The aim of the project was to investigate the possibility of producing and utilizing bioenergy from available local resources in the village Linga Linga, Mozambique. Suitable conversion techniques for producing and utilizing bioenergy were identified through a literature study. The investigated techniques were the concept of gasifier cookstoves, the method of producing charcoal from biomass and anaerobic digesters. Through observations and interviews in the village, available local resources suited for the conversion techniques were identified. In the field study, it was found that there is a surplus of solid biomass which led to the conclusion that a gasifier cookstove is suitable to implement. In order to analyze if a gasifier cookstove is suitable for the households, interviews were carried out in ten households in the village. Aprototype of a gasifier cookstove was built with local resources to determine if the technique can be applied. The prototype was tested and evaluated in order to analyze if it will contributeto a more efficient use of resources. One of the conclusions of the study was that a gasifier cookstove can be valuable for the households in several ways, but that cultural differences can make it hard to implement.

Anaerobic digestion (AD) is a sustainable waste management technology that primarily generates two products: biogas and digestate. The technology relies on the microorganisms' activity, which depends on several operational factors, such as pH, temperature, solid contents, and ammonia levels. Ammonia is an inorganic form of nitrogen resulting from the biodegradation of organic nitrogen. It is considered one of the major concerns for AD operations due to its inhibitory effects on some microorganisms, particularly methanogens. A common feedstock characterized by high nitrogen content is poultry manure (PM). PM is often avoided in anaerobic digesters due to the anticipated inhibition resulting from its high ammonia levels. However, since poultry manure is one of the most widely available organic wastes, researchers have extensively investigated ways to include PM as a primary feedstock for AD. One possible way to treat high ammonia levels in digestate is ammonia stripping, the physio-chemical separation of ammonia from a solution by introducing a stripping (carrier) gas. There are a few approaches to performing ammonia stripping in AD applications; the most commonly discussed in the literature are pre-hydrolysis and side-stream ammonia stripping. Pre-hydrolysis ammonia stripping is performed on raw feedstock after increasing pH and temperature and is usually not restricted in selecting the gas carrier. On the other hand, side-stream ammonia stripping is when a portion of the digester's working volume is filtered, and the filtrate is sent to a unit where pH and temperature are increased. The carrier gas in these systems is often limited to anaerobic gases such as biogas or steam. The third and most novel approach is post-hydrolysis ammonia stripping, conducted at an intermediate stage between hydrolysis and methanogenesis in a two-stage AD process. This configuration would address the shortcomings of the other two systems. However, there is minimal information on the feasibility and potential of this approach in the literature. This study aims to comprehensively investigate the post-hydrolysis ammonia stripping approach through the following four phases: Phase I) Proof of Concept; Phase II) Optimization; Phase III) Assessment of Alternative Carrier Gases; and Phase IV: Comparison of Different Ammonia Stripping Configurations. Phase I provided the proof of concept under the batch mode and compared the performance of post-hydrolysis ammonia stripping with two-stage AD and co-digestion to improve poultry manure's methane potential as the primary substrate. It was observed that ammonia stripping successfully improved methane potential by up to 150%, whereas improvements due to two-stage AD and co-digestion were limited to 41 and 9%, respectively. Phase II provided more insight into optimizing the ammonia stripping process. Different stripping conditions were tested (pH 7.8 (unadjusted), 9 and 10, temperature 25 (unadjusted), 40 and 55 °C, and flow rate 300 L/L/hour). The results showed that higher pH and temperature lead to higher removal efficiency. However, it was concluded that optimal conditions ultimately depend on the initial and target ammonia levels. Moreover, Analysis of Variance showed that pH and temperature were significant factors affecting the ammonia removal efficiency. In addition, it was observed that higher stripping temperatures (55 °C) enhanced the digestibility of PM and increased its methane potential more than stripping at 40 °C. It was concluded that the optimum stripping conditions were pH 9.5, temperature 40 or 55 °C, and flowrate of 100 L/L/hour to collectively increase ammonia removal while reducing the associated costs and material handling. In Phase III, renewable natural gas (RNG) was evaluated as a stripping medium in batch testing as a potential replacement for biogas and air. Ammonia stripping with RNG yielded promising results comparable to the application of air in terms of ammonia removal and enhancing biogas production from PM (60 and 69% ammonia removal for RNG and air, respectively). In addition, a metagenomic shotgun analysis showed that most biogas production was conducted through hydrogenotrophic methanogens instead of acetoclastic methanogens, which are more susceptible to high ammonia levels. Phase IV assessed the semi-continuous flow two-stage operation of mesophilic AD reactors coupled with different ammonia stripping configurations. Post-hydrolysis ammonia stripping successfully achieved a stable operation of PM mono-digestion at ammonia levels of 1700 and 2400 mg NH₃-N/L in the cases of stripping with air and RNG, respectively. In addition, post-hydrolysis ammonia stripping in semi-continuous flow mode may have promoted acetoclastic methanogens growth since volatile fatty acid concentrations were reduced in the digesters. Phase IV also proved that the performance of post-hydrolysis ammonia stripping is superior over pre-hydrolysis and side-stream ammonia stripping. In the semi-continuous flow reactors, post-hydrolysis ammonia stripping with air achieved on average 831 L biogas/ kg VS at an organic loading rate (OLR) of 2.6 g VS/L/day, whereas side-stream ammonia stripping resulted in average of 700 L biogas/ kg VS at OLR of 1.8 g VS/L/day and higher ammonia stripping requirements. Having said that, the base scenario (no ammonia stripping) was inhibited, indicating that both ammonia stripping configurations were considered successful in alleviating inhibitory effects of ammonia from poultry manure. Phase IV results also proved that air stripping repeatedly outperformed RNG as stripping mediums by having higher ammonia removal efficiencies resulting in higher methane production. However, stripping with RNG is believed to have more practical advantages than air due to avoiding the risk of oxygen infiltration into the reactor. Moreover, renewable natural gas has proven to be an efficient stripping medium that is available on-site. The final stage of Phase IV tested pre-hydrolysis ammonia stripping using air in batch mode and compared it with post-hydrolysis ammonia stripping. Pre-hydrolysis ammonia stripping provided little to no improvement to the methane potential of PM in batch mode and therefore was excluded from the semi-continuous flow experiment. The four phases of this study demonstrated the flexibility and the superiority of post-hydrolysis ammonia stripping over the other pre-hydrolysis and side-stream ammonia stripping. In addition, post-hydrolysis ammonia stripping was proven efficient and feasible for ammonia removal and enabling the mono- or co-digestion of poultry manure. The study also showed that using RNG instead of biogas can significantly reduce the operational costs of the treatment.

Anaerobic digestion is a process where biogas is generated from organic substance in the absence of oxygen. The most common application of the anaerobic digestion technology in developing countries is small-scale household digesters producing biogas for cooking purposes. These systems are usually fed with cattle dung or organic household waste. The typical small-scale digester models are fixed-dome digester, floating-drum digester and rubber-balloon digester. Biogas systems contribute to self-sustainability of energy production, improve waste management and mitigate deforestation and health problems caused by poor waste management and usage of traditional cooking fuels such as firewood and charcoal. Anaerobic digestion technology is still quite unknown in Mozambique. An initiative to implement this technology in the municipality of Quelimane located in Zambézia province in the central part of the country, was taken in 2015 and background studies were performed during spring 2015 and 2016. As a part of the study resulting in this report, performed in spring 2017, a small-scale biogas digester was installed in Quelimane city. The digester was fed with the initial input of cow manure in order to create population of anaerobic bacteria and in the future it’s planned to be fed with food waste. The purpose of the first installed digester is to serve for educational purposes and to produce cooking fuel for the few people working in the municipal location where the digester is installed. It’s estimated that the digester has a potential to produce daily 0.3 m3 of biogas from 2 kg of food waste which can be used for preparing lunch for the employees or for heating water. In the future, possible applications of anaerobic digestion technology in Quelimane are a municipal biogas plant, cooling systems for the fish industry and biogas based latrines in the less developed areas located outside of the city center.

About 83% of total energy consumed in Nepal comes directly from the solid fuels. The import of Liquified Petroleum Gas (LPG) is also growing at an exponential rate. The hospitality subsector (hotels and restaurants), one of the key economic subsectors in the country, consumes most of the energy within the commercial sector primarily for cooking purposes. The bio-waste generated from growing hospitality subsector and other sectors in Kathmandu is poorly managed. Similarly, on the other hand, Nepal has an extensive knowledge and experience of manure based anaerobic household biogas systems mainly in rural areas. Based upon this situation, the thesis investigates the opportunities for anaerobic biogas production for cooking at hotels and restaurants by utilizing their own organic waste. Currently available biogas technologies, important parameters affecting the biogas yield, policy and financial supports and case studies of various stakeholders employing the biogas technologies in the hotels and restaurants in Nepal were considered. The most applicable technology for the purpose was then chosen. The organic waste sampling study from randomly selected 4-star hotel (Yatri Spa and Suites), tourist standard hotel (Hotel Bliss International) and restaurant (Fren’s Kitchen) in Thamel, the tourist zone of Kathmandu was conducted. Similarly, various data especially focusing on the current cooking energy need, demand, supply, cost, organic waste management of the hotels and the restaurant was collected through questionnaires and series of interviews. The average amount of daily organic waste and organic waste fraction for Yatri, Bliss and Fren’s was found to be 61.3 kg and 63.0%, 18.4 kg and 82.7%, and 16.3 kg and 81.8% respectively. Similarly, the variations in weekly organic wastes and waste generated per guest was also determined. Based upon the amount and characteristics of organic waste from the sampling survey, the theoretical biogas potential of the organic waste at digester output rate of 0.27 kWh/kg/day for JUAS digesters, the technology selected for the biogas conversion, was found to be 18.4 kWh/day, 5.5 kWh/day and 4.9 kWh/day equivalent to 4.9%, 3.0% and 5.4 % of the current daily energy need for Yatri, Bliss and Fren’s respectively. Similarly, the economic implications of the small-scale biogas technology if employed in the hotels and the restaurant was scoped out. It was found that the recommended Polyvinyl Chloride (PVC) based 3000 l sized JUAS bio-digesters had positive Net Present Value (NPV), Internal Rate of Return (IRR) and payback time of around 5 years on average for all the eateries under study. The monthly life cycle cost of the integrated LPG-JUAS system is found be cheaper for all eateries as compared to the current LPG system. Levelized Cost of Energy (LCoE) of the JUAS digesters is calculated to be competitive as compared to energy from other renewables in the country. There is, however, need to improve the digester conditions to get higher biogas yields. For the wider adoption of the digesters across urban sectors, the subsidies amount should also be increased together with information dissemination regarding biogas uses and its potential among the stakeholders. / Omkring 83% av den totala energiförbrukningen i Nepal kommer direkt från det fasta bränslet. Importen av flytande petroleumgas (LPG) växer också i exponentiell takt. Underhållningsbranschen (hotell och restauranger), en av de viktigaste ekonomiska delområdena i landet, förbrukar mest energi inom kommersiell sektor, främst för matlagning. Det biologiska avfallet som genereras av växande underhållsbranschen och andra sektorer i Katmandu är dåligt förvaltad. På samma sätt har Nepal en omfattande kunskap och erfarenhet av gödselbaserade anaeroba hushållsbiogasystem, huvudsakligen i landsbygdsområden. Baserat på denna situation undersöker man avhandlingen möjligheterna till anaerob biogasproduktion för att laga mat på hotell och restauranger genom att använda eget organiskt avfall. För närvarande finns biogasteknik, viktiga parametrar som påverkar biogasutbytet, politiska och finansiella stöd och fallstudier av olika intressenter som använder biogasteknik i hotell och restauranger i Nepal. Den mest tillämpliga tekniken för ändamålet valdes sedan. Undersökning av organiska avfallsprov från slumpmässigt utvalt 4-stjärnigt hotell (Yatri Spa and Suites), turisthotell (Hotel Bliss International) och restaurang (Fren's Kitchen) i Thamel, utförs turistområdet Katmandu. På samma sätt samlades olika data som speciellt fokuserade på dagens energibehov, efterfrågan, tillgång, kostnad, organisk avfallshantering av hotellen och restaurangen genom enkäter och intervjuer. Den genomsnittliga mängden dagligt organiskt avfall och organiskt avfallsfraktion för Yatri, Bliss och Fren var visat sig 61,3 kg respektive 63,0%, 18,4 kg respektive 82,7% respektive 16,3 kg respektive 81,8%. På samma sätt bestämdes också variationerna i organiskt avfall per vecka och avfall som genererades per gäst. Baserat på mängden och egenskaperna hos organiskt avfall från provtagningsundersökningen befanns den teoretiska biogaspotentialen hos det organiska avfallet vid kokareutgångshastigheten på 0,27 kWh / kg / dag för JUAS-kokare, den teknik som valts för biogasomvandling, befunnits vara 18,4 kWh / dag, 5,5 kWh / dag och 4,9 kWh / dag motsvarande 4,9%, 3,0% och 5,4% av dagens energibehov för Yatri, Bliss och Fren. På samma sätt scenkades de ekonomiska konsekvenserna av den småskaliga biogastekniken om de anställdes i hotell och restaurangen. Det visade sig att de rekommenderade polyvinylkloridbaserade (PVC) -baserade JUAS-bioförstörare av polyvinylklorid med jämna mellanrum hade positivt nettoförsäkringsvärde (NPV), interna avkastningsräntor och återbetalningstid på cirka 5 år i genomsnitt för alla restauranger som studerades. Den månatliga livscykelkostnaden för det integrerade LPG-JUAS-systemet befinner sig vara billigare för alla matställen jämfört med det aktuella LPG-systemet. Nivånad kostnad för energi (LCoE) hos JUAS-kokare beräknas vara konkurrenskraftig jämfört med energi från andra förnybara energikällor i landet. Det är dock nödvändigt att förbättra kokareförhållandena för att få högre biogasutbyten. För det bredare godkännandet av kokare i städerna bör bidragsbeloppet också ökas tillsammans med informationsspridning avseende biogasanvändning och dess potential bland intressenterna.För det bredare godkännandet av kokare i städerna bör bidragsbeloppet också ökas tillsammans med informationsspridning avseende biogasanvändning och dess potential bland intressenterna.

This study has been carried out within the framework of the Minor Field Studies ScholarshipProgramme (MFS), which is funded by the Swedish International Development Cooperation Agency,Sida. The field study was conducted in Grenada in the spring of 2023. Grenada, along with severalcountries in the Caribbean, has under the last couple of years experienced an increasing influx ofSargassum seaweed. The seaweed accumulates on beaches and causes complications relating tohealth, recreation, economy and the ecosystems by the coast. Moreover, Grenada is dependent onimported fossil fuels which causes the country to have a relatively high ecological footprint as well asmaking the country sensitive to volatile oil prices. To produce biogas with Sargassum, and morespecifically for generating electricity, is one possible solution to the aforementioned issues. However,there is a need to investigate the prerequisites for such a solution. This was done by conducting anexperiment and a market analysis. The experiment aimed to investigate how the methane content inthe biogas is affected by mechanical pretreatment of the seaweed. The market analysis delved into thepossibilities of using biogas to generate electricity in Grenada. For the experiment, a small-scale biogas digester was used, which was located at the True Blue BayBoutique Resort. Feeding of the digester was divided into three batches with two differentcompositions of food waste and Sargassum; untreated and mechanically pretreated Sargassum. Thedigester was fed for 42 days in total while the measurements were conducted for 28 days. In terms ofthe market analysis, a literature study and 4 interviews with relevant actors were conducted. Theinterviewees were approached based on local suggestions. For the analysis, four different areas ofinterest were selected: Electricity system in Grenada, Policy and regulation, Infrastructure andAvailability of organic waste for co-digestion. The experiment revealed a weak yet positive trend in the methane yield over the measured period,indicating that mechanical pretreatment of the Sargassum could potentially increase methane yields.Specifically, the average methane concentration by volume was 57% for the untreated batch and 63%for the mechanically pretreated batch. However, it is important to note that the project's duration wasinsufficient to draw definitive conclusions. Furthermore, there might be other factors that contributedto the unusually high methane yield observed in this experiment. Firstly, the storage method of theseaweed in fresh saltwater may have played a role. Secondly, uncertainties related to gas fluxmeasurements and estimated thermal efficiency have a significant impact on the calculated final valueof the methane concentration. In terms of the market analysis, the results indicate that electricity generation through large-scalebiogas production will face challenges. The structure of the electricity system in Grenada allows forgeneration from biogas and Sargassum to exist. Moreover, such operations can play a significant rolein realizing the goals set forth by Grenada’s main policies in terms of sustainability and energy.However, the challenges that need to be dealt with include establishing regulations and policiesspecifically targeting biogas and Sargassum. Supporting infrastructure and a reliable source ofbiodegradable waste also needs to be established before electricity generation fromSargassum-derived biogas can be carried out. The aforementioned challenges relate to electricityproduction for distribution and may not be as significant for power generation for self-consumption. / Denna studie är genomförd inom ramen för stipendieprogrammet Minor Field Studies (MFS) somfinansieras av Sida och fältstudien genomfördes i Grenada våren 2023. Grenada, tillsammans medflera länder i Karibien, har under de senaste åren upplevt ett ökande inflöde av Sargassotång. Tångensamlas på stränderna och skapar problem kopplade till hälsa, rekreation, ekonomi och ekosystemenvid kusten. Vidare är Grenada beroende av importerade fossila bränslen, vilket gör att landet har ettrelativt högt ekologiskt fotavtryck, samtidigt som det är känsligt för volatila oljepriser. Att producerabiogas med sargassotång, och mer specifikt för att generera el, är en möjlig lösning till de ovannämnda problemen. Emellertid finns det ett behov att undersöka förutsättningarna för en sådanlösning. Detta gjordes genom att genomföra ett experiment och en marknadsanalys. Experimentetsyftade till att undersöka hur metaninnehållet påverkas av att mekaniskt förbehandla sargassotången.Marknadsanalysen undersökte förutsättningarna för att använda biogasen för att generera el påGrenada. För experimenten användes en småskalig biogasanläggning på True Blue Bay Boutique Resort påGrenada. Matningen delades upp i tre delar med två olika sammansättningar av matavfall ochsargassotång; obehandlade och mekaniskt förbehandlade alger. Totalt matades anläggningen i 42dagar medan experimentet med vattenkokning genomfördes 28 dagar. För marknadsanalysengenomfördes en litteraturstudie och 4 intervjuer med relevanta aktörer. Intervjupersonerna valdesutifrån lokala förslag. För analysen valdes sedan fyra områden: Elsystemet på Grenada, Policy ochreglering, Infrastruktur och Tillgänglighet av biologiskt nedbrytbart avfall. Experimentet visade en svag men positiv trend i metanhalten under den uppmätta perioden, vilkettyder på att mekanisk förbehandling av Sargassum potentiellt kan öka metanhalten. Mer specifikt varden genomsnittliga koncentrationen av metan per volym 57% för den obehandlade delen och 63% förden mekaniskt förbehandlade delen. Det är dock viktigt att notera att projektets varaktighet varotillräcklig för att dra definitiva slutsatser. Dessutom kan det finnas andra faktorer som bidrog till detovanligt höga metanhalten som observerades i detta experiment. För det första kan lagringsmetodenav sjögräset i färskt saltvatten ha spelat en roll. För det andra har osäkerheter relaterade tillgasflödesmätningar och uppskattad verkningsgrad en betydande påverkan på den beräknade slutligametankoncentrationen. Vad gäller marknadsanalysen så indikerar resultaten att elproduktion genom storskaligbiogasproduktion kommer att möta utmaningar. Utformningen av Grenadas elsystem tillåtergeneration av el från biogas och Sargassum. Vidare kan en sådan verksamhet spela en viktig roll i attuppfylla de mål som presenteras i Grenadas huvudsakliga strategier kring hållbarhet och energi.Emellertid behövs regler och policy som är specifikt inriktade på biogas och Sargassum. Därtillbehövs stödjande infrastruktur och en tillförlitlig ström av biologiskt nedbrytbart avfall. De nämndautmaningarna gäller främst för elproduktion för distribution och behöver inte vara lika signifikanta förkraftproduktion för egenkonsumtion.

More than 16,000 tons of olive cake was produced in the United States in 2017. Olive cake is a by-product of olive oil extraction, which has limited animal feed potential, and poses an environmental threat when landfilled due to its high organic load and polyphenol content. This residue has potential for biofuel (bioethanol and biomethane) production because it is rich in polysaccharides such as pectin, hemicellulose, and cellulose. Yet, olive cake contains olive stones that can impede its conversion to biofuel. Therefore, two methods of destoning, centrifugation and screening by horizontal screw press, were first compared. Both methods removed an equal percentage of stones (95%), but centrifugation partitioned the majority (57 – 79%) of digestible solids (olive pulp) with the stones. Then, two strategies were compared to maximize both biomethane and bioethanol production; enzymatic conversion of insoluble to soluble carbohydrates and destoning by screening. After 30 days of anaerobic digestion at 35 °C, both the enzymatically pretreated and the destoned olive cakes produced similar amounts of methane (~295 mL CH4/g VS), 42% more than the control (209.5 mL CH4/g VS). The biogas produced was composed of 60-70% methane. A comparison of biomethane yields with a broad range of agricultural residues demonstrated olive cake’s suitability for biomethane production. The digestate, residue from the anaerobic digestion, have high Kjeldahl nitrogen content (3.6%, db) and low polyphenol concentration (0.02 mg GAE/g), which then qualify it as an ingredient for soil amendment. Ethanol production investigations showed that after 3 days of fermentation at 32 °C, only the destoned and enzymatically pretreated olive cake produced ethanol (1.3 mg/mL). Acetic acid, an inhibitor of ethanol production, was present in all samples broth, suggesting microbial contamination was present. These results provide evidence that olive cake can be diverted from landfills to be converted into a biofuel. Sustainable pretreatments such as destoning and enzymatic pretreatment increase biomethane yield. The digestate created from the anaerobic digestion of olive cake can be used as a soil amendment, adding further value to olive cake.

This research sought to optimize anaerobic co-digestion of microalgae biomass harvested from a wastewater treatment pond facility with locally-available wastes. The goal was to produce high methane yields and stable digestion without the need for supplemental alkalinity addition. A key research question was if algae digestion could be improved via the synergistic effects of co-digestion. Cell disruption to increase digestibility was not pursued due to its relatively high mechanical complexity and high energy use. For the wastewater treatment ponds studied, the most practical co-substrates identified were municipal wastewater sludge and food waste (sorted organic municipal waste). Although wastewater sludge does not have a particularly high carbon:nitrogen (C:N) ratio, it readily and stably digests and is available in large quantities at wastewater treatment plants. This research investigated the methane productivity of algae co-digestion with municipal wastewater sludge and food waste in semi-continuous bench-scale anaerobic digesters at 37.5˚C. Digesters fed pure algae biomass loaded at a rate of 4 g Volatile Solids (VS)/L-day with a 20-day residence time exhibited stable digestion and yielded an average of 0.23 L CH4/g VS Introduced. For digesters that contained algae biomass in the feed, the greatest methane yield of 0.40 mL CH4/g VSin was observed in a digester containing 50% algae co-digested with both sorted organic municipal waste (40%), and municipal wastewater sludge (10%) at a loading rate of 2 g VS/L-day with a 20-day residence time. While adding co-substrates increased yields in all digesters, prevention of ammonia toxicity did not appear to be the mechanism. Instead, the co-substrates simply increased the concentration of readily-digestible organic carbon, leading to increased methane yields and productivities. For algae biomass, total ammonia nitrogen concentrations of 3370 mg/L did not appear to inhibit methane yield. Digesters with the same feed contents and residence time loaded at 2 and 4 g VS/L-d had similar yields but total ammonia nitrogen concentrations of 1740 and 3370 mg/L respectively. From the data from these laboratory studies, descriptive models were developed for ammonia nitrogen, alkalinity, volatile fatty acids, yield, biogas quality, and volatile solids destruction. The variables from the descriptive models with p-values above 0.05 were then used to create a compact model.

Anaerobic digestion is perhaps the simplest and most widely accepted method for solids and residuals management in the field of wastewater treatment. An emerging trend with regard to anaerobic digestion is the addition of additional organic or industrial wastes rich in degradable material (COD) that can lead to increased methane production and reduce the energy demand of the facility. The objective of this research was to evaluate the effect of adding significant quantities (>20% of feed volume) of High Strength Food Wastes (HSW) to digesters treating conventional municipal sludge by monitoring key parameters such as pH, influent and effluent solids, ammonia, Volatile Fatty Acids (VFAs) and alkalinity. Daily gas production was also closely monitored. Four digesters were set up and exposed to different food waste loading rates. A comparison was drawn between the performance of these reactors, one of which was fed only with sewage sludge and served as the control. If the bacteria in the system are able to metabolize this additional COD, it should show up as an increase in gas production with little or no increase in effluent COD. Ammonia is another crucial parameter that needs to be closely watched as it can have an inhibitory effect on methane production. As part of this study, the impact of addition of free ammonium (simulating high ammonium concentration in the feed sludge or food waste) on digester performance was assessed. The digesters were closely monitored for signs of poor performance or failure. / Master of Science

Anaerobic co-digestion of municipal sludge and food wastes high in chemical oxygen demand (COD) has been an area of interest for waste water treatment facilities looking to increase methane production, and at the same time, dispose of the wastes and increase the revenue. However, addition of food wastes containing fats, oils and grease (FOG) to the conventional anaerobic digestion process can be difficult and pose challenges to utilities. Incorporating these wastes into the treatment plants can potentially inhibit the digestion process. In this study four lab-scale, anaerobic digesters were operated under mesophilic conditions and fed municipal sludge. One of them served as the control, while the other three digesters were fed with different volumetric loadings of juice processing waste, cheese processing waste (whey), dissolved air flotation waste (DAF) from a food processor, and grease trap waste (GTW), in addition to the municipal sludge. The impact of these high strength wastes (HSWs) on digester performance was analyzed for a total period of 150 days. Among the parameters analyzed were pH, total and soluble COD (tCOD and sCOD), Total and Total Volatile Solids (TS and TVS), Total Ammonia Nitrogen (TAN), Total Kjeldahl Nitrogen (TKN), Volatile Fatty Acids (VFA), Long Chain Fatty Acids (LCFA), and alkalinity. Biogas was collected and analyzed for methane content. The dewatering characteristics of digested sludge were also studied. Volatile organic sulfur compounds were analyzed on the dewatered sludge in order to monitor odors. This study showed that different high strength wastes have different impacts on digester performance. HSWs have the ability to degrade along with municipal sludge and to increase biogas production. However, anaerobic digestion can be inhibited by the presence of FOG, and addition of these wastes might not always be cost effective. Careful selection of these wastes is necessary to ensure stable digester operation, while bringing about increases in gas production. Utilities need to be cautious before adding any high strength wastes to their digesters. / Master of Science

Producing renewable energy from biomass or from the wastewater treatment process has gained momentum in the past 20 years. Anaerobic digestion has historically been used as one step in the waste treatment process, to both reduce the mass of waste that needs to be disposed of and to generate biogas. This process is typically only able to reduce 30-40% of the waste mass because of the recalcitrant nature of the waste streams being treated. Anaerobic pretreatment with the thermophilic bacteria Caldicellulosiruptor bescii (C. bescii) has been proven to increase the percentage of mass digested and consequently increase methane production to 75%-85%. However, even with the use of pretreatment with C. bescii, it still leaves 15%-25% of the methane potential wasted. In anaerobic digestion, volatile fatty acids (VFAs) are of interest because they are the precursors to the production of methane. By using HPLC-UV-vis techniques, VFAs can be speciated and quantified in as little as 12-minutes. Depending on the pretreatment system, operational procedures for both the pretreatment and anaerobic digestion system, and substrate, the type and composition of VFAs can vary. For example, in several experiments analyzed it was found that valeric acid is a VFA that is dominate in waste activate sludge treatments, while acetic acid is in higher proportions with manure substrates. Besides methane production, VFA monitoring can detect issues with a bioreactor performance. By tracking VFA trends, the health of the system can be assessed.