Blue Growth: Applications and properties of biochar made ...

INOM EXAMENSARBETE TEKNIK,GRUNDNIVÅ, 15 HP

, STOCKHOLM SVERIGE 2021

Blue Growth: Applications and properties of biochar made out of reed

AXEL KARLSSON

PINTHIRA FAGERSTRÖM

KTHSKOLAN FÖR ARKITEKTUR OCH SAMHÄLLSBYGGNAD

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Abstract The climate on earth keeps getting warmer where heat waves, eutrophication, rising sea levels, extreme weather like flooding, droughts and wildfires are an expanding problem. The focus of this bachelor thesis is to determine the potential of mitigating eutrophication and while contributing to blue growth by harvesting and make use of reeds like Phragmites australis and Arundo donax. Reeds have the ability to quickly absorb nutrients from aquatic environments and there are opportunities to use them as a feedstock for producing biochar to be potentially used in areas such as soil improvement, fodder additive and carbon sequestration. Additionally, optimal biochar properties for the observed applications gets analysed. The thesis is based on a systematic literature review and an interview with Niclas Anvret at the non-profit organisation “Race for the Baltic”. Results show that biochar produced according to parameters such as heating rate, biomass species and especially, different temperatures, results in varied characteristics that change the biochar's adsorption abilities, nutrient retention, alkalinity, stability, surface area and porosity volume. The different applications of biochar are, however, not easily determined. This is because of the fact that certain biochar properties, that are prominent in entirely different pyrolysis conditions, could both be beneficial for the same application. Additionally, the different attributes sometimes influence each other which gives rise to unclear patterns affecting use potential. To overcome these issues, more research is needed to clarify the correlations between attributes of the biochar and to determine which characteristics of biochar are best suited for each application. In terms of how large-scale harvesting of reed could affect the ecosystem is also unclear, there is not enough research regarding the question to be able to draw clear conclusions. The reasoning behind this is that there are knowledge gaps, geographical differences, different unit measuring and methodology. The potential for biochar in the coal market is high and the demand in Sweden has risen over the past couple of years. There is also interest in using biochar as a soil amendment, to make use of nutrient content as well as applying organic matter to soils to potentially achieve long-term carbon sequestration. However, the production cost of biochar out of reed is relatively expensive, and it cannot compete with coal or other fertilisers/soil amendments on the market, with feedstock management usually being the most expensive part of production. Lastly, there is currently no harvesting method that can measure the amount of reed that needs to be harvested to be able to produce biochar on a large scale. Keywords: “Common reed”, "Phragmites australis", “Giant reed”, “Arundo donax”, “Usage”, “Utilization”, “Baltic sea”, “Sweden”, “Eutrophication”, “Overfertilization”, "Nutrient discharge", “Blue bioeconomy”, ”Soil improvement” “Feedstock”, “Pyrolysis”, “Biochar”, “Biocoal”, “Coal supplement”, “Bioenergy”, “Biofuel”, “Carbon sequestration”, “Fodder”, “Cost analysis”.

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Sammanfattning Klimatet på jorden blir allt varmare och värmeböljor, övergödning, stigande havsnivåer, extrema väder som översvämningar, torka och bränder är ett stigande problem. Syftet med denna kandidatuppsats är att undersöka potentialen att mildra eutrofiering och samtidigt bidra till blå tillväxt genom att skörda - och använda sig av vass som Phragmites australis och Arundo donax. Vass har en framträdande förmåga att absorbera näringsämnen. Det finns därför möjligheter att använda dem som råvara för att producera biokol som potentiellt kan användas i områden såsom jordförbättring, fodertillsatser och kolbindning. Utöver detta undersöks optimala egenskaper för biokol enligt de observerade applikationerna. Kandidatuppsatsen bygger på en systematisk litteraturstudie och en intervju med Niclas Anvret på den ideella organisationen ”Race for the Baltic”. Resultaten indikerar att biokol, producerad i pyrolys enligt parametrar som uppvärmningshastighet, biomassa och i synnerhet olika temperaturer, resulterar i varierande egenskaper som förändrar biokolets absorptionsförmåga, bibehållande av näring, alkalinitet, stabilitet, ytarea och porositetsvolym. De olika tillämpningarna av biokol är emellertid svåra att avgöra på grund av vissa biokolegenskaper. Dessa egenskaper är framträdande under helt olika pyrolysförhållanden men kan samtidigt vara fördelaktiga för samma typ av applikation. Dessutom påverkar de olika attributen ibland varandra vilket ger upphov till komplexa trender som påverkar användningspotentialen. För att kunna dra tydliga slutsatser behövs mer forskning för att klargöra sambandet mellan biokolens attribut och för att bestämma vilken samling egenskaper hos biokol som passar bäst för varje applikation. Hur storskalig skörd av vass kan påverka ekosystemet är fortfarande oklart. Det finns inte tillräckligt med forskning kring frågan för att kunna dra tydliga slutsatser. Detta beror på att det finns kunskapsluckor, geografiska skillnader, olika måttenheter och metoder för de studier som gjorts inom detta område. Potentialen för biokol på kolmarknaden är hög och efterfrågan i Sverige har ökat de senaste åren. Det finns också intresse för att använda biokol för jordförbättring, dels för att använda näringsinnehållet men också för att applicera biokol i jorden för att potentiellt uppnå långvarig kolbindning. Dock är produktionskostnaden för biokol gjort på vass mycket kostsam och kan därför inte konkurrera med fossilt kol eller andra gödselmedel jordförändringar på marknaden. Detta beror främst på råvaruhanteringen som är den dyraste delen av produktionen. Slutligen finns det för närvarande ingen skördemetod som kan mäta den mängd vass som behöver skördas för att kunna producera biokol i stor skala. Nyckelord: “Bladvass”, "Phragmites australis",”Italienskt rör”, “Arundo donax”, “Användning”, “Användningsområde”, “Östersjön”, “Sverige”, “Eutrofiering”, “Övergödning”, "Näringsläckage", “Blå bioekonomi”, ”Jordförbättring” “Råmaterial”, “Pyrolys”, “Biokol”, “Bioenergi”, “Biobränsle”. “Kolbindning”, “Foder”, “Kostnadsanalys”.

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Acknowledgement We would like to thank our tutor Jean-Baptiste Thomas for assistance, advice and guidance throughout the whole period of our bachelor thesis. We are very grateful for the knowledge, patience and contacts that have been given to us. Furthermore, we would like to thank Niclas Anvret for giving us time for the interview and the knowledge that has been shared during the meeting. The interview was very important for enriching the bachelor thesis with new perspectives on the industry and information in areas such as the reed-and biochar market in terms of demand and price.

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List of concepts Amazonian Terra preta - Amazonian terra preta is an artificial dark fertile earth that is made of a biochar base (Nanda et al., 2016). Aromatic forms - A molecular structure in the form of cyclic hydrocarbons that provide properties such as stability and longevity (Science direct, n.d). Carbon sequestration - Capturing and storing CO2 from the atmosphere (Nanda et al., 2016). Carbonization - the first stage of pyrolysis and involves the formation of non-porous char (Suhas et al., 2007). Cation exchange capacity - A measurement of negatively charged sites on a surface that attracts cations which are positively charged ions (Liang et al., 2006). Devolatilization - The release of volatile gases from heating a solid fuel (Glassman et al., 2015). Dissolved Organic Carbon (DOC) - an organic content of carbon that is water-soluble (Zmora et al., 2005). Eutrophication - The causation of excess plant nutrients in waters of mainly phosphorus and nitrogen which result in an unbalanced ratio of plant growth that causes oxygen depletion, growth of cyanobacterial blooms and reduced biodiversity (Istvánovics, 2020). Graphitization - A change to a graphitic microstructure for carbon composites (Burnakov & Brazgin, 1968). Gasification - To convert biomass to a gas by heating the feedstock (Zhang et al., 2019). Higher Heat Value (HHV) - A parameter that is important to detect the energetic potential of biomass different feedstocks (Wang et al., 2021 b). Heterocyclic - are cyclic compounds in a form of a ring containing carbon and other elements such as nitrogen, oxygen and sulfur (Siddiquee, 2014). Microbial communities - complex biological life that is central for almost all natural and anthropogenic ecosystems in terms of ecosystem functions such as nutrient cycling (Scholz et al., 2015). Percolation - The filtering or movement of fluids through a porous material (Dembicki, 2017).

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Pyrolysis - A process for producing biochar out of biomass. The biomass is heated in an enclosed space without an oxygen supply (Nanda et al., 2016). Phytoremediation - Using plants for nutrient targeting for cleaning contaminated air, water or soil (Carson et al., 2018). Phytotoxicity - A damaging effect relating to cultivation that delays seed germination and prevents growth (Real CCS, 2014). Riparian corridors - a unique community of plants near rivers, lakes and water (Galatowitsch et al., 2016). R50 - Recalcitrance index. It is for biochars capability of carbon sequestration and stability (Harvey et al., 2012). Soil aeration - The exchange that occurs between the soil and atmosphere (Visser, 1977). Soil organic carbon content (SOC) - SOC is the biggest carbon (C) in the majority of terrestrial ecosystems and is important for every soil process. The soil is recognised as the second biggest source of carbon after the sea and is one of the most significant parts of the biosphere (European Commission, n.d). Thermogravimetric Analysis (TGA) - an analytical tool for measuring thermal stability and volatile content by analysing the weight changes that occur for the sample when heated at a constant temperature (Rajisha et al., 2011). Thermolysis - or thermal decomposition refers to organic components or substances broken down with the help of heat (Li, 2010). Volatiles - Chemical compounds and elements that can quickly vaporise (Fiore et al., 2018).

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Table of content Abstract 1Sammanfattning 2Acknowledgement 3List of concepts 4Table of content 61. Introduction 7

1.1 Background 71.2 Aim and objectives 81.3 Method 8

2. Results 92.1 Acquiring reed 9

2.1.1 Properties of reed 92.1.2 Harvesting methods 122.1.3 How ecosystems are affected while harvesting reed 14

2.2 Methods of pyrolysis 152.3 Properties of biochar 16

2.3.1 Elemental composition 162.3.2 Pyrolysis temperature 182.3.3 Slow and fast pyrolysis 21

2.4 Biochar applications 222.4.1 Soil improvement 222.4.2 Fodder additive 222.4.3 Carbon sequestration 23

2.5 Biochar out of reed 242.5.1 Biochar out of Common reed 242.5.2 Biochar out of giant reed 27

2.6 Phosphorus - a limited resource 312.7 Potential as a coal supplement on the market 31

3. Discussion 343.1 Result highlights 343.2 Research validity & evaluation 353.3 Further research 37

4.Conclusion 385. Appendix 396. References 41

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1. Introduction

1.1 Background

The World Meteorological Organization (WMO) provisional report showcases the climate change index during 2020 where the heat of the ocean is on a record level. WMO estimates that 80% of the oceans worldwide have experienced heatwaves at one time or another during the year 2020 (World Meteorological Organization, 2020). Greenhouse gases capture the incoming heat and keep it in the atmosphere, which leads to global warming. The increase of temperature conditions causes rising sea levels, extreme weather, flooding and extreme heat which entail drought and wildfires (Nullis, 2020). Thus, societies require a fast adaptation and implementation to carbon dioxide neutral energy sources and large technical systems with sustainability as a base (Lestander et al., 2014).

There is no questioning that our present anthropogenic impact on the Baltic sea is worrying. Since the twentieth century, the Baltic Sea has been affected by a growing nutrient discharge which has resulted in eutrophication, algal blooms and hypoxia (oxygen depletion) spread around the Baltic seabed. These factors have led to disorders within the different marine species habited in these environments. These problems are partly due to the Baltic sea being semi-enclosed where the water residence time is between 30 and 40 years. Another causation is the fact that about 85 million people live near the drainage area which collects a lot of nutrient abundance and other pollutants. This gives rise to overfertilization and makes the Baltic sea one of the largest dead-zones and most environmentally deteriorated seas in the world (Ivarsson et al., 2019).

The common reed, also called Phragmites australis, growing around the coastal areas of the Baltic sea is a large perennial grass that thrives in brackish waters, rivers and lakes. Common reed favours eutrophic environments and grows well in stagnating waters. This kind of reed can grow up to 2-6 metres high, it has a high capacity to absorb nutrients and high tolerance to contaminated environments. Reedbeds are important for several mammals, fish and birds since it provides microhabitats (Bonanno et al., 2010).

Studies from IJAB (International Journal of Agriculture & Biology) show that “giant reed” and “green reed” could both be suitable wetland plants for Phyto-uptake, which is a plant's ability to contain, remove or convert toxic waste to harmless substances. According to IJAB, reed was considered to be fitting for application on constructed wetlands for processing high-nutrient wastewater. The uptake of nitrogen and phosphorus specifically are significant (Zhao et al., 2014). Harvesting reed could therefore locally mitigate eutrophication, and the biomass could be utilised for purposes like biofuel, animal fodder and as a biofertilizer (Risén et al., 2013). There are also projects looking into creating biochar out of reed, which could be important for mitigating fossil emissions to be released into the atmosphere because of its carbon negative possibilities (Supriya et al., 2017).

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This bachelor thesis aims to assess the potential of using reed to produce biochar. The project will include examining key factors and features that make high-quality biochar out of reed. Moreover, how to make this process cost-effective from the production point of view whilst still maintaining the optimal quality for the targeted utilization or industry. The focus will primarily be on Sweden and harvesting reed from the Baltic sea to contribute to the prevention of eutrophication.

1.2 Aim and objectives The aim is to assess the potential of using reed to produce biochar and consider its carbon negative effects and potential of eutrophication mitigation.

- Objective 1: Is to identify what are considered to be indicators of good quality biochar for different types of applications

- Objective 2: Is to assess when, where and how reed should be gathered to achieve the optimal results for our chosen utilization based on seasonality, location and methods of harvesting.

- Objective 3: Is to explore the ecological problems that may arise in the ecosystem connected to the harvested reed.

- Objective 4: Is to estimate the potential of the given biochar on the coal market in terms of demand and price.

1.3 Method The bachelor thesis uses a systematic literature review where keywords such as “Reed”, "Phragmites australis", “Baltic sea”, “Eutrophication”, “Pyrolysis” and “Biochar” are being tracked in both English and Swedish. The main database used for this project is the Web of Science. Before reading an article, impact factors and scientific quartiles are inspected, where only articles with an impact factor over 1.5 and Q2 are used in this thesis. This means that only the better half of the articles in terms of impact factor is considered as reliable sources of information and usable for this project. In addition to literature research, an interview with Niclas Anvret, Business manager and project leader at the non-profit organization “Race for the Baltic”, is implemented for discussing the future potential of reeds as a feedstock for producing biochar. “Race for the Baltic” is a non-profit organisation that is working towards restoring the health of the Baltic sea through solution-oriented projects (Wiwen-Nilsson, n.d). The organization often works as a catalyst for pilot projects, start-ups or already existing projects. The organisation helps the company to evolve and get a foothold in society by helping with economic drive, to improve longevity for the project (Anvret, 2021). Furthermore, this bachelor thesis is intended to be used by this organisation as a reliable source for further research within the subject of reeds potential as biochar (Wiwen-Nilsson, n.d).

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2. Results

2.1 Acquiring reed

2.1.1 Properties of reed Phragmites australis are very interesting as a biomass since it has quite varied properties during different seasons that can be utilised in entirely different applications. During late autumn and throughout winter, the Phragmites australis naturally alter from their soft green appearance into a pale and dry plant. Natural drying gives rise to large energy savings since it replaces energy-dependent artificial drying. This, together with the plant's general high productivity, are great qualities for making a high-quality energy feedstock. Potentially even one of the best feedstocks for pyrolysis (Nanda et al., 2016). Pruning or aboveground harvest of reed rejuvenates reed stands (Deák et al., 2015). Reedbeds that have been cut also attract additional species to trap nests hence to increased food accessibility when it is cut, rather than the dense-growing reedbeds (Heneberg et al., 2017). On the contrary harvesting, reed will change the habitat diversity, which will result in fewer species that usually thrive in these habitats (Valkama et al., 2008). An article written by Carson et al. (2018) states that reed have the ability to fast absorb phosphate and mineralised nitrogen which makes these species suited for phytoremediation. This means that plants can be used for nutrient targeting for cleaning contaminated air, water or soil. The article analysed the nutrient abstraction potential in dried tissue of Phragmites australis (common reed). The reed is harvested in late summer (between late August to early September) when the nutrient concentration is closest to its highest point and then dried before evaluating the percentage of nutrients. A total of 211 191 ha Great Lake coastal wetlands was identified where they estimated the percentage of dominant invasive plants. The dry weight biomass of these species was evaluated to 270 474 metric tons of Phragmites australis (see appendix 1) (Carson et al., 2018). With the help of samples, the total nutrient removal potential was estimated. By then calculating the percentage of nitrogen and phosphorus in their samples, the total amount of phosphorus and nitrogen in the species could be calculated in biomass. By calculating the content, the conclusion could be drawn to how much the invasive plants could clean the lakes from nutrients. The removal potential in dried tissue is estimated to be 2.14 ± 0.52% nitrogen respective 0.10 ± 0.02% phosphorus for Phragmites australis (See table 1). The result shows the potential nutrient removal in metric tons to be 5788.1 ±1406.5 T nitrogen and 270.5 ± 59.5 T phosphorus for Phragmites australis, see Appendix 2 (Carson et al., 2018). In a study by Wang et al. (2021), changes in nitrogen removal capacities were analysed on Phragmites australis based on the chosen time of harvest over two years. The different periods studied were either during early wilting in October, mid wilting in December or late

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wilting in February. The harvest was performed using hand tools and they were cut 10 cm above the ground. The flow of total nitrogen was different between the two years, where the first year had a total flow of 17.6-34.7 mg/Litre of total nitrogen and the second year had 3.2-10.0 mg/Litre of total nitrogen. However, despite the differences in the concentration of total nitrogen, the same trends of nitrogen removal occurred both years. Additionally, the varied amount of nitrogen didn’t change the correlation between total aboveground biomass in dry weight and nitrogen content either. This could be explained by the fact that the total amount of nitrogen doesn't necessarily reflect the number of bioavailable nitrogen compounds (Wang et al., 2021 a). It is often rather the contrary; the amount of mineral nitrogen is low when the total amount of nitrogen is high (Chan et al., 2007). However, in contrast with potassium, which is very soluble, the available amount is more often closer to the total content of the element (Windeatt et al., 2014). Although, the two years showed different results regarding the correlation between total aboveground dry weight and nutrient content. Results show that mid wilting harvest the first year contained 7.9% carbon, 46.6% nitrogen and 43.6% phosphorus the first year, while the late wilting harvest gave rise to a carbon content of 4.9%, nitrogen content of 7.8% and phosphorus content of 24.1% the second year (see table 1). The results also show that the mid wilting harvest contained more nutrients the first year and the late wilting harvest maintained more nutrients the second year. However, these changes were not particularly remarkable (Wang et al., 2021 a). Reeds like Phragmites australis is a species that can be found in all corners of the world, with a high adaptivity and competitive strength can quickly colonise areas like lakeshores, riverbanks, coasts and estuaries (Landucci et al., 2013; Packer et al., 2017). Reed such as Phragmites australis is classified as an invasive species in many parts of the world like China and North America (Xie et al., 2021; Barbiero et al., 2017). Reedbeds have a significant value for the conservation of biodiversity, these are habitats for invertebrates, vertebrates, plants, endangered- and rare species. When managed it is commonly in wintertime (Deák et al., 2015). Furthermore, samples of Phragmites australis were collected in November 2017 at the Yellow River delta in China. With 2 weeks of air drying, carbon content calculated to be 42.01 ± 0.151 %, 5.7 ± 0.339 % hydrogen and 0.59 ± 0.052 % nitrogen in the raw material (see table 1) (Wang et al., 2021 b).

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Table 1: This table summarises the studies that have been collected and carried out regarding common reed (Phragmites australis) nutrient removal potential in different seasons.

Phragmites Australis

Spring (Mar-May)

Summer (June - Aug)

Autumn (Sep-Nov)

Winter (dec-feb)

Nitrogen n.d 25.338 mg/kg [2];

15.000 mg/kg [2]BG

2.14 ± 0.52% [1]AG; 0.59 ± 0.052 % [3]AG; 9463 mg/kg nov [2]AG

46.6% (dec 2017) [4]AG; 7.8% (feb 2018) [4]AG

Phosphorous n.d 3156 mg/kg [2]AG 0.10 ± 0.02% [1]AG ; 768 mg/kg nov [2]AG

43.6% (dec 2017) [4]AG; 24.1% (feb 2018) [4]AG

Carbon n.d n.d 42.01 ± 0.151 % [3]AG 7.9% (dec 2017) [4]AG ; 4.9% (feb 2018) [4]AG

[1]: Chicago, Great lake coastal wetlands study, collected in the greater Chicago area. Samples dried in oven 65°C for ≥72 h (Carson et al., 2018).

[2]: Ireland, Wetland in West of Ireland. Biomass dried in an oven at 70°C until it reached constant weight (Mulkeen et al., 2017).

[3]: China, Yellow river delta study. Raw material, 2 weeks air dried (Wang et al., 2021 b).

[4]: China, Shanghai. Stems and leaves were oven-dried at 105 °C for 30 min, and then again at 75 °C to a consistent weight for dry mass determination (Wang et al., 2021 a).

BG: Below Ground biomass, including. roots and rhizomes.

AG: Above ground biomass.

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2.1.2 Harvesting methods There are a lot of different harvesting methods that have different advantages and disadvantages depending on the application, harvesting scale and area. In general, the investment cost is high regarding harvesting and feedstock management (W. Wang et. al. 2021; Anvret 2021). Table 2 that is presented below is a collection of harvesting methods. Table 2: This table contains a compilation of information on different harvesting methods, where there is a description of the machine and its advantages and disadvantages.

Method Description Advantage Disadvantage Source

Cutting and pulling by hand

A diver or an individual is removing the plant by hand.

The impact on the other aquatic environments and species are low. The process is selective and can thus target selected plants.

Time-consuming, labour-intensive, unfit for large harvesting areas and mass production. Pulling reed could cause a disturbance in the sediment below. The reeds will die when pulling and never regrow.

(Wagner, 2004; (Mattson & Wagner, 2004; Morganti et al., 2019; Deák et al., 2015)

Cutting aggregate units on a boat

Cutting aggregate assembled on the front or to the side of a boat.

Inexpensive investment cost and effective when removing a smaller quantity of reed.

The boat requires an amount of depth which makes it hard to reach if there is a cliff or too close to the land. Another difficulty is salvaging the reeds when it ends up in the water since it becomes wet and heavy.

(Isaksson, 2012)

Mechanically-operated machines

Different mechanically-operated machines placed on boats equipped to remove reeds.

Effective removal of the reeds on a bigger scale. Allow areas on selected depth to be targeted.

high investment cost and expensive machines/equipment. Could possibly negatively affect the aquatic fauna. There is no way to select species.

(Wagner, 2004; (Mattson & Wagner, 2004)

Truxor Multifunctional amphibious machine with a comprehensive tool program.

Can operate inland, wetlands areas and the border between without causing

Considering the truxor is an amphibious machine with a broad application, it is not as fuel-efficient as certain

(Isaksson, 2012; Anvret, 2021)

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major effects on the ground. This is because of the light buoyancy and low pressure on the ground. The mowing aggregate could be used to harvest the reed and the scoop could be used to collect the reed.

other harvesting machines specialised like a boat in water or a tractor on land.

Hydro-raking Backhoe machine on a float-like boat, the rake resembles the aggregate similar used while tilling soils.

Effective while removing root masses, submerged stumps or floating islands.

While removing existing growth other plants may spread and reproduce which can cause damage and fragmentation on the aquatic fauna. However, when removing roots the reedbed will never regrow.

(Wagner, 2004; (Mattson & Wagner, 2004;Morganti et al., 2019; Deák et al., 2015)

Rapid Euro Two wheel-tractor with two power take-off (two connection points where auxiliary systems can be connected). The Rapid Euro has several different complementary components.

Have a variety of complementary components.

Does not have a built-in collector. (Ab &

December, 2010)

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2.1.3 How ecosystems are affected while harvesting reed Litter from above-ground plants is one of the most crucial paths for nutrients and carbon fluxes to the soil (Wen et al., 2010; Tuomi et al., 2009), this could possibly impact the biogeochemical cycling process (Xu et al., 2013). In a study by Li et al. (2021), the effects of removal of native perennial grass such as Phragmites australis were studied in Chongming Island, China. In the terms of how above-ground litters could impact the properties of the sediment and therefore also the nitrification- and denitrification process. In the early growth stages in June, Phragmites australis bacteria for nitrification and denitrification were more ample compared to those in October where the grass was in a later growth phase (Li et al., 2021). Therefore, when removing Phragmites australis in the later growth phase (October), nitrification decreased by 41.8% and denitrification decreased by 25.11% in Phragmites australis. Moreover, the removal during the early growth stages (June) showed no changes in soil nitrification or denitrification. In addition, the soil organic carbon content was affected by the litter from Phragmites australis. The removal of Phragmites Australis also indirectly influenced nitrification and denitrification negatively where the effects were more distinct in the later growth stage in the soil (Li et al., 2021). Since reedbeds of Phragmites australis are common in Europe, it is not included in the European Union's list of ‘natural habitat types of community interest whose conservation requires the designation of Special Areas of Conservation’. Another reason behind not being included is that it would not be achievable to force countries that do not have these species to implement reedbeds. Phragmites australis is a species with a high potential for colonization, sub-specific strain can possibly also have an invasive behaviour, when the plant is outside of the original span. Thus, protecting reedbeds for these reasons is motiveless (Coops & Van der velde, 1995; Fér & Hroudová, 2009; Sebastián-González et al., 2012). The litter from Phragmites australis easily propagates via rhizomes or seed dispersal, with a dense growing pattern, where it’s about 200 𝑝𝑙𝑎𝑛𝑡𝑠/𝑚2. Every individual plant carries approximately 2000 seeds. The downsides of these species are the fast propagation causing a loss of biodiversity, habitat, changes in hydrology, changes in nutrient cycle, increased fire hazards, economic and social impacts (Barbiero et al., 2017). When it comes to maintenance measures, an article written by Morganti et. al. (2019) emphasise that Phragmites australis reed beds are an important habitat for biodiversity, but only when it spreads in patches with open water in between (Morganti et al., 2019). However, when reeds become invasive, it has changed riparian corridors through altering the composition, vegetation structure, reduced flows, stabilizing dynamical traits, and changing soil chemistry (Galatowitsch et al., 2016). Since reeds are an important habitat, they should be harvested above ground. If it is harvested below the waterline there is a high possibility that the plant never will grow back (Russell & Kraaij, 2008; Anvret, 2021).

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Species such as Arundo donax (giant reed) restrict the abundance and establishment of native species hence their high productivity, compact growth, solid rhizome and litter (Vasquez et al., 2005; King & Hovick, 2020). Reedbeds are important for moth populations and other potential prey of marshland birds. The magnitude of the reed patches is an essential determinant of the presence of marshland birds. Birds like a black kite, Lesser-Spotted Woodpecker, Purple Heron, Night Heron and Marsh Harrier are birds that reproduce and thrive in reedbeds. Two hectares is the perceptible minimum fragment magnitude for the reedbed to maintain a feasible moth population. Although the presence of reedbeds alone is not enough for species like birds to occur, even if it’s one of the most important features for a sustainable habitat for the reproduction of these birds are reedbeds (Morganti et al., 2019).

2.2 Methods of pyrolysis Pyrolysis is a process where organic materials undergo thermolysis in an enclosed space without an oxygen supply. Important factors for achieving the optimal results during pyrolysis are temperature, heating time, residence time, reactor configuration and what type of feedstock is being processed. These are calibrating factors to consider for achieving the optimal product, regardless of the state of aggregation (Mohan et al., 2006). Pyrolysis often categorises into slow pyrolysis and fast pyrolysis. There is also information about flash pyrolysis which is an even faster variant of fast pyrolysis (Nanda et al., 2016). According to our findings, slow pyrolysis could be in temperatures around 300-800°C, a heating rate around 0.01-2 °C/second with a residence time that ranges from anything from 600 seconds to hours or days. Slow pyrolysis is often used for obtaining biochar. Fast pyrolysis is instead used for the extraction of bio-oil. The temperatures for fast pyrolysis is everything from 400-1000°C, a heating rate of around 10-1000°C/second and a residence time below 2 seconds. Flash pyrolysis is used for similar purposes as fast pyrolysis but with a higher heating rate above 100 °C/second and an even shorter residence time below 0.1 seconds (see table 3) (Fiore et al., 2018; Nanda et al., 2016; Qambrani et al., 2017). In addition to different techniques, there is a distinction between what type of reactor the pyrolysis is performed in. The reactors are wedged through their different types of “gas-solid contact mode” which differs between fixed beds, fluidised beds and entrained beds. From a design perspective, the different reactors are categorised through rotary drums, auger reactions, fixed beds, circulating fluidised beds, bubbling fluidised beds, vacuum pyrolysers, rotative cone pyrolysers and ablative pyrolysers (Samanya et al.; 2012, Basu, 2013; Nanda et al., 2016). However, the most important factor among the parameters is the chosen temperature (Man et al., 2021). Following results are taken from an interview with Niclas Anvret, Business manager and project leader at the non-profit organization “Race for the Baltic”. Niclas Anvret has a technical background in biotechnique and a Master’s Degree in Industrial Engineering and Management with a focus on biotechnique. The motive for Niclas is to work with something

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that gives back and paves the way for a better society and environment, which is the reasoning behind working in his current workplace, as a Project manager at Race for the Baltic (Anvret, 2021). During the interview, Niclas Anvret states that there are also gasses emitted from the pyrolysis that could be either extracted and sold or to be returned back to the process as additional fuel for the pyrolysis. Once starting up pyrolysis without downtime, the process could therefore technically be more or less considered as self-sufficient. In addition to the energy efficiency, the pyrolysis method doesn’t cause any emissions of carbon dioxide (Anvret, 2021). Table 3: Pyrolysis methods describing definitions of the temperature range, heating rate and residence time for three different studies.

Sources (Fiore et al., 2018) (Nanda et al., 2016) (Qambrani et al., 2017)

Slow Pyrolysis

Temperature range [°C] 400–800 300–700 300–700

Heating rate [°C/s] < 0.2 0.1–1 0.01-2

Residence time [s] n.d 600–6000 hours/days

Fast pyrolysis

Temperature range [°C] 450–550 400–500 500–1000

Heating rate [°C/s] 100–1000 10–200 > 2

Residence time [s] < 2 0.03-1.5 < 2

Flash pyrolysis

Temperature range [°C] n.d 400–600 n.d

Heating rate [°C/s] n.d >1000 n.d

Residence time [s] n.d < 0.1 n.d

2.3 Properties of biochar

2.3.1 Elemental composition

From a physical-chemical perspective, biochar is a porous material that mostly contains ash and carbon (Rutherford et al., 2012). The ash also contains inorganic components like phosphorus and sulfur, alkali metals like sodium and potassium and alkaline earth metals like calcium and magnesium obtained by the plant feedstock during its life cycle (Nanda et al., 2013). The biochar has a different diameter and size of the pores depending on the type of feedstock and the chosen method of pyrolysis. The produced amount of biochar from the

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pyrolysis is determined by the structure of the feedstock biomass. More specifically the number of minerals, and the quantitative correlation between carbon and hydrogen in the sense of how much the content consists of hydrogen compared to the amount of carbon. In other words, H/C-ratio (Rutherford et al., 2012). This correlation is also connected to the total surface area for the biochar, this is because of the higher graphitisation during pyrolysis caused by a high H/C-ratio (Uchimiya et al., 2011). There are three main constituents of lignocellulosic biomass; cellulose, hemicellulose and lignin. They each have different reactions to pyrolysis and have different favourable levels of temperatures for decomposing. This affects what different by-products that come with the process. It takes longer for Lignin to break down compared to the other constituents. Lignin also contains a high rate of aromatic forms which gives rise to more products like biochar and bio-oil while cellulose and hemicellulose often degrade much faster and contributes to more emissions of volatiles. Other important factors that affect the time of decomposition, and thereby the finished product, is the structure, volume and physical shape of the feedstock (Fiore et al., 2018). Another study made by Klasson (2017) researched the properties of biochar from a large database of previous studies on the matter. Klasson came to the conclusion, with the help of proximate analysis, that the mass percentage of carbon (C), hydrogen (H) and oxygen (O) in the biochar can be directly connected to a mass percentage of fixed carbon (FC), ash and volatile matter (VM) in the product according to the following equations (Klasson, 2017): 𝐶 = 0.474 ∗ 𝑉𝑀 + 0.093 ∗ 𝐹𝐶 + 0.067 ∗ 𝐴𝑆𝐻 (1) 𝐻 = 0.074 ∗ 𝑉𝑀 + 0.012 ∗ 𝐹𝐶 − 0.052 ∗ 𝑉𝑀/𝐹𝐶 (2) 𝑂 = 0.469 ∗ 𝑉𝑀 + 0.010 ∗ 𝐹𝐶 − 0.069 ∗ 𝐴𝑆𝐻 (3) The same correlation could be done for determining the H/C-ratio and O/C-ratio in the biochar. These would be determined by the following equations (Klasson, 2017): 𝐻/𝐶 = 0.379 ∗ 𝑉𝑀/𝐹𝐶 + 0.251 (4) 𝑂/𝐶 = 0.188 ∗ 𝑉𝑀/𝐹𝐶 + 0.035 (5) These observations were made at a temperature over 400°C and could be used to determine the quality of the product (Klasson, 2017).

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2.3.2 Pyrolysis temperature

Pyrolysis temperature is an important parameter for the atomic O/C and H/C ratios (Ippolito et al., 2020). These atomic ratios in the biochar are important for the carbonization process within the pyrolysis (Weber & Quicker, 2018). Moreover, these relations are important for other biochar attributes like longevity and stability when applied in the soil (Ippolito et al., 2020). The stability and longevity attributes are explained by the fact that the H/C and O/C relations are critical to the thermochemical altering of aromatic ring structures which determines stability (IBI, 2015). Results from a study made by Nanda et al. (2016) indicate that higher temperature pyrolysis results in a higher proportion of carbon content and a lower content in hydrogen and oxygen. This further decreases the H/C and O/C-ratios. Additionally, the total biochar yield will be lower at higher temperatures (see table 4) (Nanda et al., 2016). O/C ratios below 0.2 give high stability and a half-life of more than a thousand years. On the contrary, O/C ratios higher than 0.6 are considered quite unstable and lead to a half-life of less than a hundred years (Spokas, 2010). The threshold value of the H/C ratios that need to be fulfilled for a complete thermochemical altering of aromatic structures is < 0.7 (IBI, 2015). Moreover, the pyrolysis temperature should not fall below 500°C for fulfilling this threshold value (Spokas, 2010). The H/C fractions also correlate with emissions of Nitrous Oxide (N2O). Threshold values for mitigating emissions of this pollutant is a H/C ratio less than 0.3 and pyrolysis temperatures higher than 600°C, whilst still achieving good stability and life duration (Cayuela et al., 2015). Another important recent research made by Nanda et al. (2016) demonstrates the versatility of biochar derived from different temperatures. This versatility is expressed through different practical applications such as soil improvement, energy usage by combustion and char gasification, carbon sequestration or as a material for industrial or biomedical implications. Biochar could also be used as activated carbon for adsorption purposes or as a catalyst for chemical reactions. This research strengthens the importance of the chosen temperature for achieving biochar with the preferred amount of volatiles, ash and carbon but also for properties such as the mineral phases, the area of the biochar surface, alkalinity, electrical conductivity, the cation exchange capacity and the quantity and size of pores (Nanda et al., 2016). Other biochar attributes that change with pyrolysis temperatures are biochar porosity and pore size which are important for usages that demand biochar with optimal adsorption (Nanda et al., 2016). This is because of an increased contact surface and pore volume that comes with the increased porosity, achieved through smaller and denser pores in a microporous design (Manya, 2012; Weber & Quicker, 2018; de Mendonça et al., 2017). The larger contact area is achieved through higher temperature pyrolysis (see table 4) (Domingues et al., 2017; Luo et al., 2015). However, these implications are mostly for adsorbing organic pollutants. For the adsorption of inorganic substances, biochar made from low-temperature pyrolysis is more favourable. This is because of the increased amount of O-containing functionalities and cationic complexes in the soil (Ahmad et al., 2014).

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Another important quality for the adsorption of organic contaminants is hydrophobicity, which also could be obtained through higher temperature pyrolysis (Nanda et al., 2016). However, optimal surface area could also be influential for soil modification by affecting soil attributes such as water retention, microbial habitat and earthworm presence (Biederman & Harpole, 2013). An example of this is biochar made out of coconut shell, where the high surface area and pore volume was pointing towards good conditions for the retention of microbial communities and good water holding capacity (Atkinson et al., 2010). In addition, the pore volume is important for soil aeration and water access through infiltration and percolation (Ajayi & Horn, 2016; Qambrani et al., 2017). According to Nanda et al., pyrolysis temperature is also important for the biochar alkalinity which is connected to the inorganic compounds found in the ash content in the form of alkali- and alkaline earth metals. Therefore, the pH gets higher along with the increased ash content obtained through high-temperature pyrolysis (see table 4). When applied in the ground, it can therefore be used to neutralise acidic soil (Nanda et al., 2016). Biochar produced from low-temperature pyrolysis has a lower pH because of the lower ash content along with the organic acids produced as a result of the degradation of cellulose and hemicellulose from the biomass (Cao & Harris, 2010). The elements found in the ash content that increases with the pyrolysis temperatures are for example phosphorus, potassium and calcium. Higher temperature pyrolysis also increases fixed carbon (see table 4), whilst the content of oxygen, hydrogen and nitrogen decreases (Weber & Quicker, 2018; Ippolito et al., 2015). This is in the form of volatilization which leads to a higher concentration of the remaining elements in the produced biochar (Kim et al., 2012; Kinney et al., 2012). Cation exchange capacity is another attribute affected by pyrolysis temperature (Nanda et al., 2016). Cation exchange capacity has important implications for soil improvements and is used for the retention of cationic nutrients from the soil and thereby counteracts contamination of groundwater from cations, maintaining the nutrients in the soil and measuring the soil fertility (Sombroek et al., 2006). The electrical conductivity from biochar is induced by the negatively charged surface of the biochar (Ahmad et al., 2014). This could be used for purposes such as estimating potential damaging salt effects from soils where biochar is applied (Lehmann & Joseph, 2009). Moreover, this negative conductivity also attracts the positively charged cations from the soil, which thereby enhances the cation exchange capacity. This due to the fact that biochar surfaces often are negatively charged which induces electrostatic attraction towards cations who are positively charged compounds (Ahmad et al., 2014). Both electrical conductivity and cation exchange capacity increases at lower temperatures (see table 4) (Azargohar et al., 2013). This parallel increase further explains why these two attributes both correlate with each other (Song & Guo, 2012). Cation exchange capacity could also increase at higher pyrolysis temperatures (see table 4). This is because of the increased alkalinity and higher pH occurring during application into the

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soil which is due to the higher amount of alkali metals and alkaline earth metals that come with the higher biochar alkalinity. These inorganic elements induce pH-dependent charges from turning into ions when the biochar raises the pH in the soil. This gives rise to more cation exchange capabilities (Nanda et al., 2016; Ippolito et al., 2017). Another explanation for the increased cation exchange capacity is precipitated particles that have not dissolved in the ash content which could be functioning as reaction surfaces for additional cation attractions (Ippolito et al., 2017). Other examples of how pH could affect the surface charges of biochar are implied in a study by Moon et al. (2013), where alkaline properties and a higher pH resulted in a higher negative charge on the surface of the biochar which strengthened the sorption of lead (Moon et al., 2013). Other similar properties come from several oxygen functional groups in biochar such as lactone, carboxyl, carbonyl and hydroxyl. These compounds could also enhance the attraction to ions in the soil (Song & Guo, 2012). Regarding volatilization; volatile matter from biochar mostly consists of light carbohydrates, carbon monoxide and carbon dioxide (Vassilev et al., 2010). This is mainly caused by dehydration and devolatilization (Nanda et al., 2016). The thermal degradation of hemicellulose is 200-300°C, cellulose is 250-350°C and lignin is 200-500°C (Carrier et al., 2011). The maximum devolatilization occurs at temperatures between 200-400°C. With pyrolysis temperatures above 400°C, the cracking of organics leads to a decreased amount of released volatiles via devolatilization to react with degrading carbohydrates to create a higher amount of fixed carbon. This further explains why lower pyrolysis temperatures result in higher volatile yields (see table 4) (Antal & Gronli, 2003). An important index of measuring biochar recalcitrance, stability and longevity for carbon sequestration purposes is the recalcitrance index (R50). According to a study made by Zhao et al. (2013), the R50 values increased at higher pyrolysis temperatures (see table 4). The study investigated the R50 values for biochar made out of palm shell, coconut shell, olive pomace, rice husk, sugarcane bagasse, cotton stalk, coconut fibre and wheat straw. Results show that the R50 values for the biomasses were in class C or class B in recalcitrance. According to Zhao et al., an increase in temperature from 500-650°C resulted in an increase in the R50 index from 0.54 to 0.71 for biochar derived from wheat straw. Additionally, with the help of the recalcitrance values, the study came to the conclusion that the least reluctant feedstock (wheat straw) could maintain 21.3% of the original biomass carbon content long-term in soil. The most reluctant feedstock (palm shell) could withhold 32.5% of the initial biomass carbon content. Comparing a total of 12 different feedstocks, the study reported that there were possibilities of 21.1% to 47.1% carbon retention from the original biomass. This was said to be correlating with the biomass content of lignin, higher aromatic properties and increased alkali metals for further catalysing the thermal degradation at lower temperatures (Zhao et al., 2013).

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Table 4: Display attributes from low respectively high-temperature pyrolysis from different studies with different types of biomass.

Attributes from different temperatures (300-700°C)

Low-temperature pyrolysis (around 300°C)

High-temperature pyrolysis (around 700°C)

Biochar yield [+/-] + -

Volatiles yield [+/-] + -

Cation exchange capacity [+/-] + - (+ pH charge)

Surface electrical conductivity [+/-] + -

pH [+/-] - +

R50 [+/-] - +

Ash content [+/-] - +

Fixed carbon [+/-] - +

Surface area [+/-] - +

Porosity/pore volume [+/-] - +

(Nanda et al., 2016; Windeatt et al., 2014; Ippolito et al., 2020; Fiore et al., 2018)

2.3.3 Slow and fast pyrolysis It's also important to determine biochar characteristics behind slow and fast pyrolysis. Biochar produced through slow pyrolysis often contains more nitrogen, sulphur, phosphorus, potassium and magnesium and is more adapted to cation-exchange capacity. Additionally, slow pyrolysis also gives rise to a bigger surface area, amount of fixed carbon, ash content and accessible concentrations of Iron and nitrate (Ippolito et al., 2020). Moreover, elemental compositions connected to biochar alkalinity are also correlated with slow pyrolysis. A study involving biochar produced from pinewood for example show that a heating rate around 0.033°C/second resulted in a higher number of alkaline elements than from biochar from the same biomass feedstock produced in fast pyrolysis with a heating rate of 7.5 °C/second (Mohanty et al., 2013).

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2.4 Biochar applications

2.4.1 Soil improvement Biochar has the inclination to enhance the soil quality for a more fertile soil (Atkinson et al., 2010). Furthermore, it can hold water and nutrients for longer which amplifies the humus content (Söderqvist & Norberg, 2021) and therefore increase the yield productivity of the arable land. When using biochar in agriculture, less conventional fertilizers are needed since more nutrients remain in the soil and a smaller amount leaks out (Atkinson et al., 2010; Söderqvist & Norberg, 2021). Henceforth soils appear to be one of the only storehouses to accommodate biochar in that order of magnitude for mitigation in the long-term, to meet the climate goals. According to Atkinson et. al. (2010) Biochar has been shown to be able to repress emissions of nitrous oxide and methane from the soil. Additionally, it also positively impacts the carbon content in the soil and contributes to the soil’s conversion to large carbon sinks. The chemical structure is heterogeneous, and the surface can show hydrophilic, hydrophobic, basic and acidic properties (Atkinson et al., 2010). The main features that are desirable for biochar as soil improvement is to retain the essential nutrients for plants and good stability against decay. The high stability is proven by the Amazonas Terra preta with property to its opposition to the rapid rate of mineralization. According to Nanda et al. (2016), Amazonian Terra preta is an artificial dark fertile earth made of a biochar base. These features together make it possible for biochar to react and alter the quality of the soil. However, the obstinacy of biochar depends on how the char is processed, precursor type, pyrolysis temperature, heating rate and soil properties (Nanda et al., 2016). Biochar has displayed positive effects on the soil where it improves bulk density and heightens the rooting pattern of plants’, available water content and soil fauna (Major et al., 2010). The micropores that the biochar has permitted the penetration of water and air and therefore are able to reduce bulkiness when mixing biochar and soil (Nanda et al., 2016).

2.4.2 Fodder additive In the recent 10 years, studies have been made for determining the effects of applying biochar in fodder for animals such as cows, pigs, chicken and fish (Lan et al., 2016; Preston, 2014; Schmidt et al., 2017; Toth & Dou, 2016). The effects of adding biochar into Fish fodder were positive for their survivability and growth (Mabe et al., 2018). The results connected to fodder for hens showed positive effects in higher productivity and quality of chicken eggs (Kutlu et al., 2001; Prasai et al., 2018). This was achieved through additional intake of minerals from the biochar, found in the ash content, magnesium, calcium and potassium which improved the sustainability of the

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eggshells (Kutlu et al., 2001). The biochar also adsorbed microbial life such as “Campylobacter hepaticus” and “Gallibacterium anatis” that would otherwise potentially lead to diseases for the chickens (Willson et al., 2019). This discovery implied possibilities for the biochar of being a supplement for antibiotic treatments in the breeding industries (Islam et al., 2014). Biochar, being a supplement for antibiotics was also discussed with interviewee Niclas Anvret where he stated that this is important for the health of the consumer as well. The reason is that antibiotics often get accumulated in the treated farm animal which is later passed on to consumers (Anvret, 2021). The high porosity in the biochar gives opportunities for further habitation of microbial communities such as gut microbes like “Methanogenic archaea”. This is important for inhibiting emissions of greenhouse gases like methane from cattle and goats (Eger et al., 2018). Another way for biochar to prevent emissions of methane is through adsorption (Danielsson et al., 2017), which strengthens the argument of applying biochar in animal fodders for reducing methane emissions (Leng, 2018). Results from Man et al. (2021) show that a mass percentage of 0.5-9% of biochar in cattle fodder could help mitigate 0.5-18.4% of the total produced methane after consumed by the cows (Man et al., 2021). Moreover, after being consumed by cows, the biochar could absorb nutrients found inside the guts of the cow. This gives rise to more nutrient-filled faeces that could be used as a soil fertilizer which thereby leaves a positive impact on the farm productivity as a whole (Joseph et al., 2015).

2.4.3 Carbon sequestration Biochar consists mostly of stable aromatic forms of carbon, which makes the product highly persistent towards returning to the atmosphere in the form of carbon dioxide, even in favourable conditions (Lehmann, 2007). Contrary to conventional carbon that is processed for thousands of years before it is released in our atmosphere as fossil emissions, biochar is produced from biomass that is already a part of the carbon cycle. Biochar could thereby be perceived as a renewable resource, for its lack of fossil carbon content (Basu, 2013; Rutherford et al., 2012). However, other renewable sources that emit carbon dioxide obtained from regular lignocellulosic (plant-based) sources are perceived as carbon-neutral sources, since the fixed carbon obtained through photosynthesis in this plant-based fuel gets released through consumption as carbon dioxide (Nanda et al., 2016). Biochar is additionally a renewable source that could preserve carbon dioxide from being released into the atmosphere because of its aromatic structure. This either by directing parts of the former biomass as biochar back into the soil or by using the product for carbon sequestration. By applying biochar into the soil, the recalcitrant carbon from the biochar that isn’t released as volatiles will be contained underground for potentially hundreds to thousands of years. This will thereby be a reverse effect in contrast to conventional fossil carbon and it can therefore be seen as a carbon-negative source (Nanda et al., 2016). Furthermore, biochar has through field trials shown the ability to immobilise heavy metals and organic pollutants (Zama et al., 2018).

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2.5 Biochar out of reed

2.5.1 Biochar out of Common reed A study made by Wang et al. (2021 b) describes different attributes and content of biochar made out of reed and how the properties correlate with pyrolysis temperatures. Samples of Phragmites australis that were collected November 2017 at the Yellow river delta in China were dried for 2 weeks and prepared for pyrolysis. Before pyrolysis, they were grinded and shifted through a 100-mesh sieve made of nylon. These samples were put under pyrolysis at five different temperatures 300-, 350-, 400-, 450- and 500°C (Wang et al., 2021 b). The results from the study show that increased pyrolysis temperature (300-500°C) induce a decrease in attributes like biochar yield (50.19% to 28.99%), oxygen content (24.62% to 9.20%), hydrogen content (5.03% to 2.95%), The H/C-ratio (1.0 to 0.5), O/C-ratio (0.3 to 0.1) and (O+N)/C-ratio (0.31 to 0.10) that strengthens the polarity and aromaticity. The water-extractable Dissolved Organic Content (DOC) also decreased with higher temperatures (2.77 to 0.21 mg/g), the highest DOC appeared in the raw, unprocessed feedstock. Nitrogen content peaked around 350°C and decreased at higher temperatures (see table 5) (Wang et al., 2021 b). The higher biochar yield could be a result of the higher content of volatiles and moisture and the decomposition of the biomasses three main components; cellulose, hemicellulose and lignin (Al-Wabel et al., 2013; Muradov et al., 2012; Wei et al., 2019). However, cellulose and hemicellulose degrade at lower temperatures than lignin (300-400°C instead of 400-500°C). This due to the complex three-dimensional structure of lignin that leads to a slower decomposition rate (Chen et al., 2016). Regarding the results of atomic relations of H/C, O/C and (O+N)/C, the O/C ratios for the biochar were decreased to lower than 0.2 at 400-500°C, which increases longevity with a half-life of 1000 years and good stability providing good carbon sequestration potentials (Spokas, 2010). The (O+N)/C ratio is more important for the polarity of the biochar (Al-Wabel et al., 2013). Increasing pyrolysis temperatures decreases this ratio which results in a loss of polar functional groups on the surface of the biochar and thereby a lower electrical conductivity (Chen et al., 2016). The decreasing H/C-ratio might be caused by dehydration reactions that result in a loss of water from the reaction (Lee et al., 2013), the lower O/C-ratio could be confirmed by observing the changes in the aromatic structure (Doumer et al., 2015). If the study were to expand to higher pyrolysis temperatures, the O/C- and H/C- ratios might be low enough to be compared to soot (Wang et al., 2021 b). DOC is important for soil improvement purposes, water retention and fertilization (Liu et al., 2019). This because of its positive effect in agricultural applications such as improving microbial health (Bruun et al., 2012; Smith et al., 2016; Smith et al., 2013), benefitting the

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plant productivity in the soil (Deenik et al., 2010; Joseph et al., 2013; Korai et al., 2018; Wu et al., 2018), enhancing biochar perseverance and mobility (Bird et al., 2015; Fu et al., 2016; Jaffe et al., 2013; Norwood et al., 2013) and strengthening the transportation of contaminants (Uchimiya et al., 2010; Wang et al., 2017). Once applied in the soil, the DOC from the biochar could dissolve and spread into the soil water and change its physicochemical attributes of soil DOC (Dittmar et al., 2012; Hockaday et al., 2006). This allows the DOC to be widely spread into soil surfaces and groundwater (Major et al., 2010; Wang et al., 2013 a; Wang et al., 2013 b). This is furthermore how the DOC could provide benefits to the soil, by mitigating carbon deficiency and transportation of DOC-related contaminants (Liu et al., 2019). Biochar made in higher temperature pyrolysis also gave rise to an increase in properties such as ash content (9% to 15%) (see table 5) (Wang et al., 2021 b). This could be explained by the accumulated minerals and the ruinous reaction of the biomass volatilization (Tsai et al., 2012; Zhang et al., 2015). The carbon content also increased from 60.72% to 72.18% (see table 5) (Wang et al., 2021 b), which could be connected to the increased carbonization degree that occurs at higher temperatures (Al-Wabel et al., 2013; Wei et al., 2019). Furthermore, the HHVs (higher heating values), which is important for the energetic potential of the biochar, also increased with higher pyrolysis temperatures (23.62 to 26.86 MJ/Kg) (see table 5). This was mostly determined by the carbon content (>80%) (Wang et al., 2021 b). According to Li & Chen (2018), higher heat value (HHV) is potentially an important attribute for biochar to be considered as a fuel. Compared to studies made on HHV for different biomass feedstocks, the HHV from biochar made out of Phragmites australis were lower than from olive mill waste with 28.55-31.03 MJ/Kg (Hmid et al., 2014). However, the HHV were higher than wood (20 MJ/Kg), rice husk (20 MJ/Kg) and corn cob (16.1 MJ/Kg) (Raveendran & Ganesh, 1996). The value of HHV was also higher than the HHV of lignite (23.35 MJ/Kg). Because of its rather high HHV, biochar made out of reed shows promising results for being a potential alternative fuel (Wang et al., 2021 b). Another attribute beneficial to higher temperatures is the biochar's carbon sequestration abilities and stability. A tool for analysing this is by researching the biochar's different oxidation resistance through Thermogravimetric analysis (TGA). TGA was used to identify the weight loss of biochar by exposing the product to different levels of constant temperatures. According to the TGA, a small weight loss occurred at temperatures between 25-125°C for all biochar, followed by a larger decrease in weight the higher the temperature. The results show that biochar obtained from the lowest temperatures (300°C) showed most weight loss per temperature increased and vice versa (Wang et al., 2021 b). Recalcitrance index R50 was also implemented for further evaluation of thermal degradation. Results show that the values of R50 ranged between 0.481 and 0.531. The values were below 0.5 at temperatures between 300 and 350°C, which categorises the carbon sequestration levels in class C (Wang et al., 2021 b). Class C refers to low carbon sequestration capabilities

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comparable to uncharred raw biomass (Harvey et al., 2012). At temperatures between 400 and 500°C, the R50 ended up in between 0.5 and 0.7 which classifies the carbon sequestration to class B (Wang et al., 2021 b). Class B describes carbon sequestration capabilities between class C and class A. Class A is classified by high carbon sequestration capabilities comparable to soot or graphite (Harvey et al., 2012). Results from the TGA show that the initial weight loss, or oxidation, at 25-150°C could possibly be due to the volatiles emitted from the dehydration of the biochar (Li & Chen, 2018). Furthermore, the decreasing weight in temperatures around 200-400°C could be a result of cellulose and hemicellulose and the weight loss at 370-550°C is suggested to be connected to the decomposition of lignin (Yang et al., 2007). The high recalcitrance is very important for the carbon sequestration properties of biochar (Cui et al., 2016). The results from determining the R50 values for the respective biochar show that thermal stability (and higher values of R50) increase parallel to increased pyrolysis temperatures. The reason behind the fact that biochar produced from 300-350°C is categorised as class C (R50 < 0.5) is because of the incomplete carbonization, whereas biochar obtained from higher temperatures (400-500°C) produces more carbonised and recalcitrant products categorised as class B (0.5 < R50 < 0.7) (see table 5) (Harvey et al., 2012). Another potential application for reed as biochar is to power fuel cells. A Direct Carbon Fuel Cell (DCFC) converts chemical energy obtained from the carbon into electricity. DCFCs is perceived as a promising power supply (Gür, 2013). A reason behind this is that the DCFC, through complete carbon oxidation, achieves almost zero entropy change (1.6 Joules per Kelvin and mol at 600°C). In theory, the energy source surpasses 100% efficiency (Cooper & Selman, 2012). In addition, it is considered a more sustainable alternative, in comparison to conventional power plants (Gür, 2016). Important factors of the carbon that affects the performance of the DCFCs is the crystal design of the carbon in terms of edges, curves and other anomalies to the surface. This gives a more reactive oxide electrolyte because of the extended surface area that gives room for an additional reaction surface. A high discharge rate is determined by fuel cells with high electrical conductivity, an acceptable reaction surface area and low crystallization (Nürnberger et al., 2010; Konsolakis et al., 2015; Cherepy et al., 2005). Moreover, biochar produced from reed is according to this study a promising carbon source for the DCFC. The attributes are achieved through its structure by pyrolysis at high temperatures around 600-750°C (see table 5) (Wang et al., 2019).

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Table 5: Elemental composition of biochar out of common reed (Phragmites australis).

Biochar out of common reed




Biochar yield [%] 50.19 28.99

Oxygen content [%] 24.62 9.20

Hydrogen content [%] 5.03 2.95

Nitrogen content [+/-] + -

H/C-ratio 1.0 0.5

O/C-ratio 0.3 0.1

(O+N)/C-ratio 0.31 0.1

DOC content [mg/g] 2.77 0.21

Ash content [%] 9 15

Carbon content [%] 60.72 72.18

HHV [MJ/Kg] 23.62 26.86

R50 classification Class C (R50 < 0.5) Class B (0.5 < R50 < 0.7)

DCFC potential [+/-] - + (600-750°C)

(Wang et al., 2021 b; Wang et al., 2019)

2.5.2 Biochar out of giant reed Giant reed, also known as Arundo donax, has suitable attributes that make the species favourable as a biomass feedstock for creating biochar. These characteristics are high growth, long lifespan over multiple growing seasons and a low input demand which gives rise to low cost in energy and effective carbon sequestration. Other beneficial characteristics of the species are the low cost of cultivation and high-stress resistance towards abiotic and biotic influences (Ceotto & Candilo, 2010; Lewandowski, 2016; Fagnano, 2015). Because of its fitting properties, giant reed has in recent years been examined as a feedstock for producing biochar through pyrolysis on a laboratory scale (Saikia et al., 2015; Zheng et al., 2013). A study made by Zheng et al. (2013) has been made for investigating the properties of biochar from giant reed at different temperatures of pyrolysis (Zheng et al, 2013). Similarly to the results found in biochar characteristics from different pyrolysis temperatures (see table 4 & 5), the giant reed produced biochar with high temperatures resulted in increased ash

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content and inorganic substances, pH and alkalinity, higher surface area, higher pore volumes and higher fixed carbon content with aromatic structures (see table 6) (Novak et al., 2009; Keiluweit et al., 2010). However, lower pyrolysis temperatures were profitable for the total mass biochar yield with 44.4% at 300°C and 30.6% at 600°C. Lower temperatures maintained more oxygen and hydrogen (see table 6). These elements are favourable for oxygen-containing functional groups that contributed to lower pH and negative surface conductivity. The amount of available nitrogen decreased with higher temperatures with a noticeable effect at 400°C and half of it was lost as volatiles at 750°C (see table 6) (Lang et al., 2005). This loss of available nitrogen in the biochar is also connected to the formation of different inaccessible nitrogen compounds such as heterocyclic nitrogen that was formed during the higher temperatures of pyrolysis (Koutcheiko et al., 2007). Biochar produced from lower temperatures are therefore more suitable in soil applications where there is a deficiency of nitrogen (Zheng et al, 2013). In contrast to nitrogen, the total amount of phosphorus was increased with higher temperatures. This is due to the loss of carbon together with the stable and heat-resilient containment of phosphorus within the biomass (Page et al., 1982). The phosphorus structures were stable during the pyrolysis which resulted in no loss of phosphorus. This was strengthened by research where all phosphorus was maintained during pyrolysis at 450°C (Bridle & Pritchard, 2004). However, the amount of available phosphorus is higher at biochar derived from lower pyrolysis temperatures below 400°C (see table 6). This is because of the decreasing crystallised structures of phosphorus-containing minerals at lower temperatures which instead leaves more soluble phosphorus content. This amount of accessible phosphorus in the low-temperature produced biochar (387-491 mg per kg) is similar to phosphorus enriched content manure (380-460 mg per kg) (Cantrell et al., 2012). Biochar produced from temperatures below 400°C could therefore be a good supplement for soils lacking phosphorus (Zheng et al, 2013). Similarly to Phosphorus, the amount of potassium remained unchanged with different pyrolysis temperatures. Although, potassium proportions increased together with its accessible amount with higher temperature pyrolysis (see table 6), this in the form of crystallised minerals. The potassium content in high-temperature biochar over 600°C (3.70 – 5.02%) is noticeably higher than the amount of potassium found in conventional organic fertilizers (0.1%-1.6%) (Chan et al., 2009). This high-temperature biochar could therefore be profitable for application on soils deficient in potassium (Zheng et al, 2013). Other important findings in the report from Zheng et al. was that more ammonium, phosphate - and potassium ions were emitted from biochar at low pH below 5. In addition, low-temperature biochar created below 400°C were better adsorbents of ammonium ions (see table 6). Taking account of the results, Zheng et al. come to the conclusion that the biochar

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produced at temperatures below 400°C is best suited for soil-improving purposes and enriching soils lacking nitrogen, phosphorus and potassium (Zheng et al, 2013). Table 6: Elemental composition of biochar out of giant reed (Arundo donax) in different temperatures.

Biochar out of giant reed




Biochar yield [%] 44.4 30.6

Oxygen content [+/-] + -

Hydrogen content [+/-] + -

Available nitrogen content [+/-] + -

Available phosphorus content [+/-] + -

Ammonium ion sorption [+/-] + -

Ash content [+/-] - +

Fixed carbon [+/-] - +

Surface area [+/-] - +

Porosity/pore volume [+/-] - +

Available potassium content [+/-] - +

pH [+/-] (pH below 5 increase sorption of ammonium- potassium and phosphite ions)

-

+

(Zheng et al, 2013) A recent study investigates different properties of biochar created by giant reeds through a pilot updraft reactor to make a pyro-gasification of the feedstock. Like the conditions of slow pyrolysis, the temperatures varied around 300-400°C and duration between 60 to 90 minutes. The two chosen parameters to investigate for the research are the airflow rates of the biochar production (natural ventilation, 0.001- or 0.0007 m3 per second) and the different harvest periods for the giant reed biomass (February or June). These factors were compared by determining how they affect the properties of the produced biochar (Carnevale et al., 2021). The results show that the biomass harvested from the summer gave an increased content of ash with 6.78% over 5.62% (Giannini et al., 2016; Nassi o Di Nasso et al., 2010), an

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increased amount of oxygen with 48.1% over 39.2% (Nassi o Di Nasso et al., 2011) and almost twice as much nitrogen with 0.62% instead of 0.36% (see table 7). The latter biochar content is explained by the maximum amount of nitrogen found in the biomass between June and August which later during the season decreases until early spring between February and April (Nassi o Di Nasso et al., 2011; Nassi o Di Nasso et al., 2013). However, the attributes from winter-harvested feedstock that prevails over the summer-harvested crop are the carbon content with 53.7% over 44.7% (see table 7), where the former is considered to be quite a high amount (Nassi o Di Nasso et al., 2010; Vassilev et al., 2010). This could be further explained by the high amount of non-structural carbohydrates that increased during autumn (Ragaglini et al., 2014). Because of the constant variations and slow growth of the biomasses above ground structural carbohydrates (in the form of lignin, cellulose and hemicellulose), an increase of non-structural carbohydrates in the form of leafiness occurred during this time of the season. This is a possible explanation for the increased carbon found in the winter-harvested crop (Nassi o Di Nasso et al., 2011). Together with airflow rates of 0.001 and 0.0007 m3 per second, the biochar produced with giant reed harvested during the Winter had more polarity, aromatic structures and water attraction (see table 7). This biochar thereby provides a better resistance for damages like phytotoxicity, when used for purposes like germination (Carnevale et al., 2021). Table 7: Elemental composition of biochar out of giant reed (Arundo donax) harvested in different seasons.

Biochar out of giant reed

Properties from seasonal harvest

Summer harvest Winter harvest

Oxygen content [%] 48.1 39.2

Nitrogen content [%] 0.62 0.36

Ash content [%] 6.78 5.62

Aromaticity [+/-] - +

Carbon content [%] 44.7 53.7

Water retention [+/-] - +

Polarity [+/-] - +

(Carnevale et al., 2021)

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2.6 Phosphorus - a limited resource Historically agriculture relied on the natural levels of nutrients such as phosphorus in the soil. However, to keep up with the rapid growth of the population and to secure the food demand, societies are dependent on mined rock phosphate. Phosphorous is an element that the world is highly dependent on and is used in our food systems (Cordell et al., 2009). The mined phosphorus is a finite resource that takes tens of millions of years to create from dead aquatic life and shells that have gone through mineralization and tectonic uplift (Filippelli, 2011). It is agreed between scientists and industry that the phosphorous will never run out. However, the high-quality reserves will one day be running out, and low quality- and concentrated phosphorus will remain and will be harder to extract. It is estimated that 90% of mined phosphorus rock is used for the production of food: 82% for the use of fertilizer, 5% to feed the animals, and 2-3% as food additives (Van Kauwenbergh, 2010).

2.7 Potential as a coal supplement on the market The production cost to produce biochar out of Phragmites australis was analysed. Production with smaller bench-scale reactors had a lot higher production price. Lager production in large-scale reactors, the production price is much more cost-effective in comparison to the bench-scale (Wang et al., 2021 b). The reason is that a substantial amount of reed could be dried, and biochar could be manufactured once in the large-scale reactor (Li & Chen, 2018). The drying process was not included since Phragmites australis often grows in environments where the water could be dried and removed naturally, with the help of the weather (Wang et al., 2021 b).

Figure 1: This figure is directly taken from the article written by Wang et al (2021 b). The figure shows the production cost for biochar made out of Phragmites australis in different pyrolysis temperatures. The cost is measured in Chinese Yuan renminbi per ton produced biochar. The different production scales are divided in different diagrams: Bench-scale (a) and large-scale (c) (Wang et al., 2021 b).

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The cost of the production also rose when the higher pyrolysis temperature increased, mainly in bench-scale because of the higher energy consumption and the smaller amount of yield. Moreover, the transportation cost resulted in a high percentage of the total production cost. The pyrolysis was powered by electricity and was generally quite low, particularly when using the large-scale reactor (Wang et al., 2021 b). However, when it is not possible to naturally dry the yield, it is considered to be one of the most expensive processes when it comes to bench-scale reactor production, increasing the size of the reactor might however decrease the cost of that process (Li & Chen, 2018). Drying processes could potentially be expensive but doesn’t necessarily have to be. Larger pyrolysis facilities recycle the excess heat from the pyrolysis to a drying chamber to be used to dry other reed biomass. This way, there are no additional costs for drying the biomass. Although, smaller facilities might need a separate drying chamber. “Stockholm stad”, for example, are using pyrolysis when producing biochar. The heat waste that is emitted in the process is used to dry their pulp (Stockholm VA, 2018). The price differences between conventional coal and biochar is currently large, it is therefore primarily public actors that are the driving force in the market (Söderqvist & Norberg, 2021). The use of biochar in urban cultivation has increased in the last few years in Sweden where the majority of the usage occurs in Stockholm. In the vast majority of cases, biochar is mainly produced from customers' requests since it’s very expensive. However, “Lantmännen Algro” is currently planning to build a heating system in Skurup. The estimated production of biochar is about 1250-1500 tons and the focus of the implementation is on soil improvement. The cost to produce biochar may be one of the bigger hurdles for market proliferation (Duku et al., 2011). The total consumption of biochar for every municipality in Sweden in 2018 was approximately 1200 tons (Söderqvist & Norberg, 2021). Soil manufacturers today mainly import biochar from the Baltic states, Germany and Finland at variable prices going from 3.800 - 1500 Swedish crowns/ton. The variation of prices is mainly depending on the quality, substrate, certification and area of use (Karlsson, 2020). Regarding large-scale productions, the price for producing a ton of reed biochar in higher temperatures are more expensive due to the increased amount of feedstock needed (Wang et al., 2021 b). Additionally, in the interview with Niclas Anvret (2021), it is mentioned that to manage a large-scale harvest, a lot more reed must be harvested than what is harvested today. However, there is currently no technology or machine that can manage to harvest the amount of reed that is needed. Furthermore, there is a need to find actors who are willing to harvest the amount needed for large-scale production. To achieve that, there also needs to be a higher demand for the use of reed (Anvret, 2021). Harvesting reed today is yet too expensive and the cutting that is being done today is mainly for aesthetic reasons, which is mostly done in springtime to prepare for summer. Furthermore, it is a quite small cutting season and to survive the year out the cost needs to

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cover for the whole year. There are few businesses that will survive only being active in springtime. Despite the economic and technological problems surrounding reed, there are great possibilities with using the reed that already has been harvested or is being planned to be harvested (Anvret, 2021). The potential of biochar is good and there is a lot of available reed to make the product successful. Biochar plants in Sweden are interested in biochar made out of reed. Although, the problem lies in the lack of testing that has been done for the subject in terms of energy content in the reeds. There is therefore an uncertainty of how much energy it is to expect from the biomass. By converting biomass into pellets beforehand, there is a much clearer perception of the size, energy content and output by-products from every respective pellet. It is also not typically expensive with palletisation (Anvret, 2021). In the report written by Söderqvist et. al. (2021), on European Union's behalf on the Greater Bio project, they evaluate the market for biochar within “Öresundregionen” and its future potential. It is said that with the right tools and competence there is potential for biochar to be a product with great demand and a long list of potential applications. However, these applications are developed in different ways and with different amounts of progress. The market analysis needs to assess what type of applications that are appropriate to invest in. The results in that analysis display the application with the biggest potential in the near future is biochar as soil improvement. There is currently a higher willingness to pay for biochar as a soil improvement (Söderqvist & Norberg, 2021), and will most certainly become a focal point for biochar in the next 5 years to come (Anvret, 2021).

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3. Discussion

3.1 Result highlights This because of the high nutrient removability from reeds and the carbon-negative potential of biochar. However, it is important to note that acquiring biomass for biochar production, and pyrolysis itself, often require transportation and fossil-powered machines fossil inputs which ultimately counteracts at least a part of the carbon negativity. Biochar generally shows clear differences in properties when being produced in different temperatures (see table 4). Biochar made out of reed show similar results (see table 5). Furthermore, electrical conductivity and cation exchange capacity could be recognised in the low temperature reed biochar. This is because of the higher (O + N)/C ratio (see table 5) which provides the biochar with increased polarity. Higher alkalinity and pH in high temperature reed biochar could also be identified by the increased ash content (see table 5), which contains alkali metals and alkaline earth metals. Low temperature reed biochar showed high DOC content (see table 5), which provided important attributes for soil-improving applications. This is especially important since soil improvement is currently the focus point of application for reed biochar in Sweden. Biochar derived from reed at higher temperatures also had high HHVs (see table 5) which showed great potential for being used as a biofuel. Additionally, there is a potential implication of reed as a DCFC (Direct Carbon Fuel Cells). Moreover, due to the high productivity and widespread nature of reed as a species, there is certainly plenty of biomass available to be used as a potential energy feedstock in the future. However, it could be considered unethical to use biochar for combustion since it has a high phosphorus content. Not only for the fact that phosphorus is a limited resource, but also because it has huge importance for the world's food security. Morocco alone accounts for 74% of the world's total phosphorus assets (Cordell et al., 2009). There is a need for a more circular economy where we manage our resources to reuse and recycle as much as possible, to efficiently use our resources (Domenech & Bahn-Walkowiak, 2019). Considering this issue, biochar should be preferred in soil application purposes. There are plenty of different harvesting methods in the market today. However, there are no harvesting machines that are able to harvest reed in the amount that it is needed to make the production large-scale. Furthermore, when harvesting reed during winter where lakes and seas are frozen, a possible way of harvesting could be tractors. Harvesting during this time will limit the disturbance of marshlands birds, since they are not nesting. However, harvesting reed during winter has shown to disturb the nitrification and denitrification processes. These processes are especially important in areas surrounding the Baltic sea considering their function as a natural resistance against eutrophication.

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Moreover, harvesting solely on the winter does not correspond with the aspire to make the product large-scale, since companies will not get through with harvesting reed in such a small period of time. This is also of great importance for Swedish farmers, who are dependent on harvesting as an income. It they were to rely on reed harvesting for productional purposes, they would have to be able to cut reed every season to be able to make a profit the whole year. This undoubtedly leaves Swedish farmers and companies in a challenging position since reeds harvested from different seasons give rise to different characteristics, possibly optimized for entirely different usages. Results indicates that removing reed could negatively affect the presence of species that have reedbeds as their habitat and reduce the biodiversity in those areas. However, in eutrophicated waters, reeds also tend to become invasive and change the riparian corridor, soil chemistry and reducing flows (Galatowitsch et al., 2016). It could also reduce biodiversity and increase the risk of fire hazards (Barbiero et al., 2017). Therefore, to mitigate ecological impact whilst harvesting reed in the Baltic sea, a balance has to be achieved regarding the quantity of harvesting. The optimal amount of harvested reed should in theory be equal to the excess amount of reed that had been growing as a result of the eutrophication, since it leaves the remaining part of the reed that naturally has appeared in the ecosystem. Results indicate that large-scale harvesting might impact the flora and fauna. However, comparing the ecological impact from the harvesting to the current damages from the eutrophication in the Baltic sea, there is a matter of prioritisation to achieve the optimal health of the ecosystems in the Baltic. Therefore, the disturbance of ecosystems from large-scale reed removal is according to our interpretation, not as prioritised. Results suggest that expensive biochar production and harvest methods seem to be the biggest obstacles for a greater demand. This is partly because of the low price of conventional coal and that the usage of biochar in the market is driven by individuals of public actors (Söderqvist & Norberg, 2021). However, the demand for biochar is increasing, where the majority of the usage in Sweden is mainly in Stockholm. Approximately 1200 tons of biochar was consumed in Sweden in 2018 (Söderqvist & Norberg, 2021). There is thus a great possibility that reed biochar would evolve to be more popular and thereby, more affordable to produce. An example that could be improved for lowering the production costs are the recycling of excess heat in the pyrolysis process. This will also lower the impact on the climate which in of itself could be associated with both ecological and economic benefits.

3.2 Research validity & evaluation This Bachelor thesis has used a systematic literature review, mainly based on articles that had impact factors higher than 1.5 and scientific quartiles Q1 and Q2. However, we do have sources that do not have these scientific value measures, such as the report written by Söderqvist et. al. on European Union's behalf on the Greater Bio project where they evaluate

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the market for biochar in the Öresundregion and future potential. Another source that also does not have the value measures is Isaksson, K that wrote a report about reed harvest for the production of biogas. This source evaluated different harvest methods which were used in this report. In the introduction, the World Meteorological Organization (WMO) provisional report was used to give the reader a context to the ongoing climate change, and to motivate the importance of climate-neutral substitutes. In terms of validity, this thesis has been studying the intended subject. The purpose was to assess the potential of using reed to produce biochar and analyse its carbon negative effects and potential of eutrophication mitigation. We acknowledge that, in a credible study, it is important to question, control and theoretically interpret the results of the study throughout the research process. This thesis has put together research and information that can be used to shed light on the knowledge gaps that exist around reed biochar today. Generally, it has been difficult to evaluate some of the results and set them against each other since some studies were conducted in different ways. For evaluating the validity of harvesting results; there have been differences regarding chosen harvesting method, drying method, units of measure and geographical differences which changes climate and time of season. Results regarding reeds impact on the ecosystem are unclear in terms of which method and what amount of reed that can be removed without affecting biodiversity and microbial life. Furthermore, the cost analysis of reed biochar was made in China and might not fully reflect the production price of reed biochar in Sweden. The price range of biochar imported from the Baltics, Germany and Finland is presented but it is the price of biochar generally, and not the price of biochar specifically made out of reed. There is also a need for clarifying a clearer spectrum of how pyrolysis temperatures highlight different biochar characteristics. This is because the attributes affect each other and therefore show unclear patterns in certain temperatures. Additionally, certain biochar characteristics that thrive in opposite temperature measures are beneficial for the same application, which further complicates biochar optimisation. An example of this is how biochar attributes like porosity and cation exchange capacity grow from high and low pyrolysis temperatures respectively, although both of these attributes could be important for soil improvement. These sources of errors are important for determining whether the chosen objectives have been answered. There is an overall satisfaction of the results of the bachelors’ thesis, however there are some parts of the objectives that has not been fulfilled. Biochar attributes have separately been connected to certain applications. However, it is difficult to determine which complete biochar characteristics that are best for each area of use. Despite differences in methodology, this thesis has discovered patterns of the elemental composition of reed based on season and harvesting methods, with the exception of differences in location. The ecological impact of reed harvesting has been evaluated, although the optimal method and reed removal threshold for securing Swedish biodiversity has not been determined. Finally, biochar’s potential on the market has been evaluated and there are tendencies of increased demand for the product.

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If the thesis were to be repeated, more interviewees would have been implemented for broadening the perspectives on the reed produced from biochar and adding more depth to the research. Farmers who harvest reed, municipalities and reed wetland conservation associations are examples of important actors that could have been interviewed. Additionally, a life cycle assessment could also be implemented for further researching the overall environmental impact of the reed biochar production process. A cost analysis of a large-scale reed harvesting would also clarify the need for remodeling the reed management sector to be more production-adapted. Another addition that would have enriched this thesis is the inclusion of keywords searches in other languages in countries around the Baltic sea. This would have taken a lot of time, but it would have potentially brought more research data about reed in areas with similar climate as Sweden, and in best cases data from the Baltic sea. It would thereby prevent sources of errors from geographical differences. Disregarding limitations such as time and funding, there would be interesting to investigate the nutrient removal potential during the four seasons in a field study where reed samples from different parts of the Baltic sea could be analysed in a laboratory to achieve clear results of how the elemental compositions of reed differs in different seasons. This would be particularly useful since there currently is a lack of results with the same measures of units present in the thesis. It would also be interesting to further analyse the elemental composition of biochar made out of reed, to get a more profound understanding on how different pyrolysis circumstances change the relations of the properties of biochar. Other critique that could be connected to this thesis is that it is quite long and condensed with literary research. Implementing other sources of information like interviews, field studies or life cycle assessment would not only make the thesis more multilayered but also further validate the content and make the research more interesting which compensates for the length of the thesis.

3.3 Further research Further research has to be done for investigating reed biochar application optimization and the complex relation between biochar attributes needs to be clarified. Suggestively, experimentation with different pyrolysis parameters when producing reed biochar and investigating the impact of the biochar in different applications would add a lot to the subject. Another interesting subject is to further research the properties of Phragmites australis from the Baltic sea in different seasons. Additionally, reed harvesting methods needs to be looked into, in ecological and economical aspects. Different ways to make the complete reed biochar production cycle more affordable, as well as methods of increasing the demand of reed biochar are key points for expanding this reed biochar production to a large-scale industry.

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4.Conclusion This bachelors’ thesis has conducted an assessment of the potential of using reed biomass to produce biochar to analyse the carbon negative effects and the potential to mitigate eutrophication.

Biochar as soil improvement is when using biochar in agriculture, biochar enhances the soil in terms of nutrient and water retention, amplify the humus content, protection against contaminations and improved microbial life. Important Indicators of a high-quality biochar for soil improvement are cation exchange capacity, Dissolved Organic Content (DOC), surface area and porosity. Furthermore, indicators for high-quality biochar in animal fodder is porosity and surface area. To use the biochar as a carbon sequestration source important indicators is primarily aromaticity for stability and longevity. Harvesting reed for optimal results indicate summer harvest to be more nutrient rich and less impactful on the nitrification and denitrification processes. There is also more oxygen, nitrogen and ash content in the biochar made from reed harvested in summertime. Reed harvested during winter are more carbon rich. Moreover, the harvest could be done with a tractor since the waters are frozen. Biochar produced with reed harvested in wintertime contains more aromaticity, carbon content and have a higher water retention and polarity. Reedbeds are important for many species, the available amount of the reed patches is important for the presence of species like marshland birds, moths, fish, vertebrates and invertebrates. However, if the reed is growing too dense and becomes invasive there is a risk of losing biodiversity causing changes in the riparian corridor, changes in the nutrient cycle and increased fire hazards. The production price is yet high regarding biochar made from reed considering harvesting, especially in large-scale productions, while pyrolysis temperature is expensive in smaller scale productions. To redirect reed harvesting towards production purposes, the demand of reed products must be raised to match the production cost. There is therefore a need for further research in areas such as reed harvesting, reeds impact on ecosystems, reed biochar properties and demand on the market.

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5. Appendix

Appendix 1: (Carson et al., 2018).

Appendix 2: (Carson et al., 2018).

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Appendix 3: (W. Wang, 2021))

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