Circularity Assessment of Water and Waste in Cities
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Circularity Assessment of Water and Waste in Cities A Proposed Framework for Sustainable Performance Evaluation using LCA and LCC Kavitha Shanmugam Department Of Chemistry Umeå 2021
Transcript of Circularity Assessment of Water and Waste in Cities
Circularity Assessment of Water and
Waste in Cities
A Proposed Framework for Sustainable Performance
Evaluation using LCA and LCC
Kavitha Shanmugam
Department Of Chemistry
Umeå 2021
This work is protected by the Swedish Copyright Legislation (Act 1960:729) Dissertation for PhD ISBN: 978-91-7855-527-7 (print) ISBN: 978-91-7855-528-4 (pdf) Cover Art: Harish Kumar with Kavitha Shanmugam Electronic version available at: http://umu.diva-portal.org/ Printed by: VMC-KBC,Umeå University Umeå, Sweden 2021
To my Dad and Mom
I love you both a lot, appreciate your effort, and love in bringing me up
to be a better individual
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Table of Contents
Abstract ............................................................................................. 3
Abbreviations .................................................................................... 5
Definitions ........................................................................................ 8
Sammanfattning på svenska ............................................................. 9
List of Publications .......................................................................... 11
Authors Contributions ..................................................................... 12
1. Introduction ................................................................................. 13
2. Objective of this Thesis ................................................................. 17
3. Urban System ............................................................................... 19 3.1 Elements of an Urban System .................................................................................. 19 3.2 Essential Municipal Services ................................................................................... 20
3.2.1 Wastewater Treatment Service ...................................................................... 21 3.2.2 Municipal Solid Waste (MSW) Treatment Service ...................................... 23
3.3 Management of Essential Municipal Services in Cities Complying with Circular
Economy Principles ........................................................................................................ 27
4. Tool & Methodology ..................................................................... 31 4.1 Life Cycle Assessment ............................................................................................... 31
4.1.1 Goal & Scope Definition .................................................................................. 33 4.1.2 Life Cycle Inventory (LCI) Analysis ...............................................................35 4.1.3 Life Cycle Impact Assessment ........................................................................ 36 4.1.4 Interpretation of Results ................................................................................ 39 4.1.5 Uncertainty Analysis ....................................................................................... 41 4.1.6 Scenario Analysis ........................................................................................... 42 4.1.7 Limitations of LCA .......................................................................................... 43
4.2 Life Cycle Costing (LCC) ......................................................................................... 44 4.3 Environmental Externalities Cost ........................................................................... 45
5. Contribution of Papers to the Development of the Framework ....47
6. Assessment Framework for Treatment of Municipal Services in
Cities ............................................................................................... 50 6.1 Proposed Assessment Framework ........................................................................... 51 6.2 Attributes of the Framework .................................................................................... 55
6.2.1 Assessment Framework - Data Requirements .............................................. 55 6.2.2 Assessment Framework – Stage-wise Technology Options for carrying out
LCAs ......................................................................................................................... 58 6.2.3 Total Cost Calculation .................................................................................... 60 6.2.4 Future Work to Develop the Framework ...................................................... 61 6.2.5 Unique Features of the Model........................................................................ 62
6.3 Case Study of a Wastewater Treatment Plant ........................................................ 62
7. Conclusion & Future work ............................................................67
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8. Acknowledgements ..................................................................... 69
References ....................................................................................... 71
Appendix ............................................................................................ 1
Papers I-V ......................................................................................... 5
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Abstract
Urbanization is a global phenomenon, happening on a massive scale and at a
rapid rate, with 68% of the planet’s population predicted to be living in cities by
2050 (UN-DESA, 2018). The sustainability of a city (Goal 11 of UN SDGs)
undergoing rapid urbanization depends on its ability to maintain a low
consumption of resources and materials at any given time (referred to as the
urban metabolic rate), whilst simultaneously providing essential municipal
services to its inhabitants, such as a water supply, wastewater treatment and solid
waste management. The latter must comply with circular economy principles,
meaning recovery of byproducts, prevention of discharge of toxic pollutants, and
avoidance of landfill usage. The appended papers in the thesis (Papers I–V)
describe sustainable assessments of wastewater and waste services to increase
their degree of circularity, using tools such as Life Cycle Assessment (LCA) and
Life Cycle Costing (LCC). Paper I describes the environmental performance of
using the biogas from a Wastewater Treatment Plant (WWTP) and converting it
to Liquefied Biomethane (LBM), which can used as fuel in Tractor-Trailers (TT).
Overall, the study suggests that changing from diesel to LBM fuel improves the
environmental performance of TT. However, the magnitude of environmental
benefit depends on an alternate source of electricity required for operation of the
WWTP. Paper II evaluates the Social Cost-Benefit Analysis (SCBA) of
Compressed Biomethane (CBM) obtained from a food waste digestion plant in
Mumbai, India for use as a fuel in transit buses. SCBA results indicate that the
food waste-based CBM model can save 6.86 billion Indian rupees (99.4 million
USD) annually for Mumbai. Paper III describes the Sustainable Return on
Investment (SROI) of lightweight Advanced High Strength Steel (AHSS) and
Carbon Fiber Reinforced Polymer (CFRP) intensive multi-material Body in White
(BIW) for automobiles. The SROI of CFRP BIWs is maximized when carbon fiber
production uses energy from a low carbon-intensity electric grid or decentralized
sources such as waste-to-energy incineration plants. Paper IV assesses the
ecoefficiency of a thermal insulation panel that consists of a Polyurethane (PU)
foam core sandwiched between two epoxy composite skins, prepared by
reinforcing Glass Fibers (GF) and SFA (Silanized Fly Ash) in epoxy resin. The
results revealed that the ecoefficiency of the composite panels is positive (47%)
and superior to that of market incumbent alternatives with PU foam or rockwool
cores and steel skins. Paper V quantifies the Total Cost to Society (TCS) (sum of
private cost and environmental externalities cost) of a centralized urban WWTP,
including the operation as well as byproduct utilization stream. The
environmental performance and circular compliance are both factored in, when
determining the TCS of a WWTP. The results revealed savings of 1.064 million
USD, which include direct and indirect revenues to the plant, as well as avoidance
costs attributed to environmental externalities. Based on the studies described in
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these papers, a five-stage assessment framework for determining the overall
sustainability performance of essential treatment services in a city is proposed in
this thesis. The framework considers the combined effect of urban metabolic
features and initiatives aimed at improving circular compliance of essential
services.
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Abbreviations
AD Anaerobic Digestion
AHSS Advanced High Strength Steel
AP Acidification Potential
BAU Business as Usual
CBM Compressed Biomethane
CED Cumulative Energy Demand
CF Characterization Factor
CFRP Carbon Fiber Reinforced Polymer
CNG Compressed Natural Gas
EEC Environmental Externalities Cost
EU European Union
FDP Fossil Depletion Potential
FEP Freshwater Eutrophication Potential
FETP Freshwater Ecotoxicity Potential
FU Functional Unit
GDP Gross Domestic Product
GF Glass Fibers
GWP Global Warming Potential
HH-CP Human Health-Cancer Potential
HH-NCP Human Health-Non-Cancer Potential
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HTP Human Toxicity Potential
IFA Incineration Fly Ash
ISO International Standard Organization
LCA Life Cycle Assessment
LCC Life Cycle Costing
LCEE Life Cycle Environmental Externalities
LCI Life Cycle Inventory
LCIA Life Cycle Impact Assessment
LUP Land Use Potential
MCDA Multi Criteria Decision Analysis
MFDP Mineral Fossil Depletion Potential
MSW Municipal Solid Waste
OD Ozone Depletion
OFW Organic Food Waste
PMFP Particulate Matter Formation Potential
POFP Photochemical Ozone Formation Potential
PU Polyurethane
SCBA Social Cost Benefit Analyses
SDGs Sustainable Development Goals
SFA Silanized Fly Ash
SROI Sustainable Rate of Returns
SRR Sustainable Rate of Returns
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TCMS Total Cost of Municipal Services
TCS Total Cost to Society
TCUMR Total Cost of Urban Metabolic Rate
TEP Terrestrial Ecotoxicity Potential
TPC Total Private Cost
TT Tractor-Trailers
UMR Urban Metabolic Rate
UN United Nations
WtE Waste-to-Energy
WWTP Waste Water Treatment Plant
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Definitions
Urbanization is defined as an increase (population shift) in the proportion of
people living in urban areas compared to rural areas. An urban area is a built-up
area such as a town or city.
Sustainability is defined as meeting our own needs without compromising the
ability of future generations to meet their own needs (the ability to exist
constantly).
Ecological Footprint measures how fast human activities consume resources
and generate waste compared to how fast nature can absorb that waste, and
regenerate.
Total Cost is defined as the sum of private costs plus environmental externality
costs associated with the system studied.
Urban system refers to the area around a city.
Circular Economy or Circularity is an economic system aimed at
minimizing waste with the continual use of resources (contrast to linear economy
– take, make, dispose).
Framework is defined as a basic structure underlying a system, concept or text.
Municipality is an urban administrative division having corporate status that is
connected to other municipalities, regions, states and international communities
through resource areas, financial systems, social influences and transnational
paradigms.
Essential Municipal Services, in this thesis, are considered to be wastewater
treatment, waste services including organic waste management, and residual
waste management provided by the municipality.
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Sammanfattning på svenska
Urbanisering är ett globalt fenomen som sker i stor skala och i snabb takt, där
68% av jordens befolkning förutspås bo i städer år 2050 (UN-DESA, 2018).
Hållbarheten för en stad (UN SDG, Mål 11) som genomgår en snabb urbanisering
beror på dess förmåga att upprätthålla en låg förbrukning av resurser och
material vid varje given tidpunkt (kallas urban metabolic rate), samtidigt som den
tillhandahåller viktiga kommunala tjänster till dess invånare, såsom
vattenförsörjning, avloppsvattenrening och hantering av fast avfall. De senare
måste följa principerna för cirkulär ekonomi, vilket innebär återvinning av
biprodukter, förebyggande av utsläpp av giftiga föroreningar och undvika
material på deponi. Artiklarna i avhandlingen (Papers I – V) beskriver
hållbarhetsbedömningar av avloppsvattenrening och avfallstjänster för att öka
deras grad av cirkularitet med hjälp av verktyg som Life Cycle Assessment (LCA)
och Life Cycle Costing (LCC). I Paper I beskrivs miljöprestandan för att använda
biogasen från ett reningsverk (ARV) och omvandla den till flytande biometan
(LBM), som kan användas som bränsle i tyngre fordon. Sammantaget föreslår
studien att byte från diesel till LBM-bränsle förbättrar miljöprestandan.
Storleken på miljöfördelarna beror dock på vilken alternativ el som krävs för drift
av reningsverket. Paper II utförs en sociala kostnadsnyttoanalysen (SCBA) av
komprimerad biometan (CBM) som producerasvid en matavfallsanläggning i
Mumbai, Indien för användning som bränsle i bussar. SCBA-resultaten tyder på
att den livsmedelsbaserade CBM-modellen kan spara 6,86 miljarder indiska
rupier (99,4 miljoner USD) årligen för Mumbai. Paper III beskriver hållbar
avkastning på investeringar (SROI) av avancerat lättvikts höghållfast stål (AHSS)
och kolfiberförstärkt polymer (CFRP) som komponeneter i materialstommen i
bilar. SROI maximeras när kolfiberproduktion använder elenergi med låg
koldioxidintensitet eller från decentraliserade källor, såsom
avfallsförbränningsanläggningar. I Paper IV bedöms ekoeffektiviteten för en
värmeisoleringspanel som består av en polyuretanskumkärna (PU) som lager
mellan två epoxikompositsidor, och med förstärkning av glasfibrer (GF) och SFA
(Silanized Fly Ash) i epoxiharts. Resultaten visar att ekoeffektiviteten hos
kompositpanelerna är positiv (47%) och överlägsen den för de befintliga
alternativen på marknaden med PU-skums- eller stenullskärnor och ståls. Paper
V kvantifierar den totala kostnaden för samhället (TCS) (summan av privata
kostnader och miljökostnader) för ett centraliserat stadsnätverk, inklusive drift
och biproduktanvändning. Miljöprestanda och graden av cirkularitet inkluderas
vid bestämning av TCS för ett avloppsreningsverk. Resultaten visar på stora
besparingar (1.064 miljoner USD i exemplet), som inkluderar direkta och
indirekta intäkter till anläggningen, samt undvikande av kostnader som
hänförstill externa miljöeffekter.
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Baserat på studierna som beskrivs i dessa artiklar föreslås i avhandlingen en fem-
stegs utvärderingsram för bestämning av den övergripande
hållbarhetsprestandan för viktiga behandlingstjänster i en stad.
Bedömningsramverket tar hänsyn till den kombinerade effekten av
stadsmetaboliska funktioner och initiativ som syftar till att förbättra
cirkulariteten hos viktiga tjänster.
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List of Publications
All the following papers are provided as appendices.
I. Shanmugam, K., Tysklind, M. and Upadhyayula. V.K.K. (2018) Use of
Liquefied Biomethane (LBM) as a Vehicle Fuel for Road Freight
Transportation: A Case Study Evaluating Environmental Performance of
Using LBM for Operation of Tractor Trailers. Life Cycle Engineering
Procedia CIRP 69 ,517 – 522
II. Shanmugam, K., Baroth, A., Nande, S., Yacout, D.M.M., Tysklind, M. and
Upadhyayula, V.K.K. (2019) Social Cost Benefit Analysis of Operating
Compressed Biomethane (CBM) Transit Buses in Cities of Developing
Nations: A Case Study. MDPI Sustainability August 2019,11,4190
III. Shanmugam, K., Gadhamshetty, V., Yadav, P., Athanassiadis, D.,
Tysklind, M. and Upadhyayula, V.K.K. (2019) Advanced high strength
steel and carbon fiber reinforced polymer composite body in white for
passenger cars: Environmental performance and sustainable return on
investment under different propulsion modes. ACS Sustainable
Chemistry and Engineering January 2019, 7, 4951-4963
IV. Shanmugam, K., Jansson, S., Gadhamshetty, V., Matsakas, L., Rova, U.,
Tysklind, M., Christakopoulos, P. and Upadhyayula, V.K.K. (2019)
Ecoefficiency of Thermal Insulation Sandwich Panels Based on Fly Ash
modified With Colloidal Mesoporous Silica. ACS Sustainable Chemistry
& Engineering November 2019, 7, 20000-20012
V. Shanmugam, K., Gadhamshetty, V., Tysklind, M., and Upadhyayula,
V.K.K. (2021) Total Cost Assessment Framework for Sustainable and
Circular Management of Activated Sludge Based Centralized Wastewater
Treatment Plants. Submitted Manuscript.
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Authors Contributions
Paper I
The author was involved in planning the scope of the study, modeling parameters,
processing data and writing the manuscript.
Paper II
The author was involved in planning the goal and scope of the study, modeling,
collecting data and writing the manuscript.
Paper III
The author was involved in designing the scope of the study, modeling the scope,
reporting results and drafting the manuscript.
Paper IV
The author was involved in partly planning the scope of the study, designing the
scope, data processing, modeling and reporting the results.
Paper V
The author was involved in planning the scope, calculation of design parameters,
modeling the study and co-writing the manuscript.
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1. Introduction
In the 21st century, urbanization is one of the five signature megatrends that will
permanently change the definition of human sustenance (approach to
sustainability) on this planet [1]. The concept of urbanization can be described as
the migration of people to urban settlements i.e. cities, in anticipation of better
opportunities for employment, and thereby enjoyment of the benefits of
improved living standards [2]. Historically, urbanization has been associated
with significant economic and social transformations (urban living is linked to
higher levels of literacy and education, better health, longer life expectancy) [3].
While this contribution to socio-economic development is true, an accelerated
urbanization also brings a multitude of challenges that a nation must deal with in
order to avoid any dire sustainability consequences [2]. The world population is
projected to reach 9.7 billion by 2050 and, by then, around 68% of the people will
reside in urban areas [4]. Urbanization occurring at such unprecedented rates
presents numerous sustainability challenges to policy makers and governing
authorities. In particular, it exerts tremendous pressure on cities and towns [4,
5]. Cities are responsible for provision of three essential municipal services to the
residents: (a) supply of water for potable and non-potable needs, (b) treatment of
wastewater, and (c) management of solid waste (including organic waste)
generated by the inhabitants [6]. Ensuring sustainability of these essential
services becomes increasingly difficult for city authorities with increases in the
inflow of population. Figure 1 shows the various environmental implications
resulting from rapid urbanization [7] [8] [9].
Figure 1. A simplified illustration of various environmental implications
resulting from rapid urbanization
Due to rapid urbanization, many cities around the world are experiencing
difficulties due to inefficiencies (lack of financial resources, proper organization,
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complexity and system multi-dimensionality) associated with the management of
essential services [8]. For instance, some cities are resource constrained in
relation to the supply of drinking water. Recently (in 2018), the city of Cape Town
in South Africa ran out of water (high per capita water consumption) [10]. Ten
other major cities, including London and Tokyo, are predicted to follow the same
path and will be facing severe drinking water shortages by 2040 [10]. For other
cities, especially in developing countries, lack of adequate treatment of
wastewater is one of the major causes of public health concern [11]. It is estimated
that, globally, 80% of wastewater resulting from human activities is discharged
into fresh and marine water bodies without undergoing any treatment for
removal of chemical and biological pollutants [11]. Discharge of untreated or
partially treated municipal wastewater into natural waters exacerbates
eutrophication and ecotoxicity impacts [9], and endangers numerous aquatic
species [12]. Also, given the shortage of freshwater, reuse of wastewater for
agricultural purposes is practiced in some regions [4] [13]. However, reusing
untreated and partially treated wastewater for irrigation has been shown to have
a direct link with food-borne disease outbreaks [4] [13]. Even the use of treated
wastewater from crop cultivation can have public health repercussions that may
vary from season to season [13] [14]. Lastly, management of municipal solid
waste (MSW) has also emerged as a serious issue. The global production of MSW
is expected to reach 3.4 billion tonnes by 2025 [15] and its disposal without
causing social externalities will be an uphill task for cities worldwide [14]. The
problem is more pronounced for many cities in developing nations, where MSW
is predominantly landfilled [1] [8].
In this thesis, Sweden is used as an exemplar country (data for modeling comes
from a Swedish city) and the findings can be applied to countries with similar
practices. Sweden is not an exception for urbanization challenges, but Swedish
cities are different from many other parts of the world for two reasons. First,
Sweden was mentioned in the World Wide Fund for Nature Living Planet Report
(2016) for its high import-oriented resource (material and food) consumption
pattern, which means transferring environmental impacts elsewhere in the world
[16] [17] [18]. Second, a large proportion of the population (87% as of 2018) in
Sweden already resides in urban areas. Over recent decades, there has been a shift
of largest population increase in the large urban areas [19]. However, all major
Swedish cities have efficient essential municipal service operations in place. They
fulfill at least one of the three major criteria for circular compliance in waste
management: (a) byproduct utilization, (b) minimization of residual waste to
landfill, and (c) prevention of the leakage of nutrients and emerging
contaminants (e.g. pharmaceutical residues) into the biosphere [20]. Over the
years, municipalities in Sweden have mastered the ability to recover byproducts
with energy value (e.g. biogas from wastewater treatment plants (WWTPs) and
organic waste bio-digestion plants, and energy from MSW incineration plants)
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and put them to beneficial use in the society. [21] In addition, some Swedish cities
have already begun to treat their emerging contaminants from wastewater while
others are expected to acquire this ability shortly [22]. Also, rigorous efforts are
underway to ban the landfilling of residual waste streams and increase their use
in the technosphere. EU legislation and waste hierarchy have played a key role in
improving the sustainable performance of the municipal services in Sweden [23].
However, the problem for Swedish city municipalities still lies with the disposal
of residual waste streams (sludge and ashes) and removal of emerging
contaminants from wastewater [24].
From the above perspective, it would be of great scientific and societal value to
develop a methodology that combines the urban metabolic rates of cities with
their current and future initiatives, with the aim of achieving circular compliance
of their essential municipal service operations. The urban metabolism (UM) is a
model that facilitates the description and analysis of energy and material flow
within cities. UM involves the study of the interaction of natural and human
systems in specific regions [25]. There are several urban metabolism models
described in literature [25–29]. They are designed to measure the resources
flowing within, and waste streams flowing out of, a city, understand how different
forces (e.g. social and cultural aspects) influence a city’s metabolic rate, and can
be well integrated with urban planning efforts towards building sustainable cities
[30]. However, assessment models also exist that quantify sustainability aspects
of municipal service operations and develop indicators reflecting their
performance [16, 27, 31–33]. A combined effort to assess the sustainable
implications of the urban metabolic rate and circularity of essential treatment
services in cities is yet to be undertaken.
In this thesis, the recess is addressed by proposing an assessment methodology
designed to understand the sustainable implications of cities, by taking their
urban metabolic rates and performance of essential municipal services into
consideration. The integrated model proposed in this thesis is potentially more
helpful for cities to deduce strategies and make decisions related to sustainable
urbanization (focusing on water-waste-energy). Papers I–IV of this thesis served
as a basis for evolving such a conceptual framework. The work in these papers
was formulated to evaluate the sustainable performance of municipal treatment
services (wastewater and solid waste) to comply with circularity at the treatment
plant level. These papers showed the way to identify the different stages of the
proposed framework. Paper V describes the evaluation of the stages of the
framework applied to the wastewater treatment service. A structured five-stage
framework for evaluation of sustainable operation of essential municipal services
of a city using the supporting logic i.e. an assessment based on application of life
cycle assessment (LCA) [34] and life cycle costing (LCC) tools, is presented in this
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thesis. Other environmental assessment tools, such as Environment Impact
Assessment (EIA), Ecological Risk Assessment (ERA) and Material Flow Analysis
(MFA), along with those based on economic metrics such as Cost Benefit Analysis
(CBA), can also be used for such an evaluation [35]. These tools can be used
depending on the objectives to be fulfilled, and address other aspects of
sustainability. For the purpose of this thesis, LCA is used as it quantifies the
environmental effects and implications of essential services at various levels of
adherence to circular economy compliance [34]. Second, it quantifies the
environmental performance contribution made by the essential service systems
in improving sustainability of cities.
The data used for modeling in this thesis were obtained from Umeå city
stakeholder companies (Papers I, II and IV). The assessment of the essential
services (wastewater and solid waste) carried out for the papers/modeling
approach can be applied to cities with a similar population (approx. 130,000
inhabitants as of 2020, similar to most European medium-sized cities [36]) and
technology practices. The population of the city is predicted to reach 200,000 (an
increase of 60,000 houses by 2050 in order to meet the growing population) by
2050, meaning there is a greater demand for housing, transport and other
services likely to produce more waste [36]. Transition in cities (to sustainable
technologies to meet the requirements of the population) of the above nature can
be handled by our unique modeling approach, where combining urban
metabolism and circular economy concepts, while measuring the sustainable
performance of a city or an urban community, is essential.
The framework can serve as a basis for development of a decision support system
that cities can apply to evaluate iteratively and improve their sustainability
performance. Finally, the framework allows for the establishment of grounds for
comparison between cities, based on how environmentally - friendly the essential
services are run in each city and the extent to which they contribute to the
sustainable performance of that city. The structure of the five-stage LCA
framework is clearly explained in subsequent chapters of the thesis.
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2. Objective of this Thesis
The goal of this thesis is to describe a systems-oriented modeling framework for
comprehensively evaluating the sustainable performance of essential services
(wastewater and solid waste) in cities. The modeling framework is designed to
consider collectively the concepts of urban metabolism and circular economy
while evaluating the sustainable performance of the city. A city (municipality,
society) must provide essential municipal services to its residents, including the
crucial services treatment of wastewater, and municipal solid waste management
(MSW) (e.g. disposal in landfills and prevention of leakage of toxic contaminants
into the biosphere). Umeå city (data and treatment techniques for modeling) was
used as a test case to develop the framework, with real-time data (obtained from
Umeå Energi, Vakin) being used in the modeling approach of the papers in order
to reduce data uncertainty and make better decisions. Papers I–V, appended to
this thesis, form part of this objective of evaluating the environmental
performance of the essential services in the city using sustainable assessment
tools such as LCA and LCC. Figure 2 shows how these papers describe the
different stages of the proposed framework.
Figure 2. The stages of the assessment framework with the current and future
scenarios of essential treatment services, as described in Papers I–V
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The following objectives are discussed in this thesis:
1. Gather and outline the wastewater and household waste treatment
technologies in the city. Assess the environmental performance of the current
treatment processes using LCA. (Papers I, II, IV and V)
2. Collect site-specific information on treatment processes, byproduct
utilization, residual stream disposal and advanced treatment techniques
planned for a future sustainable scenario. Evaluate the environmental
performance of the future scenario. (Papers I–V)
3. Amalgamate the different LCA studies, allowing for the development of an
assessment framework, which can analyze the overall environmental
performance of essential municipal services in cities and its contribution to
the utility needs of the city, along with the urban metabolic rate of the city.
4. Based on the results obtained from these three objectives, calculate the total
cost for essential services and urban metabolic rate of cities (part of Paper V).
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3. Urban System
This chapter describes the major essential municipal services considered in the
thesis. The wastewater treatment service and the municipal solid waste
(household waste, recyclables, organic food waste) service are both included.
In this thesis, a city [37] is considered to be an urban system and is viewed as a
combination of five elements. Figure 3 shows these elements.
Figure 3. Five elements that determine the sustainable performance of an urban
system, with systemic features focusing on infrastructure, material flows,
cultural dimensions, essential ecosystem services and utilities
3.1 Elements of an Urban System
The elements of an urban system are described as follows [38]:
Physical Element: Denotes physical infrastructure e.g. individual houses,
apartment buildings, industrial buildings, offices, commercial complexes etc.
Human Element: The actual people (residents, employees etc.) of an urban
system.
Services Element: Represents three essential municipal services i.e. water
supply, wastewater treatment and management of MSW. A city might be
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comprised of other essential (e.g. fire station, healthcare) services. However,
these and other services are not in the scope of the present work.
Utility Element: Two critical utilities i.e. energy (electricity and heat) and
public transportation. The city municipalities are either direct service
providers of these utilities or contract them to third party companies.
Materials Element: This includes a wide range of materials, either those
directly consumed by the city residents or those that the city is indirectly
responsible for the production and utilization of elsewhere. Direct material
consumption includes products such as cosmetics, pharmaceuticals, metals,
plastics wood etc., which can have a profound influence on the operational
efficiency of the services element. Indirect consumption refers to materials
such as fertilizers and pesticides used for local food production (i.e. food
produced and consumed in cities in the same country) and exported from
elsewhere (i.e. food produced in one country and consumed in another
country).
All five elements collectively determine the sustainable performance of an urban
system. The sustainability performance of the physical element is related to
physical infrastructure i.e. materials used in construction and land use, and
affected by several other criteria such as energy and water efficiency etc., as
stipulated by green building standards for individual buildings [39]. The
sustainable performance of the human element depends on a wide range of
factors such as socio-economic conditions, ethnographic influences, awareness of
people and their sense of responsibility towards sustainability challenges faced
by urban systems. The services, utility and material elements collectively
determine the operational sustainability performance of urban systems (urban
metabolic rate). Furthermore, essential municipal services, depending on how
they are managed, can positively influence the sustainable performance of the
material and utility elements. Therefore, a comprehensive understanding and
application of a systems approach is critical in managing the services element.
3.2 Essential Municipal Services
The major essential municipal services investigated in this thesis are the
treatment of wastewater and the management of solid waste (including organic
waste) generated by the residents. The treatment practices discussed are the most
commonly used practices by Swedish municipalities. The treatment services in
Sweden are managed by waste companies (stakeholder companies) that are
responsible, or have been hired by the municipality, for these services and have
signed contracts to supply treatment and management services [23]. Figure 4
shows the wastewater/waste/recyclables treatment service in Umeå (Umeå data
were used for modeling purposes) [40]. Umeå is situated in northern Sweden and
has a population of 130,000 inhabitants (similar to most European medium-sized
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cities) as of 2020. It is well connected to municipal services [36] [41]. Umeå is
one of the fastest growing European cities and is the center of growth in northern
Sweden, which has a great effect on the use of natural resources and its
infrastructure [36]. In Sweden, a symbiotic city network (a mutually beneficial
arrangement between cities to ensure environmental sustainability) between
municipalities exists to ensure the sustainable treatment of waste. Here, for
example, waste from different municipalities is transported between cities
depending on where the treatment plant is located [40]. These treatment steps
can vary for cities in Sweden; only the most common treatment practices (as used
in Umeå in this case) are considered in this thesis.
Figure 4. A simplified illustration of wastewater, organic waste, residual
combustible waste and recyclables waste treatment services in Umeå [40]
3.2.1 Wastewater Treatment Service
Umeå’s WWTP is designed for 166,000 inhabitants (included industrial loads)
and can purify a maximum 8100 cubic meters of wastewater per hour [42].
Depending on its physical area, population, and sewer network connectivity, a
city will require one or more centralized WWTPs. According to Statistics Sweden
(2018), more than 8.5 million people in Sweden (total population 9.7 million) had
access to municipal wastewater treatment in 2015 [43]. Figure 5 shows the
schematic view of Umeå’s WWTP. The wastewater in Umeå is treated aerobically
22
(i.e. using a biologically activated sludge process) in combination with anaerobic
digestion of sewage sludge generated during the treatment as an additional
optional step. The effluent treatment train involves a primary step, meant for grit
removal and suspended solids separation in a primary clarifier using FeCl3
coagulant, and a secondary step involving an activated sludge process. This
process microbiologically metabolizes organic compounds present in the primary
treated wastewater under aerobic conditions, followed by settling of the
biologically active sludge in the secondary clarifier.
Figure 5. Workflow of the wastewater treatment process in Umeå including the
effluent treatment, sludge management and byproduct processing
The sludge from the secondary clarification unit is recycled to the aeration tank
to maintain a desired concentration of mixed liquor suspended solids (MLSS),
with excess sludge removed periodically through the sludge drain line. This
clarified effluent is sent for further treatment where phosphorus is removed
through precipitation by addition of FeCl3. Finally, this wastewater effluent is
pumped to the receiving body (in this case, the Ume river) [43–45].
In the sludge streams (raw sludge from the primary clarifier, excess secondary
sludge, and polymer thickened tertiary sludge), the sludge is anaerobically
digested, thereby generating biogas and dried digestate as byproducts. Biogas
(containing 50–70% CH4, 30–40% CO2 and other trace elements) is used to
produce heat and electricity, with a certain amount being flared. The heat
produced is used within the plant and seasonal excess heat is sold to the
municipality. Paper I describes an investigation into diverting the biogas from
WWTP and treating it so that it can be used as a Liquefied Biomethane (LBM)
23
fuel to operate heavy-duty trucks. The environmental performance of the
consequential use of biogas as a fuel was assessed in this paper.
The dried sewage sludge is used as a soil conditioner for agricultural use (it was
converted into pellets but this was stopped due to lack of demand), but only when
the concentration of heavy metals and emerging contaminants is lower than the
criteria established by regulations. It is also used for capping of landfills and the
remaining sludge is disposed of in landfill [44]. The current ban on landfilling
sludge in Sweden has triggered incineration of the sewage sludge [24].
Incineration of sludge results in the destruction of harmful substances such as
pharmaceutical residues, multi-resistant bacteria, micro plastics and harmful
organic substances. The possibility of eliminating the undesired substances found
in sewage sludge that have detrimental effects on the ecosystem, along with the
potential for recovery of phosphorus, makes incineration one possible circular
option [24]. In Paper V, a scenario analysis described, which evaluated the
environmental performance of WWTP where the sewage sludge had been
incinerated for energy recovery.
3.2.2 Municipal Solid Waste (MSW) Treatment Service
MSW management in Swedish cities involves actors having a clear division of
responsibilities. Municipalities are obliged to have a waste management plan and
bear the responsibility of collecting and disposing of household waste, except for
the product categories covered by the so-called producer responsibility [46].
Waste minimization is the top priority according to the EU Waste Framework
Directive (2008/98/EC)[47]. Households in Sweden generated an average of
466kg/ year / person as of 2018. According to Avfall Sverige report in 2018, the
quantity of Swedish household waste treated was 4,583,000 tonnes. The
proportion of household waste taken for biological treatment was 15.5%, while
50% was used for waste-to-energy recovery and 33.8% was recycled (0.5%
landfilled) [48].
Combustible domestic waste and food waste are collected using a curbside
system, with a “green bin” for combustible waste and a “brown bin” for organic
food waste (see Figure 4). Packaging materials, such as glass, paper/cardboard,
plastic, metal packages and newspapers, are collected in recycling stations
around the municipality. In addition to the recycling stations, a majority of the
apartment buildings have recycling rooms where tenants can sort their packaging
waste into separate bins. Bulky waste, waste for reuse and garden waste are
collected at recycling centers normally run by the municipalities [40, 48].
24
(a) Organic Food Waste Treatment
Organic food waste (OFW) in Umeå is transported to the Skellefteå biogas plant.
Figure 6 illustrates the workflow of an OFW treatment plant in Skellefteå. The
plant receives organic waste from households and local slaughterhouse waste
daily. The waste first undergoes a pre-treatment process (a sand trap to remove
unwanted materials). The mass is diluted with water (36–40ºC), with the larger
particles bigger than 6mm being removed, dewatered and sent to the incineration
plant. The remaining organic matter and the blood and slaughter waste are sent
directly to the grinding unit to provide an optimal digestion process [48, 49].
Figure 6. Organic food waste treatment process at the Skellefteå biogas plant
with anaerobic digestion of waste to produce biogas, which is converted to CBM
for use as fuel in buses, and sludge for use as soil conditioner
The organic slurry is sanitized (at 70ºC to kill pathogenic bacteria and then cooled
to 55ºC in a heat exchanger) before being pumped into the digestion chamber.
Anaerobic digestion can be achieved over different temperature ranges including
mesophilic digestion at temperatures of 35–40ºC and thermophilic digestion at
temperatures between 50–60ºC (which is faster and produces more gas). The
residence time in the digester is about 18 to 20 days and produces biogas.
Specifically in certain cities like Skellefteå, the biogas is then sent to an
upgradation unit (for removal of CO2, H2S from biogas, either to meet the vehicle
fuel standard or to meet the required natural gas quality for use in the natural gas
grid) [50]. The upgradation unit consists of a water scrubber, carbon molecular
sieves, and selexol scrubbing to obtain Biomethane (99% CH4) which is then sent
to a storage tank. This is known as Compressed Bio Methane (CBM) when used
in vehicles [50] [51]. In Skellefteå, pipelines were recently built to transport the
gas to the town center. The buses (short distance and selected long distance) in
the city and municipal passenger cars run on CBM. The sludge obtained from the
digestion process is dewatered and thickened (by adding cationic polyacrylamide
25
polymer), then used as soil conditioner on grasslands and forestry. Paper II
describes a study of the transfer of technology for treating organic food waste
from developed nations to developing nations, where a significant amount of food
waste is routinely open dumped. The societal cost benefits of using CBM as a fuel
for buses and cars in Mumbai, India was evaluated in this paper.
(b) Waste-to-Energy Plants
The fraction of combustible domestic waste not extracted for recycling at source
or separated out in Sweden is used in Waste-to-Energy (WtE) plants for energy
generation [52]. The thermal process converts waste to generate fly ash, bottom
ash, emissions to the air, and process water. Of the total waste stated above that
goes into the MSW treatment service, almost 50% of household waste in Sweden
is used for energy generation [36]. Incineration is a waste treatment process that
involves the combustion of organic substances contained in waste materials, and
is one of the most robust ways to replace fossil fuels and reduce CO2 emissions.
The emissions from these plants are treated (flue gas treatment) to meet the
stringent regulations, and hence provide improved air quality in many cities [53].
A typical waste incineration facility includes the following operations [54]:
Waste storage and feed preparation
Combustion in a furnace, producing hot gases and a bottom ash residue
for disposal
Gas temperature reduction, frequently involving heat recovery using
steam generation
Treatment of the flue gas (cleaning using filters, scrubbers, sieves) to
remove air pollutants, and disposal of fly ash obtained from this
treatment process
Dispersion of the treated gas to the atmosphere using draft fans or stacks
Depending on the capacity and type of waste, there are different types of
incinerator technologies used e.g. Rotary kiln Incineration, Grate incineration
and Liquid, Gases and fumes incineration [54].
Figure 7 shows the workflow of a WtE plant such as the one in Umeå. The
incineration process (fluid bed boiler) is fed with oxygen (O2) so that the waste
has enough caloric value to burn without support fuel; fuel oil is only used to start
the combustion process. The working temperature in the boiler is approximately
950ºC and the residence time of the waste in the furnace varies from 45 to 90
minutes. After the combustion step, there remains heavier bottom ash,
accounting for around 10% of the original volume of waste (97000 tonnes of
household waste in 2018), and high temperature flue gases.
26
Figure 7. Workflow of a WtE Plant in Umeå with fluid bed boiler that produces
heat and electricity for households, flue gas purified to 99.7% and ash used in
the construction industry (Umeå Energi)
The bottom ash is cooled and particles bigger than 40mm are separated (sieving).
An electromagnet is used to separate the metals from the ashes; the ash is stored
in an ash bunker. The semiconductors and some toxic substances (e.g. As, Cd, Cr
and Zn) are separated from the ashes. After this treatment, the bottom ash
contains fewer toxic compounds and can be used in construction materials. The
main part of the WtE plant cleans the flue gas before releasing it into the
atmosphere. The European directives for emissions specify important
restrictions on using an incinerator plant [52]. The residue from the flue gas
treatment (fabric filters, an acid scrubber, and an SO2 scrubber are all used to
purify the gases to 99.7%) is fly ash which contains hazardous substances such as
dioxins, furans, chlorine, bromine etc. The fly ash is transported to landfills
specializing in hazardous waste storage. Energy recovery from these plants can
produce heat in combination with electricity used in households (district heating
network) [52] [55]. Paper IV describes an evaluation of the environmental
performance of using fly ash from WtE plants (currently landfilled) as a filler
(after immobilizing the heavy metal content in the fly ash) in epoxy composite
panels with a PU foam core for use in the building industry. The ecoefficiency of
silanized fly ash epoxy composite sandwich panels compared to the steel-skinned
incumbent market sandwich panels was calculated in that work.
(c) Recyclables
According to the EU waste hierarchy, recycling is the most preferred option after
prevention (non-waste) and preparation for reuse [56]. In Sweden, the
27
recyclables sorted from households are transported to recycling stations/centers
at different locations within cities. In addition, there are several unmanned
container-based sorting options that are covered by Producer Responsibility
Obligations Regulations for packaging, newspapers, tires, and cars along with
electrical and electronic products, whose producers are responsible for dealing
with end-of-life processing [21, 40].
The common items collected from recycling stations/waste rooms in Umeå as of
2019 (Avfall-Web) are glass packaging (3156 tonnes), cardboard (443 tonnes),
metals (1643 tonnes), plastic packaging (1276 tones), paper (4055 tonnes), paper
packaging (2960 tonnes) textiles (117 tonnes), wood (3764 tonnes), lightbulbs,
batteries (portable-22 tonnes, car batteries-84 tonnes), and electronic waste
(1604 tonnes). The data above are expressed in tonnes/year (2019). The possible
amount of recyclables collected was 27% in the year 2018. The remaining fraction
that cannot be reused or recycled were transported to WtE plants[36].
3.3 Management of Essential Municipal Services in Cities
Complying with Circular Economy Principles
In general, managing essential municipal services in an urban system has
undergone a major transformational change over recent years [4, 12]. Over the
last few years in Sweden, essential services in a city only needed to undertake
basic functions. This meant that the wastewater and MSW were treated and
managed to reduce health and ecological threats otherwise posed by these
streams when untreated or mismanaged. The influent wastewater from the city
was treated in centralized WWTP using secondary methods such as an activated
(aerobic) sludge process. Further, the residual waste, such as undigested sewage
sludge from WWTPs, was disposed of in landfills [45, 57]. MSW from cities was
collected and treated in a waste-to-energy plant (with the ashes disposed of in
landfills), organic material was composted or anaerobically digested, with the rest
sent to landfill [57, 58, 59]. These were considered to be common practices by
cities [60].
At present, cities are expected to fulfil their functional requirements and to
achieve a greater degree of conformity to circular economy compliance (EU
legislation) [61–63]. Figure 8 shows the energy, material and resource values
potentially recoverable and extractable that are generated by essential municipal
services management [36]. To meet these criteria, essential municipal services
have to satisfy two requirements. First, leakage of hazardous contaminants (e.g.
release of heavy metals from waste incineration fly ash into landfill or
micropollutants entering natural water streams from wastewater treatment
discharge) into the biosphere must be prevented. Second, operation of essential
municipal services will generate byproducts and residual waste streams. These
28
residual streams must be further processed, if needed, and their economic value
must be extracted and put to beneficial use within the technosphere [36, 64].
Figure 8. Essential municipal services management that complies with
circularity in order to produce energy value, material value, and fuel value in
cities
Generally, cities having a WtE plant incinerate the refuse fraction of MSW and
generate high-pressure steam and electricity. The cities in cold climate regions,
such as Umeå, use a large proportion of the steam to meet the heating and hot
water needs of buildings, converting a relatively smaller proportion into
electricity [54]. Cities with smaller district heating demands prefer to operate
their WtE plants maximized for electricity production. The electricity generated
by a WtE plant can also be used to support electric transportation in a city
(electric cars, city buses etc.) [65].
Biogas can be generated from three sources within municipal service operations:
(a) the WWTPs that have the infrastructure and capability to anaerobically digest
their sewage sludge, (b) cities treating their organic fraction of MSW in anaerobic
digestion facilities, and/or (c) cities landfilling MSW-generated organic material
and equipped with a biogas collection system [66]. Biogas sourced from these
sites can be used either to produce heat and electricity, or converted to
biomethane and used as a fuel for public and private transportation vehicles in a
city [50, 51]. Papers I and II describe an investigation and assessment of the
29
environmental impacts of diverting the biogas from wastewater and organic food
waste treatment for use as fuel in heavy-duty trucks, buses and cars. The societal
benefits of using such renewable fuel compared to a baseline using diesel or
gasoline are expressed in terms of cost equations.
The output in terms of material value resulting from a city’s essential municipal
service operations can include secondary materials and materials obtained from
the residual waste streams [67] [68]. The secondary materials, such as metals,
plastic, wood, glass etc., are produced from a city’s MSW recyclable waste fraction
by using reuse, recycling and recovery techniques in that order of hierarchy [21].
The principal reason why a city separates and processes its MSW recyclable
fraction is to increase the circularity of existing materials and minimize the
dependency on natural sources to provide virgin materials. Residual waste
streams can potentially be a cheaper raw material source for generation of value-
added materials.
Nutrients, such as phosphorus, can be extracted from digested sewage sludge
generated by WWTPs [24]. Alternatively, it can be used to produce biochar, which
serves as a cheaper raw material in a variety of industrial applications [68]. The
digestate from MSW organic digestion facilities has significant nutrient value and
can be directly applied as a conditioner to agricultural land [49]. In addition,
some cities treat their food waste in composting facilities and the compost thus
generated is used as an organic fertilizer [23]. Multiple industrial pathways have
been established for recycling and upcycling the bottom and fly ash from a WtE
plant (discussed in detail in Paper IV) [69]. Paper IV describes the upcycling of
fly ash (using silanization to immobilize the heavy metals) as a filler in composite
panels, and stated the ecoefficiency of the silanized fly ash composite panel.
Finally, tertiary treated wastewater is a resource value that can be assigned to
WWTPs. This may not be of concern to cities where freshwater (surface or
ground) is available in abundance. However, for cities facing extreme water
stress, tertiary treated wastewater is of great value and reduces freshwater
withdrawal rates [13]. In 2018, the summer was very dry in Sweden, causing a
drought in some regions. Wastewater reuse, unlike in other water stress regions,
is not common in Sweden and there is no legislation specifically regulating this
[67, 70]. Thus, environmental regulations and policies play a significant role in
implementing a circular economy. Paper V describes a review of the overall
circular performance of WWTP. The total cost (environmental cost and operating
cost) related to achieve the circularity of such plants operating in cities was also
determined.
30
Thus, achieving circular compliance with respect to operation of essential
municipal services is important, owing to its valuable contribution in improving
the services’ overall environmental performance [67].
31
4. Tool & Methodology
4.1 Life Cycle Assessment
Life Cycle Assessment (LCA) is a methodology used to evaluate the environmental
impacts associated with a product or service from cradle to grave. LCA studies
can explore large industrial systems by collecting and analyzing large amounts of
environmental information [71]. In order to know which action is the most
environmentally preferable and avoid the causes of major emissions (hotspots)
in a product/service, a structured assessment tool is needed. One such tool used
in the thesis is LCA. The LCA procedure has four steps according to ISO 14040
and 14044 [71], as shown in Figure 9.
Figure 9. Steps for carrying out an LCA as described in ISO (14040) [72, 73] and
followed in all the papers appended to the thesis
First, the product studied is described and the purpose of the LCA is specified by
the goal and scope definition, including system boundaries and functional unit.
The LCI step involves the construction of the life cycle model and a calculation of
the emissions produced and resources used during the life cycle of the
product/process. The emissions and resources are related to various
environmental problems through classification and characterization weighting.
These are calculated in the LCIA step. Finally, the results are interpreted to the
32
target group and can be used for direct applications in product development and
improvement, strategic planning, public policy making etc. [72].
Many research groups have set up their own software to handle environmental
impacts, using packages such as Microsoft Excel. In addition, there are a number
of LCA software packages commercially available [71]. The software has been
developed for any type of LCA and some are designed for particular LCA
applications or specific industry sectors (all comply with ISO 14040 standards).
This classification is based on the computational capacity of the tool and the
extent to which quality of data used in calculations can be reviewed [74]. Some
commonly used LCA software includes GABI, Simapro, OpenLCA, and Umberto
[74]. Data collection is also time-consuming when carrying out LCA calculations,
especially for complex activities. The foreground data are specified by the
supplier/industry; the background data are obtained from a set of representatives
who build local, national and international databases in coordinated efforts from
several countries [75, 76]. In addition, industries have taken initiatives to set up
public LCA databases as a way of maintaining control over the data used in LCA
studies. The databases are maintained and combined by public authorities,
(national and international levels), industry sector organizations, consultants and
research institutes [71].
The LCA studies carried out in this thesis were modeled using the Simapro PhD
8.2.0 software - Pre 2017. SimaPro is a professional tool for collecting, analyzing
and monitoring the sustainability performance data of products and services. It
enables a student or a researcher to examine an entire life cycle thoroughly with
a set of powerful and unique features [77]. The ecoinvent database (v. 3.2) was
used for background LCI datasets [78]. It provides well-documented process data
for thousands of products and is the best source in terms of transparency and
consistency [78]. The foreground data for modelling (Papers I–V) were obtained
from industry, literature and treatment plants (Umeå Energi, Dåva DAC, Vakin,
Skellefteå biogas plant). Data obtained from supplier or site-specific data were
preferred for LCAs (reduced uncertainty, data regionalized) over predicted or
generic datasets [79]. Real-time data from sites can provide environmental
information for better process understanding and improved decision-making. It
can assist stakeholders in making more effective and efficient decisions (timely
and more accurate).
There are three types of LCA [71]:
Attributional LCA: inputs and outputs are attributed to the functional
unit of a product system. They are used for comparison of existing
products.
33
Consequential LCA: product system are linked in modelling such that
activities are included that are expected to change as a result of differing
demand for the functional unit. They are used in comparison, product
development, building design and process choice decisions, such as waste
management options or recycling schemes. The work described in Papers
I–V uses consequential modeling approach.
Standalone LCA: describes a single product and some important
environmental characteristics (identify hotspots) of that product.
4.1.1 Goal & Scope Definition
The initial goal and scope definition in an LCA establishes the purpose of the
assessment and determines decisions made about the details of the product
system being studied before any data are collected. The transformation of the
general goal to a more specific purpose to make relevant methodological choices
in modeling is necessary [72]. The goal and scope definition needs to answer the
following questions [80]:
What is the main application and who are the target groups of the study?
What would the environmental consequences of changing a certain process
be?
What kind of data and quality of input data are required and which
assumptions need to be made based on the level of detail in the study?
What type of environmental impacts are being considered (a default list of
impacts is considered in most LCAs), and what are the limitations based on
the study?
This is a very important phase of LCA methodology because this is where the
exact approach to be followed is determined. The goal and scope definition
phase includes determining the functional unit, system boundaries, data
reflecting process-specificity or genericness (i.e. foreground or background)
data.*
Functional Unit & System Boundary
The functional unit (FU) and system boundary are specified in the goal scope
definition. LCA relates environmental impacts to a product, specifically to the
functional unit of the product system. Thus, there is a need to express the FU in
quantitative terms such as passenger transportation in person kms, or amount of
waste incinerated per year. The FU corresponds to a reference flow to which all
other modeled flows of the system are related. Products or processes often fulfill
more than one function, therefore, depending on the goal of the study, one of the
functions must be chosen that is related to one reference flow. The amount of
product needed to fulfill the FU is the reference flow [71].
34
The system boundary describes (flow model) which process to include, based on
the choices made in the goal and scope definition. According to Tillman et al.
(1994) [81], system boundaries need to specified in several dimensions:
Geographical boundaries i.e. electricity production, waste management,
transport from one region to another
Boundaries related to natural systems i.e. where is a product’s cradle
(beginning) and grave (end)
Time boundaries i.e. number of years considered in the study
Boundaries within the technical system i.e. capital goods, personnel,
allocation to be included in the product/process studied.
Figure 10 shows examples of the different system boundaries which can be
considered in an LCA.
Figure 10. System boundary examples considered in an LCA, shown as a
conceptual line that divides the system being studied from 'everything else' that
is not a part of the system
The most commonly used system boundaries are [82]:
Cradle to Grave LCAs are the most comprehensive and commonly used
to compare products and generate Environmental Product Declarations
(EPD) etc.
Cradle to Gate LCAs are used when product functionality remains the
same but the changes occur in raw materials and manufacturing.
Gate to Gate LCAs are carried out when a specific stage of the product
changes.
35
For example, for Paper II, a cradle to grave LCA was carried out to investigate the
possible benefits of using CBM as a fuel to operate buses in Mumbai, India. The
food waste from the city is transported to a biogas plant where it is processed by
anaerobic digestion (AD). Compressed biomethane (CBM) is obtained by
converting (water scrubbing) the biogas produced as a byproduct and is then used
to fuel buses within the city. In this case, the functional unit chosen was the total
distance driven in bus-kilometers (bus-km) in a year by buses operating on CBM
fuel produced from a biomethane-producing plant treating food waste generated
by Mumbai residents. The environmental performance results were compared to
an equivalent distance driven in a baseline scenario using a diesel and
compressed natural gas (CNG) bus.
4.1.2 Life Cycle Inventory (LCI) Analysis
The Inventory analysis step (Step 2 in Figure 9) builds a systems model according
to the requirements of the goal and scope definition. The resulting mass and
energy balance is incomplete in the sense that only relevant environmental flows
(emissions, use of resources) are considered [72]. LCI models are normally
created to be static and linear, so time is not used as a variable and all
relationships are simplified to be linear [83]. Consequently, efforts to build
dynamic LCI models have explicitly incorporated dynamic process modeling in
the context of temporal and spatial variations [84]. The LCI analysis includes:
Flowchart construction according to the determined system boundaries
Data collection for all activities in the product system (raw materials,
emission to air, water and solid waste) followed by documentation of data
Calculation of environmental load (amount of resource use and pollutant
emission) with respect to the FU
The LCI analysis is complex since many technical processes produce more than
one product. The environmental load for such processes are allocated, that is
partitioned, between different products within the system [85]. Table 1 shows the
typical parameters of an LCI, illustrated with data from Paper I where the
conversion (amine scrubbing and liquefaction) of biogas from a WWTP is used as
an LBM fuel in tractor-trailers (TT). The inventory for the LBM lifecycle for the
FU of 16,000,000 ton-km of a TT transporting products and goods is also shown.
Table 1. Life cycle inventory of LBM-TT life cycle (Paper I)
Inputs
Outputs/
FU
Unit Paper I (Input
/Output)
Quantity
36
Input
Raw
Materials
Mass/Volume
Clean biogas (after amine
scrubbing)
364,000 Nm3
Utilities
Heat
Electricity
Fuel
Joules
KWh
Liters
Electricity from Swedish
grid
Electricity credit from
biogas
1745 MWh
- 1184 MWh
Output
End
products
Waste
disposal
Mass/Volume
Liquefied Biomethane
(LBM)
Fuel consumption LBM
TT
280,000 kg
28 kg/100 km
0.0175 kg/tonne-
km.
Emission
Air
Water
Soil
Mass
Biogenic CO2
CH4
NOx
PM
798 tonnes
14 tonnes
420 tonnes
2.4 kg
4.1.3 Life Cycle Impact Assessment
Life Cycle Impact Assessment (LCIA) (Step 3, Figure 9) aims to highlight the
impacts and environmental consequences of the environmental load quantified
in the LCI. It transforms the inventory results into more environmentally relevant
information (acidification, ozone depletion etc.) [86]. The ISO standard (14042)
for LCIA contains the following sub-phases [72, 87, 88]:
Impact category definition is the specification of environmental
impacts relevant to the goal and scope definition. The decision to include
these categories is based on completeness, practicality, relevance,
scientific method. i.e. midpoint indicators and endpoint indicators
Classification is used to sort the inventory parameters according to
the environmental impact they contribute to i.e. the cause-effect
pathway.
Characterization is the relative contribution of the emissions and
resource consumption to each type of impact calculated e.g. total
emissions of greenhouse gases are combined into one indicator for global
warming.
Normalization relates the characterization results to a reference value.
The main aim is to gain a better understanding of the magnitude of the
environmental impacts caused e.g. relating the impacts of the studied
product to the impacts of the total amount of pollutants in a region.
Grouping means to sort and possibly rank the indicators
37
Weighting means to combine the characterization results across impact
categories
Data quality analysis means to carry out a sensitivity analysis to
obtain a better understanding of the reliability of the LCIA results e.g. the
most polluting activities, the most crucial inventory data, and the
significance of alternative methodological choices.
Not all sub-phases in the LCIA have the same level of importance. An LCA study
typically includes core phases such as classification, characterization and
normalization.
The most commonly used LCIA methods in this thesis were RECIPE Europe (H)
(Paper I), RECIPE World (H) (Paper II), and ILCD 2011 (Papers III and IV) [75,
88, 89]. These methods were used based on their goal and scope, which
determines the region (Europe, World) over which the study was carried out,
important environmental impacts to be included in the study, and environmental
costs available for the LCIA methods. The commonly used midpoint indicators
(Papers I–V) are listed in Table 2.
Table 2. Midpoint indicators/impact categories considered in LCIA
Midpoint Impact
Category
Unit Cause Effect Pathway
Global Warming Potential
(GWP)
kg CO2 eq. Greenhouse gas impacts
depend on changes in
radiative forcing
(expressed as W/m2)
Ozone Depletion Potential
(ODP)
kg CFF-11 eq. A number of persistent
gaseous compounds
released to the air may
result in an increase of
chlorine and bromine
concentrations in the
stratosphere, causing a
reduction in the
stratospheric ozone
concentration.
Acidification Potential
(AP)
kg SO2 eq./mole
H+ eq.
Substances causing
acidification, such as sulfur
dioxide and nitrogen
oxides, are diffused while
carried in an air stream.
These substances will be
38
transformed to acidifying
substances such as sulfuric
acid or nitric acid through
oxidization and
photochemical reactions.
Freshwater
Eutrophication Potential
(FEP)
kg P eq. Airborne substances
involving nitrogen and
waterborne substances
containing nitrogen and
phosphorus may promote
eutrophication on land and
in water areas (surface
water/freshwater).
Human Toxicity Potential
(HTP)
kg 1–4 DB
eq./CTUh
Available characterization
factors for toxicological
impacts on human health
in LCA that account for
chemical fate, human
exposure, and toxicological
effects.
Photochemical Ozone
Formation Potential
(POFP)
kg NMVOC eq. Photochemical smog is
caused by the creation of
ground level (tropospheric)
ozone from the interactions
of volatile organic
substances (VOCs) and
oxides of nitrogen.
Particulate Matter
Formation Potential
(PMFP)
kg PM10 eq. The change in ambient
concentration of PM2.5 after
the emission of a precursor
i.e. NH3, NOx, SO2 and
primary PM2.5, was
predicted using the
emission-concentration
sensitivities matrices for
emitted precursors.
Terrestrial Ecotoxicity
Potential (TEP)
kg 1,4 DB eq.
/CTUe
Ecotoxicity is treated in a
similar way to human
toxicity including both fate
and effect; exposure is
generally implicitly taken
Freshwater Ecotoxicity
(FETP)
kg 1,4 DB
eq./CTUe
39
into account in the effect
factor.
The LCIA methods normally assign a factor to each elementary flow in an
inventory table [75]. For example, to measure the GWP as carbon dioxide
equivalent, the following factors are considered: releasing 1 kg of CH4 into the
atmosphere is roughly equivalent to releasing 84 kg of CO2. Similarly, releasing 1
kg of N2O into the atmosphere is roughly equivalent to releasing about 298 kg
of CO2 [90]. For all the appended papers, these midpoint impact categories were
investigated in order to evaluate the overall environmental performance of the
process studied with the tradeoffs between the impacts explained using
supporting (substances/process causing the impact) information.
4.1.4 Interpretation of Results
According to ISO 14040, Life Cycle Interpretation (LCI) (Step 4, Figure 9) is a
systematic technique to identify, quantify, check, and evaluate information from
the results of the LCI and/or the LCIA [86, 91]. The large number of parameters
generated in the calculation of the quantitative LCA must be processed before
interpretation and visualization of results. Using a city as an example, the
municipal stakeholders are the target audience and hence the results must be
presented as an overview of the system studied, as well as identify the hotspots
which cause specific environmental impacts. However, researchers and scientists
who understand chemistry, the behavior of chemical compounds in the
environment and their transformation in air, water and soil need detailed
inventory results to examine the processes that cause such compounds. The
advantage of an LCA is that it not only illustrates the whole life cycle, but also
makes it possible to delve inside the different parts of the life cycle. A contribution
analysis can be carried out to interpret the critical contributions from the life cycle
stages (individual unit processes or groups of processes). A contribution analysis
was carried out in the study described in Paper II in order to identify which
environmental loads (activities) contributed to the total environmental impact of
various life cycle stages in the conversion of food waste to CBM fuel. This
contribution analysis is shown in Figure 11 below.
40
Figure 11. Contribution analysis of the environmental impacts (Table 2) of life
cycle stages in the conversion of food waste to CBM fuel. The stages include the
anaerobic digestion plant, cogeneration unit, sludge and waste management,
conversion of biogas to biomethane, CBM service station, use of CBM as fuel in
buses
As can be seen in Figure 11, the biogas plant (which includes the pretreatment of
food waste and production of raw biogas by AD) contributed 57–86% of the total
impact in the GWP, ODP, FEP, HTP, TEP and FETP categories. GWP was mainly
driven by methane slip emissions (2%) from the AD plant whereas the other five
impacts are caused by addition of FeCl3 in the digester to inhibit high
concentrations of gases such as H2S and NH3. The use stage contributed to high
AP, POFP and PMFP impacts (80–89% of total impact). Release of NOx
emissions due to combustion of CBM fuel is responsible for AP and POFP impacts
whereas particulate matter emissions increase PMFP. However, the absolute
scores of these impact categories for CBM buses are much lower than CNG or
diesel buses.
The sludge and waste management stage (i.e. sludge thickening and drying, and
disposal of non-biodegradable waste in open dumps) contributes to a reduction
in ODP, HTP, FEP and FETP impacts by 28–42% and completely negates (100%)
the TEP burden imposed by other stages of the life cycle. This is attributed to
environmental credits associated with the application of digested sludge as bio
fertilizer. However, open dumping of non-biodegradable waste reduces the
41
benefits, particularly in the GWP and FEP impact categories. The results of this
type of analysis are important for comparing resource use, and emissions at the
characterization level. One can also see the dominance of different stages of the
life cycle (raw material, manufacturing, use, end of life) and their contribution to
the environmental impacts. These analyses allow identification of improvements
(processes, chemicals, energy) that are most wanted or needed. The quality of
results must be transparent and also, according to ISO14040/44, the reporting of
LCA results must contain in-depth information along with robustness checks of
results that include [80]:
Completeness check – Data gaps in inventory
Consistency check – Within the defined goal and scope, check for
appropriateness of life cycle modeling and methodological choices
Uncertainty analyses - Effect of uncertain data
Sensitivity analyses – Identify and check effect of critical data
Variation analyses – Effect of alternative scenarios and life cycle models
Data quality assessments - The background data use the unit process
from the ecoinvent database with a specified uncertainty. The foreground
data use the pedigree matrix. The pedigree matrix (PM) is a post-normal
approach to assigning uncertainty. It is a framework, that measures data
quality based on the indicators’ reliabilities, completeness, temporal
correlation, geographical correlation, and technology correlation.
In the final step of an LCA, all conclusions based on the previous steps of the
interpretation, should be qualified in terms of their robustness, and
4.1.5 Uncertainty Analysis
The imprecision of data used for LCA can be evaluated by using uncertainty
analysis. The range of possible values over an interval for a particular material
introduces variability. The information obtained from different suppliers and
production processes under different conditions can affect the environmental
performance of the product [84]. There are also other different sources of data
uncertainty [92]:
Uncertainty in measurements and estimates
Uncertainty in consumer behavior in the use and disposal phases
Uncertainty in future disposal scenarios
Uncertainty in impact assessment factors
The interval over which the data can range can be an important piece of
information for comparison (e.g. minimum and maximum values). It is of crucial
importance to collect all variability in the data used for the LCI so that the interval
42
and distribution can be established. Table 3 shows, as an example, the variation
in fuel economy, methane slip and tail pipe emissions of different fuels (CBM,
diesel, CNG used in buses) used for calculating uncertainties in the study
described in Paper II, and investigate how these uncertainties influenced the
environmental impacts.
Table 3. Variation of key modeling processing parameters for
uncertainty analysis (Paper II)
Parameter Range Varied Notes
Methane slip
emissions 2–4% of CBM produced
Based on minimum and
maximum slip emissions
for AD and conversion
units. This results in
variation in bus-km from
1,213,297 to 1,257,997 bus-
km (same range considered
for CNG and diesel buses).
Fuel economy 0.48–0.6 Nm3/km
Baseline considered 0.57
Nm3/km of CBM and CNG
buses
Tailpipe emissions
CO 0.36–3.00g/km
(Diesel);
0.4–1.5 g/km (CNG)
Based on driving cycle and
actual emission studies
CO2 700–1200 g/km
(Diesel and CNG buses)
NOx 6–11 g/km (Diesel)
0.5–6.5g/km(CNG
and CBM)
PM 0.1–0.5 g/km (Diesel)
0–0.03 g/km (CBM
and CNG)
4.1.6 Scenario Analysis
Scenario analysis is a strategic process for analyzing decisions by considering
alternative possible outcomes. It provides a basis for further analyses, discussions
and developments to gain greater knowledge of various scenarios in LCA. It is
seen as an investigation of the effects of changing parts of the life cycle model or
changing life cycle processes in the system studied [85, 93]. The results of the
scenario analyses make it possible to see which changes would lead to substantial
reductions in environmental load and which would lead only to marginal changes.
43
Paper II describes the scenario analysis of the influence of using an external
energy supply (Indian electricity mix) in biomethane plants on the overall
environmental performance of using buses fueled with CBM. Significant tradeoffs
were seen when the electricity powering the biomethane plant was supplied from
an external source i.e. Indian electrical grid mix [94](coal 75%, gas & oil 8%,
renewables 17%, nuclear 3% as of 2019) and when all the biogas produced was
converted and used to fuel buses. CBM buses still performed better than CNG and
diesel buses in most impact categories (ODP, FDP, TEP) and marginally better
with respect to reduction in GWP.
From an environmental perspective, coal is the worst source of fuel for electricity
production since it increases environmental problems such as acidification
eutrophication, human and freshwater ecotoxicities [95]. Combustion of coal to
produce electricity also increases particulate matter emissions. However, since
the emission comes from stationery (power plants) sources, the environmental
externalities attributed to damage caused to a society are lower than tailpipe
emissions resulting from diesel combustion in vehicles.
Interestingly, in spite of methane losses and use of electricity from the high
carbon intensity electrical grid, CBM buses reduce GHG emissions marginally by
8–10% but can decrease FDP by 46–56% compared to diesel and CNG buses. This
can significantly reduce crude oil imports to India. The scenario analysis results
suggest that the monetary valuation of environmental externalities caused by a
trio of impacts (GWP, PMFP and FDP) can still be lower than the status quo,
considering that traffic-related particulate matter emissions have higher damage
costs than power plant emissions [96]. Further, converting all the biogas to CBM
may be reasonable from a perspective of reducing capital expenditure for a
biomethane plant that is self-sufficient in energy i.e. installation of a CHP unit
and biogas conversion plant can be extremely capital intensive [96].
4.1.7 Limitations of LCA
LCA studies are based on assumptions and scenarios because they assess the real
world using a simplified model. The LCA methodology has its own limitations
that can lead to doubt about the results. The main problem lies in the idea that
methodological choices, such as system boundaries and functional units, tend to
be inconsistent which means that it is very challenging to compare different
studies [84]. Although there have been increasing concerns about the use of LCAs
for marketing claims, the concept of life cycle studies has developed over the
years. A whole series of LCA standards has been published as a code of practice,
providing a rigid methodology applicable to a large range of products used in
different contexts for different purposes [97]. Another critical issue debated is the
44
impacts associated, are if the outcome from the LCA should be considered
potential or real impacts. The difference between a potential and real impact
depends on the location of the impact (e.g. acidification depends on the buffering
capacity of lakes and soil). To quantify real impacts, more data (data on locations,
receiving bodies, background concentrations of pollutants) and work are
required. It is important to emphasize that the potential impacts reported by an
LCA will be the greatest possible for that scenario, and so are not underestimated
[84, 97].
Allocation is another major issue that has been discussed frequently in LCA
forums (e.g. Forum for sustainability through Life Cycle Initiative, Nordic
Dialogue Forum for LCA). The problem of how the environmental loads of a
process are shared among themselves as well as among different products has
been debated. The recent guidelines (ISO 14044:2006) [80] have a way to deal
with allocation (types of allocation), but the issue has not been completely
resolved. These are general limitations and not all are necessarily applicable to
the context of the study carried out in this thesis.
4.2 Life Cycle Costing (LCC)
LCC is a tool similar to LCA that includes all costs over a product life cycle [98].
LCC or Whole Life Costing (WLC) determines the most cost-effective option from
different competing alternatives (e.g. disposal of an object, or process alternatives
for maintenance, operation) [99]. Figure 12 shows the flowchart for WLC. The
strengths of carrying out an LCC are that it can accurately identify cost hotspots
over a product/process life cycle [99]. This can be essential and valuable
information (municipality, stakeholder companies) for selecting the most cost-
efficient alternatives. Papers II, III, IV, and V in this thesis describe LCC
calculations for their respective scopes.
45
Figure 12. Flowchart to evaluate the whole life cycle costs including the financial
(planning, design, construction and acquisition, operations, maintenance,
renewal and rehabilitation, depreciation) cost which is relatively simple to
calculate and also the environmental and social costs, which are more difficult
to quantify and assign numerical values to [99]
4.3 Environmental Externalities Cost
The environmental impacts obtained from the life cycle analysis of the
product/process can be monetized as the Environmental Externalities Cost
(EEC). The consequence of an action by any agent affecting the environment for
which the agent does not pay compensation or is penalized is defined as
environmental externalities [89]. These externalities arise when the agent
responsible (individual, country) for the activity does not bear all the costs
(negative externalities) or benefits (positive externalities) of that activity. The
environmental pricing used in this thesis is based on damage costs. These
damages are based on the environmental pollution with respect to a range of
midpoints; a value is assigned to the additional overall damage caused by an
additional kilogram of a given emission [100]. Environmental prices are thus
rough-and-ready estimates that are not necessarily valid in specific situations. In
practice, environmental prices can support decision making in two ways [100]:
46
In environmental analyses such as LCA and EIA, these prices can be used
to weight the various impacts identified. Weighting the impacts is used
in LCA to express the results as a single score indicator.
In Social Cost Benefit Analyses (SCBA), environmental prices are used
primarily for valuation, providing a means of comparing environmental
impacts with financial items to arrive at integral consideration* of all the
impacts associated with an (investment) decision.
The values for the environmental prices of midpoints indicators in this thesis are
mostly unit environmental externality prices published in the literature [89]. In
addition, regional environmental prices were also considered from the literature
to obtain specific cost values [101]. The Life Cycle Environmental Externalities
(LCEE) cost can be calculated using the formula [100]:
LCEE = ∑ (Unit Externality Price in €
Impact) (Env. Impact from LCA Results)
For Paper IV, the ecoefficiency of using fly ash from WtE plants as a filler in epoxy
composite PU panels compared to that of incumbent steel skin sandwich panels
used in the building industry was calculated using:
Ecoefficiency = [1 − (LCEE costs
LCC Private Actors)] × 100
By monetizing the adverse environmental impacts identified in the LCA, the
environmental externalities resulting from the product’s use that are imposed on
society as well as the private costs incurred by stakeholders are measured.
Ecoefficiency was widely used by large chemical companies (e.g. BASF and
AkzoNobel) [102] to evaluate the potential societal environmental gains
achievable by using their products (which may result from, for example, reducing
negative environmental externalities) as well as their own private costs [103].
Similar cost indicators, such as Sustainability Return on Investment (SROI) and
Social Cost Benefit Analysis (SCBA) are calculated in Papers II and III, and can
be used in making investment decisions, product development and in mapping
value chain related environmental and energy risks.
47
5. Contribution of Papers to the
Development of the Framework
Papers I–V presented in this thesis describe the assessment of different
technology levels within wastewater and MSW treatment plants, including a
system expansion of the boundary studied. System expansion is part of the
consequential LCA method where a consequence of a certain activity is used to
capture changes in environmental impact and obtain information on the
consequences of certain actions [34, 79]. The papers were aligned to different
services of the city i.e. WWTP, OFW Plant, and WtE plant. A framework was
proposed that evaluated the sustainability of the essential municipal services of
an urban system in fulfilling their functional duties and achieving a greater degree
of circular economy compliance (see Figure 7). Figure 13 shows the contributions
of the papers in this thesis to the creation of the proposed framework.
Figure 13. Different stages of circularity in wastewater and waste treatment
plants identified in Papers I–V included in this thesis that led to development of
the five-stage framework
The different stages of the framework identified in these papers are described
below:
Business as usual (BAU) and future alternative scenario. In Paper I,
the objective was to compare the environmental performances of
Liquefied Biomethane (LBM) and Diesel as a fuel to operate Tractor-
48
Trailers (TTs). The LBM was obtained by converting biogas from WWTP
(Biogas from OFW digestion and landfills can also be a potential source).
Currently, based on the Umeå study, the WWTP uses biogas, produced
onsite for co-generation of heat and electricity, thereby meeting its
energy needs. A system expansion approach was applied where the
electricity and heat equivalents to the amount of biogas used for LBM
production are supplied from the Swedish grid (SE) mix (65% hydro and
nuclear power, 20% wind power and others 15%) and incineration of
wood chips respectively. The plant has currently no liquefaction
technology (converting biogas to LBM).
Additional processing of byproducts. In Paper II, the sustainable
performance of producing CBM from an Organic Food Waste (OFW)
treatment plant to be employed as a fuel in transit buses was evaluated.
In developing countries, the transportation sector is excessively
dependent on conventional fuels such as diesel and petrol, which has
resulted in severe reduction in the urban air quality in their cities.
Therefore, adopting a strategy to connect food waste management and
the operation of transit buses can positively improve the sustainable
performance of cities in developing nations. The sludge obtained after
digestion is used as a fertilizer or soil conditioner and hence the residual
stream is handled by returning nutrients to the biosphere.
Future alternative scenario. In Sweden, the energy obtained from
WtE plants is typically used for meeting the district heating needs of a
city. However, in some countries, such as South Korea, WtE plants are
an integral part of eco industrial parks, where the energy obtained by
combusting MSW is used to meet the needs of an industrial
manufacturing unit (used for electricity and a heat source for
industries) [104, 105]. Thus, in Paper III, a similar scenario was
considered where the energy from a WtE plant was used to power the
carbonization step in carbon fiber (CF) production. This study
evaluated the Sustainable Return on Investment (SROI) of lightweight
Advanced High Strength Steel (AHSS) and Carbon Fiber Reinforced
Polymer (CFRP)-intensive multi-material Body in White (BIW) for
automobiles. The SROI depends on the lightweight BIW
manufacturing cost and the difference in sustainable cost between a
baseline (mild steel) BIW and the lightweight alternative (AHSS,
CFRP). The SROI of CFRP BIWs was maximized when CF was
produced using energy from a low carbon intensive electric grid or
decentralized sources such as waste-to-energy incineration plants. This
scenario of using energy from WtE plants for industrial manufacturing
49
describes the concept of industrial symbiosis and contributes to
creation of a circular economy.
Handling of residual streams. The incineration of MSW results in
the formation of bottom ash and fly ash, two undesirable forms of
residual byproducts. Bottom ash is a non-hazardous material which can
be easily recycled as a material in road pavements and concrete. Fly ash,
on the other hand, contains toxic components including heavy metals
(e.g., Pb, Cd, Zn, etc.) and dioxins. Thus, incineration plants permanently
dispose of the fly ash in hazardous waste landfills as enforced by the
environmental regulations in many nations. In Paper IV, an evaluation
of the environmental performance of upcycling the fly ash is described. A
thermal insulation panel that consisted of a Polyurethane (PU) foam core
sandwiched between two epoxy composite skins prepared with
reinforcing Glass Gibers (GF) and Silanized Fly Ash (SFA) in epoxy resin
was considered.
Circular compliance. In Paper V, a holistic systems level assessment
decision-making framework that allows urban municipalities (in
collaboration with other key stakeholders) to prepare a long-term
sustainable wastewater management strategy for their cities was
described. From a city perspective, the framework encapsulates two
ideas. First, the sustainable performance of centralized urban WWTPs
will improve with increased circular economy compliance. Second, the
sustainability benefits of a circular compliant urban WWTP will extend
beyond its boundary (application of byproducts and residual stream) and
can be realized at a city, or even at a national, level.
In summary, Papers I to V describe the different layers (BAU, byproducts
processing, residual treatment, advance treatment) within the modeling of a
circular compliant treatment plant for essential municipal services. Thus, the
framework was created (using LCA and LCC tools) from a city perspective to
increase the circularity of these treatment services and included the urban
metabolic rate in order to give a holistic view of the utilization of resources within
an urban system.
50
6. Assessment Framework for Treatment
of Municipal Services in Cities
As described previously, municipalities currently include sustainability at the top
of their agendas with their ambitions aligned to the sustainability goals of their
respective nations [106]. Sustainable city-centric techno-entrepreneurial
concepts, such as development of low cost and modular technologies for removal
of micropollutants from treated wastewater [107], conversion of MSW to biofuels,
recovery of phosphorus from sewage sludge, and implementation of
decentralized treatment methods etc. have gained significant traction over recent
years [8, 22, 24, 66, 67, 108, 109]. The proposed assessment framework in this
thesis is designed to evaluate the essential services provided by municipalities,
along with the urban metabolic rate of the city, to optimize the overall resource
use. This also helps us understand the relationship between human activities and
the natural environment.
Several quantifiable approaches to measure the sustainable performance of
essential services of a city are available. Sustainable method indicators [110] [111],
the green city index indicators [112], biophysical metrics [113], urban
environment and social inclusion index [114] etc. have been developed. For
instance, the green city index proposed by ESPON, 2015 [112] uses metrics to
measure the ecological footprint in a particular city. The index also includes
indicators related to management of essential services in a city [112]. Assessment
models also exist to quantify sustainability aspects of municipal service
operations and develop indicators reflecting their performance [115]. For
instance, an approach for assessing municipal level sustainability indicators in
Sweden, proposed by Anderson (2013), was developed for Falun Municipality in
Dalarna County, Sweden [33]. There have been individual studies that have
investigated model-based decision support for measuring sustainable water
services combining numerous aspects using tools such as multi-criteria decision
analysis (MCDA) [116].
There are also urban metabolism models described in the literature [29, 117, 118].
They are designed to measure the resources flowing into, and waste streams
flowing out of, a city, and to help understand how different forces (e.g. social and
cultural aspects) influence a city’s metabolic rate [119]. They can be integrated
well with urban planning efforts to build sustainable cities [120]. For example,
Goldstein (2016) addressed the environmental sustainability of food systems in
an urban setting by analyzing their resource flows. This Danish approach is a
hybrid LCA (economic input output/LCA) urban metabolism model looking at
developing the overall material and energy flows in urban agriculture in Denmark
51
[121]. The metabolism of cities is another open source data hub of data about
resources flowing within different cities around the globe [120]. In addition,
urban metabolism models for use within local authorities for furniture, have also
been assessed [30]. There are also projects such as NEOM 2030 in Saudi Arabia,
which is run by the crown prince and is a sustainable ecosystem generating new
ideas and solutions focused on setting new standards for community health,
environmental protection and the effective and productive use of new technology
[122].
The intention of the framework was to combine both aspects of essential
treatment services of a city (including their contribution in value-added streams
such as ash and biogas) and the urban metabolic rate of the city to evaluate their
sustainable performance. Several frameworks already exist for providing a
comparative analysis of how urban metabolism can be integrated into planning
of cities in different locales [27, 31, 123–125]. These frameworks describe the
capacity, demand, and flow of urban regulating ecosystem services, and related
benefits (the location, typology, and size of urban green infrastructure) controlled
by urban planning. However, a comprehensive understanding of how the
environmental performance of an urban system, such as a city, will be affected
when (a) new technologies are implemented, (b) essential services are
decentralized, and (c) policy-related changes take place with respect to essential
services management, is yet to be achieved.
Thus, it is important to create a strategic framework that encompasses short and
long-term developments within the domain of three essential municipal services
i.e. water supply (potable and non-potable needs), wastewater treatment and
MSW management, and link the framework to the ecological footprint of a city.
This would help to enhance the understanding of the forces (material, energy)
that shape urban metabolism and how these forces affect urban living and
environment. Once validated, the modeling framework proposed in this thesis
can serve as a basis for development of a decision support system (e.g. software)
that will enable authorities to plan strategies for sustainable cities. In addition,
using sustainable assessment tools such as LCA and LCC provides an insight for
emerging technologies in a market that might prove to be innovative.
6.1 Proposed Assessment Framework
The suggested framework assists the evaluation of a comprehensive sustainability
performance of essential municipal service operations within an urban system,
by using a combination of Life Cycle Assessment (LCA) and Life Cycle Costing
(LCC) approaches. The proposed five-stage assessment framework is shown in
Figure 14. The left side of the figure represents essential municipal service
operations structured in five stages. The right side represents total demand of an
52
urban system including the contribution of energy, material and fuel, obtained
from treating residual wastes generated by essential municipal service
operations. The stages are briefly described as follows.
Stage 1. Business as Usual (BAU) Scenario. Includes current best available
treatment and management practices followed by a city with respect to operation
of their essential municipal services. Papers I–V assessed the BAU scenario in
order to evaluate the environmental impacts of the current practices followed and
to track the tradeoffs in the environmental performance when new treatment
steps are added.
Stage 2. Byproduct Processing. In this stage, the sustainable performance of
additional processing (e.g. converting biogas from the bio digester of the WWTP)
of byproducts (if needed) obtained from Stage 1 is quantified. Papers I, II, III
describe the processing/alternative use of byproducts i.e. Paper I describes the
evaluation of the alternative use of biogas as LBM fuel for heavy-duty trucks
instead of used as energy within the WWTP (current practice). Paper II describes
how biogas obtained from AD of organic food waste was converted to CBM fuel
to be used in buses in Mumbai, India. The alternative use of electricity from a
WtE plant utilized in the manufacturing sector (Carbon fiber) was described in
Paper III.
Stage 3. Treatment of Residual Waste Streams. This stage measures the
sustainable performance of residual waste streams generated from BAU
operations (Stage 1). The residual waste streams include sewage sludge from
WWTP, and bottom and fly ash from a WtE plant. The main intention here is to
optimize the final amount of waste materials disposed of in landfill. Papers IV
and V describe the detailed investigation into the treatment of the residual waste
streams. Paper IV describes the environmental performance of using fly ash
(residue) from WtE plants to be used as filler in epoxy composite panels (building
industry). The environment and cost performances of nutrient recovery, energy
recovery options of sewage sludge from WWTP are discussed in Paper V.
Stage 4. Advanced Treatment Techniques. Determines the sustainable
performance of treatment options that address inefficiencies of BAU operational
practices followed in Stage 1. Treatment of secondary wastewater for removal of
emerging micropollutants is an example of a Stage 4 operation. In Paper V,
ozonation was considered as an advanced treatment option to remove/reduce the
micropollutants load from wastewater and to reuse the effluent water (industry,
farming) from WWTP.
Stage 5. Game-changing Concepts. This refers to entirely different methods
of essential municipal service operations. Treating wastewater using microbial
fuel cells [126] instead of the conventional activated sludge process, or utilizing
the MSW-refuse fraction for biofuel [61] instead of incineration, are both
examples of game-changing concepts. For a city, the sustainable implications of
53
replacing conventional technologies with novel technologies must be understood
holistically i.e. how replacement affects urban metabolic rates etc.
The Urban Metabolic Rate (UMR) [118] of a city is illustrated to the right in
Figure 14. The UMR is defined as the rate at which resources (water, energy, food,
materials) are consumed by the inhabitants of a city over a given time period.
Using the UMR will enable cities to have a summative picture of all value streams
generated from their services to utilize them effectively towards meeting the
energy, fuel, material, nutrients and water demand of the entire urban system.
54
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an
met
ab
oli
c ra
te.
55
6.2 Attributes of the Framework
Figure 15 is a flowchart of a systematic evaluation of the essential municipal
services and urban metabolic rate as proposed by the framework. The total cost
(private cost + environmental externalities cost) of operating essential municipal
services (A) in a city is calculated in the left pane. The right pane is the flowchart
for obtaining total cost of urban metabolic rate (B+C) of the city.
6.2.1 Assessment Framework - Data Requirements
Collection of aggregate data from relevant sources is a key component in
evaluating the proposed assessment framework. Various data collection methods
such as interviews, surveys, documents, and focus groups can be implemented
from a city perspective [118]. These data collected are of crucial importance to
describe, and draw insights on, the performance of the essential municipal
services and also the urban metabolic rate of the city. The following data should
be collected:
Data on Essential Municipal Services Operations of Cities
Business as Usual (BAU) scenario of municipal service operations
Population served by centralized water, wastewater and MSW (all fractions)
treatment plants and treatment cost
Amount of residual waste generated from municipal service operations
Future plans of the city to improve circular compliance of existing treatment
trains (Stages 3 and 4) or adopting game-changing concepts (Stage 5)
Some treatment plants meet their energy needs from byproducts generated
internally, with the surplus sold to the city, whereas others sell everything and
meet their energy needs from external sources (e.g. Swedish grid). This
information should also be collected.
A sample data - collection sheet is shown in Appendix A1.
Data on Urban Metabolic Rate of Cities
The data on total urban metabolic rate, including the contribution from essential
municipal service operations and from other sources, should be established. Data
on the following should be collected:
Water demand of a city
Residential energy demand of a city
Fuel demand based on transportation characteristics (i.e. use of public and
private transport), types of transport fuels used
Material (glass, paper, plastic and metals) consumption of a city, and the
distribution of primary or secondary (recycled) materials
A sample data - collection sheet is shown in Appendix A2.
56
In Sweden, these data can be obtained in collaboration with city municipalities,
site visits, and by reference to open literature sources such as Waste Management
Reports and other sources (e.g. SCB, Avfalls-Web) [47]. For Umeå, the data were
obtained from municipal stakeholder companies (Vakin, Umeå Energi, Skellefteå
biogas plant) as a collaborative effort, and from open literature (Umeå EGCA
report). The data sources can vary in different countries.
57
Fig
ure
15
. F
low
cha
rt t
o e
va
lua
te t
he
esse
nti
al
mu
nic
ipa
l se
rvic
es a
nd
urb
an
met
ab
oli
c ra
te a
s p
rop
ose
d b
y t
he
fra
mew
ork
. T
he
wo
rkfl
ow
in
clu
des
d
ata
co
llec
tio
n,
carr
yin
g
ou
t L
CA
a
nd
L
CC
o
n
the
esse
nti
al
serv
ices
trea
tmen
t p
lan
t, m
ak
ing
im
pro
ved
dec
isio
ns
ba
sed
on
th
e in
dic
ato
rs,
ad
din
g t
he
va
lue
stre
am
s fr
om
th
e
mu
nic
ipa
l se
rvic
es t
o t
he
urb
an
met
ab
oli
c ra
te o
f th
e ci
ty,
mo
net
izin
g t
he
imp
act
s a
nd
ca
lcu
lati
ng
th
e to
tal
cost
(pri
va
te c
ost
+L
CE
E)
58
6.2.2 Assessment Framework – Stage-wise Technology Options for
carrying out LCAs
The BAU treatment techniques related to operation of three essential municipal
services (Stage 1), technology options available to achieve a greater degree of
circular compliance of approaches (Stages 2 through 4), and the game-changing
technology concepts (Stage 5) used to provide municipal services (i.e. Wastewater
and MSW fractions) are summarized in Tables 4–6.
Table 4. Technology options for water treatment service
Water Treatment Service [108, 127, 128]
BAU Scenario (Stage 1) Conventional water treatment train
involving coagulation, flocculation and
sedimentation followed by sand filtration
and disinfection using chlorine-based
chemicals (sodium hypochlorite, UV light
or ozone)
Byproducts Processing (Stage
2)
Not applicable
Residual Waste Treatment
(Stage 3)
Not applicable
Advanced Treatment
Technologies (Stage 4)
Treatment for removal of micropollutants
(associated with conventional water
treatment)
Membrane or thermal desalination
techniques (Alternative treatment
technologies)
Game-changing Concepts
(Stage 5)
Not applicable
Table 5. Technology options for WWT service
Wastewater Treatment Service [22, 24, 62, 63, 68, 126, 129, 130]
BAU Scenario (Stage 1) Includes primary, biological secondary and
tertiary treatment steps as well as sludge
management with, or without, anaerobic
digestion (AD) process.
Byproduct Processing (Stage
2)
Conversion of biogas
Residual Waste Treatment
Pathways (Stage 3)
Direct nutrient recovery from digested
sewage sludge
Upcycling as secondary raw material for
industries
59
Advanced Treatment Steps
(Stage 4)
Removal of micropollutants
Game-changing Concepts
(Stage 5)
Microbial fuel cell or algae-based
wastewater treatment
Table 6. Technology options for MSW service
Treatment of Municipal Solid Waste Service
MSW-Refuse [21,
52, 54, 61, 65, 66,
69] [53, 131, 132]
MSW-Organics
[49, 133-136]
MSW-
Recyclables
[23, 40, 52, 57,
137]
BAU
Scenario
(Stage 1)
Incineration with
energy recovery
Organic waste
pretreated followed
by AD. Biogas and
digestate obtained
as byproducts.
Biogas used as
energy or fuel
source. Sludge
digestate sold as
organic compost.
Glass, paper,
metal, plastic
are recycled.
Electronics,
batteries etc.
are producer’s
responsibility.
Byproduct
Processing
(Stage 2)
Conversion of
biogas
Residual
Waste
Treatment
(Stage 3)
Fly ash
utilization
pathways
Nutrient recovery
from dried sludge
digestate.
Integrated process
based on
combination of AD
& other
thermochemical
processes [138].
Residues that
cannot be
recycled are
sent to WtE
plants for
energy
recovery.
Advanced
Technology
Initiatives
(Stage 4)
Address problems
of incomplete
combustion
Carbon capture
and storage
Improving district
heating efficiency
Hydrogen
Separation from
biogas produced by
AD units
Converting
plastics to
fuel
(pyrolysis)
60
Game-
changing
Concepts
(Stage 5)
Gasification or
pyrolysis for
biofuel
production
Recycling,
selective sorting
and production of
fuel
Gasification and
pyrolysis of waste
Fermentation of
food waste
Once the system boundary for the treatment services has been decided, LCAs are
carried out to calculate the environmental impacts of the process. The functional
unit (FU) of the LCA and LCC studies is “Providing essential municipal services
to residents of the city for one year”. A sample system boundary is shown in
Appendix A3.
Similarly, the functional unit for carrying out LCA and LCC studies on the UMR
is “Urban metabolic rate met by a city per year”. The system boundary is shown
in Appendix A4.
Monetization of Environmental Impacts. The midpoint environmental impacts
(shown in Table 2) determined by the LCA study are subsequently monetized by
multiplying the impact score with unit environmental externality prices specified
by literature (see Chapter 4) [89] [101].
In this framework, LCC is applied to determine private costs incurred by the city
to operate its essential municipal services and for meeting its urban metabolic
rate (Chapter 4) [98]. The cost sector is added to the framework to translate the
LCA results to the societal value (environmental effects of production and
consumption that affect consumer utility) of reducing impacts on the
environment.
6.2.3 Total Cost Calculation
Total Cost of Municipal Services TC (MS)
The sustainable value of essential municipal service operations is determined
for cities considering two scenarios: (a) BAU and (b) future initiatives scenarios
(e.g. phosphorus recovery from sludge).
The TCMS (measured in Swedish Krona (SEK)) is determined as follows,
𝐓𝐂(𝐌𝐒) = [(𝐓𝐏𝐂) + (𝐄𝐄𝐂)] 𝐌𝐮𝐧𝐢𝐜𝐢𝐩𝐚𝐥 𝐒𝐞𝐫𝐯𝐢𝐜𝐞𝐬
where
61
TPC = Total Private Costs incurred by a city to provide essential municipal
services to its residents. This includes costs of basic treatment and byproduct
processing (Stages 1 and 2) + cost of treating/disposal of residual streams (Stage
3) + cost of advanced treatment costs (Stage 4).
EEC = Environmental Externality Costs. The LCA results are monetized and,
ultimately, the EEC is determined as the sum of the monetized values of
individual impacts. It also includes credits from the secondary material obtained
from residual waste (Stage 3).
Total Cost of Urban Metabolic Rate TC (UMR)
The TC (UMR) (in SEK)) is determined as follows:
𝐓𝐂 (𝐔𝐌𝐑) =
{[(𝐓𝐏𝐂) + (𝐄𝐄𝐂)]𝐎𝐭𝐡𝐞𝐫 𝑺𝒐𝒖𝒓𝒄𝒆𝒔 + [(𝐓𝐏𝐂) + (𝐄𝐄𝐂)]𝐕𝐚𝐥𝐮𝐞 𝐚𝐝𝐝𝐞𝐝 𝐬𝐭𝐫𝐞𝐚𝐦𝐬 𝐟𝐫𝐨𝐦 𝐌𝐒 }
where
Total Private Costs (TPC) = Sum of cost of water, energy, fuel, and material
consumption costs of a city per year i.e. other sources (electricity from solar,
hydro, wind, imports, bioenergy, fuel demand met by diesel, gasoline, biofuels
etc.) and municipal service value streams.
Environmental Externality Costs (EEC). LCA is carried out to quantify
environmental impacts corresponding to urban metabolic rate with the results
monetized.
6.2.4 Future Work to Develop the Framework
The framework could be developed further to produce information about cities
such as a qualitative rating (circular compliance) developed for municipal
services, and environmental indicators measuring the sustainable performance
of a city.
A qualitative rating indicating the circularity of essential municipal service
operations can be developed for each city. The qualitative scale could be
developed based on predefined criteria such as: (a) population connected to
centralized WWTP, (b) MSW recycling rate, (c) planned initiatives to manage
residual waste, and (d) use of advanced treatment technologies to remove
emerging trace contaminants from wastewater or reduce inefficiencies in the
district heating network etc.
In addition, environmental performance indicators such as waste
generated/capita, CO2 emissions/capita, air pollution, energy consumption/
62
capita etc. could be developed based on the output of the framework to optimize
the utilization of resources within a city. These indicators should have scientific
validity, sensitivity, responsiveness and use data available about past situations
[139]. They should reflect a city’s sustainable performance in its present form and
could identify hotspots for future improvement. For example, based on these
performance indicators, a city may choose to use byproducts from essential
municipal service operations differently (e.g. use biogas for cars and trucks
instead of buses) or consider game-changing concepts e.g. production of biofuels
from MSW refuse might be undertaken instead of incineration when the future
fuel demands of the city increased. Stakeholder groups might use these results to
make sustainable decisions.
6.2.5 Unique Features of the Model
The framework has three unique features.
1. The framework is designed to capture all (current and future) activities
associated with essential municipal service operations of a city that are either
targeted at addressing circular compliance (Stages 2 to 4) established for
existing technologies or consider entirely new technology (Stage 5) as a
potentially sustainable alternative.
2. All resources flowing into (from external sources), generated and used within
(energy and fuel from essential municipal service operations), and moving out
of the city (material credits from municipal services) are grouped in the urban
metabolic rate. This allows for greater accountability of resources and
provides an opportunity to improve their usage. For example, a city may
choose to use biogas/biomethane fuel for cars and trucks instead buses. In
addition, the structuring framework supports the intention of developing
decision support software that can be applied to develop strategies for
sustainable urbanization.
6.3 Case Study of a Wastewater Treatment Plant
The challenges associated with treating wastewater as a part of urban sanitation
service are both complex and diverse in nature. In the developing world, where
urbanization is accelerating, inadequate treatment of wastewater has become a
major concern [9,10,64,140,141]. For a specified level of circular compliance
(effluent reuse, energy recovery, nutrient recovery), the proposed assessment
framework quantifies the sustainability performance of a centralized WWTP of a
city. By applying the model, total costs can be calculated, with private costs of
treatment and residual waste management calculated using life cycle costing
(LCC) and the related environmental externality costs calculated using life cycle
assessment (LCA) approaches (stage-wise technology options). Figure 16 shows
63
the use of the assessment framework for a particular municipal service, treating
wastewater in a city.
Figure 16. Illustration of the framework applied to a case study of a WWTP to
evaluate the sustainable performance of operating a circular compliant WWTP
in a city (based on Paper V)
The five stages included in the operation of a WWTP in a city are:
Stage 1. Business as Usual (BAU) Scenario Includes the conventional WWTP
where the water is treated aerobically (i.e. biologically activated sludge process)
in combination with anaerobic digestion of sewage sludge generated during the
treatment as an additional optional step. The dried sewage sludge is landfilled in
this scenario.
Stage 2. Byproducts Processing In this stage, the biogas (66% methane and
remaining CO2) obtained from AD unit is treated (amine scrubbing) to remove
CO2 and other trace elements (H2S, water), and used as Compressed Biomethane
(CBM) to fuel vehicles.
Stage 3. Treatment of Residual Waste Streams This stage includes the
treatment of sewage sludge from WWTP. The sludge is incinerated for energy
recovery (heat and electricity for the city) and phosphorous is recovered from the
ash using chemical treatments.
Stage 4. Advanced Treatment Techniques includes the treatment of
secondary wastewater to remove emerging micropollutants. An ozonation unit is
added as an advanced treatment option in the WWTP to remove/reduce the
64
micropollutants load from wastewater and to reuse the effluent water (industry,
farming).
Stage 5. Game-changing Concepts refers to an entirely different method of
treating wastewater in a city. Microbial fuel cell systems have the potential to
enhance energy, water and nutrient resource recovery from a WWTP.
The Urban Metabolic Rate (UMR) includes resources flowing into a city from
other sources, and the contribution of value-added streams from operation of a
WWTP. The water, heat, electricity and fuel demands of the city, and the extent
to which operating a circular compliant WWTP with the previously mentioned
technologies contributes to these resources, are calculated.
LCAs are carried out utilizing the information from different stages, with the
functional unit “operating a WWTP in a city for one year”.
A detailed discussion of the possible technology levels to be used in a WWTP
within the internal boundary of treating wastewater and the external boundary of
possible utilization pathways of biogas and sewage sludge is given in Paper V.
Figure 17 shows the schematic for calculating the total cost to a society of
operating a centralized WWTP by obtaining data from LCAs carried out with the
different technology levels (Stages 1 to 5).
65
Fig
ure
17
. S
chem
ati
c fo
r ca
lcu
lati
ng
th
e to
tal
cost
to
so
ciet
y o
f o
per
ati
ng
a c
entr
ali
zed
WW
TP
in
clu
din
g t
he
effl
uen
t
trea
tmen
t tr
ain
BA
U a
s th
e in
tern
al
bo
un
da
ry a
nd
ass
essm
ent
of
dif
fere
nt
step
s o
f ci
rcu
lari
ty i
n W
WT
P (
effl
uen
t
reu
se,
ener
gy
rec
ov
ery
, re
sid
ua
l m
an
ag
emen
t) c
on
sid
ered
as
the
exte
rna
l b
ou
nd
ary
66
The internal boundary cost for a WWTP refers to the total cost of wastewater
treatment operations i.e. the sum of treatment (capital and operational
expenditures) and environmental externality costs (LCAs) incurred by the
WWTP. This includes gathering details about the treatment capacity of the plant,
percentage of the population of the city connected to the central WWTP,
wastewater influent and effluent quality parameters, along with operational data
from within the plant boundary (inventory data e.g. chemicals and electricity
consumed during wastewater treatment). The total external boundary cost is the
cost of byproduct management outside the physical boundary of a WWTP. This
means that data on the utilization of three WWTP byproducts (treated effluent,
biogas (if produced)) and sludge) within the external boundary have to be
consolidated.
Both the BAU scenario (Stage 1 of the assessment framework), and any future,
potentially improved, circular compliance scenarios (Stages 2 to 4 of the
assessment framework) that are under consideration by city authorities (and
other stakeholders) are included in this phase. Additional information on
regional factors such as the water stress index of the city, public and private
transportation within the city (e.g. fuels used, annual distance covered by buses
and cars in a city etc.) will be needed. These data can be factored into the total
cost assessment process reflecting sustainability performance of choices made by
stakeholders with respect to utilization of WWTP byproducts in the external
boundary. The Total Cost is the sum of private and environmental externality
costs associated with wastewater treatment operations and byproduct
management within the internal and external boundaries of a centralized WWTP
respectively.
A life cycle costing (LCC) approach is used to carry out stage-wise quantification
of private costs of all activities related to internal and external boundaries of the
WWTP. The corresponding environmental externality costs are obtained by
monetizing life cycle impact assessment results obtained from the LCA study. The
calculation of such costs comprehensively accounts for the operation of a
centralized urban WWTP, reflecting sustainability performance and different
levels of circular compliance (indicators can also be developed at this point).
Based on the results obtained from the assessment framework in terms of
sustainable value/sustainable cost, stakeholders can establish how operating
such services in a city perform environmentally, and to what extent they
contribute to the sustainability of the city. Paper V describes in detail the
application of the framework to wastewater treatment services of a city in order
to quantify the overall ecoefficiency scope of operating a centralized urban
WWTP.
67
7. Conclusion & Future work
The world’s population is predicted to grow by 2.5 billion by 2050. Rapid
urbanization without proper planning can lead to a potential environmental
disaster. For city municipalities who play a critical role in planning
implementation, this challenge (proper management of resources) has become
the objective of running the city (i.e. provision of essential services such as heat,
power, water, waste management etc.) with low ecological footprints.
This thesis proposes a strategic assessment framework to guide the assessment
of essential municipal service operations at different technology levels and the
calculation of the urban metabolic rate of a city, using LCA and LCC tools. The
framework was developed with the intention of significantly reducing the
environmental burdens caused by municipal treatment services. From this
perspective, this thesis is most relevant to Sustainable Development Goal (SDG)
11 – Sustainable Cities and Communities that aims to make our cities sustainable
by 2030 [142].
The intention of this systems-oriented assessment framework is to assist city
authorities in developing strategies for sustainable urbanization, implement
them and monitor their progress. The integrated modeling approach (essential
municipal service operations and urban metabolic rate) shows how increased
contributions from byproducts (Stage 2) of municipal services reduce the
dependency on primary energy/fuel sources and, therefore, make a city cleaner
and more resource efficient. However, these byproduct flows must be correlated
to the total urban metabolic rate of a city to plan their utilization wisely (urban
planning target indicator of SDG 11). Stage 3 analyzes the sustainability potential
of emerging technologies for treating residual wastes e.g. phosphorus from
sludge, and heavy metals from fly ash (SDGs 9 and 12). Stage 4 measures the
efficacy of methods for the removal of micropollutants from wastewater
(prevention of leakage of toxic materials into environmental systems (SDG 6 and
9)). These stages address the main criteria for circular compliance. The urban
metabolic rate includes imports, and determines the environmental tradeoffs
occurring elsewhere in the world due to imported food products to Swedish cities
(SDG 12) [106].
The framework needs to be developed further to ensure validation (using data for
all services of a city) of a city’s sustainable performance. The qualitative rating for
circular compliance of municipal services has to be developed, along with the
definition of environmental performance indicators for the urban metabolic rate
(based on LCA and LCC results). The indicators will be qualitative and
quantitative in nature, and reflect multiple factors (technical feasibility,
68
consumption of resources) that affect the sustainability of a city. The framework
is well suited for medium-sized cities (such as Umeå with 130,000 inhabitants)
[64], where limited number of treatment plants exist, to manage the essential
municipal services. For megacities (over 10 million inhabitants) [143], quite
extensive data collection and technology validation is needed for the framework.
In cities with a greater number of treatment plants that follow different treatment
technology pathways, the complexity of modeling will increase dramatically.
Nevertheless, if the framework can be converted into software, with the
comprehensive modeling approach integrating other sustainability assessment
tools (ecosystem services, social LCA to identify waste behavioral patterns,
consumption patterns), it might then be feasible to use extensive data and
calculate the sustainable performance of operating essential services in
megacities. The framework also does not take into consideration informal waste
management practices that are commonly followed in many developing nations
[144].
The framework itself will be of great value to academic researchers who are
working on projects related to circular transition of municipal service operations
and urban metabolism. In addition, there are three main groups that may have
interest in this thesis: (a) the scientific community, (b) targeted stakeholders, and
(c) non-targeted readers. The targeted stakeholder group includes actors at a city
level as well as municipality companies responsible for crucial municipality
services (e.g. wastewater treatment plants, waste-to-energy plants etc.). Other
important stakeholders include state-funded circular economy platforms that
promote circular economy initiatives, such as Smart City Sweden [145]. The
results of the framework generated in the form of sustainability indicators will
allow a comparison between cities and provides a basis for ranking them. This
would be of general interest for different actors in society, including public actors
as well as private companies.
69
8. Acknowledgements
Thanks to almighty God for all the blessings upon me. Among many people who
contributed to this thesis, I would like to start by thanking my supervisor Venkata
Krishna Upadhyayula for your guidance, advice, discussion and help in
developing ideas during my PhD. It has been a pleasure to work under your
supervision. I have learnt a lot from you. Thank you for your support and inputs
for the Papers appended to the thesis.
I would like to extend my gratitude to my co-supervisor Mats Tysklind for giving
me the opportunity to work on the Green Technology and Environmental
Economics project. Thank you for all the interesting discussions and support
provided during my PhD. Thank you to my other co-supervisor Runar Brännlund
for lending a helping hand during my PhD. I am thankful to Patrik Andersson and
Dimitris Athanassiadis for their work as committee members and guidance
throughout my PhD.
I would like to extend my thanks to the Umeå municipality companies VAKIN,
Umeå Energi, and Dåva DAC for our fruitful collaboration and also for arranging
site visits, providing data and answering emails and questionnaires whenever
requested. It was very helpful to gather data, which was used in Papers I and IV.
Thanks to Skellefteå Biogas plant at Tuvan for arranging site visits and providing
data for modeling in Paper II. Thanks to the Bio4Energy systems analysis group
and Anna Ström for insightful meetings and discussions.
I am thankful for the Wallenberg Travel grant, AFORSK travel grant received
during my PhD. Thanks to ARCUM Artic Research Centre at Umeå University for
selecting and supporting me in my attendance at the Summer Barents School,
Archangelsk, Russia, in 2017. Special thanks go to the International Office Umeå
University for the short project grant provided for me to carry out research in
India.
Thanks to my co-authors, Stina Jansson, Venkataramana Gadhamshetty, Dalia
Abdelfattah, Leonidas Matsakas, Paul Christakopoulos and Ulrika Rova for
contributions to the papers.
A special thanks to Harish Kumar for drawing the cover of my thesis book. Thanks
to Majid Mustafa for discussions on wastewater treatment.
I want to thank Laxmi Mishra, Alexandra Charlson, Pierre Oesterle, Ioana
Cheicea, and Piotr Jablonski for their interactions during the PhD Council and
after parties. I would like to extend my thanks to Dalia Abdelfattah and Pooja
70
Yadav for interesting discussions about LCA and for the fun involved. I would also
like to thank the PhD council and Journal Club groups for all our fun-filled
discussions. Thanks to Veronica Benavente and Elena Dracheva for making it
very comfortable to share the same room for work. I want to thank Josef Meens
Eriksson (Sef) at CERE for LCA and costing-related discussions.
I would like to thank Venkata Krishna Kumar Upadhyayula and Mats Tysklind
for allowing me to take different courses during my PhD, which allowed me to
have a broader perspective of modeling. I want to thank Maria Jansson and
Birgitta Berglund for all their help with administrative processes throughout my
PhD.
Finally, I want to thank my family and friends for their support at all times.
Thanks to my dad Shanmugam and mom Vijayatharani for their love and care
and for always looking out for me. A special mention of the support, love and care
from my husband during my PhD, a big hug to you Suresh Kumar, you made it
easier for me. It would have been hard to achieve this without you. Also my son
Dhruv Adhiran, who is a bundle of joy and kept me going through all the hard
times. I want to extend my gratitude to my in-laws Siva Ragunath and
Prabhavathy, my sister Jayalakshmi Shanmugam and brother-in-law Yuvaraj
Sekar, for all their support.
71
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Appendix
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Papers I-V
