; Oñoro, Alberto Evangelio; Hélix-Nielsen, Claus; Fotidis, Ioannis. Biogas production from brewery wastewater in forward-osmosis anaerobic-membrane bioreactors. Sustain Conference 2018, 2018, Technical University of Denmark (DTU), Lyngby, Denmark (Poster presentation. Poster prize)

García-Aguirre, Jon; Fotidis, Ioannis; Alvarado-Morales, Merlin; Schneider, Carina; Angelidaki, Irini. Recovery of acetic, succinic and lactic acid through Forward Osmosis – a novel down-streaming ap-proach. Sustain Conference 2018, 2018, Technical University of Den-mark (DTU), Lyngby, Denmark (Poster presentation)

Valverde Pérez, Borja ; Pape, Mathias L.; Schneider, Carina ; Kjeld-gaard, Astrid Friborg ; Zachariae, August A. ; Hélix-Nielsen, Claus ; Zarebska, Agata ; Smets, Barth F. Use of Forward Osmosis to Harvest Methane Oxidizing Bacteria Producing Single Cell Protein. Danish Water Forum Annual Water Conference 2018 - abstract book, pages: 25-25, 2018, Danish Water Forum, Lyngby, Denmark

Schneider, Carina; Zarebska, Agata; Hélix-Nielsen, Claus. Combined forward osmosis-reverse osmosis for the treatment of brewery wastewater. Proceeding for 11th International Congress on Membranes and Membrane (Oral presentation)

Schneider, Carina; Sathyadev Rajmohan, Rajath; Zarebska, Agata; Hélix-Nielsen, Claus. Influence of feed composition and membrane fouling on forward osmosis performance. 16th Nordic Filtration Symposium 2016: Book of abstract, 2016, Lappeenranta University of Technology Press , Lappeenranta, Finland (Poster presentation)

vi

Acknowledgements

This thesis is the result of a more than three years-long journey. Moving to a new country, meeting so many amazing people, learning a new language and starting a PhD all at the same time was an amazing experience and I would like to thank all the people who were part of this.

Firstly, I would like to thank my main supervisor Claus Hélix-Nielsen, for his guidance, his confidence in my work and for giving me the freedom to ex-plore my own interests within this research project. I would also like to thank my co-supervisor Ioannis Fotidis, for taking over the co-supervision over one year into my project. Thanks for your support on everything biogas related.

I would further like to thank all my co-authors and project partners. Thanks to Victor Yangali Quintanilla and Mads Veje Knudsen from Grundfos for your tremendous help with the pilot plant, for all the discussions and input for my manuscripts. Thanks to all the lovely people at Aquaporin who have pro-vided me with countless FO membranes and their membrane expertise.

Special thanks to Agata Zarebska, for being so incredibly supportive when I had just moved here and helping me getting started both in this country and on my PhD. Thank you for your patience and for sharing your membrane fouling knowledge.

Thanks to Rajath Sathyadev Rajmohan, Alberto Evangelio, Giorgio Paradies, JianGui Li and all the other talented students I pleasure to work with. I learned so much from supervising you and hope I was able to teach you a thing or two as well.

Thanks to Hamse Kjerstadius, for showing me his MBR plant at Lund Uni-versity, sharing his experiences and answering all of my questions.

Additionally, I would like to thank all the current and former lab technicians at DTU Environment, especially Hector Hernan Caro Garcia, Sinh Hy Ngu-yen, Jens Schaarup Sørensen for their help with analysing samples and to Bent Henning Skov and Erik Rønn Lange for helping me at Dybendalsvej.

Thanks to Preben Bøje Hansen from DTU Brewery and Poul Åge Olsen and Jimmy Laugesen from Carlsberg for providing me with thousands of litres of brewery wastewater.

Very big thanks go to all my former and current colleagues and office mates (Sigurd, Fynn, Pedram, Borja, Agata, Anna, Vanessa, Joachim, Victoria, and

vii

Radek) and all the beautiful people from Friday Bar and Cake Club. It would not have been the same without you.

I would also like to extend my thanks to Beatrice, my very talented sister who created the cover of my thesis. Also big thanks to her and my mom for al-ways believing in me, supporting me and being there for me in tough times.

Last but not least, big thanks to my wonderful boyfriend Henrik, who’s been by my side for the last two years, for always being there and supporting me through all of this.

viii

Dunkel war’s, der Mond schien helle,

schneebedeckt die grüne Flur,

als ein Wagen blitzesschnelle,

langsam um die Ecke fuhr.

Drinnen saßen stehend Leute,

schweigend ins Gespräch vertieft,

als ein totgeschoss’ner Hase

auf der Sandbank Schlittschuh lief.

ix

Summary

In the light of global water scarcity and increasing water and energy demand, new ways to provide safe and clean water and renewable energy sources have to be found. This topic does not only affect developing countries, but affects industrialized countries as well.

The perception of wastewater has changed in recent years, from being seen as waste to being seen as a resource for water, energy and valuable compounds.

Membrane technology can be used to reclaim water from municipal and in-dustrial wastewater. In recent years, forward osmosis (FO) has raised increas-ing interest as an emerging membrane technology, because of its ability to efficiently reject pathogens and almost all solutes in the wastewater. When forward osmosis is integrated into hybrid systems, for example in combina-tion with reverse osmosis (RO), high-quality water can be recovered. FO can also be combined with anaerobic membrane bioreactors (FO-AnMBR) in or-der to simultaneously treat wastewater and produce biogas, which is a renew-able energy source.

The overall aim of this thesis is to evaluate biomimetic FO membranes for water recovery and biogas production. The goals are 1) to investigate the FO membrane performance in terms of water flux and nutrient rejection, both in stand-alone FO as well as in combination with RO 2) to analyse the fouling mechanisms and cleaning efficiency and 3) investigate process performance in terms of water flux and biogas production in FO-AnMBRs.

The results show that a wide variety of wastewaters, ranging from anaerobi-cally digested manure to microbial biomass, can be treated with FO, and high rejection of nutrients (ammonia, orthophosphate, chemical oxygen demand (COD)) can be achieved. The predominant fouling mechanisms in these cases were organic fouling, as well as biofouling. When FO was combined with RO, the double-barrier mechanisms achieved very high nutrient removal. Chemical cleaning was able to restore 75% of the initial water flux of the pristine membrane.

When FO was integrated into an anaerobic membrane bioreactor, it was found that the methane production rate increased in comparison to the mem-brane-less start-up phase, indicating that a higher organic loading rate can be achieved due to the membrane. However, bioreactor performance in terms of

x

methane production yield and rate remained unstable, possibly indicating shear stress or inadequate C/N ratio of the brewery wastewater.

Taken together, these results show the feasibility of water recovery from wastewater and simultaneous biogas production, using biomimetic FO mem-branes. However, further work will be required in the future to optimise the processes and gain a deeper understanding with regards to fouling, cleaning and pretreatment strategies, as well as the optimisation of operational condi-tions in osmotic anaerobic membrane bioreactors.

xi

Dansk sammenfatning

I lyset af globalt vandmangel og øgede vand- og energibehov, er der behov for at finde nye metoder til at levere rent og sikkert vand og vedvarende en-ergikilder. Dette behov påvirker ikke kun udviklingslande, men også indus-trialiserede lande.

Hvor spildevand førhen er blevet opfattet som et affaldsprodukt, har opfattel-sen ændret sig til at se spildevand som en kilde til vand, energi og værdifulde stoffer.

Membranteknologi kan benyttes til at genindvinde vand fra kommunalt og industrielt spildevand. Osmose, herefter benævnt forward osmosis (FO), har i de seneste år oplevet øget interesse som en ny membranteknologi, takket være dens evne til effektivt at tilbageholde patogener og næsten alle opløste stoffer i spildevandet. Når FO integreres i hybride systemer, for eksempel i kombination med omvendt osmose, herefter benævnt reverse osmosis (RO), kan rent vand af høj kvalitet udvindes. FO kan også kombineres med anaer-obe membranbioreaktorer, for at kombinere rensning af spildevand med produktion af biogas, som er en vedvarende energikilde.

Det overordnede formål med denne afhandling er at vurdere biomimetiske FO-membraners anvendelse til genindvinding af vand og produktion af bio-gas. Målene er at 1) undersøge FO-membraners ydeevne i form af vandgen-nemstrømning og tilbageholdelse af ammoniumkvælstof, orthofosfat og COD (chemical oxygen demand), både i FO alene og i FO kombineret med RO, 2) at analysere tilstopningsmekanismer og rensningseffektivitet, og 3) undersøge processens ydeevne i form af vandgennemstrømning og biogasproduktion, når FO-membranen er integreret i en anaerob membranbioreaktor.

Resultaterne viser at et bredt udvalg af spildevand, fra gødning til mikrobisk biomasse kan behandles med FO, samt at høj tilbageholdelse af ammoni-umkvælstof, orthofosfat og COD kan opnås. De vigtigste til-stopningsmekanismer var organisk tilstopning og mikrobiologisk tilstopning. Anvendelse af FO kombineret med RO resulterede i endnu højere tilbage-holdelse af næringsstoffer. Kemisk rensning af membranen genetablerede 75% vandgennemstrømning, sammenlignet med en ubrugt membran.

xii

Ved integration af FO i en anaerob membranbioreaktor, øgedes produktionen af metan sammenlignet med opstartsfasen uden brug af FO-membranen, hvil-ket indikerer at en øget organisk ladningsrate kan opnås ved hjælp af FO-membranen. Bioreaktorens ydeevne forblev imidlertid ustabil, hvilket kan indikere celleskader som følge af turbulens eller utilstrækkeligt C/N-forhold i bryggerispildevandet.

Tilsammen viser disse resultater muligheden for samtidig genindvinding af vand fra spildevand og produktion af biogas, gennem anvendelse af biomi-metiske FO-membraner. Imidlertid er der behov for yderligere arbejde for at optimere processerne og opnå en dybere forståelse omkring tilstopning og rengøring af membraner, samt forbehandling af spildevand og optimering af driftsbetingelser i osmotiske anaerobe membranbioreaktorer.

xiii

Table of contents

Preface .......................................................................................................... iii

Acknowledgements ...................................................................................... vi

Summary ...................................................................................................... ix

Dansk sammenfatning ................................................................................. xi

Table of contents ....................................................................................... xiii

Abbreviations.............................................................................................. xv

1 Introduction ............................................................................................. 1

1.1 Background and Motivation .......................................................................... 1

1.2 Objectives ..................................................................................................... 2

1.3 Structure of this thesis .................................................................................. 3

2 Theory ...................................................................................................... 5

2.1 Wastewater treatment ................................................................................... 5

2.2 Membrane technology for wastewater treatment ........................................... 6

2.3 Osmotic membrane processes ....................................................................... 8

2.3.1 Forward osmosis and reverse osmosis principles ...........................................8

2.3.2 Forward osmosis wastewater applications ................................................... 11

2.3.3 Forward osmosis membrane fouling and cleaning........................................ 13

2.4 Membrane bioreactors ................................................................................ 18

2.4.1 Historical development of membrane bioreactors ........................................ 18

2.4.2 Membrane bioreactors in wastewater treatment ........................................... 18

2.4.3 Membrane bioreactor processes and operation ............................................. 21

2.4.4 Osmotic membrane bioreactors.................................................................... 23

3 Forward osmosis for water and nutrient recovery .............................. 26

3.1 Forward osmosis for the treatment of anaerobic digestion effluents (Paper I) 27

3.1.1 Introduction and aim ................................................................................... 27

3.1.2 Methods ...................................................................................................... 28

3.1.3 Results and conclusions ............................................................................... 29

3.2 Forward osmosis for the dewatering of methane oxidizing bacteria (Paper III) 33

3.2.1 Introduction and aim ................................................................................... 33

3.2.2 Methods ...................................................................................................... 33

3.2.3 Results and conclusions ............................................................................... 35

4 Forward osmosis hybrids for brewery wastewater treatment ............ 37

4.1 Forward osmosis-reverse osmosis hybrid for water recovery from brewery wastewater (Paper IV) ....................................................................................... 38

4.1.1 Introduction and aim ................................................................................... 38

xiv

4.1.2 Methods ...................................................................................................... 38

4.1.3 Results and conclusions ............................................................................... 39

4.2 Anaerobic osmotic membrane bioreactor I: Lab-scale setup (Paper II) ....... 42

4.2.1 Introduction and aim ................................................................................... 42

4.2.2 Methods ...................................................................................................... 42

4.2.3 Results and conclusions ............................................................................... 44

4.1 Anaerobic osmotic membrane bioreactor II: Pilot-scale setup .................... 47

4.1.1 Introduction and aim ................................................................................... 47

4.1.2 Design and construction .............................................................................. 48

5 Conclusions ............................................................................................ 51

5.1 Forward osmosis for water and nutrient recovery ....................................... 51

5.2 Forward osmosis hybrids for brewery wastewater treatment ....................... 51

6 Perspectives and translation into technology ...................................... 53

6.1 FO .............................................................................................................. 53

6.2 FO-RO ........................................................................................................ 53

6.3 FO-AnMBR ................................................................................................ 54

7 References .............................................................................................. 55

8 Papers .................................................................................................... 69

xv

Abbreviations

AD anaerobic digestion AL-FS active layer-feed side AnMBRs anaerobic membrane bioreactors ATP adenosine triphosphate BMP biochemical methane potential CF concentration factor COD chemical oxygen demand CSTR continuous stirred tank reactors ECP external concentration polarisation EDS energy-dispersive X-ray spectroscopy EDTA ethylenediaminetetraacetic acid FID flame ionization detector FO forward osmosis FTIR Fourier-transform infrared spectroscopy HRT hydraulic retention time IC ion chromatography ICP internal concentration polarisation ICP-OES inductively coupled plasma optical emission spectrometry MBR membrane bioreactor MD membrane distillation MF microfiltration MOB methane oxidizing bacteria NF nanofiltration OL organic loads OLR organic loading rate OPEX operational expenditure RO reverse osmosis SCP single cell protein SEM Scanning electron microscope SRT solid retention time STP sodium triphosphate TAN total ammonia nitrogen TFC thin-film composite TKN total Kjeldahl nitrogen TS total solids UF ultrafiltration

xvi

VFA volatile fatty acids VS volatile solids

xvii

Figures

Figure 1 Structure of the thesis. ..................................................................... 4

Figure 2 Overview over membrane processes. ............................................... 7

Figure 3 Overview over osmotic membrane processes. ................................. 9

Figure 4 Illustration of cake layer structure and physical cleaning effects in FO and RO. .................................................................................................. 15

Figure 5 Comparison of a (A) typical sewage treatment process with a conventional activated sludge (AS) treatment and (B) membrane bioreactor (MBR) process.. ........................................................................................... 20

Figure 6 Membrane bioreactor classifications. ............................................ 21

Figure 7 The two main MBR process configurations: A) pressure-driven external side-stream and B) vacuum-driven submerged MBR configuration. ..................................................................................................................... 23

Figure 8 Schematic representation of the lab-scale FO setup. ...................... 29

Figure 9 Membrane autopsy of fouled FO membranes. ............................... 32

Figure 10 Effect of draw solution on water flux and reverse salt flux.. ....... 35

Figure 11 Effect of fouling on water flux.. .................................................. 36

Figure 12 Simplified schematic drawing of the FO-RO system. .................. 39

Figure 13 FO (A) and RO (B) flux of brewery wastewater. ......................... 40

Figure 14 Nutrient rejection of real (A) and synthetic (B) brewery wastewater. ................................................................................................... 41

Figure 15 FO flux of the cleaned membrane after a multi-step chemical cleaning procedure with NaOH and citric acid, in comparison to the pristine, unused membrane ......................................................................................... 42

Figure 16 Schematic representation of a lab-scale osmotic membrane bioreactor. .................................................................................................... 43

Figure 17 Methane yield (A) and rate (B) of Rsynth and Rreal. ..................... 45

Figure 18 The measured water flux (Jw) and expected water flux Jw(th) of FO membranes for A) Rreal and B) Rsynth. ............................................................ 46

Figure 19 Process overview over the pilot-scale FO-AnMBR-RO. .............. 48

Figure 20 Rendering of the pilot-scale FO-AnMBR-RO. ............................ 50

Figure 21 Pilot-scale osmotic FO-AnMBR-RO. H ...................................... 50

xviii

Tables

Table 1 Aerobic vs anaerobic membrane bioreactors, adapted from (Stephenson, Brindle et al. 2000, Chan, Chong et al. 2009, Judd 2010) ....... 22

Table 2 AD effluent characteristics ............................................................. 28

Table 3 FO performance and methane yield results of AD effluents ............ 31

Table 4 FO experiments in Paper III ............................................................ 34

Table 5 Operational parameters in different periods .................................... 44

xix

Symbols

A [L m-2h-1bar-1] water permeability coefficient � � �, � [bar] draw bulk osmotic pressure � , � [bar] feed bulk osmotic pressure

B [L m-2h-1] salt permeability coefficient

cf [mol/L] feed concentration

cp [mol/L] permeate concentration

D [m2/s] diffusion coefficient

Js [g m-2h-1] reverse salt flux

Js,Mg [g m-2h-1] reverse salt flux of Mg2+

JsCl [g m-2h-1] reverse salt flux of Cl-

Jw [L m-2h-1] water flux

Jw(th) [L m-2h-1] theoretical water flux

Jw,ave [L m-2h-1] averaged water flux

Jw,FO [L m-2h-1] FO water flux

Jw,RO [L m-2h-1] RO water flux

S [µm] structural parameter

ΔP [bar] hyrdaulic pressure difference over the membrane

Δπ [bar] osmotic pressure difference over the membrane

σ [-] reflection coefficient

Jw,ICP [L m-2h-1] water flux under consideration of ICP effects

1

1 Introduction

1.1 Background and Motivation One of the most pervasive issues of this century is the global scarcity of clean and safe water, as well as the growing energy demand (WWAP, 2015). The rapidly increasing consumption of these resources can’t be satisfied by tradi-tional means alone, but new ways to provide water and renewable energy have to be found. The reclamation of water from industrial or municipal wastewater sources can help to increase water supply in water-stressed re-gions and reduce the costs for wastewater disposal for the industrial sector (Elimelech, 2006; Shannon et al., 2008). Additionally, biogas can be generat-ed via anaerobic digestion, turning the organic matter in the wastewater into renewable energy.

Membrane technology has been used to treat wastewater since the 1960ies (Baker, 2004). However, many membrane processes don’t yield adequate wa-ter quality for re-use applications, have high energy demands, or suffer from severe fouling, rendering the membrane process uneconomic (Lutchmiah et al., 2011).

In recent years, forward osmosis (FO) has gained increasing interest as an energy-efficient membrane technology that is capable of rejecting pathogens and almost all solutes in the wastewater (Tzahi Y Cath, Childress, & Elimelech, 2006). Forward osmosis is a natural process, where water is trans-ported through a semipermeable membrane from a side with low high osmot-ic pressure (feed side), such as wastewater, to a side of high osmotic pressure (draw side. For wastewater treatment, FO is often combined with other pro-cesses, as the end product is a diluted draw solution that has to be treated fur-ther in order to produce clean water and re-concentrate the draw solution for further use.

Although FO is considered a low-fouling membrane technology, fouling still has to be taken in to consideration, as it lowers membrane performance, in-creases operational costs and shortens membrane lifespan. Many studies have focused on investigating fouling mechanisms by using a solution of model foulants or synthetic wastewater (S. Lee, Boo, Elimelech, & Hong, 2010; Mi & Elimelech, 2008). So far, little is known about the fouling mechanisms when using authentic industrial wastewaters.

2

Previous studies have made efforts to integrate FO membranes into hybrid systems, such as combining it with reverse osmosis (RO) or osmotic anaero-bic membrane bioreactors (FO-AnMBR), to reclaim clean water or nutrients from wastewater sources (Choi, Kim, & Hong, 2016; Y. Gu et al., 2015; Lutchmiah, Verliefde, Roest, Rietveld, & Cornelissen, 2014; Rodrigo Valladares Linares et al., 2013; J. Zhang, She, Chang, Tang, & Webster, 2014). However, more research is required to investigate their applicability for simultaneous reclamation of clean water from wastewater and biogas pro-duction from industrial wastewater.

1.2 Objectives

The overall objective of this thesis is to evaluate biomimetic FO membranes for water reclamation from wastewater sources, using three different FO pro-cesses (FO, FO-RO and FO-AnMBR). The goal is to answer the following questions:

What FO membrane performance in terms of water flux and rejection of nutrients, such as ammonia, orthophosphate and COD can be achieved for the treatment of anaerobic digestion effluents and microbial biomass?

What draw solution is the most suitable for water reclamation from micro-bial biomass?

What is the water flux and nutrient rejection of a combined FO-RO pilot plant, when treating brewery wastewater?

What is the methane production and water flux during the start-up period of FO-AnMBRs treating brewery wastewater?

How does the hydraulic retention time (HRT) and solids retention time (SRT) affect the FO-AnMBR performance in terms of methane production and water flux?

3

1.3 Structure of this thesis This thesis includes four original research articles, with the main findings represented in chapter 3 and 4. The structure of the paper is displayed in Fig-ure 1.

Chapter 3 covers the pre-studies with FO as a stand-alone technology for wastewater treatment (Paper I) and nutrient recovery (Paper III). The goal of these studies was to identify potential applications for biomimetic FO membranes by testing a wide variety of wastewater sources.

The results of these studies were used to design the FO hybrid systems de-scribed in Chapter 4. Here, the focus lies on water recovery and biogas pro-duction from brewery wastewater, because this has been identified as a prom-ising industrial case for water recovery.

Paper II is focussing on integrating FO membranes into a lab-scale osmotic membrane bioreactor setup, while Paper IV is investigating FO-RO hybrids

as an alternative to membrane bioreactors, while also covering economic as-pects.

4

Figure 1 Structure of the thesis. This thesis contains four papers and one extra chapter about the design of a pilot-scale anaerobic osmotic membrane bioreactor

FO hybrids

FO pre-studies

Forward osmosis for the treatment of anaerobic digestion effluents

Paper I

Forward osmosis for dewatering methanotrophiccultures

Paper III

FO-AnMBR

Anaerobic osmotic membrane bioreactor II: Pilot-scale setup

Anaerobic osmotic membrane bioreactor I: Lab-scale setup

Paper II

FO-RO

Forward osmosis-reverse osmosis hybrid for water recovery from brewery wastewater

Paper IV

5

2 Theory

2.1 Wastewater treatment Although the surface of planet earth is covered in water to 80%, 97% of the water is salt water and only 3% is fresh water, of which a large part is tied in polar ice caps (Rao, Senthilkumar, Byrne, & Feroz, 2013). With the increas-ing global population, the demand for the supply of clean and safe water is rising as well. This also leads to an increase in domestic and industrial wastewater volumes.

Wastewater contains pathogens, heavy metals, nutrients like nitrogen and phosphorous that can lead to eutrophication in water bodies, as well as solids and biodegradable material. Therefore, it needs to be treated to protect the environment, prevent pollution of the groundwater and sea water and protect public health, before it can safely be discharged into natural bodies of water (Fane, 2011). On the other hand, wastewater is increasingly seen as a re-source for nutrients and water. Reclaimed water from wastewater can be re-used either indirectly or directly. In indirect reuse, it is highly treated and then returned to a stream or groundwater reservoir whereas direct reuse in-cludes e.g. as irrigation water for agriculture or golf courses, industrial appli-cations as process water for cooling or cleaning or other non-potable applica-tions, such as toilet flushing (Schrotter, 2010; WEF, 2006)

Wastewater can be treated with various different methods, based on the wastewater source, type of contaminants and treatment goals (Rao et al., 2013; Woodard & Curran, 2006). The treatment methods can be generally classified as follows

Physical methods, which rely on gravitational settling of particles or physical barriers. Physical treatment methods include sedimentation, floatation, screening and multimedia or sand filtration or membrane tech-nology,

Chemical methods, including precipitation, coagulation and flocculation, chemical oxidation or reduction. Disinfection of wastewater can also be achieved via chemical treatment methods, such as chlorination or ozona-tion

Biological methods, where microorganisms degrade organic compounds in the wastewater. In general, biological methods can be divided into aer-

6

obic processes (requiring air), where organic material is converted to CO2, NH3 and H2O and anaerobic processes (in the absence of air), which are slower and more complex, where CH4 and CO2 are the end products.

2.2 Membrane technology for wastewater

treatment Membranes are a physical wastewater treatment technology, which has exist-ed since the 1960ies (Baker, 2004). However, membrane technology has strongly increased in popularity in recent years and has been identified as one of the most promising treatment technologies (Fane, 2011; T. C. Zhang et al., 2012). This is partly due to stringent regulations in industrialized countries regarding effluent quality as well as increasing global water scarcity.

In comparison to conventional wastewater treatment technologies, mem-branes allow for the selective removal of a wide range of contaminants, re-duce the number of unit operations, can recover valuable compounds and low space requirement (T. C. Zhang et al., 2012). Figure 2 depicts the most com-mon membrane processes, including the particle size typically removed, as well as the driving force of the processes. Depending on the quality of the raw water and the targeted water quality (drinking water, reclaimed water, process water), the different membrane processes or a combination of these processes can be used (Schrotter, 2010). The most commonly used membrane processes are:

Microfiltration (MF) can be used to filter colloidal particles of a size from 0.1 – 10 μm and microorganisms, including yeast and bacteria (Fritzmann, Löwenberg, Wintgens, & Melin, 2007)

Ultrafiltration (UF) is capable to filter viruses and macromolecules and particles from 1 – 100 nm, such as proteins (F. I. Hai & Yamamoto, 2011)

Nanofiltration (NF) removes, pesticides, endotoxins, divalent ions and particles from 0.5 – 5 nm

Reverse osmosis (RO) is one of the most commonly used membrane technologies for wastewater treatment. They are commonly nonporous and achieve removal of monovalent ions and particles from 0.1 – 1 nm

7

However, membranes are often not used as a stand-alone wastewater treat-ment technology, but integrated into a treatment scheme. It is common to in-clude a pretreatment step before membrane filtration, in order to protect the fragile membrane from coarse particles, hydrocarbons or chlorine in the wastewater that could cause damage, remove solid loading to reduce mem-brane fouling and achieve higher fluxes, as well as reduce operation costs and prolong membrane lifespan (Schrotter, 2010). Gross solids can be removed, by cartridge filters, fine screens, or strainers, while coagulation or floccula-tion may be in order to reduce organic matter. MF or UF is often used as a pretreatment for dense NF and RO applications (Judd & Jefferson, 2003; Schrotter, 2010).

Membranes can also be combined with biological treatment, for example in membrane bioreactors or used after conventional biological sludge treatment.

Figure 2 Overview over membrane processes. Adapted from McGraw-Hilll Education (WEF, 2012) and Shon et al (2013)

0,001 0,01 0,1 10 1001,0 1000

ionic molecularmacro

molecularmacroparticle

microparticle

0,0001

particle filtration

MF

UF

RO

NF

FO

virusesmetal

ion

albumin

yeast cell

beach sand

sugar

red

blood

cell

human

hair

bacteriarelative size of

commonsubstances

particlesize[µm] log scale

driving forceΔP

driving forceΔπ

ΔT membrane distillation

10.000

8

2.3 Osmotic membrane processes

2.3.1 Forward osmosis and reverse osmosis principles

Osmosis is a process that can be observed in nature, for example with the crinkling of cherry skin after rain (Sekse, 1995) and plays a role in many pro-cesses, such as water uptake in plant roots (Maurel, 1997) and regulation of red blood cells (Fung & Tong, 1968).

Unlike many traditional membrane processes, forward osmosis (FO) doesn’t rely on hydraulic pressure, but is driven by the difference in osmotic pressure between a solution of low solute concentration and osmotic pressure (feed side) and a solution of high solute concentration and high osmotic pressure (draw side) (Figure 3).Water is diffusing over a semipermeable membrane, which is permeable to the water but not to the solute. This results in a volume reduction on the feed side and a dilution of the solution on the draw side. The diluted draw solution can then be treated further to reconcentrate the draw solution and recover water. In many cases, FO is not the only treatment step, but can be regarded as a high level pretreatment. The draw solution can be reconcentrated via RO, MD or thermal distillation processes (Achilli, Cath, & Childress, 2010; H. Song, Xie, Chen, & Liu, 2017).

Advantages of FO include lower fouling propensity and lower energy de-mands, due to absence of hydraulic pressure, as well as high rejection of small molecules, such as trace organic pollutants, as well as soluble organic matter and pathogens (Lutchmiah et al., 2014).

Disadvantages of FO include the lower fluxes in comparison to other mem-brane processes, the need to reconcentrate the draw solution and reverse salt flux from the draw solution into the feed solution (Achilli et al., 2010; Lutchmiah et al., 2014). This decreases the driving force and is potentially detrimental to the process the membrane is involved in, which is an issue e.g. in the food industry (when liquid food or beverages are concentrated via FO) or bioreactors, where microorganisms can suffer from salt toxicity (Parkin & Owen, 1986). It is therefore important to select a draw solution, that is easily recoverable, cheap, able to create high osmotic pressure and non-toxic (Achilli et al., 2010; Bowden, Achilli, & Childress, 2012).

9

Figure 3 Overview over osmotic membrane processes. In equilibrium, the osmotic pres-sure in both solutions is equal. In FO, there is a water flux from the side of lower osmotic pressure to the side of higher osmotic pressure. In RO, the hydraulic pressure applied has to be higher than the osmotic pressure difference in order to yield a water flux from the side of high osmotic pressure to the side of low osmotic pressure. Adapted from (Tzahi Y Cath et al., 2006)

The water flux in FO can generally be described by the following equation (Tzahi Y Cath et al., 2006) �� = � � �, � − � , � 1

with � � �, � and � , � as osmotic pressure [bar] in the bulk of the

draw and the feed solution, and as A the water permeability coefficient [L m-

2h-1bar-1]. However, this equation assumes that the membrane is impermeable to the draw solution and that no concentration polarisation occurs. Concentra-tion polarisation can be described as the depletion or accumulation of solutes in the vicinity of the membrane (Tzahi Y Cath et al., 2006).

When the active layer of the membrane is facing the feed side (AL-FS mode), dilutive internal concentration (dilutive ICP) occurs, in which water diffuses through the membrane, via the thin active membrane layer into the porous support layer, diluting the draw solution and decreasing the effective driving force.

The water flux with consideration of dilutive ICP effects can be described as

��,��� = � �� � � �, � +� , � + + ��,��� 2

equilibrium

feed draw

FO (ΔP=0) RO (ΔP> Δπ)

Δπ Δπ

ΔP

feed draw

10

where D is the diffusion coefficient of the draw solute [m2/s], B is the salt permeability coefficient [L m-2h-1], A the water permeability coefficient [L m-

2h-1bar-1] and S the structural parameter [µm] of the membrane (McCutcheon & Elimelech, 2006). The parameters A, B and S describe the intrinsic charac-teristics of a FO membrane, which do not change under different experi-mental conditions (Tzahi Y Cath et al., 2006; B. Kim, Gwak, & Hong, 2017). The parameters A and B are referring to the active layer of the membrane, describing water flux and reverse draw solute flux at a given osmotic pres-sure difference. S describes the average distance a solute molecule must trav-el through the membrane support layer on its way from the draw solution to the feed solution (Phillip, Yong, & Elimelech, 2010).

Biomimetic FO membranes incorporating aquaporin proteins are inspired by biological cell membranes which possess high water permeability, while also being highly selective towards solutes (Giwa et al., 2017; Chuyang Tang, Wang, Petrinić, Fane, & Hélix-Nielsen, 2015; CY Tang, Zhao, Wang, Hélix-Nielsen, & Fane, 2013). Aquaporins are ubiquitous pore-forming integral membrane proteins that are governing water transport in microbes, plants and mammals (Fu & Lu, 2007). They are highly selective towards water mole-cules while also achieving a high permeability, because the water molecules are able to pass through the aquaporin channels at almost diffusion rate (Xin et al., 2011). Biomimetic FO membranes incorporating aquaporin proteins are aiming to leverage these desirable properties for water treatment applications.

Over the past forty years, reverse osmosis (RO) has become increasingly popular as a desalination technology, due to their high quality in produced water (efficiently rejecting dissolved matter and monovalent ions), while also requiring less energy than thermal desalination applications (Greenlee, Lawler, Freeman, Marrot, & Moulin, 2009).

In RO, the applied feed pressure has to be larger than the osmotic pressure difference to reverse the water flux from the side with high osmotic pressure to the side of low osmotic pressure (Figure 3). Required pressure depends on the application and ranges from 6-30 bars in brackish water RO up to 60-80 bar for seawater desalination (Alghoul, Poovanaesvaran, Sopian, & Sulaiman, 2009; Fritzmann et al., 2007; Greenlee et al., 2009)

In general, water flux in RO can be described by

11

�� = ∆� − �∆� 3

where ΔP [bar] is the pressure difference over the membrane and Δπ [bar] is the osmotic pressure difference. σ [-] is the reflection coefficient, that de-scribes the deviation of the semipermeable membrane from the ideal (Mulder, 1996).

Both in FO and in RO, rejection of solutes can be calculated as

= − ��� � % 4

with cp as the permeate concentration and cf as the feed concentration, respec-tively (Greenlee et al., 2009; P. Liu, Zhang, Feng, Shen, & Yang, 2015)

2.3.2 Forward osmosis wastewater applications

In recent years, FO has attracted increasing interest as an emerging mem-brane technology for a wide variety of applications. FO has mainly become popular for applications that require high-quality effluents or low energy de-mands, where other treatment options are not viable or “gentle” handling of feed streams is essential (Coday et al., 2014). In the concentration of fruit juices and whey, FO is an alternative to thermal processes like evaporation, that can negatively affect the nutrient content and lead to the loss of volatile aroma compounds (G. Q. Chen, Artemi, Lee, Gras, & Kentish, 2019; Dova, Petrotos, & Lazarides, 2007; Jiao, Cassano, & Drioli, 2004). FO has also been used for direct drinking water reclamation from impaired water sources: so-called hydration bags are designed for emergency situa-tions, to turn contaminated surface water into a safe, drinkable fluid, using a concentrated glucose or fructose as a draw solution. The FO membrane re-jects pathogens and most macromolecules, without requiring an external power supply (Tzahi Y Cath et al., 2006)

However, since the main focus of this thesis is FO for wastewater treatment, the main focus of this chapter is wastewater applications:

Landfill leachate is a heavily contaminated and also highly variable wastewater stream, polluted with heavy metals, organic and inorganic nitrogen, dissolved salts, as well as organic pollutants. The dissolved salts, such as sodium chloride and sodium bicarbonate have proven es-pecially complicated to remove. Here, FO (in combination with RO) is an energy-efficient alternative to evaporation. FO helps to greatly re-

12

duce the volume of the wastewater (up to 95%) and yields high-quality effluent that is suitable for irrigation or discharge (Iskander, Zou, Brazil, Novak, & He, 2017; York, Thiel, & Beaudry, 1999).

FO has also been investigated for municipal wastewater treatment. Since the COD of municipal wastewater is generally low, FO can be used to pre-concentrate the organic matter for subsequent biogas pro-duction via anaerobic digestion (AD) (Ashley J. Ansari, Hai, Price, Drewes, & Nghiem, 2017; Hey et al., 2017). FO has been shown to be more efficient at retaining organic matter in comparison to previously suggested methods, including dynamic sand filtration or flocculation (Ashley J. Ansari et al., 2016) as well as being less prone to fouling than other high-retention membrane processes like nanofiltration or re-verse osmosis. Further on, FO has also suggested as an energy-efficient way to re-claim clean water from municipal wastewater. In combination with membrane distillation (MD), FO achieved 80% water recovery and re-moved 91-98% of trace organic contaminants (Xie, Nghiem, Price, & Elimelech, 2013). FO can also be used to recover resources (nitrogen and phosphorous), where conventional methods would not be econom-ic due to the low-strengths character of from municipal wastewater (Z. Wang, Zheng, Tang, Wang, & Wu, 2016; Xue, Tobino, Nakajima, & Yamamoto, 2015). Xue et al achieved a 3-to4-fold concentration of to-tal phosphorous and a 2.1-fold concentration of ammonia (Xue et al., 2015; Xue, Yamamoto, & Tobino, 2016)

The textile industry is one of the largest producers of highly contami-nated wastewater, containing dyes, heavy metals, mineral oil, suspend-ed solids and organic matter. Since some of the contents are poorly de-gradable or even toxic and the composition and pH of the waste streams can vary greatly over time, textile wastewater is generally re-garded as very difficult to treat (Han et al., 2016; Makki, Wahab, & Said, 2013; Petrinić, Bajraktari, & Hélix-Nielsen, 2015). FO is able to reject even low-molecular weight dyes and has been successfully test-ed for the pre-concentration of textile wastewater streams, before they are treated further by coagulation or flocculation. It was found that the FO membrane rejects the dyes remarkably well (99.9% rejection) and membrane fouling was reversible (Han et al., 2016).

13

Wastewater from oil and gas manufacturing industries (e.g. drilling mud, hydraulic fracturing flowback water, produced waters), is highly polluting and difficult to treat (Coday et al., 2014; Lutchmiah et al., 2014). Conventional wastewater treatment methods fail to efficiently remove hydrocarbons or high salinity from the wastewater, require large amounts of chemicals or are too expensive for implementation (Coday et al., 2014). In an effort to minimize the environmental impact of those wastewaters, Zhang et al proposed a combined FO-MD for water recovery from produced water. FO-MD was demonstrated to be suitable for oily wastewaters with high salinity, attaining 90% water recovery and almost complete rejection of oil and NaCl (2014).

2.3.3 Forward osmosis membrane fouling and cleaning

Membrane fouling is a major problem in all membrane processes, since it causes a decline in permeate flux, shortens membrane lifespan, affects per-meate quality and increases operational expenses, when operational down-time for expensive cleaning cycles is required (Motsa, Mamba, & Verliefde, 2018; R. Valladares Linares et al., 2016). In recent years, many studies have been focussing on the development of low-fouling membrane materials (Guo et al., 2018; W. J. Lee, Goh, Lau, Ong, & Ismail, 2018; Salehi, Rastgar, & Shakeri, 2017; Xiangju Song, Wang, Tang, Wang, & Gao, 2015; Tiraferri, Kang, Giannelis, & Elimelech, 2012), but they have not been implemented in commercially available membrane products as of yet and fouling remains un-avoidable. It is therefore also necessary to achieve a sound understanding fouling mechanisms in order to optimise wastewater pretreatment strategies and cleaning methods.

In FO, fouling is dependent on membrane orientation (active layer facing the feed side vs. active layer facing the draw side), hydrodynamic conditions (such feed crossflow velocity and as the presence of spacers), feed character-istics (such as foulant concentration, pH, functional groups, shape and size of the foulant) and draw solution properties (such as concentration and compo-sition) as well as membrane properties (such as surface hydrophobicity, roughness) (Q. She, Wang, Fane, & Tang, 2016).

Membrane fouling in FO has been observed to be more reversible than in RO due to lower fluxes and absence of hydraulic pressure, while the fouling in RO might was described as less reversible under the same hydrodynamic

14

conditions (Figure 4) (S. Lee et al., 2010; Mi & Elimelech, 2010b; Xie, Lee, Nghiem, & Elimelech, 2015; Yu, Lee, & Maeng, 2016). However, this obser-vation has also been doubted by a recently study from Siddiqui et al. (2018). This study found no evidence that hydraulic pressure plays a critical role in RO fouling and observed a greater fouling propensity in FO due to changes in ICP and therefore changes in the driving force. However, self-compensating effects in ICP cause the water flux in FO to be more stable against fouling than in RO.

In general, the types of fouling occurring in FO can be classified as

Organic fouling, where macromolecules adsorb to the membrane and can form a gel layer. This is a very common type of fouling n FO pro-cesses, since macromolecules, such as polysaccharides, proteins and humic substances are ubiquitous in wastewater and natural waters. They can also stem from microbial secretion (Mi & Elimelech, 2008; Q. She et al., 2016; Z. Wang et al., 2014)

Inorganic fouling/ scaling, where inorganic components like silica or gypsum crystallize and precipitate on the membrane, because their sol-ubility product is exceeded (J. Zhang et al., 2012)

Colloidal fouling, where colloidal particles deposit on the membrane (Boo, Lee, Elimelech, Meng, & Hong, 2012)

Biofouling, where microorganisms like bacteria or microalgae adsorb and grow on the membrane surface, eventually developing a biofilm (Bogler, Lin, & Bar-Zeev, 2017)

When the dense active layer of the FO membrane is facing the feed side, fouling occurs mainly externally (Parida & Ng, 2013). The foulants deposit on the membrane surface and form a “cake layer”, that can easily be re-moved by e.g. increasing feed crossflow velocity (Q. She et al., 2016).

Another important factor in FO fouling is reverse salt flux. It has been shown that divalent cations like Mg2+, Ca2+ can act as promoters for organic and col-loidal fouling by interacting with carboxyl groups of foulants like alginate. These foulant-foulant interactions, in addition to foulant-membrane surface interactions, have been shown to play an important role in fouling. Further on, divalent cations can act as scaling precursors and aggravate inorganic scaling (Mi & Elimelech, 2008; Motsa, Mamba, & Verliefde, 2015; Qianhong She, Jin, Li, & Tang, 2012).

15

Biofouling is influenced by the feed water characteristics (pH, ionic strength, and temperature), surface chemistry, charge, roughness and hydrophobicity of the membrane surface as well as surface properties and growth phase of the microorganism (Goulter, Gentle, & Dykes, 2009; Hermansson, 1999). Bio-fouling is an especially problematic type of fouling for the long-term opera-tion of membrane processes, because biofilms tend to be very hard to remove, once they have formed (Bogler et al., 2017). Biofilm formation is commonly preceded by the development of a “conditioning layer” of proteins, polysac-charides and lipids that facilitates the attachment of microorganisms to the membrane surface It can hardly be avoided and gravely impacts permeate flux (Bogler et al., 2017).

Figure 4 Illustration of cake layer structure and physical cleaning effects in FO and RO. In absence of hydraulic pressure, the formed cake layer is rather lose and easily removed by shear force during physical cleaning. Hydraulic pressure, on the other hand, contributes to a more compact cake layer that is more difficult to remove. Adapted from Mi et al (2010a)

Cleaning of the FO membrane can be achieved via chemical, physical or bio-logical cleaning methods (Q. She et al., 2016). Physical methods are based on providing vigorous hydrodynamic conditions to facilitate the removal of fou-lants from the membrane (Ashley J Ansari, Hai, He, Price, & Nghiem, 2018). Physical cleaning methods include increasing of crossflow velocity, ultrason-ification, pulsed crossflow, air scouring or osmotic backwashing, where the draw solution is replaced by deionised water to reverse the osmotic pressure

FO (No hydraulicpressure)

RO (under hydraulicpressure)

alginate

Ca2+

membrane membrane

membrane membrane

shear force shear force

cake

layer

str

uctu

rephysic

al

cle

anin

g

A B

16

gradient and thereby create a water flux from draw side to feed side that lifts the fouling layer of the membrane (Ashley J Ansari et al., 2018; C. Kim, Lee, & Hong, 2012; Xie et al., 2015). The advantage of physical cleaning methods is generally faster than chemical cleaning and that no chemicals are used. Chemical cleaning can potentially damage the membrane- especially cellu-lose acetate membranes can be hydrolysed at low pH (Mulder, 1996), is cost-ly and produces chemical waste (Judd, 2010). However, physical cleaning can be energy intensive, consume large volumes of fresh water for membrane flushing and can also damage the membrane (Q. She et al., 2016). It is also worth noting that physical cleaning is more effective in AL-FS mode than in AL-DS mode.

Chemical cleaning (Mohammadi, 2001; Z. Wang et al., 2015) works by dis-solving and thereby removing the foulants from the membrane surface. Chemical cleaning can be more effective than physical cleaning when there is a strong interaction between foulant and membrane (Q. She et al., 2016). Chemical cleaning is commonly conducted by alternating flushing steps with clean water and soaking steps, where the membrane is steeped in the chemi-cal cleaning agent. When more than one chemical cleaning agent is applied, rinsing with water between the cleaning steps is recommended to flush out residual cleaning agent and dissolved foulants (H. Li & Chen, 2010).

Based on the nature of the foulant, a number of different chemicals can be used:

Acids like phosphoric acid, hydrochloric acid or citric acid are very ef-fective to remove inorganic fouling, such as CaCO3, SiO2 and metal oxides. The acids react with the inorganic deposits, forming a soluble salt. However, hydrochloric acids may lead to corrosion problems with membranes and stainless steel elements, leading to inorganic fouling. Citric acid, on the other hand, is a milder acid, that can be rinsed easily and also has chelating abilities and can therefore form complexes with metal ions (Al-Amoudi & Lovitt, 2007; Koh, Ashokkumar, & Kentish, 2012; H. Li & Chen, 2010)

Alkaline solutions, such as NaOH, can be used to treat organic fouling and biofouling. Alkaline cleaning agents can saponificate fats and li-pids, hydrolyze proteins to amides, polysaccharides to monosaccha-rides and neutralize humic acids (H. Li & Chen, 2010; Z. Wang et al., 2014).

17

Chelating agents, such as ethylenediaminetetraaceticacid (EDTA), cit-rates or sodium triphosphate (STP) are applied to remove scaling where acids are not effective enough, such as calcium, magnesium, or barium sulfate. They can also form bonds to single metal atoms, form-ing soluble complexes (Baker, 2004; H. Li & Chen, 2010)

Detergents are often used in combination with alkaline cleaners to re-move bacteria from the membrane surface (Baker, 2004). Due to their amphiphilic nature, with a hydrophilic portion and a hydrophobic por-tion of the molecule, they can also be used to remove fats and oils from the membrane surface (Koh et al., 2012)

Oxidants and disinfectants (H2O2, NaOCl, formaldehyde) are used to control and remove organic fouling and biofouling. Oxidants work by oxidizing functional groups of foulants to ketonic, aldehydic and car-boxylic groups, which increases the hydrophilicity of the foulant and decreases the adhesion to the membrane (Gadelha et al., 2014; Mulder, 1996)

Chemical cleaning protocols should be optimised with regards to strength of chemical cleaning agents, temperature and cleaning time. A compromise has to be found between the cleaning being harsh enough to successfully remove foulants, yet mild enough in order not to shorten membrane lifespan or dam-age membrane integrity, cause prolonged operational downtime or yield large volumes of chemical waste effluent (H. Li & Chen, 2010; Z. Wang et al., 2014).

Biological cleaning can be achieved by enzymes that degrade macromolecu-lar foulants into smaller soluble molecules, which can then be flushed from the membrane surface (Q. She et al., 2016). Enzymatic cleaners can be e.g. proteases, amylases or glucanases (Mulder, 1996). However, enzymes are very costly and enzymatic degradation is much slower than chemical degra-dation, so this cleaning option is not widely used. However, they can be use-ful in applications, where the membrane is very sensitive to chemicals or a biological treatment step is combined with the membrane process (Koh et al., 2012; Mulder, 1996).

18

2.4 Membrane bioreactors

2.4.1 Historical development of membrane bioreactors

A membrane bioreactor (MBR) is a process that combines the biological treatment of a bioreactor with membrane separation (Faisal I Hai, Yamamoto, Nakajima, & Fukushi, 2010).

MBRs have been developed in the 1960ies, after membrane science had made major advances with the invention of asymmetric cellulose acetate mem-branes (Sidney & Srinivasa, 1964) and MF and UF membranes became com-mercially available. The membranes used for these early MBRs were mostly flat sheet membranes which were mounted in a side-stream configuration (Figure 7). The first commercial application of these early MBRs was the treatment of activated sludge on board of ships, developed by Dorr Oliver (Bailey, Bemberis, Hubbard, & Presti, 1971) However membranes were still expensive, had a short lifetime and the MBRs suffered from poor economic performance, so MBRs were mostly limited to niche applications in remote areas like ski resorts and trailer parks (F. I. Hai & Yamamoto, 2011; Ladewig & Al-Shaeli, 2016). Consequently, for a long time, MBRs were seen as infe-rior to conventional active sludge treatment due to being more costly and more energy intensive.

In the 1990s, MBRs had their breakthrough, driven by a combination of fac-tors: improved and less expensive membrane material made the process more economic. Additionally, submerged MBRs were invented, which helped to further decrease the operational costs for larger scale applications (Ladewig & Al-Shaeli, 2016). Further on, stricter legislation on water discharge quality for municipal wastewater treatment plants required improved treatment tech-nology. In combination with local water scarcity and the growing awareness for the benefits of water reclamation from wastewater, this lead to a rapid increase in MBR plant installations (WEF, 2012).

2.4.2 Membrane bioreactors in wastewater treatment

In a classic sewage treatment process (Figure 5A), pretreatment of the wastewater, including the removal of larger objects and coarse material, is followed by primary treatment in sedimentation tanks or clarifiers to remove settle-able solids and floating scum. In the secondary treatment step, the con-ventional activated sludge process (CAS); organic material is degraded by microorganisms in aerated basinets. The microorganisms accumulate into

19

flocs, which are suspended in the wastewater. After the treatment step, the flocs are then removed from the liquid in a secondary settler. However, this process depends on easily settle-able flocs and can be disturbed by variations in wastewater volumes or composition.

Here, MBRs (Figure 5B) can replace secondary treatment and offer many ad-vantages: MBRs enable the decoupling of SRT and HRT, because the bio-mass is retained in the bioreactor by the membrane. This allows for longer SRTs, which benefits slow-growing nitrifying bacteria or methanogenic ar-chaea and results in better biodegradation of organic material, while HRTs can be kept short (Yeo, Goh, Zhang, Livingston, & Fane, 2015). MBRs can replace biological treatment and gravitational settling or clarifier, because they can handle larger concentrations of solids than CAS systems, which are limited by the sedimentation rate (Leiknes, 2010). Since MBRs eliminate the need for large sedimentation tanks, they are relatively compact plants and have been reported to require up to 50% less space in comparison to conven-tional wastewater treatment plants (Leiknes, 2010). This is often a crucial requirement for selecting a wastewater treatment process on industrial sites (Judd, 2010).

Due to the small pore size of MF/UF membranes, suspended solids and or-ganic matter are efficiently removed from the wastewater, so MBRs are also able to produce high quality effluent, which can then be re-used for non-potable applications (WEF, 2012). This is an advantage in areas where fresh water is in short supply or for wastewater treatment plants located in protect-ed nature, where demand on effluent quality for discharge is high.

Down-sides of MBR technology include relatively the requirement for pre-treatment to prevent membrane damage from coarse material, high energy requirements and capital expenditure as well as the requirements for highly trained personnel (Faisal I. Hai, Yamamoto, & Lee, 2014). Further on, mem-brane fouling, which decreases membrane performance and therefore process productivity (Faisal I. Hai et al., 2014), is still an issue, shortening membrane lifespan and driving up operational costs, when membranes have to be cleaned or replaced. MBR technology is still more expensive than CAS, but costs go down as more MBR plants are implemented. Additionally, MBR technology is still perceived as “novel”, with MBR equipment being unique to each supplier, which hinders a more wide-spread implementation (Judd, 2010). However, as MBR knowledge becomes more widespread, confidence in the technology increases and membrane prices drop, thereby further reduc-

20

ing operational costs, MBRs are expected to become rapidly more wide-spread.

Figure 5 Comparison of a (A) typical sewage treatment process with a conventional acti-vated sludge (AS) treatment and (B) membrane bioreactor (MBR) process. Adapted from (Leiknes, 2010).

MBRs have been tested on a lab-scale or pilot-scale, for a wide variety of wastewater sources, including municipal wastewater, manure, food pro-cessing wastewater, industrial wastewaters (pulp and paper, textile, tannery), landfill leachate and wastewater from oil and gas industries (Liao, Kraemer, & Bagley, 2006; Lin et al., 2012).

On a full-scale, MBRs are most commonly implemented in municipal wastewater treatment and, to a lesser extent, in on-site treatment of industrial wastewater, mostly for pharmaceutical and food and beverage industries and the treatment of landfill leachate (Lesjean & Huisjes, 2008).

AS

sludge

treatment

pretreatment

sludge

treatment

MBR

secondary treatmentprimary

treatmentscreen and grit

chamberprimary

settler

secondary

settler

A

B

21

2.4.3 Membrane bioreactor processes and operation

MBR processes can be classified by the type of membrane used and the oper-ation mode (anaerobic/aerobic) (Figure 6). The benefits and disadvantages of osmotic membranes in comparison to pres-sure-driven membranes in MBRs are discussed in chapter 2.4.4.

Figure 6 Membrane bioreactor classifications. Membrane bioreactors can generally be described according to the membrane process used (pressure driven membranes vs. osmot-ic membranes), as well as their operation mode

The main benefits and drawbacks of aerobic (AeMBR) and anaerobic MBRs (AnMBRs) are listed in

Table 1. In anaerobic processes, microbial growth is slower than in aerobic processes, which leads to lower biomass production and therefore lower sludge production. For anaerobic processes to work efficiently, usually long SRTs and large reactor volumes are therefore required. The slow growth of methanogens is also the reason, why, in traditional biological treatment where SRT and HRT are coupled, anaerobic treatment is generally preferred for high-strength wastewater, while aerobic treatment is preferred for low-strength wastewater (Stephenson, Brindle, Judd, & Jefferson, 2000). Howev-er, since MBRs decouple SRT and HRT, longer SRTs can be achieved, so AnMBRs have been investigated for low-strength wastewater as well. Here, AnMBRs allow for higher organic loading rates and preventing biomass washout (Liao et al., 2006).

membranebioreactors

pressure-driven membranes

osmoticmembranes

anaerobic aerobicanaerobic aerobic

membrane

process

operation

mode

22

In contrast to AeMBRs, AnMBRs do not require aeration, but instead gener-ate renewable energy in the form of biogas. Aeration is expensive and con-tributes to up to 80% of energy costs, which in turn make up 79.6% of OPEX (Lin et al., 2012). Unlike AnMBRs, AeMBRs are already widely used in full-scale wastewater treatment plants, while AnMBR technology still seems to be “under development”, mostly due to the complexity of the anaerobic diges-tion process that is easily inhibited by toxic compounds in the wastewater (de Lemos Chernicharo, 2015; Lin et al., 2012; Skouteris, Hermosilla, López, Negro, & Blanco, 2012).

Table 1 Aerobic vs anaerobic membrane bioreactors, adapted from (Chan, Chong, Law, & Hassell, 2009; Judd, 2010; Stephenson et al., 2000)

Feature Aerobic MBR Anaerobic MBR

Organic removal efficiency High High

Organic loading rate High Low

Sludge production High Low

Energy requirement High Low

Start-up time Weeks Months

Microbial growth rate Faster Slower

Biogas production No Yes

Odour problems Less likely More likely

The two most common MBR process configurations are displayed in Figure 7. Both side-stream (A) and submerged MBR configuration (B) have their advantages and disadvantages. Side-stream MBRs are considered more ener-gy-intensive, since a powerful pump is required to circulate large volumes of wastewater from the reactor to the membrane module and back. On the other hand, side-stream configuration limits fouling and requires less membrane area due to higher shear and higher crossflow velocities and higher fluxes, respectively. Due to the membrane being placed outside the reactor, it is easi-er to operate, can be chemically cleaned in-situ without affecting the bioreac-tor and the membrane can be replaced quickly, limiting operational downtime (Judd, 2010).

Benefits of the submerged MBRs include the simpler design, ease of sludge discharge and higher energy efficiency. On the downside, submerged MBRs can handle lower concentrations of suspended solids, than side-stream MBRS. The submerged configuration is commonly used for large-scale ap-

23

plications involving low-strength wastewater and is currently dominating the market, while side-stream configuration is more common for small-scale ap-plications and difficult to treat wastewaters (Judd, 2010).

Figure 7 The two main MBR process configurations: A) pressure-driven external side-stream and B) vacuum-driven submerged MBR configuration. In A), the effluent is recir-culated by a pump from the bioreactor, to the membrane module situated in an external loop. The concentrated stream is returned into the bioreactor. In B), the permeate is r e-moved by vacuum

2.4.4 Osmotic membrane bioreactors

In osmotic membrane bioreactors (OMBRs), FO membranes are integrated into MBRs instead of pressure-driven membranes, which are commonly UF or MF membranes. In most cases, OMBRs are combined with an RO process downstream in order to reconcentrate the draw solution and extract clean wa-ter from the diluted draw solution (Blandin, Le-Clech, et al., 2018). When

Abioreactor

membrane

sludge

permeate

wastewaterin

air

recirculated stream

Bbioreactor

sludge

permeate

wastewaterin

air

24

seawater is used as a draw solution, it can also be used for simultaneous sea-water desalination (Luo, Phan, et al., 2017).

The advantages of osmotic MBR systems include improved effluent quality and higher retention of trace organic contaminants, such as pharmaceuticals, endocrine disruptors and pesticides, solids, viruses and ions, where porous MF or UF membranes might not yield adequate effluent quality. This is due to the dense double barrier of FO and RO (Blandin, Le-Clech, et al., 2018). In the case of anaerobic processes, this could also imply that FO-AnMBRs are better suited for biogas production from dilute wastewater sources than MF or UF-AnMBRs, because they allow for higher retention of solids and bio-mass (C. Chen et al., 2016). As a result, larger volumes of wastewater can be treated without risking wash-out of the slow growing methanogens (Liao et al., 2006).

OMBRs also achieve higher retention of total nitrogen and phosphorous in comparison to conventional MBRs (Ryan W. Holloway et al., 2015; X. Wang, Chang, & Tang, 2016; Z. Wang, Wu, Yu, Liu, & Zhou, 2006).

Further on, smaller contaminants in the wastewater can be degraded more efficiently, because they are retained in the bioreactor for longer (Y. S. Gu et al., 2015; Holloway, Achilli, & Cath, 2015; Xinhua Wang et al., 2017). When conventional MBRs with MF or UF membranes are coupled with RO mem-branes for further downstream treatment, severe fouling on these RO mem-branes can be observed. When dense FO membranes are used instead, RO membrane fouling can be substantially reduced (Ryan W Holloway et al., 2015). Another main advantages of osmotic MBRs is the lower energy con-sumption, because no high pressure pumps are required (L. Chen et al., 2014).

The use of FO membranes also leads to some disadvantages: the water flux is lower than in conventional MBRs (typically under 10 Lm-2h-1) and the use of draw solutions is necessary, which has to be replaced or reconcentrated via a further process step (C. Chen et al., 2016; X. Wang et al., 2016). Further on, reverse salt flux and high salt rejection of the osmotic membrane give rise to elevated salt level in the membrane bioreactor and reduces the osmotic pres-sure gradient and water flux. Salt accumulation in the bioreactor is aggravat-ed by the relatively long SRTs and short HRTs in osmotic MBRs: HRT und SRT affect the import of salt into and transport out of the bioreactor. In order to keep salinity low, long HRTs and short SRTs would be required. However,

25

HRTs are commonly kept short and SRTs rather long to achieve effective biological treatment and keep capital costs and reactor volumes low (Xiaoye Song, Xie, Li, Li, & Luo, 2018). In the long run, ammonia and alkalinity could also accumulate in the reactor (C. Chen et al., 2016). The elevated salt levels change biomass characteristics inside the bioreactor, elevate soluble microbial products and extracellular polymeric substances and contribute to fouling (Ryan W Holloway et al., 2015; Luo, Phan, et al., 2017; Xiaoye Song et al., 2018). However, the fouling layer may be less compacted due to ab-sence of hydraulic pressure and more reversible than in pressure driven mem-brane MBRs (Hu, Wang, Wang, Li, & Ren, 2017; X. Wang et al., 2016).

Interestingly, anaerobic osmotic MBRs (FO-AnMBRs) have been reported to be more resistant to accumulated salinity in the reactor and little impact on biogas production could be observed (Y. Gu et al., 2015). Salinity build-up is one of the biggest challenges that hinder its more widespread implementation of osmotic MBRs (Kai Yin Tang & Ng, 2014; Xiaoye Song et al., 2018). One possible solution is the selection of a suitable draw solution, for example or-ganic based draw solutes like sodium acetate that are readily biodegradable in the bioreactor and do not contribute to salinity build-up, or mixing inorganic draw solutions with surfactants like Triton X-114 in order to reduce the re-verse salt flux, but maintain the high osmotic pressure (Xiaoye Song et al., 2018). Another possibility is the use of highly selective FO membranes with high water flux and low reverse salt flux. Biomimetic FO membranes with aquaporin channels have been identified as having low reverse salt flux with-out a trade-off with water flux and therefore being suitable for osmotic MBRs (Luo, Xie, et al., 2017) .

26

3 Forward osmosis for water and nutrient

recovery

From 1980-2004, global meat consumption has doubled. Since nearly one third of the water used in agriculture is needed for meat production, this puts further pressure on the diminishing global freshwater resources (Mekonnen & Hoekstra, 2012). One possible solution to reduce the water footprint of meat is by finding new protein sources for animal feed, such as single cell proteins (SCPs) (Ravindra, 2000). They can be produced using microbial biomass fed with agricultural and industrial wastes and therefore don’t require farm land for their production. However, harvesting of the biomass is still a challenge (Pragya, Pandey, & Sahoo, 2013).

FO has previously been tested as a method for biomass dewatering and the recovery of water and valuable compounds, such as SCPS, or nutrients, such as N, K and P, from wastewater. (Holloway, Childress, Dennett, & Cath, 2007; Q. Liu et al., 2016; Lutchmiah et al., 2011; Munshi et al., 2018; J. Zhang et al., 2014). FO is used for these application due to its low energy demand, high rejection capabilities and low fouling propensity (Lutchmiah et al., 2014). The benefits of FO for wastewater treatment have been discussed in chapter 2.3.2.

However, little is known about whether AD effluents or microbial biomass be treated directly with novel biomimetic FO membranes incorporating aqua-porin proteins and what membrane performance in terms of water flux Jw and reverse salt flux Js can be achieved. Further on, FO fouling mechanisms are complex and hard to predict. Many studies have been focussing on using syn-thetic wastewaters of defined compositions and model foulants such as algi-nate or bovine serum albumin (BSA) (S. Lee et al., 2010; Mi & Elimelech, 2008), but the mechanisms when treating real wastewater are not fully under-stood. Since fouling is one of the main disadvantages hindering the more widespread implementation of membrane processes for wastewater applica-tions, as discussed in chapter 2.3.3, creating a better understanding of what type of fouling (biofouling, organic fouling, inorganic fouling) can be ex-pected will help to develop suitable pretreatment and cleaning strategies.

Another important topic is the selection of the most suitable draw solution. Ideally, the draw solution should induce a high Jw, while keeping the Js as small as possible. It should also be non-toxic, easily recoverable, inexpensive

27

and not inhibit microbial growth in an anaerobic bioreactor (Achilli et al., 2010; Bowden et al., 2012).

Paper I focuses on the water recovery from AD effluents, while Paper III in-vestigates the dewatering of methane oxidizing bacteria for the harvest of SCPs. The membranes used in both studies were flat sheet TFC membranes, supplied by Aquaporin A/S (Copenhagen, Denmark) and all experiments were run in AL-FS configuration.

The findings of Paper I and Paper III were used towards the integration of biomimetic membranes in to FO-AnMBRs.

3.1 Forward osmosis for the treatment of

anaerobic digestion effluents (Paper I)

3.1.1 Introduction and aim

In Paper I, water was extracted from eight different types of AD effluents (both synthetic and real) with varying strength in terms of total organic car-bon (TOC) and solids concentration using flat-sheet biomimetic FO mem-branes (see Table 2).

The aim of the study was to evaluate the membrane performance in terms of Jw, Js and nutrient rejection. Further on, membrane fouling was examined to determine the composition of the fouling layer.

Additionally, methane potential of the wastewater previously digested in an-aerobic bioreactors was analysed. The results of this study were used in order to create better understanding of what an ideal wastewater candidate would be for use in an integrated FO-AnMBR-MD/RO process.

28

Table 2 AD effluent characteristics

Real effluents Synthetic effluents

swine

ma-

nure

potato

starch

wastewa

ter

cattle ma-

nure, ther-

mophilic

cattle

manure,

meso-

philic

BA

medi-

um +

GTO

BA

medi-

um +

glucose

BA

medi-

um +

mix-

ture

BA

medi-

um +

casein

TOC

[g/L]

1.51

±0.01

1.37

±0.12

4.55

±0.00

7.11

±0.05

1.95

±0.15

1.42

±0.15

1.18

±0.01

0.90

±0.48

TS [g/L] 7.73

±0.00

8.68

±0.35

6.51

±3.18

8.27

±0.26

7.06

±0.02

18.55

±0.04

6.72

±0.30

21.81

±0.07

VS [g/L] 3.21

±0,33

1.82

±1,57

4.26

±2,84

3.7

±0,25

3.53

±1,83

10.91

±0,99

4.15

±2,92

15.14

±6,81

TSS [g/L] 11.92

±0.33

13.70

±1.57

23.17

±2.84

23.02

±0.25

21.03

±1.83

14.12

±0.99

19.35

±2.92

12.79

±6.81

TKN

[g/L]

1.68

±0.01

1.19

±0.09

3.34

±0.00

2.20

±0.00

5.97

±0.01

4.84

±0.01

3.80

±0.00

2.69

±0.32

TAN

[g/L]

2.08

±0.00

0.91

±0.06

3.41

±0.00

1.66

±0.00

5.80

±0.00

4.46

±0.01

3.24

±0.00

1.79

±0.02

Ortho-P

[g/L]

0.12

±0.00

0.19

±0.06

0.31

±0.00

0.28

±0.01

0.59

±0.00

0.67

±0.00

0.57

±0.00

0.83

±0.00

Density

[kg/L]

1.00

±0.00

1.00

±0.00

1.02

±0.00

1.01

±0.00

1.00

±0.00

1.00

±0.00

1.00

±0.00

1.01

±0.00

Dynamic

viscosity

μ [mPas]

1.35

±0.00

1.15

±0.00

2.00

±0.00 -*

1.39

±0.00

1.44

±0.00

1.24

±0.00

1.45

±0.00

Kinemat-

ic viscosi-

ty

[mm2/s]

1.35

±0.00

1.15

±0.00

2.00

±0.00 -*

1.37

±0.02

1.44

±0.00

1.23

±0.02

1.43

±0.00

* Viscosity could not be measured due to high TS content

3.1.2 Methods

The FO experiments in this paper were conducted in a lab-scale FO cross-flow setup, as shown in Figure 8.The active layer of the membrane was fac-ing the feed solution (AL-FS). Feed and draw solution (0.66 M MgCl2) were

29

recirculated by gearing pumps at a crossflow velocity of 8 cm/s for a duration of 24 h. After completion of the FO experiments, a membrane autopsy is conducted. The overall morphology of the fouling layer is analysed using scanning electron microscopy (SEM). Elemental composition of the fouling layer is analysed using energy-dispersive X-ray spectroscopy (SEM-EDS). Fourier-transform infrared spectroscopy (FTIR) is used to identify organic foulants, while inductively coupled plasma optical emission spectrometry (ICP-OES) and ion chromatography (IC) are employed for the determination inorganic foulants. To examine biological fouling, Adenosine Triphosphate (ATP) analysis is conducted.

A more detailed description of the methods can be found in Paper I.

Figure 8 Schematic representation of the lab-scale FO setup. The arrows indicate the di-rection of water streams. The dotted line represents the transfer of data

3.1.3 Results and conclusions

The main results of the FO experiments are displayed in Table 3. All results can be found in Paper I.

The results show that the average water flux Jw,ave varies greatly for the dif-ferent AD effluents and that there were also clear differences in flux decline: potato starch wastewater reached 30% feed recovery within 12 h, while ther-mophilic cattle manure and mesophilic cattle manure reached the same recov-ery only after 16 h and 21 h, respectively. However it was not possible to di-rectly correlate feed properties of the AD effluent with the flux decline. This becomes clear when comparing the flux decline in the synthetic effluents

30

with the real effluents: Although Jw,ave of the real effluents, with the excep-tion of potato starch wastewater, generally declined with increasing dynamic viscosity and TOC content, the opposite trend could be observed with the synthetic effluents. It is therefore likely that the differences in flux decline can be attributed to fouling and ICP effects (Blandin, Vervoort, Le-Clech, & Verliefde, 2016).

The results also show that biomimetic FO membranes are able to achieve high TAN and orthophosphate-P rejection. The former can be explained by the use of MgCl2 as a draw solution: reverse salt flux of Cl--ions (Js, Cl) ex-ceeds the reverse salt flux of Mg2+-ions (Js, Mg), causing a charge imbalance. This induces anions from the feed solution to diffuse over the membrane into the draw solution in order to restore the charge equilibrium and causes accu-mulation of NH4+ on the feed side (Donnan equilibrium) (Hu et al., 2017). The high orthophosphate-P rejection can be explained by repulsion of the rel-atively large and negatively charged molecule by the membrane surface that also has a negative charge at pH 6. 7.

31

Table 3 FO performance and methane yield results of AD effluents

Real effluents Synthetic effluents

swine ma-nure

potato starch wastewater

cattle ma-nure, thermo-philic

cattle manure, meso-philic

BA medi-um + GTO

BA me-dium + glucose

BA me-dium + mixture

BA medium + casein

Jw, ave

[L/(m2h)]

3.3

±0.10

3.0

±0.22

2.4

±0.01

1.9

±0.17

3.1

±0.07

2.9

±0.38

2.9

±0.15

2.4

±0.63

Flux de-

cline [%]

40.67

±10.37

61.58

±2.91

59.92

±10.50

76.16

±4.85

66.12

±4.03

56.09

±5.53

71.03

±0.94

74.88

±19.81

Js, Mg

[g/(m2h)]

0.09

±0.02

0.31

±0.06

0.62

±0.02

0.41

±0.05

-0.08

±0.00

-0.10

±0.01

0.10

±0.00

0.01

±0.01

Js, Cl

[g/(m2h)]

2.41

±1.02

1.09

±0.06

2.46

±0.15

0.55

±0.26

2.17

±0.42

1.03

±0.78

2.2

5±1.50

1.26

±1.24

CH4 yield

[mL CH4/

gVS]

368

.±24

313.75

±54 166.00 188

574

±50

314

±25

271

±32

338

±35

TAN rejec-

tion [%] 92.34 85.53 96.95 95.34 81.25 96.55 80.76 85.38

Ortho-

phosphate-

P rejection

[%]

98.74 99.18 99.56 99.52 99.74 99.78 99.74 99.83

When deciding on a suitable wastewater source for treatment in an FO-AnMBR, both membrane performance (in terms of Jw) and bioreactor per-formance (methane yield) should be considered to yield an economically via-ble process. Out of the real effluents, potato starch wastewater and swine ma-nure achieve both a high Jw and higher methane yield, combined with a mod-erate flux decline, making them interesting wastewaters candidates.

Membrane autopsy of the fouled membranes showed that biological fouling and organic fouling occurred. A selection of results can be seen in Figure 9.

32

The full results can be found in Paper I. SEM pictures reveal that the surface of the clean membrane (Figure 9D) is fully covered by a fouling layer after 24 h of FO filtration (Figure 9C) and microorganisms on the membrane sur-face can be observed. FTIR (Figure 9A and B) indicated the presence of pol-ysaccharides (–CH and –OH groups: distinctive peak at 3241-3290 cm-1) and proteins (amide I C=O: peaks at 1627-1638 cm-1) in the fouling layer.

Figure 9 Membrane autopsy of fouled FO membranes. (A) and (B): FTIR of fouled FO membranes. (C) and (D): Exemplary SEM picture of the membrane fouled with BA medi-um + glucose and the clean FO active layer surface, respectively. SEM pictures of all membranes fouled with AD effluents can be found in Paper I.

The results of paper I show that biomimetic FO membranes can treat a wide variety of AD effluents, achieving high nutrient rejection in terms of TAN and orthophosphate-P (80.8-97.0% and 98.7-99.8%, respectively). FO mem-

D

30 µm 10 µm

microoganisms in clusters

C

30 µm

33

brane performance (Jw and Js) was reasonable, although organic fouling and biofouling occurred.

When selecting a suitable wastewater candidate, no compromise has to be made between high Jw and methane yield necessarily, as feed properties do not directly correlate with methane yield, fouling potential and FO perfor-mance. Jw, methane yield, high nutrient rejection and Js are critical aspects when designing a FO-AnMBR-RO process. High nutrient rejection of the FO membrane is important in order to achieve high product water quality and to reduce fouling on the RO membrane, as discussed in chapter 2.3.3. Methane yield and Jw are having large impacts on the economic viability of a FO-AnMBR-RO process, as they determine the output of the overall process.

Further studies with regards to re-concentration of the FO draw solution, as well as wastewater pretreatment and cleaning strategies are in order.

3.2 Forward osmosis for the dewatering of

methane oxidizing bacteria (Paper III)

3.2.1 Introduction and aim

In Paper III, biomimetic FO membranes were tested for the dewatering and cell harvesting of methane oxidizing bacteria (MOB) biomass containing SCPs. The aim of this paper was to investigate the effect of draw solution selection on Jw and Js. Further on, the effect of fouling on the Jw was ana-lysed.

3.2.2 Methods

An overview of the conducted FO experiments is displayed in Table 4. For the selection of the draw solution, MQ water was used as a feed, while the fouling experiments were conducted with MOB in dAMS medium as a feed solution. Like in Paper I, the duration of the FO experiments was 24h.

Four draw solutions were preselected for this application: NaCl, MgCl2, brine and glycerol. All of these are known to be non-toxic, not inhibit microbiolog-ical growth in low concentrations, comparably inexpensive and are able to create high osmotic pressure when dissolved in water (Achilli et al., 2010; Bowden et al., 2012; Stavros Kalafatakis et al., 2017). NaCl and MgCl2 are selected because they are amongst the most commonly used draw solutions in FO. The brine was made by dissolving NaCl and MgCl2 in water, with the concentrations of both chosen in order to resemble brine from seawater desal-

34

ination (Tepavitcharova, Todorov, Rabadjieva, Dassenakis, & Paraskevopoulou, 2011). Glycerol, which is also generated as a by-product in biodiesel production, was chosen in order to include one organic draw solute that could also be used as a substrate by the MOB.

Table 4 FO experiments in Paper III

Feed Solution (FS) Draw solution

(DS)

DS osmotic pres-

sure

[atm]

Aim

1 MQ-water NaCl 60

Effect of osmotic

pressure in DS on

Jw and Js

2 MQ-water NaCl 30

3 MQ-water MgCl2 60

4 MQ-water MgCl2 30

5 MQ-water Brine 60

6 MQ-water Brine 30

7 MQ-water Glycerol 60

8 MQ-water Glycerol 30

9 MOB in dAMS MgCl2 30

Impact of biofouling

on Jw and Js

10 MOB in dAMS MgCl2 60

11 MOB in dAMS NaCl 30

12 MOB in dAMS NaCl 60

13 MOB in dAMS Glycerol 30

14 MOB in dAMS Brine 30

The FO setup was similar to that used in Paper I, except that a gas bag was attached to the FO feed solution bottle in experiment 9-14 in order to supply gas (a mixture of 60% O2 and 40% CH4) for the methane oxidizing bacteria in the biomass during the course of FO experiments.

A more detailed description of the methods can be found in Paper III.

35

3.2.3 Results and conclusions

The impact of the draw solution on Jw and Js are displayed in Figure 10. When MQ water was used as a draw solution, NaCl and brine achieved the highest Jw, which is in agreement with the results found in literature (Achilli et al., 2010).

Figure 10 Effect of draw solution on water flux and reverse salt flux. Experiments were conducted at two draw side bulk osmotic pressures for all draw solutes, namely 30 atm and 60 atm. Error bars represent the average deviation of the mean of duplicate results.

The lowest Jw was observed with glycerol as a draw solute, while at the same time yielding the highest Js. Since the same bulk osmotic pressure was chosen for all draw solutions, the differences in Jw could be explained by dilutive internal concentration polarisation (ICP) effects (Achilli et al., 2010; Bowden et al., 2012), which is caused by the permeation of water molecules in the porous support layer. This results in the dilution of the draw solution, reduc-ing the effective osmotic pressure difference over the membrane and lower-ing Jw. The extent of ICP is influenced by differences in ion diffusivity, with a low diffusivity leading to severe ICP and low water flux (Ashley J. Ansari et al., 2015; Cornelissen et al., 2008).

Jw /Js was established as a useful tool to assess the amount of salt lost during forward osmosis, in comparison to the recovered water volume at a given osmotic pressure (Achilli et al., 2010; Nathan T. Hancock & Cath, 2009). In this study, MgCl2 was found to provide the best compromise between a high Jw and a low Js.

36

The effects of fouling on Jw are displayed in Figure 11. The results in indi-cate, that (with the exception of 60 atm NaCl) there is little difference with regards to Jw, when the active MOB culture is used as a feed solution in com-parison to MQ water, although the membrane was visibly fouled at the end of the FO experiments (see Paper III). Fouling was easily removed by rinsing with DI water. This indicates that after 24 h the fouling layer consisted of loosely adsorbed organic matter and microorganisms and that no biofilm had developed, which would be much harder to remove (Q. She et al., 2016). This is in agreement with results from previous studies, where it was found that membrane fouling was more severe at higher initial Jw levels (Qianhong She et al., 2012; C. Y. Tang, She, Lay, Wang, & Fane, 2010; Zou et al., 2013).

Figure 11 Effect of fouling on water flux. Experiments were conducted at two draw side bulk osmotic pressures for NaCl and MgCl2 (60 atm and 30 atm), while experiments for brine and glycerol were conducted for 30 atm only. Error bars represent the average devia-tion of the mean of duplicate results.

In conclusion, FO can be used to harvest biomass from methane oxidizing bacteria. However, long-term studies should be conducted in order to investi-gate the development of the fouling layer over a longer time period. Another factor is to identify a suitable process to reconcentrate the draw solution, which has not been a port of this study. Further on, an economic analysis comparing the costs of FO with other suitable cell harvesting methods should be conducted.

37

4 Forward osmosis hybrids for brewery

wastewater treatment

Approximately 40 % of the wastewater in Denmark treated by wastewater treatment plants is industrial wastewater (Thomsen, 2016). In light of high water prices and increasing wastewater disposal costs in order to comply with stricter EU legislation (EU, 2000), as well as concerns about freshwater shortage, the interest to reduce wastewater volumes and reclaim clean water for on-site usage is increasing (Dalgaard, 2016; Simate et al., 2011).

Beer is the fifth-most consumed beverage in the world (Fillaudeau, Blanpain-Avet, & Daufin, 2006). Unfortunately, beer brewing is also a process that generally requires 4-8 litres of drinking for the production of one litre of beer (Kunze, Wainwright, & Mieth, 1999). Since the composition, pH and pollu-tion load in brewery wastewater can vary greatly, it is also considered diffi-cult to treat and several treatment steps are required (Simate et al., 2011).

In chapter 2.3.2, FO applications for wastewater treatment was discussed. Since the end product of FO is a diluted draw solution, FO is often combined with other processes in order to reclaim clean water a reconcentrate the draw solution. In this chapter, two options of FO hybrids are discussed: combined FO-RO or the integration into an FO-AnMBR (see chapter 2.4.4).

FO-RO has been successfully tested to recover potable water from wastewater sources like municipal wastewater (Choi et al., 2016; Hickenbottom et al., 2013; Volpin et al., 2018) or impaired or brackish sur-face water (Tzahi Y. Cath, Hancock, Lundin, Hoppe-Jones, & Drewes, 2010; Chun et al., 2016). The double barrier of FO and RO efficiently retains pollu-tants and achieves high-quality product water (Nathan T Hancock, Xu, Heil, Bellona, & Cath, 2011; Hickenbottom et al., 2013). However, little is known about the applicability of FO-RO for brewery wastewater treatment.

While FO-AeMBRs have seen increasing interest over the past years, little research has been conducted on FO-AnMBRs, with most studies focusing on low-strength and/or synthetic wastewater (L. Chen et al., 2014; Y. Gu et al., 2015; Hu et al., 2017; S. Li et al., 2017; Xinhua Wang et al., 2017). To the best of my knowledge, they have not been tested for high-strength food pro-cessing wastewater, such as brewery wastewater, as of yet.

38

Paper IV focuses on brewery treatment using FO-RO, while Paper II exam-ines the use of an FO-AnMBR, with focus on the start-up period.

Further on, the design and construction of a pilot-scale FO-AnMBR-RO sys-tem is described.

4.1 Forward osmosis-reverse osmosis hybrid

for water recovery from brewery wastewater

(Paper IV)

4.1.1 Introduction and aim

The aim of this paper was to investigate the water reclamation from brewery wastewater for non-potable reuse, using a FO-RO system. The focus is on FO-RO membrane performance (Jw, nutrient rejection), as well as FO clean-ing efficiency in terms of flux recovery

4.1.2 Methods

All FO-RO experiments were conducted in a pilot-scale FO-RO setup, as shown in Figure 12. The membranes used for this study was hollow fibre FO modules, supplied by Aquaporin A/S (Copenhagen, Denmark). Two modules were mounted in parallel in order to achieve a total membrane are of 1.2 m2, in AL-FS configuration.

Two types of brewery wastewater were used as a feed solution. The authentic brewery wastewater was collected from a brewery in Copenhagen, Denmark, where the wastewater was produced from all steps within the brewing process and collected in a storage container. The synthetic wastewater was modelled after a recipe proposed by Tam and colleagues (2005). Additionally, baseline testes with RO water as a feed solution were performed in order to establish the FO-RO performance in absence of fouling.

After each experiment, a multi-step chemical cleaning was conducted, using citric acid (10 g/L) and NaOH (0.08 g/L) alternated by rinsing steps with clean water.

A more detailed description of the used methods can be found in Paper IV.

39

Figure 12 Simplified schematic drawing of the FO-RO system. Rounds symbols marked with T represent temperature sensors, c conductivity sensors, LT level meters and FT flow meters, respectively. The green line represents the water streams on the FO feed side, or-ange for the FO draw side, blue for the RO feed side and yellow for RO permeate side.

4.1.3 Results and conclusions

FO and RO performance of the real and synthetic brewery wastewater are displayed in Figure 13. As can be seen in Figure 13 (A), there is little differ-ence in Jw,FO for both types of brewery wastewater at the same feed recovery after an initial sharp flux decline. However, the real brewery wastewater only reaches 61% feed recovery, while the synthetic brewery wastewater reaches 69% feed recovery within the same time span. This could potentially be ex-plained by the higher organic content of real brewery wastewater (7.90 gCOD/L), in comparison to the synthetic brewery wastewater (4.05 gCOD/L). This is in agreement with finding of previous studies: Parida and colleagues found that an increase in organic content in the feed can lead to more severe FO fouling and therefore a stronger flux decline (Parida & Ng, 2013). Since the active layer, which is facing the wastewater, is on the inner side of the fibre, which only has an inner diameter of 300µm, it is possible that fouling is exacerbated in comparison to flat-sheet membranes (see Paper I and III).

Subsequent RO was conducted at a constant pressure of 40 bars. It could be observed that Jw,RO decreased over the course of the experiment. This is due to the fact that the driving force decreased over time, because osmotic pres-sure of the draw solution increased, while the RO feed pressure was kept con-stant (Figure 13b).

40

Figure 13 FO (A) and RO (B) flux of brewery wastewater. The displayed data represents the average of duplicates. FO was run for 210 minutes and RO was run for 60 minutes sub-sequently.

With regards to nutrient rejection (Figure 14), a moderate COD and TN rejec-tion over the FO membrane could be achieved (ranging from 78.4% to 93.3%). TP rejection is consistently high (89.1% for real brewery wastewater and 96.4% for synthetic brewery waste), which is in line with results found in the literature and can be explained by repulsion of negatively charged phos-phate by the negatively charged membrane, in combination with steric hin-drance (Holloway et al., 2007; Xue et al., 2015).

The moderate TN rejection in FO is also consistent with results from previous studies for TFC membranes (Rodrigo Valladares Linares et al., 2013; Z. Wang et al., 2016). In contrast, the combined rejection of the double barrier of the FO and RO membrane is high, achieving efficient removal of COD (98.2%), TN (99.0%) and TP (99.9%) in the case of real brewery wastewater. Overall, this shows that with the combined FO and RO barrier, high effluent quality can be achieved.

A B

Jw

[Lm

-2h

-1]

41

Figure 14 Nutrient rejection of real (A) and synthetic (B) brewery wastewater. The di s-played data represents the average of duplicates and the error bars represent the average deviation of the mean of duplicate results

Jw,FO for the pristine and cleaned membrane, using the real brewery wastewater is shown in Figure 15. Jw,FO of the cleaned membrane is visibly smaller than that of the pristine membrane, indicating the presence of fouling remnants that could not be removed. When comparing the average Jw, of the clean membrane (4.5 Lm-2h-1) and after cleaning (3.4 Lm-2h-1), it can be stat-ed that approximately 75% of the baseline Jw can be recovered after chemical cleaning. Further optimisation of the chemical cleaning protocol is in war-ranted in order to achieve better flux recovery. Further on, the long-term ef-fects of the chemicals on membrane integrity should be investigated.

42

Figure 15 FO flux of the cleaned membrane after a multi-step chemical cleaning proce-dure with NaOH and citric acid, in comparison to the pristine, unused membrane

4.2 Anaerobic osmotic membrane bioreactor I:

Lab-scale setup (Paper II)

4.2.1 Introduction and aim

The overall goal of Paper II was to analyse the feasibility of brewery wastewater treatment using AnMBRs incorporating biomimetic FO mem-branes. The start-up of two lab-scale FO-AnMBR reactors was assessed and the effect of stepwise HRT reduction on bioreactor performance in terms of methane production, volatile fatty acids (VFA) accumulation, solid retention time (SRT), pH fluctuation and Jw was observed.

4.2.2 Methods

Two lab-scale continuous stirred tank reactors (CSTR) combined with for-ward osmosis flat-sheet modules were used (Figure 16). One reactor was fed with synthetic brewery wastewater (Rsynth) and the second was fed with real brewery wastewater (Rreal).

43

In P1, the CSTR was run without a membrane in order to establish a baseline for the bioreactor performance. In P2-P4, the membrane was connected to the CSTR in side-stream configuration. For this study, the side-stream configura-tion was chosen, because it allows for easy access to the membrane module without disturbing the bioreactor.

The hydraulic retention time (HRT) was reduced stepwise, from 20 days to 2.5 days, by adjusting the draw solution concentration and increasing the feeding rate. Methane yield and rate, Jw, VFA, pH was monitored continu-ously. Further on, samples from inside the bioreactor were taken and the morphology of the cells was analysed using confocal microscopy (for the complete results, see Paper II). A more detailed description of the methods can be found in Paper II.

An overview over the operation is given in Table 5.

Figure 16 Schematic representation of a lab-scale osmotic membrane bioreactor. A con-tinuous stirred tank reactor (2L) was connected to a FO flat-sheet module (140m2) in side-stream mode. The volume of the draw tank was 20L in order to minimise draw solution dilution

44

Table 5 Operational parameters in different periods Reactor Period HRT

[days] Expected SRT [days]

Expected Jw(th) [L m

-2 h

-1]

OLR [gCOD/L reac-tor]

Membrane

Rsynth 1 20 20 - 0.28 -

2 10 ∞ 0.60 0.57 +

3 5 ∞ 1.19 1.13 +

4 2.5 ∞ 2.38 2.26 +

Rreal 1 20 20 - 0.24 -

2 10 ∞ 0.60 0.49 +

3 5 ∞ 1.19 0.98 +

4 2.5 ∞ 2.38 1.96 +

4.2.3 Results and conclusions

The development of methane yield and rate over time is displayed in Figure 17. In P1, where the reactor was run in CSTR mode and no membrane was connected, the methane yield was fluctuating between 40-130 mL CH4 g-1 COD (Figure 17A) and the methane production rate was 32.0±8.0 and 39.9±14.6 mL CH4 L

-1 day-1 (B) for Rreal and Rsynth, respectively. In P2, when

the membrane was integrated, a sharp increase in methane yield and rate for RReal could be observed, reaching 109.5 mL CH4 L-1

day-1 and 117.5 mL CH4 gcod

-1 L

-1day-1 and dropping again afterwards. Similar effects could be observed in P3. The strong fluctuations could be due to difficulties of the in-oculum to adapt to the brewery wastewater. Shear stress stemming from con-tinuous pumping of the microorganisms to the FO module or back could also be an influence, by influencing the activity of the anaerobic biomass and dis-turbing the interaction between acetogens and hydrogen consuming methano-gens (see Paper II) (Brockmann & Seyfried, 1997; Dereli et al., 2012; M. Kim, Ahn, & Speece, 2002). In P4, Rsynth collapsed and the experiments were stopped.

Comparing P1 and P2-4, the results indicate that FO-AnMBRs (P2-P4) can achieve higher OLR and methane production rate in comparison to CSTR re-actors (P1). However, it was also apparent that the AD process did not stabi-lise; instead after 110 days, Rsynth production collapsed and the experiment was stopped.

45

Figure 17 Methane yield (A) and rate (B) of Rsynth and Rreal. In P1, the CSTR reactor was operated without the membrane module connected. The HRT was 20 days (P1), 10 days (P2), 5 day (P3) and 2,5 days (P4) respectively

The development of Jw is shown in Figure 18. Overall, it could be observed that Jw increased with decreasing HRT. However he targeted theoretical max-imum Jw(th) in order to achieve the selected HRT was not reached. As the draw solution volume was large (20L) in comparison to the bioreactor vol-ume (2L), this discrepancy can’t be explained by draw solution dilution. It is

46

therefore likely that combined effect of fouling and ICP was the explanation (Y. Gu et al., 2015).

Figure 18 The measured water flux (Jw) and expected water flux Jw(th) of FO membranes for A) Rreal and B) Rsynth. In P1, the CSTR reactor was operated without the membrane module connected. The HRT was 20 days (P1), 10 days (P2), 5 day (P3) and 2.5 days (P4) respectively

Overall, these results demonstrate the general feasibility of FO-AnMBR for brewery wastewater treatment. It is necessary to further optimise the process with regards to HRT/SRT, OLR and C/N ratios. Further on, the solute accu-mulation within the reactor is a known problem in FO-AnMBRs. Salinity

47

build-up could potentially be reduced by bleeding the reactor intermittently, or disconnecting the membrane module from the bioreactor for short periods to operate the bioreactors in CSTR mode. This would wash out accumulated VFA and salts. Further on, FO membrane cleaning strategies without affect-ing microbial growth in the bioreactor should be developed.

4.1 Anaerobic osmotic membrane bioreactor II:

Pilot-scale setup

4.1.1 Introduction and aim

Water management and wastewater disposal is a critical topic for every brew-ery, both for environmental and economic reasons (Fillaudeau et al., 2006). The composition of wastewater can vary greatly, with regards to composition, the amount of organic particles, pH and temperature. As there are often addi-tional charges for surpassing the pollution limits, there is an incentive for breweries to reduce wastewater volume and organic loading on-site before discharging their wastewater into municipal treatment systems (Briggs, Boulton, Brookes, & Stevens, 2004).

One way to achieve this goal is with a combined FO-AnMBR-RO system. In this integrated process, brewery wastewater can be treated, clean water can be reclaimed for non-potable application and biogas is generated (Figure 19). The reclaimed water can for example be used for boiler feed water, cooling system make-up water, washing and cleaning applications as well as for sprinkler water in fire protection systems. The biogas produced by AD can be used for boilers or combined heat and power units and help to become more independent of external energy supply (Simate et al., 2011).

However, full-scale implementation of industrial water reclamation is de-pending on many different factors such as economic viability, social ac-ceptance, legislation, discharge requirements, the reliability of the wastewater source, and the required water quality and quantity needed (EIB, 2008; Holmgren, 2016)

While there some pilot-scale FO-AeMBRs, to the best of my knowledge, no pilot-scale FO-AnMBR-RO has been built yet, (Blandin, Gautier, et al., 2018; Ryan W. Holloway et al., 2015; Qin et al., 2010)

48

The aim of this part of the PhD project was the design and construction of a pilot-scale FO-AnMBR-RO in order to demonstrate the technical feasibility of the process and identify challenges for implementation.

Figure 19 Process overview over the pilot-scale FO-AnMBR-RO, highlighting the possi-bility of biogas production and water recovery from brewery wastewater.

4.1.2 Design and construction

A rendering of the pilot-scale can be seen in Figure 20 and a picture of the constructed setup is displayed in Figure 21.

In this setup, a 200L CSTR bioreactor is continuously fed with wastewater stored in an intermediate bulk container. The feeding pump is also controlled by the level in the reactor, in order to avoid overfilling or emptying the reac-tor, in case Jw deviates from the chosen set point. The CSTR bioreactor is equipped with a pH/ oxidation reduction potential (ORP) meter and a conduc-tivity meter. The biogas is led out of the reactor through tube with a gas flow meter and a non-return valve and is released into the atmosphere outside the

49

building. The entire setup can be controlled via a programmable logic con-troller (PLC) unit.

The FO module is connected to the CSTR in side-stream mode. This configu-ration was chosen, because it allows for easier access to the membrane for cleaning and maintenance purposes, while also leaving greater flexibility in terms of the type and size of FO module used. In this case, a tubular FO module was selected, provided by Aquaporin A/S. The membrane is 1m long, has an active membrane area of 2.16 m2 and must be mounted vertically.

The draw solution in the draw solution container is mixed intermittently in order to avoid the formation of concentration gradients. The conductivity, pH and temperature of the draw solution are also measured.

The draw solution is circulated to a RO module (Dow SW SW30-2540), where clean water is produced. The conductivity and flow rate of the RO permeate and it is discharged into the drain.

wastewaterstorage

CSTR bioreactor

drawsolution

container

biogas outlet

RO module

PLC unit

FO module

50

Figure 20 Rendering of the pilot-scale FO-AnMBR-RO. The FO module is connected to the 200L CSTR bioreactor in side-stream mode. The diluted draw solution is circulated to the RO module and the RO permeate is discharged. The PLC unit monitors and controls process operations

Figure 21 Pilot-scale osmotic FO-AnMBR-RO. Here, the setup is equipped with a tubular FO module with a membrane area of 2.16 m2

51

5 Conclusions

5.1 Forward osmosis for water and nutrient

recovery

Biomimetic FO membranes were tested for the recovery of water and single cell proteins from AD effluents and MOB biomass. The goals were the analy-sis of Jw, Js, nutrient rejection and membrane fouling.

In the case of AD effluents, it was found that high rejection of TAN and or-thophosphate-P (up to 96.9% and 99.8%, respectively) and low Js were achieved. Membrane fouling after 24h was mainly organic fouling and bio-fouling. Jw was in the moderate to good range, ranging from 1.9-3.3 Lm-2h-1 for AD effluents and up to 12.2Lm-2h-1 for MOB biomass.

This shows that the biomimetic FO membranes are suitable for integration into FO hybrid systems, such as FO-RO or FO-AnMBR-RO, where high nu-trient rejection and low Js are vital for a stable operation of the system. How-ever, higher further work with regards to optimising pretreatment and clean-ing strategies is necessary.

5.2 Forward osmosis hybrids for brewery

wastewater treatment

FO membranes were integrated into FO-RO hybrids and FO-AnMBRs. The overall aim was to demonstrate the feasibility of water recovery from brew-ery wastewater for these processes.

For FO-RO, the main focus was on nutrient rejection and flux recovery after chemical cleaning, while the FO-AnMBR study focused on describing the start-up process and analysing the effect of HRT changes on Jw, methane pro-duction yield and rate.

The results of the FO-RO study indicated that the double barrier of FO and RO efficiently retains COD (98.2% rejection), TN (99.2% rejection) and TP (99.9% rejection), achieving high-quality effluent. Cleaning efficiency yield-ed approximately 75% flux recovery. This indicates that FO-RO can be used for water recovery from brewery wastewater, which can be used for non-

52

potable applications. Also in this case, further work to optimise pretreatment and cleaning protocols is recommended.

For FO-AnMBR, it was found that the integration of FO increased the me-thane production rate. However, process stability decreased with decreasing HRT, eventually leading to the collapse of Rsynth, which could be caused by shear stress or inadequate adaption of the inoculum. The results of the study indicate that brewery wastewater treatment in FO-AnMBR bioreactors is fea-sible, but more work in order to optimise HRT/SRT, reduce shear stress and lessen the accumulation of solutes inside the bioreactor is in order.

53

6 Perspectives and translation into

technology

6.1 FO

Results from Paper I and III show, that FO can be used to extract water from various wastewater sources. However, FO is usually used in hybrid systems, as further separation processes are necessary to recover clean water from the diluted draw solution, which requires more energy input. One solution to make FO processes more energy efficient is the use of waste heat from indus-trial processes or geothermal energy, where available, e.g. for FO-MD (Aydiner, Sen, Koseoglu-Imer, & Can Dogan, 2016). Another option is the use of a thermolytic draw solution (ammonia–carbon dioxide), in which the salts decompose to ammonia and carbon dioxide gas, when low-grade heat is supplied. The product water contains low concentrations of ammonia, and the gases can be reused to reconcentrate the draw solution (McGinnis & Elimelech, 2008).

Another concern sometimes raised about FO is the cost of chemicals used for draw solution. This could be solved (in some cases) by using waste streams or by-products of high osmotic pressure (e.g. glycerol from biodiesel produc-tion (S Kalafatakis et al., 2018). Another option is the use of sea water as draw solution (Xue et al., 2016), however, this could lead to fouling on the draw side of the membrane due to organic matter present in the seawater.

Further on, the mechanisms of FO fouling are not fully understood yet, espe-cially with regards to possible interaction of different types of foulants. In real wastewater, commonly a mixture of foulants are present, but foulant studies are often conducted using solutions of one or two model foulants in water, so more research is required.

6.2 FO-RO

One promising application for FO-RO is indirect desalination combined with water recovery from pretreated wastewater in coastal regions (Linares et al., 2014; Yangali-Quintanilla et al., 2015). Impaired water or treated water from a wastewater treatment plant is used as a feed and seawater, brackish water or brine from desalination plant as draw solution in FO, which is then desalinat-

54

ed by RO. FO reduces the fouling on RO membranes, as well as operational costs due to lower energy consumption, because less operational pressure is needed for the diluted draw solution in comparison to sea water.

Overall, further research is needed with regards to increasing FO flux levels in order to increase the economic viability of the process, as well as further upscaling in order to assess the challenges this technology could face in full-scale setups. Additionally, further analysis of CAPEX and OPEX should be conducted in order to point towards scenarios, where FO-RO is a viable op-tion.

6.3 FO-AnMBR

Although FO-AnMBRs have not received as much attention as FO-AeMBRs, it is a promising new technology with regards to process outcomes (biogas, high-quality effluent), but little is known in which cases it can compete with or replace conventional wastewater treatment technologies. They could be applied for the treatment of industrial wastewaters, where wastewater leaving the industrial process is discharged at 20-37°C, so little further heating in the bioreactor is necessary for anaerobic digestion. Further on, they could be used to treat dilute wastewater streams, which currently can’t be treated by currently existing anaerobic digesters. FO could be used to concentrate the wastewater stream in the reactor, leading to higher OLRs while preventing the slow-growing biomass from being washed out.

Another possibility would be to combine FO-AnMBRs with previous aerobic treatment in order to yield better removal of nitrogen and phosphorous.

However, further research is necessary, before this technology can be imple-mented in full-scale, especially with regards to long- term operation strate-gies, mitigation of salt accumulation in the reactor, as well as optimisation of HRT/SRT.

55

7 References

Achilli, A., Cath, T. Y., & Childress, A. E. (2010). Selection of inorganic-based draw solutions for forward osmosis applications. Journal of

Membrane Science, 364(1), 233-241. Al-Amoudi, A., & Lovitt, R. W. (2007). Fouling strategies and the cleaning

system of NF membranes and factors affecting cleaning efficiency. Journal of Membrane Science, 303(1–2), 4-28. doi:http://dx.doi.org/10.1016/j.memsci.2007.06.002

Alghoul, M. A., Poovanaesvaran, P., Sopian, K., & Sulaiman, M. Y. (2009). Review of brackish water reverse osmosis (BWRO) system designs. Renewable and Sustainable Energy Reviews, 13(9), 2661-2667. doi:https://doi.org/10.1016/j.rser.2009.03.013

Ansari, A. J., Hai, F. I., Guo, W., Ngo, H. H., Price, W. E., & Nghiem, L. D. (2015). Selection of forward osmosis draw solutes for subsequent integration with anaerobic treatment to facilitate resource recovery from wastewater. Bioresource technology, 191, 30-36. doi:http://dx.doi.org/10.1016/j.biortech.2015.04.119

Ansari, A. J., Hai, F. I., Guo, W., Ngo, H. H., Price, W. E., & Nghiem, L. D. (2016). Factors governing the pre-concentration of wastewater using forward osmosis for subsequent resource recovery. Science of The

Total Environment, 566–567, 559-566. doi:http://dx.doi.org/10.1016/j.scitotenv.2016.05.139

Ansari, A. J., Hai, F. I., He, T., Price, W. E., & Nghiem, L. D. (2018). Physical cleaning techniques to control fouling during the pre-concentration of high suspended-solid content solutions for resource recovery by forward osmosis. Desalination, 429, 134-141.

Ansari, A. J., Hai, F. I., Price, W. E., Drewes, J. E., & Nghiem, L. D. (2017). Forward osmosis as a platform for resource recovery from municipal wastewater - A critical assessment of the literature. Journal of

Membrane Science, 529, 195-206. doi:http://dx.doi.org/10.1016/j.memsci.2017.01.054

Aydiner, C., Sen, U., Koseoglu-Imer, D. Y., & Can Dogan, E. (2016). Hierarchical prioritization of innovative treatment systems for sustainable dairy wastewater management. Journal of Cleaner

Production, 112, 4605-4617. doi:https://doi.org/10.1016/j.jclepro.2015.08.107

Bailey, J. R., Bemberis, I., Hubbard, P., & Presti, J. B. (1971). Shipboard

Sewage Treatment System. Retrieved from Baker, R. W. (2004). Membrane technology and applications: J. Wiley. Blandin, G., Gautier, C., Sauchelli Toran, M., Monclús, H., Rodriguez-Roda,

I., & Comas, J. (2018). Retrofitting membrane bioreactor (MBR) into osmotic membrane bioreactor (OMBR): A pilot scale study. Chemical

56

Engineering Journal, 339, 268-277. doi:https://doi.org/10.1016/j.cej.2018.01.103

Blandin, G., Le-Clech, P., Cornelissen, E., Verliefde, A. R. D., Comas, J., & Rodriguez-Roda, I. (2018). Can osmotic membrane bioreactor be a realistic solution for water reuse? npj Clean Water, 1(1), 7. doi:10.1038/s41545-018-0006-x

Blandin, G., Vervoort, H., Le-Clech, P., & Verliefde, A. R. D. (2016). Fouling and cleaning of high permeability forward osmosis membranes. Journal of Water Process Engineering, 9, 161-169. doi:http://dx.doi.org/10.1016/j.jwpe.2015.12.007

Bogler, A., Lin, S., & Bar-Zeev, E. (2017). Biofouling of membrane distillation, forward osmosis and pressure retarded osmosis: principles, impacts and future directions. Journal of Membrane Science. doi:http://dx.doi.org/10.1016/j.memsci.2017.08.001

Boo, C., Lee, S., Elimelech, M., Meng, Z., & Hong, S. (2012). Colloidal fouling in forward osmosis: role of reverse salt diffusion. Journal of

Membrane Science, 390, 277-284. Bowden, K. S., Achilli, A., & Childress, A. E. (2012). Organic ionic salt

draw solutions for osmotic membrane bioreactors. Bioresource

technology, 122, 207-216. Briggs, D. E., Boulton, C. A., Brookes, P. A., & Stevens, R. (2004). Brewing:

Science and Practice (pp. 1-881): Elsevier Ltd. Brockmann, M., & Seyfried, C. F. (1997). Sludge activity under the

conditions of crossflow microfiltration. Water science and technology,

35(10), 173-181. doi:https://doi.org/10.1016/S0273-1223(97)00204-7 Cath, T. Y., Childress, A. E., & Elimelech, M. (2006). Forward osmosis:

principles, applications, and recent developments. Journal of

Membrane Science, 281(1), 70-87. Cath, T. Y., Hancock, N. T., Lundin, C. D., Hoppe-Jones, C., & Drewes, J. E.

(2010). A multi-barrier osmotic dilution process for simultaneous desalination and purification of impaired water. Journal of Membrane

Science, 362(1–2), 417-426. doi:http://dx.doi.org/10.1016/j.memsci.2010.06.056

Chan, Y. J., Chong, M. F., Law, C. L., & Hassell, D. (2009). A review on anaerobic–aerobic treatment of industrial and municipal wastewater. Chemical Engineering Journal, 155(1-2), 1-18.

Chen, C., Guo, W., Ngo, H. H., Lee, D.-J., Tung, K.-L., Jin, P., . . . Wu, Y. (2016). Challenges in biogas production from anaerobic membrane bioreactors. Renewable energy, 98, 120-134.

Chen, G. Q., Artemi, A., Lee, J., Gras, S. L., & Kentish, S. E. (2019). A pilot scale study on the concentration of milk and whey by forward osmosis. Separation and Purification Technology, 215, 652-659. doi:https://doi.org/10.1016/j.seppur.2019.01.050

57

Chen, L., Gu, Y., Cao, C., Zhang, J., Ng, J.-W., & Tang, C. (2014). Performance of a submerged anaerobic membrane bioreactor with forward osmosis membrane for low-strength wastewater treatment. Water research, 50, 114-123.

Choi, B. G., Kim, D. I., & Hong, S. (2016). Fouling evaluation and mechanisms in a FO-RO hybrid process for direct potable reuse. Journal of Membrane Science, 520, 89-98. doi:http://dx.doi.org/10.1016/j.memsci.2016.07.035

Chun, Y., Zaviska, F., Kim, S.-J., Mulcahy, D., Yang, E., Kim, I. S., & Zou, L. (2016). Fouling characteristics and their implications on cleaning of a FO-RO pilot process for treating brackish surface water. Desalination, 394(Supplement C), 91-100. doi:https://doi.org/10.1016/j.desal.2016.04.026

Coday, B. D., Xu, P., Beaudry, E. G., Herron, J., Lampi, K., Hancock, N. T., & Cath, T. Y. (2014). The sweet spot of forward osmosis: Treatment of produced water, drilling wastewater, and other complex and difficult liquid streams. Desalination, 333(1), 23-35. doi:http://dx.doi.org/10.1016/j.desal.2013.11.014

Cornelissen, E., Harmsen, D., De Korte, K., Ruiken, C., Qin, J.-J., Oo, H., & Wessels, L. (2008). Membrane fouling and process performance of forward osmosis membranes on activated sludge. Journal of

Membrane Science, 319(1), 158-168. Dalgaard, O. G. P., Per Overgaard; Nielsen,Per Henrik (2016). Unlocking the

potential of wastewater. Retrieved from Copenhagen: de Lemos Chernicharo, C. A. (2015). Anaerobic Reactors. Water Intelligence

Online, 6(0), 9781780402116-9781780402116. doi:10.2166/9781780402116

Dereli, R. K., Ersahin, M. E., Ozgun, H., Ozturk, I., Jeison, D., van der Zee, F., & van Lier, J. B. (2012). Potentials of anaerobic membrane bioreactors to overcome treatment limitations induced by industrial wastewaters. Bioresource technology, 122, 160-170. doi:http://dx.doi.org/10.1016/j.biortech.2012.05.139

Dova, M. I., Petrotos, K. B., & Lazarides, H. N. (2007). On the direct osmotic concentration of liquid foods. Part I: Impact of process parameters on process performance. Journal of Food Engineering,

78(2), 422-430. EIB. (2008). Identification and Removal of Bottlenecks for extended Use of

Wastewater for Irrigation or for other Purposes RG/2008-01/FTF

Retrieved from Elimelech, M. (2006). The global challenge for adequate and safe water.

Aqua, 55, 3-10. Directive 2000/60/EC The EU water framework directive—integrated river

basin management for europe (2000).

58

Fane, A. G. (2011). Membranes and the water cycle: challenges and opportunities. Applied Water Science, 1(1), 3-9. doi:10.1007/s13201-011-0002-5

Fillaudeau, L., Blanpain-Avet, P., & Daufin, G. (2006). Water, wastewater and waste management in brewing industries. Journal of Cleaner

Production, 14(5), 463-471. Fritzmann, C., Löwenberg, J., Wintgens, T., & Melin, T. (2007). State-of-the-

art of reverse osmosis desalination. Desalination, 216(1-3), 1-76. Fu, D., & Lu, M. (2007). The structural basis of water permeation and proton

exclusion in aquaporins (Review). Molecular membrane biology, 24(5-6), 366-374.

Fung, Y., & Tong, P. (1968). Theory of the sphering of red blood cells. Biophysical journal, 8(2), 175-198.

Gadelha, G., Nawaz, M. S., Hankins, N. P., Khan, S. J., Wang, R., & Tang, C. Y. (2014). Assessment of micellar solutions as draw solutions for forward osmosis. Desalination, 354, 97-106. doi:https://doi.org/10.1016/j.desal.2014.09.009

Giwa, A., Hasan, S. W., Yousuf, A., Chakraborty, S., Johnson, D. J., & Hilal, N. (2017). Biomimetic membranes: A critical review of recent progress. Desalination, 420, 403-424. doi:http://dx.doi.org/10.1016/j.desal.2017.06.025

Goulter, R., Gentle, I., & Dykes, G. (2009). Issues in determining factors influencing bacterial attachment: a review using the attachment of Escherichia coli to abiotic surfaces as an example. Letters in applied

microbiology, 49(1), 1-7. Greenlee, L. F., Lawler, D. F., Freeman, B. D., Marrot, B., & Moulin, P.

(2009). Reverse osmosis desalination: Water sources, technology, and today's challenges. Water research, 43(9), 2317-2348. doi:https://doi.org/10.1016/j.watres.2009.03.010

Gu, Y., Chen, L., Ng, J.-W., Lee, C., Chang, V. W.-C., & Tang, C. Y. (2015). Development of Anaerobic Osmotic Membrane Bioreactor for Low-Strength Wastewater Treatment at Mesophilic Condition. Journal of

Membrane Science. Gu, Y. S., Chen, L., Ng, J. W., Lee, C., Chang, V. W. C., & Tang, C. Y. Y.

(2015). Development of anaerobic osmotic membrane bioreactor for low-strength wastewater treatment at mesophilic condition. Journal of

Membrane Science, 490, 197-208. doi:10.1016/j.memsci.2015.04.032 Guo, H., Yao, Z., Wang, J., Yang, Z., Ma, X., & Tang, C. Y. (2018).

Polydopamine coating on a thin film composite forward osmosis membrane for enhanced mass transport and antifouling performance. Journal of Membrane Science, 551, 234-242. doi:https://doi.org/10.1016/j.memsci.2018.01.043

59

Hai, F. I., & Yamamoto, K. (2011). 4.16 - Membrane Biological Reactors A2 - Wilderer, Peter Treatise on Water Science (pp. 571-613). Oxford: Elsevier.

Hai, F. I., Yamamoto, K., & Lee, C.-H. (2014). Introduction to membrane biological reactors. In F. I. Y. K. L. C. H. Hai (Ed.): IWA PUBLISHING.

Hai, F. I., Yamamoto, K., Nakajima, F., & Fukushi, K. (2010). Recalcitrant industrial wastewater treatment by membrane bioreactor (MBR).

Han, G., Liang, C.-Z., Chung, T.-S., Weber, M., Staudt, C., & Maletzko, C. (2016). Combination of forward osmosis (FO) process with coagulation/flocculation (CF) for potential treatment of textile wastewater. Water research, 91, 361-370. doi:https://doi.org/10.1016/j.watres.2016.01.031

Hancock, N. T., & Cath, T. Y. (2009). Solute Coupled Diffusion in Osmotically Driven Membrane Processes. Environmental science &

technology, 43(17), 6769-6775. doi:10.1021/es901132x Hancock, N. T., Xu, P., Heil, D. M., Bellona, C., & Cath, T. Y. (2011).

Comprehensive bench-and pilot-scale investigation of trace organic compounds rejection by forward osmosis. Environmental science &

technology, 45(19), 8483-8490. Hermansson, M. (1999). The DLVO theory in microbial adhesion. Colloids

and Surfaces B: Biointerfaces, 14(1), 105-119. doi:https://doi.org/10.1016/S0927-7765(99)00029-6

Hey, T., Bajraktari, N., Davidsson, Å., Vogel, J., Madsen, H. T., Hélix-Nielsen, C., . . . Jönsson, K. (2017). Evaluation of direct membrane filtration and direct forward osmosis as concepts for compact and energy-positive municipal wastewater treatment. Environmental

technology, 1-13. doi:10.1080/09593330.2017.1298677 Hickenbottom, K. L., Hancock, N. T., Hutchings, N. R., Appleton, E. W.,

Beaudry, E. G., Xu, P., & Cath, T. Y. (2013). Forward osmosis treatment of drilling mud and fracturing wastewater from oil and gas operations. Desalination, 312, 60-66.

Holloway, R. W., Achilli, A., & Cath, T. Y. (2015). The osmotic membrane bioreactor: a critical review. Environmental Science: Water Research

& Technology, 1(5), 581-605. Holloway, R. W., Childress, A. E., Dennett, K. E., & Cath, T. Y. (2007).

Forward osmosis for concentration of anaerobic digester centrate. Water research, 41(17), 4005-4014.

Holloway, R. W., Wait, A. S., Fernandes da Silva, A., Herron, J., Schutter, M. D., Lampi, K., & Cath, T. Y. (2015). Long-term pilot scale investigation of novel hybrid ultrafiltration-osmotic membrane bioreactors. Desalination, 363, 64-74. doi:http://dx.doi.org/10.1016/j.desal.2014.05.040

60

Holmgren, K. E. L., Hong; Verstraete, Willy; Cornel, Peter (2016). State of

the Art Compendium Report on Resource Recovery from Water. Retrieved from

Hu, T., Wang, X., Wang, C., Li, X., & Ren, Y. (2017). Impacts of inorganic draw solutes on the performance of thin-film composite forward osmosis membrane in a microfiltration assisted anaerobic osmotic membrane bioreactor. RSC Advances, 7(26), 16057-16063.

Iskander, S. M., Zou, S., Brazil, B., Novak, J. T., & He, Z. (2017). Energy consumption by forward osmosis treatment of landfill leachate for water recovery. Waste Management, 63, 284-291. doi:https://doi.org/10.1016/j.wasman.2017.03.026

Jiao, B., Cassano, A., & Drioli, E. (2004). Recent advances on membrane processes for the concentration of fruit juices: a review. Journal of

Food Engineering, 63(3), 303-324. Judd, S. (2010). The MBR book: principles and applications of membrane

bioreactors for water and wastewater treatment: Elsevier. Judd, S., & Jefferson, B. (2003). Membranes for Industrial Wastewater

Recovery and Re-use (pp. 1-291): Elsevier Inc. Kai Yin Tang, M., & Ng, H. Y. (2014). Impacts of different draw solutions

on a novel anaerobic forward osmosis membrane bioreactor (AnFOMBR). Water Science & Technology, 69(10).

Kalafatakis, S., Braekevelt, S., Carlsen, V., Lange, L., Skiadas, I. V., & Gavala, H. N. (2017). On a novel strategy for water recovery and recirculation in biorefineries through application of forward osmosis membranes. Chemical Engineering Journal, 311(Supplement C), 209-216. doi:https://doi.org/10.1016/j.cej.2016.11.092

Kalafatakis, S., Braekevelt, S., Lymperatou, A., Zarebska, A., Hélix-Nielsen, C., Lange, L., . . . Gavala, H. (2018). Application of forward osmosis technology in crude glycerol fermentation biorefinery-potential and challenges. Bioprocess and biosystems engineering, 1-13.

Kim, B., Gwak, G., & Hong, S. (2017). Review on methodology for determining forward osmosis (FO) membrane characteristics: Water permeability (A), solute permeability (B), and structural parameter (S). Desalination, 422, 5-16. doi:http://dx.doi.org/10.1016/j.desal.2017.08.006

Kim, C., Lee, S., & Hong, S. (2012). Application of osmotic backwashing in forward osmosis: mechanisms and factors involved. Desalination and

Water Treatment, 43(1-3), 314-322. Kim, M., Ahn, Y. H., & Speece, R. E. (2002). Comparative process stability

and efficiency of anaerobic digestion; mesophilic vs. thermophilic. Water research, 36(17), 4369-4385. doi:10.1016/S0043-1354(02)00147-1

61

Koh, L., Ashokkumar, M., & Kentish, S. (2012). Membrane fouling, cleaning and disinfection. Membrane Processing: Dairy and Beverage

Applications, 73-106. Kunze, W., Wainwright, T., & Mieth, H. (1999). Technology brewing and

malting (Vol. 669): Vlb Berlin,, Germany. Ladewig, B., & Al-Shaeli, M. N. Z. (2016). Introduction to Membrane

Bioreactors (pp. 1-12): Springer Singapore. Lee, S., Boo, C., Elimelech, M., & Hong, S. (2010). Comparison of fouling

behavior in forward osmosis (FO) and reverse osmosis (RO). Journal

of Membrane Science, 365(1), 34-39. Lee, W. J., Goh, P. S., Lau, W. J., Ong, C. S., & Ismail, A. F. (2018).

Antifouling zwitterion embedded forward osmosis thin film composite membrane for highly concentrated oily wastewater treatment. Separation and Purification Technology, 214, 40-50. doi:10.1016/j.seppur.2018.07.009

Leiknes, T. (2010). Membrane Bioreactors. In K.-V. P. a. S. P. Nunes (Ed.), Membrane Technology. Weinheim: WILEY-VCH Verlag GmbH & Co. KGaA.

Lesjean, B., & Huisjes, E. H. (2008). Survey of the European MBR market: trends and perspectives. Desalination, 231(1), 71-81. doi:https://doi.org/10.1016/j.desal.2007.10.022

Li, H., & Chen, V. (2010). Membrane fouling and cleaning in food and bioprocessing Membrane Technology (pp. 213-254): Elsevier.

Li, S., Kim, Y., Phuntsho, S., Chekli, L., Shon, H. K., Leiknes, T., & Ghaffour, N. (2017). Methane production in an anaerobic osmotic membrane bioreactor using forward osmosis: Effect of reverse salt flux. Bioresource technology, 239, 285-293. doi:https://doi.org/10.1016/j.biortech.2017.05.044

Liao, B.-Q., Kraemer, J. T., & Bagley, D. M. (2006). Anaerobic Membrane Bioreactors: Applications and Research Directions. Critical Reviews in

Environmental Science and Technology, 36(6), 489-530. doi:10.1080/10643380600678146

Lin, H., Gao, W., Meng, F., Liao, B.-Q., Leung, K.-T., Zhao, L., . . . Hong, H. (2012). Membrane Bioreactors for Industrial Wastewater Treatment: A Critical Review. Critical Reviews in Environmental

Science and Technology, 42(7), 677-740. doi:10.1080/10643389.2010.526494

Linares, R. V., Li, Z., Sarp, S., Bucs, S. S., Amy, G., & Vrouwenvelder, J. (2014). Forward osmosis niches in seawater desalination and wastewater reuse. Water research, 66, 122-139.

Liu, P., Zhang, H., Feng, Y., Shen, C., & Yang, F. (2015). Influence of spacer on rejection of trace antibiotics in wastewater during forward osmosis process. Desalination, 371, 134-143.

62

Liu, Q., Liu, C., Zhao, L., Ma, W., Liu, H., & Ma, J. (2016). Integrated forward osmosis-membrane distillation process for human urine treatment. Water research, 91, 45-54. doi:http://dx.doi.org/10.1016/j.watres.2015.12.045

Luo, W., Phan, H. V., Xie, M., Hai, F. I., Price, W. E., Elimelech, M., & Nghiem, L. D. (2017). Osmotic versus conventional membrane bioreactors integrated with reverse osmosis for water reuse: Biological stability, membrane fouling, and contaminant removal. Water

research, 109, 122-134. doi:http://dx.doi.org/10.1016/j.watres.2016.11.036

Luo, W., Xie, M., Song, X., Guo, W., Ngo, H. H., Zhou, J., & Nghiem, L. D. (2017). Biomimetic aquaporin membranes for osmotic membrane bioreactors: Membrane performance and contaminant removal. Bioresource technology. doi:https://doi.org/10.1016/j.biortech.2017.09.170

Lutchmiah, K., Cornelissen, E. R., Harmsen, D. J., Post, J. W., Lampi, K., Ramaekers, H., . . . Roest, K. (2011). Water recovery from sewage using forward osmosis. Water Science & Technology, 64(7), 1443-1449.

Lutchmiah, K., Verliefde, A., Roest, K., Rietveld, L. C., & Cornelissen, E. R. (2014). Forward osmosis for application in wastewater treatment: a review. Water research, 58, 179-197.

Makki, H. F., Wahab, M. I. A., & Said, R. R. (2013). Forward osmosis process for the treatment of wastewater from textile industries. Journal

of Engineering, 19(12), 1557-1565. Maurel, C. (1997). Aquaporins and water permeability of plant membranes.

Annual Review of Plant Physiology and Plant Molecular Biology, 48 , 399-429.

McCutcheon, J. R., & Elimelech, M. (2006). Influence of concentrative and dilutive internal concentration polarization on flux behavior in forward osmosis. Journal of Membrane Science, 284(1–2), 237-247. doi:http://dx.doi.org/10.1016/j.memsci.2006.07.049

McGinnis, R. L., & Elimelech, M. (2008). Global challenges in energy and water supply: the promise of engineered osmosis. Environmental

science & technology, 42(23), 8625-8629. Mekonnen, M. M., & Hoekstra, A. Y. (2012). A Global Assessment of the

Water Footprint of Farm Animal Products. Ecosystems, 15(3), 401-415. doi:10.1007/s10021-011-9517-8

Mi, B., & Elimelech, M. (2008). Chemical and physical aspects of organic fouling of forward osmosis membranes. Journal of Membrane Science,

320(1), 292-302. Mi, B., & Elimelech, M. (2010a). Organic fouling of forward osmosis

membranes: Fouling reversibility and cleaning without chemical

63

reagents. Journal of Membrane Science, 348(1–2), 337-345. doi:http://dx.doi.org/10.1016/j.memsci.2009.11.021

Mi, B., & Elimelech, M. (2010b). Organic fouling of forward osmosis membranes: fouling reversibility and cleaning without chemical reagents. Journal of Membrane Science, 348(1), 337-345.

Mohammadi, T. (2001). Chemical cleaning of a polyamide membrane. Desalination, 139(1), 381. doi:http://dx.doi.org/10.1016/S0011-9164(01)00336-8

Motsa, M. M., Mamba, B. B., & Verliefde, A. R. D. (2015). Combined colloidal and organic fouling of FO membranes: The influence of foulant-foulant interactions and ionic strength. Journal of Membrane

Science, 493, 539-548. doi:10.1016/j.memsci.2015.06.035 Motsa, M. M., Mamba, B. B., & Verliefde, A. R. D. (2018). Forward osmosis

membrane performance during simulated wastewater reclamation: Fouling mechanisms and fouling layer properties. Journal of Water

Process Engineering, 23, 109-118. doi:https://doi.org/10.1016/j.jwpe.2018.03.007

Mulder, M. (1996). Basic principles of membrane technology. Dordrecht: Kluwer Academic Publishers.

Munshi, F. M., Church, J., McLean, R., Maier, N., Sadmani, A. H. M. A., Duranceau, S. J., & Lee, W. H. (2018). Dewatering algae using an aquaporin-based polyethersulfone forward osmosis membrane. Separation and Purification Technology, 204, 154-161. doi:https://doi.org/10.1016/j.seppur.2018.04.077

Parida, V., & Ng, H. Y. (2013). Forward osmosis organic fouling: Effects of organic loading, calcium and membrane orientation. Desalination, 312, 88-98.

Parkin, G. F., & Owen, W. F. (1986). Fundamentals of anaerobic digestion of wastewater sludges. Journal of Environmental Engineering, 112(5), 867-920.

Petrinić, I., Bajraktari, N., & Hélix-Nielsen, C. (2015). Membrane technologies for water treatment and reuse in the textile industry Advances in Membrane Technologies for Water Treatment (pp. 537-550): Elsevier.

Phillip, W. A., Yong, J. S., & Elimelech, M. (2010). Reverse Draw Solute Permeation in Forward Osmosis: Modeling and Experiments. Environmental science & technology, 44(13), 5170-5176. doi:10.1021/es100901n

Pragya, N., Pandey, K. K., & Sahoo, P. (2013). A review on harvesting, oil extraction and biofuels production technologies from microalgae. Renewable and Sustainable Energy Reviews, 24, 159-171.

Qin, J.-J., Kekre, K. A., Oo, M. H., Tao, G., Lay, C. L., Lew, C. H., . . . Ruiken, C. J. (2010). Preliminary study of osmotic membrane bioreactor: effects of draw solution on water flux and air scouring on

64

fouling. Water science and technology, 62(6), 1353-1360. doi:10.2166/wst.2010.426

Rao, D. G., Senthilkumar, R., Byrne, J. A., & Feroz, S. (2013). Wastewater Treatment Advanced Processes and Technologies Introduction. In D. G. S. R. B. J. A. F. S. Rao (Ed.): CRC PRESS-TAYLOR & FRANCIS GROUP.

Ravindra, P. (2000). Value-added food:: Single cell protein. Biotechnology

advances, 18(6), 459-479. Salehi, H., Rastgar, M., & Shakeri, A. (2017). Anti-fouling and high water

permeable forward osmosis membrane fabricated via layer by layer assembly of chitosan/graphene oxide. Applied Surface Science, 413, 99-108. doi:10.1016/j.apsusc.2017.03.271

Schrotter, J.-C. B.-S., Bengu. (2010). Current and Emerging Membrane Processes for Water Treatment. In K.-V. P. a. S. P. Nunes (Ed.), Membrane Technology. Weinheim: WILEY-VCH Verlag GmbH & Co. KGaA.

Sekse, L. (1995). FRUIT CRACKING IN SWEET CHERRIES (PRUNUS-AVIUM L) - SOME PHYSIOLOGICAL-ASPECTS - A MINI REVIEW. Scientia Horticulturae, 63(3-4), 135-141.

Shannon, M. A., Bohn, P. W., Elimelech, M., Georgiadis, J. G., Marinas, B. J., & Mayes, A. M. (2008). Science and technology for water purification in the coming decades. Nature, 452(7185), 301-310.

She, Q., Jin, X., Li, Q., & Tang, C. Y. (2012). Relating reverse and forward solute diffusion to membrane fouling in osmotically driven membrane processes. Water research, 46(7), 2478-2486. doi:https://doi.org/10.1016/j.watres.2012.02.024

She, Q., Wang, R., Fane, A. G., & Tang, C. Y. (2016). Membrane fouling in osmotically driven membrane processes: A review. Journal of

Membrane Science, 499, 201-233. doi:10.1016/j.memsci.2015.10.040 Shon, H., Phuntsho, S., Chaudhary, D., Vigneswaran, S., & Cho, J. (2013).

Nanofiltration for water and wastewater treatment-a mini review. Drinking Water Engineering and Science.

Siddiqui, F. A., She, Q., Fane, A. G., & Field, R. W. (2018). Exploring the Differences between Forward Osmosis and Reverse Osmosis Fouling. Journal of Membrane Science. doi:10.1016/j.memsci.2018.08.034

Sidney, L., & Srinivasa, S. (1964). High flow porous membranes for separating water from saline solutions: Google Patents.

Simate, G. S., Cluett, J., Iyuke, S. E., Musapatika, E. T., Ndlovu, S., Walubita, L. F., & Alvarez, A. E. (2011). The treatment of brewery wastewater for reuse: State of the art. Desalination, 273(2–3), 235-247. doi:http://dx.doi.org/10.1016/j.desal.2011.02.035

Skouteris, G., Hermosilla, D., López, P., Negro, C., & Blanco, Á. (2012). Anaerobic membrane bioreactors for wastewater treatment: a review. Chemical Engineering Journal, 198, 138-148.

65

Song, H., Xie, F., Chen, W., & Liu, J. (2017). FO/MD hybrid system for real dairy wastewater recycling. Environmental technology, 39(18). doi:10.1080/09593330.2017.1377771

Song, X., Wang, L., Tang, C. Y., Wang, Z., & Gao, C. (2015). Fabrication of carbon nanotubes incorporated double-skinned thin film nanocomposite membranes for enhanced separation performance and antifouling capability in forward osmosis process. Desalination, 369, 1-9. doi:https://doi.org/10.1016/j.desal.2015.04.020

Song, X., Xie, M., Li, Y., Li, G., & Luo, W. (2018). Salinity build-up in osmotic membrane bioreactors: Causes, impacts, and potential cures. Bioresource technology, 257, 301-310. doi:https://doi.org/10.1016/j.biortech.2018.02.101

Stephenson, T., Brindle, K., Judd, S., & Jefferson, B. (2000). Membrane

bioreactors for wastewater treatment: IWA publishing. Tam, K., Yang, C. H., Matsumoto, M. R., Crowley, D. E., & Sheppard, J. D.

(2005). Comparison of PCR‐ DGGE and Selective Plating Methods for Monitoring the Dynamics of a Mixed Culture Population in Synthetic Brewery Wastewater. Biotechnology progress, 21(3), 712-719.

Tang, C., Wang, Z., Petrinić, I., Fane, A. G., & Hélix-Nielsen, C. (2015). Biomimetic aquaporin membranes coming of age. Desalination, 368, 89-105.

Tang, C., Zhao, Y., Wang, R., Hélix-Nielsen, C., & Fane, A. (2013). Desalination by biomimetic aquaporin membranes: Review of status and prospects. Desalination, 308, 34-40.

Tang, C. Y., She, Q., Lay, W. C., Wang, R., & Fane, A. G. (2010). Coupled effects of internal concentration polarization and fouling on flux behavior of forward osmosis membranes during humic acid filtration. Journal of Membrane Science, 354(1), 123-133.

Tepavitcharova, S., Todorov, T., Rabadjieva, D., Dassenakis, M., & Paraskevopoulou, V. (2011). Chemical speciation in natural and brine sea waters. Environmental monitoring and assessment, 180(1-4), 217-227.

Thomsen, M. (2016). Wastewater treatment and discharge. Retrieved from Tiraferri, A., Kang, Y., Giannelis, E. P., & Elimelech, M. (2012).

Superhydrophilic thin-film composite forward osmosis membranes for organic fouling control: fouling behavior and antifouling mechanisms. Environmental science & technology, 46(20), 11135-11144.

Valladares Linares, R., Li, Z., Abu-Ghdaib, M., Wei, C.-H., Amy, G., & Vrouwenvelder, J. S. (2013). Water harvesting from municipal wastewater via osmotic gradient: An evaluation of process performance. Journal of Membrane Science, 447, 50-56. doi:http://dx.doi.org/10.1016/j.memsci.2013.07.018

Valladares Linares, R., Li, Z., Yangali-Quintanilla, V., Ghaffour, N., Amy, G., Leiknes, T., & Vrouwenvelder, J. S. (2016). Life cycle cost of a

66

hybrid forward osmosis – low pressure reverse osmosis system for seawater desalination and wastewater recovery. Water research, 88, 225-234. doi:http://dx.doi.org/10.1016/j.watres.2015.10.017

Volpin, F., Fons, E., Chekli, L., Kim, J. E., Jang, A., & Shon, H. K. (2018). Hybrid forward osmosis-reverse osmosis for wastewater reuse and seawater desalination: Understanding the optimal feed solution to minimise fouling. Process Safety and Environmental Protection, 117, 523-532. doi:https://doi.org/10.1016/j.psep.2018.05.006

Wang, X., Chang, V. W. C., & Tang, C. Y. (2016). Osmotic membrane bioreactor (OMBR) technology for wastewater treatment and reclamation: Advances, challenges, and prospects for the future. Journal of Membrane Science, 504, 113-132. doi:10.1016/j.memsci.2016.01.010

Wang, X., Wang, C., Tang, C. Y., Hu, T., Li, X., & Ren, Y. (2017). Development of a novel anaerobic membrane bioreactor simultaneously integrating microfiltration and forward osmosis membranes for low-strength wastewater treatment. Journal of

Membrane Science, 527, 1-7. doi:http://dx.doi.org/10.1016/j.memsci.2016.12.062

Wang, Z., Ma, J., Tang, C. Y., Kimura, K., Wang, Q., & Han, X. (2014). Membrane cleaning in membrane bioreactors: A review. Journal of

Membrane Science, 468, 276-307. doi:https://doi.org/10.1016/j.memsci.2014.05.060

Wang, Z., Tang, J., Zhu, C., Dong, Y., Wang, Q., & Wu, Z. (2015). Chemical cleaning protocols for thin film composite (TFC) polyamide forward osmosis membranes used for municipal wastewater treatment. Journal

of Membrane Science, 475, 184-192. doi:http://dx.doi.org/10.1016/j.memsci.2014.10.032

Wang, Z., Wu, Z., Yu, G., Liu, J., & Zhou, Z. (2006). Relationship between sludge characteristics and membrane flux determination in submerged membrane bioreactors. Journal of Membrane Science, 284(1), 87-94. doi:https://doi.org/10.1016/j.memsci.2006.07.006

Wang, Z., Zheng, J., Tang, J., Wang, X., & Wu, Z. (2016). A pilot-scale forward osmosis membrane system for concentrating low-strength municipal wastewater: performance and implications. Scientific

reports, 6. WEF. (2006). Membrane Systems for Wastewater Treatment. Introduction,

Chapter 1Membrane Systems for Wastewater Treatment: McGraw Hill Professional, Access Engineering. Retrieved from https://www.accessengineeringlibrary.com:443/browse/membrane-systems-for-wastewater-treatment/p200180a69970001001.

WEF. (2012). Membrane Bioreactors: WEF Manual of Practice, No. 36.

Woodard, & Curran, I. (2006). 7 - Methods for Treating Wastewaters from Industry. In Woodard & I. Curran (Eds.), Industrial Waste Treatment

67

Handbook (Second Edition) (pp. 149-334). Burlington: Butterworth-Heinemann.

WWAP. (2015). The United Nations World Water Development Report 2015:

Water for a Sustainable World. Retrieved from Paris: https://www.unesco-ihe.org/sites/default/files/wwdr_2015.pdf

Xie, M., Lee, J., Nghiem, L. D., & Elimelech, M. (2015). Role of pressure in organic fouling in forward osmosis and reverse osmosis. Journal of

Membrane Science, 493, 748-754. doi:http://dx.doi.org/10.1016/j.memsci.2015.07.033

Xie, M., Nghiem, L. D., Price, W. E., & Elimelech, M. (2013). A forward osmosis–membrane distillation hybrid process for direct sewer mining: System performance and limitations. Environmental science &

technology, 47(23), 13486-13493. Xin, L., Su, H., Nielsen, C. H., Tang, C., Torres, J., & Mu, Y. (2011). Water

permeation dynamics of AqpZ: a tale of two states. Biochimica et

Biophysica Acta (BBA)-Biomembranes, 1808(6), 1581-1586. Xue, W., Tobino, T., Nakajima, F., & Yamamoto, K. (2015). Seawater-driven

forward osmosis for enriching nitrogen and phosphorous in treated municipal wastewater: Effect of membrane properties and feed solution chemistry. Water research, 69, 120-130.

Xue, W., Yamamoto, K., & Tobino, T. (2016). Membrane fouling and long-term performance of seawater-driven forward osmosis for enrichment of nutrients in treated municipal wastewater. Journal of Membrane

Science, 499, 555-562. doi:http://dx.doi.org/10.1016/j.memsci.2015.11.009

Yangali-Quintanilla, V., Olesen, L., Lorenzen, J., Rasmussen, C., Laursen, H., Vestergaard, E., & Keiding, K. (2015). Lowering desalination costs by alternative desalination and water reuse scenarios. Desalination and

Water Treatment, 55(9), 2437-2445. Yeo, B. J., Goh, S., Zhang, J., Livingston, A. G., & Fane, A. G. (2015).

Novel MBRs for the removal of organic priority pollutants from industrial wastewaters: a review. Journal of chemical technology and

biotechnology, 90(11), 1949-1967. York, R., Thiel, R., & Beaudry, E. (1999). Full-scale experience of direct

osmosis concentration applied to leachate management. Paper presented at the Proceedings of the Seventh International Waste Management and Landfill Symposium (Sardinia’99), S. Margherita di Pula, Cagliari, Sardinia, Italy.

Yu, Y., Lee, S., & Maeng, S. K. (2016). Forward osmosis membrane fouling and cleaning for wastewater reuse. Journal of Water Reuse and

Desalination. doi:10.2166/wrd.2016.023 Zhang, J., Loong, W. L. C., Chou, S., Tang, C., Wang, R., & Fane, A. G.

(2012). Membrane biofouling and scaling in forward osmosis membrane bioreactor. Journal of Membrane Science, 403, 8-14.

68

Zhang, J., She, Q., Chang, V. W., Tang, C. Y., & Webster, R. D. (2014). Mining nutrients (N, K, P) from urban source-separated urine by forward osmosis dewatering. Environmental science & technology,

48(6), 3386-3394. Zhang, S., Wang, P., Fu, X., & Chung, T.-S. (2014). Sustainable water

recovery from oily wastewater via forward osmosis-membrane distillation (FO-MD). Water research, 52, 112-121.

Zhang, T. C., Surampalli, R. Y., Vigneswaran, S., Tyagi, R. D., Ong, S. L., & Kao, C. M. (2012). Membrane Technology and Environmental Applications: American Society of Civil Engineers (ASCE).

Zou, S., Wang, Y.-N., Wicaksana, F., Aung, T., Wong, P. C. Y., Fane, A. G., & Tang, C. Y. (2013). Direct microscopic observation of forward osmosis membrane fouling by microalgae: Critical flux and the role of operational conditions. Journal of Membrane Science, 436, 174-185. doi:https://doi.org/10.1016/j.memsci.2013.02.030

69

8 Papers

I Schneider, C., Rajmohan, R. S., Zarebska, A., Tsapekos, P., & Hélix-Nielsen, C. (2019). Treating anaerobic effluents using forward osmosis for combined water purification and biogas production. Science of the Total Environment, 647, 1021-1030

II Schneider, C., Oñoro A. E., Hélix-Nielsen C., Fotidis, I. Start-up of for-ward-osmosis anaerobic-membrane bioreactors for brewery wastewater remediation. Manuscript draft

III Pape, M. L., Valverde-Pérez, B., Astrid F. Kjeldgaard, August A. Zacha-riae, Schneider, C., Hélix-Nielsen C., Zarebska, A., Smets, B. F. Evalua-tion of forward osmosis to harvest methane oxidizing bacteria cultivated for single cell protein production. Manuscript under submission

IV Schneider, C., Zarebska, A., Wakefield, E., Yangali-Quintanilla, V., Hé-lix-Nielsen, C. Combined forward osmosis-reverse osmosis for the treat-ment of brewery wastewater. Manuscript draft

In this online version of the thesis, paper I-IV are not included but can be obtained from electronic article databases e.g. via www.orbit.dtu.dk or on request from.

DTU Environment Technical University of Denmark Miljoevej, Building 113 2800 Kgs. Lyngby Denmark info@env.dtu.dk.

DTU Environment

Department of Environmental Engineering

Danmarks Tekniske Universitet

Bygningstorvet

Bygning 115

2800 Kgs. Lyngby

Tlf. 45 25 16 00

Fax 45 93 28 50

www.env.dtu.dk

The Department of Environmental Engineering (DTU Environment) conducts science-based

engineering research within five sections: Air, Land & Water Resources, Urban Water Systems,

Water Technology, Residual Resource Engineering, Environmental Fate and Effect of Chemicals.

The department dates back to 1865, when Ludvig August Colding gave the first lecture on

sanitary engineering.