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Anaerobic digestion (AD) can be used as a stand-alone process or integrated as part of a larger biorefining process to produce biofuels, biochemicals and fertiliser, and has the potential to play a central role in the emerging circular bioeconomy (CBE). Agricultural residues, such as animal slurry, straw, and grass silage, represent an important resource and have a huge potential to boost biogas and methane yields. Under the CBE concept, there is a need to assess the long-term impact and investigate the potential accumulation of specific unwanted substances. Thus, a comprehensive literature review to summarise the benefits and environmental impacts of using agricultural residues for AD is needed. This review analyses the benefits and potential adverse effects related to developing biogas-centred CBE. The identified potential risks/challenges for developing biogas CBE include GHG emission, nutrient management, pollutants, etc. In general, the environmental risks are highly dependent on the input feedstocks and resulting digestate. Integrated treatment processes should be developed as these could both minimise risks and improve the economic perspective.

Microalgae can produce biofuels, nutriceuticals, pigments and many other products, but commercialization has been limited by the cost of growing, harvesting and processing algal biomass. Nutrients, chiefly nitrogen and phosphorus, are a key cost for growing microalgae, but these nutrients are present in abundance in municipal wastewater where they pose environmental problems if not removed. This is not a traditional review article; rather, it is a fact-based set of suggestions that will have to be investigated by scientists and engineers. It is suggested that if microalgae were grown as biofilms rather than as planktonic cells, and if internal illumination rather than external illumination were employed, then the use of microalgae may provide useful improvements to the wastewater treatment process. The use of microalgae to remove nutrients from wastewater has been demonstrated, but has not yet been widely implemented due to cost, and because microalgae derived from wastewater treatment has not yet been demonstrated as a commercial source for value-added products. Future facilities are likely to be called Municipal Resource Recovery Facilities as wastewater will increasingly be viewed as a resource for water, biofuels, fertilizer, monitoring public health and value-added products. Advances in photonics will accelerate this transition.

This study uses a new approach for the recycling of plant nutrients by co-digesting sewage sludgewith fly ash from a wood combustion. Sewage sludge and fly ash both are enriched with nutrientsof the wastewater resp. wood, which makes these products an enhanced source for recycledfertilizers. The effects of the ash addition to the anaerobic digestion are studied in several labscale experiments including effects on the gas production and microbial activity. Following that,the fertilizing qualities of the digestate are evaluated by plant growth experiments. The resultsshow that the fertilizing qualities of the digested sludge were improved by the ash addition.Next to this, gas production results show that the methane production was not affected by theash addition, while the total gas release was reduced. The sulphur addition by the ashstimulated sulphate reducing bacteria. The sulphate reducing bacteria did not markedly inhibitthe methanogens. Validerad;2022;Nivå 2;2022-05-06 (hanlid)

26 páginas, 5 tablas, 3 figuras. -- This is a post-peer-review, pre-copyedit version of an article published in Waste and Biomass Valorization. The final authenticated version is available online at: http://dx.doi.org/10.1007/s12649-020-01137-8, One strategy to re-use solid urban wastes is the production of energy by anaerobic digestion. This process also generates high volume of digestates, which are frequently disposal in landfills. The aim of this work is to assess anaerobic digestates as agricultural inputs. Three different biomethanation wastes from different plants were collected. Firstly, a complete physico-chemical characterization of the wastes was done according to the Spanish regulation, showing that the materials had the 90% of the particles below 25 mm, high values of pH, electric conductivity, organic matter, humic acids and soluble nutrients such as NO3−, SO42−, Ca2+, Mg2+, PO43− and K+. Total concentrations of heavy metals and microbiological parameters were below the threshold levels allowed for agricultural use. The wastes were then treated with a strong acid and a strong base having two different solutions (ATr and BTr, respectively) which were evaluated as biostimulants for tomato plants in hydroponic culture. Those liquid extracts, ATr and BTr, demonstrated their biostimulant ability towards root system of tomato enhancing the hair root density and plant biometric parameters including plants weight and chlorophyll content. This work demonstrates the re-use feasibility of treated digestates in agriculture as fertilizers and more over as feedstock for biostimulants production., The city Hall of Madrid funded this work.

There is a recognized need for mineralizing aquaculture-derived sludge in aquaponics systems in order to reduce waste production. Many recent studies of aquacultural waste treatment have focused only the production of biogas as opposed to the potential for mineralization of nutrient-rich sludge. Upflow anaerobic sludge blanket (UASB) reactors provide one possible solution for breaking down sludge into bioavailable nutrients that can subsequently be delivered to plants. As such, this study examines the mineralization performance of sequential UASB reactors that are designed with an expanded granular sludge bed (EGSB) and compared to standard aerobic and anaerobic batch reactors. Results of our experiments demonstrate that only chemical oxygen demand reduction is significantly different. An unexpected drop in pH of one of the three reactor systems revealed that a pH below 6 was able to significantly increase the mineralization and mobilization of nutrients. Approximately 25% of phosphorus, potassium, and calcium could also be recovered from the sludge under lower pH conditions, as compared to the mineralization performance of standard UASB reactors running at a higher pH. However, the opposite effect was observed with respect to organic sludge reduction, where diminished performance was observed in the low-pH reactor. The current study implies that anaerobic reactors operating at low pH can potentially contribute towards improved nutrient recovery in multi-loop aquaponics systems and reduction of additive agents for pH control of the hydroponic subsystem.

Most of the world’s inhabitants still do not have access to sanitation facilities, particularly in remote or poor regions. Consequently, efficient solutions for decentralized wastewater treatment are urgently needed. This study investigates the technical feasibility of the coupling of an anaerobic membrane bioreactor (AnMBR) process with microalgae cultivation for decentralized domestic wastewater treatment. The results presented in this work are based on the 327-days operation of an 850-L AnMBR pilot-plant installed in a residential building in Hamburg, Germany, as well as on lab-scale and full-scale experiments conducted with the effluent of the AnMBR process (permeate) and with three microalgae species (Acutodesmus obliquus, Chlorella vulgaris and Chlorella sorokiniana). Over the eight main experimental phases of the AnMBR operation, chemical oxygen demand (COD) concentration in wastewater amounted to between 0.97 and 2.49 g∙L-1. Since between 86 % and 94 % of the COD was removed during the process, this showed a higher performance than other small decentralized wastewater treatment plants (WWTPs) and even competed with conventional German WWTPs. However, the organic loading rate, methane production and the hydraulic retention time were in the lower range of reported AnMBR-related values. This was due to a lower microorganism concentration in the reactor. Overall, 95 - 99 % of total nitrogen (TN) and 79 - 87 % of total phosphorus (TP) present in the wastewater were recovered in the permeate. During the lab-scale and full-scale experiments, the three microalgae species were able to assimilate the nutrients contained in the permeate and grow in this culture medium. Altogether, a similar performance to synthetic fertilizers was achieved. During the lab-scale experiments with Acutodesmus obliquus and Chlorella vulgaris, initial TN and TP concentrations were 64 - 115 mg∙L-1 and 7.1 - 14 mg∙L-1 respectively. During these experiments, a decrease of TN removal and biomass growth was punctually observed. This was due to a lack of iron in the permeate and could be easily counterbalanced by the supply of an iron salt and a chelating agent into the culture. Initial TN and TP concentrations were comparatively higher during the experiments conducted with Chlorella sorokiniana and ranged from 98 to 160 mg∙L-1 and 16 to 37 mg∙L-1 respectively. The reduced TN/TP ratio in the permeate led to an incomplete TP removal. For unfavorable TN/TP ratios, a solution leading to a complete TP removal must be implemented, such as the use of another microalgae species capable of adapting to low TN/TP ratios, pH increase or the use of iron or aluminum salts leading to TP precipitation. During the two full-scale experiments conducted with two flat panel photobioreactors in the fall and summer, ammonium and TP were completely removed. However, TN was totally assimilated only during the summer. The incomplete TN removal during the fall season was caused by the supply of flue gas containing NOx combined with a low irradiance making the assimilation of NOx by the microalgae impossible. Nutrient uptake was usually higher than and biomass production similar to the values for similar light conditions reported in the literature. Overall, the results related to nutrient removal during microalgae cultivation indicate that this new process can compete with conventional WWTPs. In this study, the technical feasibility of the combination of an AnMBR process and microalgae cultivation was proved. If the different processes, especially the cultivation and harvesting of microalgal biomass, are energetically optimized, this new technology will be an adequate solution to the need for efficient decentralized wastewater treatment technologies., Ein Großteil der Weltbevölkerung hat keinen Zugang zu sanitären Einrichtungen, insbesondere in abgelegenen oder armen Regionen. Daher sind effiziente Lösungen für dezentrale Abwasserbehandlung dringend erforderlich. Diese Studie untersucht die Machbarkeit der Kopplung eines anaeroben Membranbioreaktors (AnMBR) mit Mikroalgenkultivierung zur dezentralen häuslichen Abwasserbehandlung. Die vorgestellten Ergebnisse basieren auf einem 327-Tage langen Betrieb einer 850-L AnMBR Pilotanlage in einem Hamburger Wohnhaus, sowie auf Labor- und Full-Scale-Versuchen mit dem Ablauf des AnMBR Prozesses (Permeat) und drei Mikroalgenarten (Acutodesmus obliquus, Chlorella vulgaris und Chlorella sorokiniana). Während der acht Hauptversuchsphasen des AnMBR-Betriebs betrug der chemische Sauerstoffbedarf (COD) im Abwasser zwischen 0,97 und 2,49 g∙L-1. Mit einer Entfernung des COD zwischen 86 % und 94 % zeigte der Prozess eine höhere Leistung als dezentrale Kleinkläranlagen und kann diesbezüglich auch mit konventionellen deutschen Kläranlagen konkurrieren. Die Leistung bezüglich Raumbelastung, Methanproduktion und hydraulischer Verweilzeit war jedoch im unteren Bereich der Literaturwerte. Dies ist auf eine geringere Konzentration von Mikroorganismen im Reaktor zurückzuführen. Insgesamt wurden 95 - 99 % des gesamten Stickstoffs (TN) und 79 - 87 % des gesamten Phosphors (TP) im Permeat zurückgewonnen. Während der Labor- und Full-Scale-Versuche konnten die drei Mikroalgenarten die Nährstoffe erfolgreich aufnehmen und wachsen. Insgesamt wurde eine ähnliche Leistung wie bei synthetischen Düngemitteln erzielt. Während der Laborversuche mit Acutodesmus obliquus und Chlorella vulgaris lagen die TN- und TP-Konzentrationen zunächst bei 64 - 115 mg∙L-1 bzw. 7.1 - 14 mg∙L-1. Während dieser Experimente wurde zum Teil eine Senkung der TN-Entfernung und des Biomassewachstums durch Eisenmangel im Permeat beobachtet, was durch die Zufuhr eines Eisensalzes und eines Chelatbildners problemlos ausgeglichen werden konnte. Die anfänglichen TN- und TP-Konzentrationen während der Laborversuche mit Chlorella sorokiniana waren im Vergleich höher und betrugen 98 - 160 bzw. 16 - 37 mg∙L-1. Das reduzierte TN/TP-Verhältnis führte zu einer unvollständigen TP-Entfernung. Für ungünstige TN/TP-Verhältnisse sind daher entsprechende Konzepte nötig, wie z.B. die Verwendung einer anderen Mikroalgenart, die sich an niedrige TN/TP Verhältnisse anpassen kann, eine pH-Erhöhung oder die Verwendung von Eisen- oder Aluminiumsalzen um TP-Ausfällungen herbeizuführen. Bei zwei Full-Scale-Versuchen im Herbst und im Sommer mit zwei Flach-Photobioreaktoren wurden Ammonium und TP vollständig entfernt. Allerdings wurde TN nur während des Sommers vollständig aufgenommen. Eine unvollständige TN-Entfernung im Herbst wurde durch die Zufuhr von NOx-haltigem Rauchgas in Verbindung mit schlechten Lichtverhältnissen verursacht. Im Vergleich zu Literaturwerten für ähnliche Lichtverhältnisse war die Nährstoffaufnahme höher und die Biomasseproduktion ähnlich. Bezüglich der Nährstoffentfernung konnte der Prozess mit konventionellen Kläranlagen konkurrieren. In dieser Studie wurde die technische Machbarkeit der Kombination eines AnMBR-Verfahrens mit Mikroalgenkultivierung nachgewiesen. Wenn die verschiedenen Prozesse, insbesondere die Kultivierung und Ernte von Mikroalgenbiomasse, energetisch optimiert werden, wird diese neue Technologie eine adäquate Lösung für den Bedarf an effizienten dezentralen Abwasserbehandlungstechnologien werden.

Processing of organic residues may affect plant-availability of phosphorus (P) and thus the potential to recycle the nutrient, i.e., recyclability, but empirical evidence in the field is lacking. In field experiments in clay and silt loam soils with low available P, impact on P recyclability by cattle manure and sewage sludge processing methods (composting, anaerobic digestion, lime-stabilization, acid-oxidizer) and three application rates were assessed. Synthetic nitrogen (N) and potassium (K) fertilizers were supplied in surplus and NPK served as a reference. The differences in plant response were small at relevant application rates and not consistently explained by solubility of fertilizer P. Least P was required in composted manure for the same P uptake in silt loam, and composting was beneficial to plant response in clay as well. Lime-stabilization of sewage sludge had an adverse effect on P uptake in silt loam. Increasing application rates of sewage sludge hardly enhanced but did not lower P uptake or yield even at an excessive rate. Soil water-extractable P in the autumn liable to leaching was increased by NPK only. In clay soil, sewage sludges performed better than manures obviously due to anaerobic conditions caused by high precipitation, but in silt loam the contrary was the case. In conclusion, the availability of P in processed residues is more susceptible to weather and soil variables than in synthetic fertilizer. P fertilization benefits in cereal cropping in current north European conditions appear to be generally small.

To provide sufficient quantities of food and feed, farming systems have to overcome limiting factors such as the nutrient depletion of arable soils. Nitrogen being the main mineral element required for plant growth, has led to the extensive use of chemical fertilizers causing nitrogen pollution of the ecosystems. This field study investigates the use of biogas residues (BRs) as biofertilizers and their contribution to the mitigation of nitrate leaching in agricultural soils, while also demonstrating the polluting nature of chemical fertilizers. Nine different fertilization treatments classified in three schemes and two nitrogen doses were tested for three consecutive years on a grassland in the Walloon Region of Belgium. Residual soil mineral nitrogen, percentage contribution of treatments in residual nitrate and agronomic performance were assessed for each fertilization treatment. The results obtained showed significant differences on treatment and scheme level regarding nitrate accumulation in the soil, with chemical fertilizers posing the highest nitrate leaching risk. BRs did not cause nitrate accumulation in the soil, and were N rate and rainfall independent, while the chemical treatments indicated a cumulative tendency under high N rate and low precipitation. Forage yield did not demonstrate statistical differences on treatment and scheme level but varied with changing precipitation, while the maximum application rate suggested a plateau. Aboveground nitrogen content was significantly higher after the application of chemical fertilizers only in the first year, while all the chemical treatments indicated a dilution effect under elevated annual rainfall. Finally, the partial substitution of chemical fertilizers by raw digestate reduced the concentration of NO 3 − in the soil without having a negative impact on the yield and N content of the biomass. These results strongly advocate for the environmental benefits of BRs over chemical fertilizers and underline their suitability as biofertilizers and substitutes for chemical fertilizers in similar agricultural systems., SCOPUS: ar.j, info:eu-repo/semantics/published

Hydrothermal Liquefaction (HTL) for algal biomass conversion is a promising technology capable of producing high yields of biocrude as well as partitioning even higher quantity of nutrients in the aqueous phase. To assess the feasibility of utilizing the aqueous phase, HTL of Nannochloropsis sp. was carried out in the temperature range of 275 to 350 °C and Residence Times (RT) ranging between 5 and 60 min The effect of reaction conditions on the NO 3 − , PO 4 3 − , SO 4 2 − , Cl − , Na + , and K + ions as well as Chemical Oxygen Demand (COD) and pH was investigated with view of recycling the aqueous phase for either cultivation or energy generation via Anaerobic Digestion (AD), quantified via Lifecycle Assessment (LCA). It addition to substantial nutrient partitioning at short RT, an increase in alkalinity to almost pH 10 and decrease in COD at longer RT was observed. The LCA investigation found reaction conditions of 275 °C/30 min and 350 °C/10 min to be most suitable for nutrient and energy recovery but both processing routes offer environmental benefit at all reaction conditions, however recycling for cultivation has marginally better environmental credentials compared to AD.

In horse keeping horse manure is produced, which can be utilized as a fertilizer or considered a waste. Horse manure constitutes a resource in terms of both plant nutrients and energy. In addition energy policies and objectives aim at replacing fossil fuels with renewable energy sources. The interest to improve resource recovery of horse manure increases due various incentives for renewable vehicle fuels, legal requirements on management of manure, and environmental impact from current horse manure management. This thesis aims at describing horse manure management in a life cycle perspective. This is made by (1) identifying factors in horse keeping affect­ing the possibility to use horse manure as a biogas feedstock and to recycle plant nutrients, (2) analysing factors in anaerobic digestion with influence on methane potential and biofertilizer nutrient content and (3) comparing the environmental impact from different horse manure treatment methods. Literature reviews, systematic combining, and simulations have been used as research methods. The results show that horse keeping activities such as feeding, indoor keeping, outdoor keeping and manure storage affect the amount and charac­teristics of horse manure and thereby also the possibilities for anaerobic digestion horse manure. Transport affects the collected amount and spread­ing affects loss of nutrients and nutrient recycling. Simulation results in­dicate the highest methane yield and energy balance from paper bedding, while straw and peat gave a higher nutrient content of the biofertilizer. The highest methane yield was achieved with a low rate of bedding, which in the cases of woodchips and paper is also preferable for plant nutrient recycling. Still, results indicate the best energy balance from anaerobic digestion with a high ratio of bedding. The environmental impact assessment indicates a reduction in global warming potential for anaerobic digestion compared to incineration or composting. Vid hästhållning alstras hästgödsel som kan användas som växtnäring eller anses vara ett avfall. Hästgödsel utgör både en växtnäringsresurs och en energi resurs. Dessutom styr uppsatta energimål mot att förnybar energi ska ersätta fossila bränslen. Intresset för att öka resursutnyttjandet av hästgödsel ökar på grund av olika incitament för förnybara drivmedel, lagstiftning om gödselhantering och miljöpåverkan från dagens hantering av hästgödsel. I den här avhandlingen beskrivs hästgödselhantering i ett livscykel­perspektiv genom att (1) identifiera olika faktorer vid hästhållningen som påverkar möjligheten att utvinna biogas ur hästgödsel och återföra näringen till jordbruksmark, (2) analysera faktorer i biogasprocessen som påverkar den specifika metanmängden och innehållet av växtnäring i gödseln och (3) jämföra olika gödselhanteringsmetoders miljöpåverkan. Metoderna i avhan­dlingen har varit litteraturstudier, systematisk kombination av teori och em­piri samt simulering. Resultaten visar att utfodringen, om och hur hästarna hålls inomhus och utomhus och hur hästgödsel lagras påverkar mängden hästgödsel och dess egenskaper, och därmed också hur den fungerar som ett biogassubstrat. Trans­porterna har betydelse för hur mycket gödsel som kan samlas in och spridas, medan gödselspridningen påverkar näringsförluster och närings återföring. Resultaten från simuleringarna indikerar högst metanutbyte och bäst energi­balans från papper som strömaterial, medan halm och torv gav högre växt­näringsinnehåll i biogödseln. De högsta resultaten på specifik metanmängd nåddes med låg andel strö, vilket också var positivt för växtnäringsinnehållet vid scenarierna med spån och papper. Samtidigt indikerar resultaten att en hög andel strömaterial ger den bästa energibalansen. Miljöpåverkansbedöm­ningen indikerar att potentialen för klimatpåverkan minskar om hästgödsel behandlas i en biogasprocess jämfört med förbränning eller kompostering.

A transition to renewable energy sources and a circular economy has increased interest in renewable resources not usually considered as energy sources or plant nutrient resources. Horse manure exemplifies this, as it is sometimes recycled but not often used for energy purposes. The purpose of this study was to explore horse manure management in a Swedish municipality and prospects for energy recovery. The case study includes a survey of horse manure practices, environmental assessment of horse manure treatment in a biogas plant, including associated transport, compared to on-site unmanaged composting, and finally a simplified economic analysis. It was found that horse manure management was characterized by indoor collection of manure most of the year and storage on concrete slabs or in containers, followed by direct application on arable land. Softwood was predominantly used as bedding, and bedding accounted for a relatively small proportion (13%) of the total mix. Anaerobic digestion was indicated to reduce potential environmental impact in comparison to unmanaged composting, mainly due to biogas substituting use of fossil fuels. The relative environmental impact from transport of manure from horse facilities to anaerobic digestion plant was small. Results also indicate a relatively high cost for horse keepers to change from composting on site to anaerobic digestion in a centralized plant.

Avloppsvatten innehåller näring, bland annat kväve och fosfor som kan orsaka övergödningom det kommer ut i sjöar och vattendrag. Samtidigt behöver stora mängder näringsämnen tillföras i jordbruket för att producera mat. Ett sätt att effektivt ta till vara på näringen i avlopp och återföra den till jordbruket skulle kunna vara källsortering av avlopp. På så sätt samlas näringsämnena i en mindre volym och blandas inte med bad-, disk-, och tvättvatten. Examensarbetet syftade till att undersöka rötning som behandlingsmetod och teknik för att utnyttja energin i latrin. I rötning bryter mikroorganismer ner organiskt material anaerobt och producerar energirik biogas som kan användas till värme, el eller fordonsbränsle. Rötresten som blir kvar efter rötningen innehåller näringsämnen men också föroreningar. I studien undersöktes latrinens innehåll av tungmetaller och läkemedelsrester och hur läkemedelshalten påverkades under rötningsprocessen. För att utvärdera rötning som behandlingsmetod av latrin gjordes 44 satsvisa utrötningsför-sök i laboratorium. Latrinen hämtades från en latrininsamling i Norrtälje. Ymp från två aktiva rötningsanläggningar blandades med latrinen i gastäta glasflaskor vilka sattes på skakbord i ca 60 dagar. En del flaskor innehöll en tillsats av läkemedel lösta i metanol. Två parallella försök utfördes i olika temperaturer, i mesofil temperatur (37ºC) och i termofil temperatur (52ºC). Gasproduktion och gasens metanhalt mättes under försöksperioden för att beräkna latrinens biogaspotential. Efter avslutad rötningsperiod separerades vätskan och det fasta materialet i rötresten och frystes in i väntan på analys av läkemedelsrester. Biogasproduktionen var drygt 250 Nml CH4/g VS (ml metan per gram organiskt material vid tryck 1 atm och 0ºC) efter 60 dagar, vilket antas vara biogaspotentialen hos latrin. Det är i samma nivå som biogaspotentialen från hönsgödsel och svinkletgödsel. Gasproduktionen i flaskorna med tillsats av läkemedel var något högre och någon inhibering av processen kunde alltså ej påvisas. Kvävehalten i latrinen var 3,7 g/l, fosforhalten 1,0 g/l, kaliumhalten 1,0 g/l. Latrinens tungmetallhalter var under Naturvårdsverkets föreslagna gränsvärden för avloppsfraktioner som tillförs åkermark och skulle därför kunna användas som gödsel med dagens regelverk. Kadmiumfosforkvoten var 25 mg Cd/kg P vilket är lika mycket som medelvärde av Revaq-certifierat avloppsslam. Flera saker tyder på att latrinen som användes innehöll mer fekalier än urin i förhållande till vad som borde produceras och därmed inte fullt ut representerar ett komplett toalettavfall. Analyser gjordes av läkemedelskoncentrationer i vätskefasen av rötningsmaterialet före och efter olika långa perioder av rötning. Rötning visade sig inte vara någon effektiv metod för att rena latrin från läkemedel. Det var i fler fall som koncentrationen av läkemedel ökade än minskade under rötning. Ökningen kan bland annat ha att göra med att adsorptionsegen-skaper hos materialet förändras under rötningen och därmed frigörs substanserna och syns bättre i analysen av vätskefasen. Förekomsten av läkemedel i miljön är relativt väl undersöktmen däremot behövs mer förståelse för riskerna med läkemedel i vattenmiljö men framför-allt i jordbruksmiljö där kunskapsluckorna är stora Wastewater contains nutrients such as nitrogen and phosphorous which can cause eutrophi-cation in lakes and streams. Meanwhile, large quantities of nutrients are used in agriculture in order to produce food. One way to utilize nutrients in wastewater and return them to agriculture could be source separation of sewage. This way, nutrients are collected in smallvolumes and are not mixed with bathing, washing, and cleaning water. This thesis aimed at investigating anaerobic digestion as a treatment method and technology to make use of the energy in latrine. In anaerobic digestion, microorganisms degrade organic material and produce energy rich biogas that can be used for heating, electricity, or vehicle fuel. The residue remaining after digestion contains nutrients but also pollutants. The study examined the content of heavy metals and drug residues in latrine, and to what extent the digestion process affected the pharmaceutical content. To evaluate the anaerobic digestion as treatment of latrines, 44 batch experiments wereperformed at laboratory scale. Latrine was taken from a collection basin in Norrtälje. Inoculum from two active anaerobic digestion plants were mixed with latrine in sealed glass bottles and put on shaking tables for approximately 60 days. Some bottles contained an addition of eight drugs dissolved in methanol. Two parallel experiments were performed one at mesophilic temperature (37ºC) and one at thermophilic temperature (52ºC). The volume of gas produced and methane content was measured for calculation of the biogas potential. After completion of the digestion period, the liquid and solids were separated and frozen pending analysis of drug residues. The biogas produced was a little over 250 Nml CH4/gVS after 60 days being comparable to production from pig and chicken manure. The bottles containing added substances showed no inhibition of the biogas process since the gas production was slightly greater in these. The nitrogen content of latrine was 3.7 g/L, the phosphorus content 1.0 g/L and potassium content of 1.0 g/L. The cadmium-phosphorus ratio was 25 mg Cd/kg P, same as the average of Revaq certified sewage sludge. The heavy metal concentrations were below the limits allowed for sewage fractions applied on arable land as proposed by the Swedish Environ-mental Protection Agency. The latrine could be used as fertilizer with current and proposed regulations. Several things indicate that the latrine used contained a higher feces-urine ratio than expected and therefore does not fully represent a complete blackwater. Analyses on drug concentrations were preformed on the liquid phase of the material before and after various periods of anaerobic digestion. Anaerobic digestion proved not to be an effective method to reduce pharmaceuticals in latrine. There were more cases where the concentration of the drug increased rather than decreased during digestion. The increase could be due to changes in adsorption properties of the material during digestion, making them more observable in the analysis. The presence of pharmaceuticals in the environment is relatively well known but more understanding is needed on the hazards of pharmaceutical residues in aquatic and especially agricultural environment.

The increasing awareness of natural resource depletion, the increasing demand of nutrients and energy for food production, and the more and more stringent nutrient discharge and fertilization levels, have resulted in an increased attention for nutrient recovery from municipal and agricultural wastes. This PhD dissertation aims at stimulating the transition to a bio-based economy by providing (tools to develop) sustainable strategies for nutrient recovery from organic wastes following bio-energy production through anaerobic digestion (= bio-digestion waste). Particular attention is paid to the valorization of the recovered products as renewable substitutes for chemical fertilizers and/or as sustainable organo-mineral fertilizers in agriculture. Three complementary research phases were conducted: 1) technology inventory and product classification, 2) product value evaluation, 3) process modelling and optimization. In the first phase, a systematic technology review and product classification was performed. In phase 2, product characterizations and mass balance analyses at full-scale waste(water) resource recovery facilities (WRRFs) were executed. An economic and ecological evaluation of different bio-based fertilization scenarios was conducted and the most sustainable scenarios were selected for subsequent agronomic evaluation at field and greenhouse scale. In phase 3, a generic nutrient recovery model library was developed aiming at fertilizer quantity and quality as model outputs. Increased insights in unit process performance and interactions were obtained through global sensitivity analyses. The models were successfully used as a tool for treatment train configuration and optimization. Based on all acquired knowledge, a generic roadmap for setting up nutrient recovery strategies as function of fertilizer markets, legislations, and waste characterization was established. As such, the present dissertation further develops the concepts of maximally closing nutrient cycles in a cradle-to-cradle approach. The work reveals important evidence of the positive impact of recovered products on the economy, agronomy, and ecology of intensive plant production. Moreover, it provides the fundamental information and tools to facilitate the implementation and optimization of sustainable nutrient recovery strategies. All of this may open up new opportunities for sustainable and more bio-based economic growth and thus create a win-win situation for the environment, the society, and the economy in Belgium, Canada, and beyond.

In the transition from a fossil to a bio-based economy, it has become an important challenge to maximally recuperate valuable nutrients coming from waste streams. Nutrient resources are rapidly depleting, significant amounts of fossil energy are used for the production of chemical fertilizers, whereas costs for energy and fertilizers are increasing. In the meantime, biogas production through anaerobic digestion produces nutrient-rich digestates. In high-nutrient regions, these products cannot or only sparingly be returned to agricultural land in its crude unprocessed form. The consequent processing of this digestate requires a variety of technologies producing a lot of different derivatives, which could potentially be re-used as green fertilizers in agriculture. As such, a sustainable alternative for fossil-based mineral fertilizers could be provided. The aim of this study is to characterize the physicochemical properties of digestates and derivatives, in order to identify the fertilizer value and potential bottlenecks for agricultural re-use of these products, in line with European legislative constraints. In addition, the economic and ecological benefits of substituting conventional fertilizers by digestates and derivatives are quantified and evaluated. Waste water from acidic air scrubbers for ammonia removal shows potential as N-S-fertilizer, whereas concentrates resulting from membrane filtrated liquid fraction of digestate show promise as N-K-fertilizer. Substituting artificial fertilizers by air scrubber water or membrane filtration concentrates theoretically always results in significant economic and ecological benefits for the agriculturist. Field research is now on-going in order to evaluate the impact on soil and crop production by application of these new green fertilizers.

In nitrate vulnerable zones application of animal manure to land is limited. Digestate from anaerobic digestion plants competes with manure for nutrient disposal on arable land, which forms a serious hinder for the biogas sector to develop in these regions. Hence, one of its biggest challenges is to find cost-effective and sustainable ways for digestate processing or disposal. Furthermore, primary phosphorus resources are becoming scarce and expensive and will be depleted within a certain time. This urges the need to recycle P from secondary sources, like digestate or manure. From a sustainability point of view, it seems therefore no more than logical that digestate processing techniques switched their focus to nutrient recovery rather than nutrient removal. This paper gives an overview of digestate processing techniques, with a special focus on nutrient recovery techniques. In this paper nutrient recovery techniques are delineated as techniques that (1) create an end-product with higher nutrient concentrations than the raw digestate or (2) separate the envisaged nutrients from organic compounds that are undesirable in the end-product, with the aim to produce an end-product that is fit for use in chemical or fertiliser industry or as a mineral fertiliser replacement. Various nutrient recovery techniques are described, with attention for some technical bottlenecks and the current state of development. Where possible, physicochemical characteristics of the endproducts are given.

In the transition from a fossil to a bio-based economy, it has become an important challenge to maximally recuperate valuable nutrients coming from waste streams. Nutrient resources are rapidly depleting, significant amounts of fossil energy are used for the production of chemical fertilizers, whereas costs for energy and fertilizers are increasing. In the meantime, biogas production through anaerobic digestion produces nutrient-rich digestates as a waste stream. In high-nutrient regions this product cannot or only sparingly be returned to agricultural land in its crude unprocessed form. The consequent processing of digestate requires a variety of technologies producing lots of different derivatives, which could potentially be re-used as green fertilizers in agriculture. As such, a sustainable alternative for fossil-based mineral fertilizers could be provided. The aim of this study was to evaluate the impact on soil and crop production by means of a field trial, in which artificial fertilizers and/or animal manure are substituted by biodigestion waste in eight different cultivation scenarios. Nutrient balances were assessed and the physico-chemical soil quality, including the nitrate residue, salt content, pH, sodium adsorption ratio, as well as phosphorus and heavy metal accumulation was evaluated. Finally, the biogas yield of the harvested energy crops was determined by means of an anaerobic digestion batch test. As such, the nutrients coming from the digestate are again recycled to the anaerobic digestion plant and nutrient cycles are maximally closed. Results show that one-year application of waste water from acidic air scrubbers for ammonia removal, digestates and their liquid fraction does not cause significant differences in crop yield, physico-chemical soil fertility and soil quality compared to the common practice (animal manure + artificial fertilizers). Moreover, it is observed that the use of biodigestion waste can stimulate phosphate and potassium mobilization from the soil, thereby providing a potential path to recycle these valuable, but depleting, nutrients in a sustainable way. In addition, the energetic potential per hectare of harvested energy maize was slightly higher when digestate derivatives were used, as compared to animal manure. It is therefore clear that the use of these bio-based products should be stimulated in European legislation and that the results obtained in this study should be widely spread. Further field research is on-going in order to validate the results and evaluate the impact on soil quality in the longer term. A challenge exists in developing environmental technical solutions to neutralize the pH of the air scrubber water and to practically apply this product to the field.