Production of biogas is one of several alternatives to meet sustainable energy solutions and waste management. However, managing the by-product (digestate) can be problematic with its high handling costs. Digestate from wet co-digestion biogas plants contains large volumes of water, causing high transportation costs and low concentration of the valuable nutrients. An alternative to try and reduce the associated costs is by processing the digestate. Processing the digestate for volume reduction allow for more economic and resource efficient ways of handling the product. This master thesis was performed on an initiative from Tekniska verken AB and address digestate handling from Linköping biogas plant, a large co-digestion biogas plant in Sweden. The project aimed to find a feasible, more resource efficient management of their digestate by looking at digestate processing alternatives.The approach systematically evaluated a large number of processing techniques by both literature and communication with TvAB or experts. A selection of techniques were further evaluated were studies in laboratory and a market analysis on digestate provided complementary information, aiding the economical evaluation. Results suggest that processing by centrifuge is a viable, economic option when digestate management is costly and a liquid fraction can be recirculated in the process. It has the potential to significantly reducing digestate management costs. Other processing alternatives may be beneficial if transportation distance can be greatly reduced and/or synergies can be found, but the findings in this project suggest that only treatment with centrifuge is of interest. The results are subject to a number of conditions (such as size of the plant) and assumptions (such as recirculation of a liquid fraction) and therefore need individual adaption to be applicable at any specific plant. Conclusive remarks are that although site specific conditions affect the choice of processing, a project such as this may help reducing the necessary time spent on evaluation. Both research process and results may provide valuable findings for similar evaluations in any industry.

This diploma thesis deals with dewatering technologies of fermentation residues from biogas plants and aims to design an integration of selected technology into the biogas plant. Fermentation residues (or digestate), which are a by-product of anaerobic biomass fermentation in biogas plants, contain a certain amount of nutrients and are usually used as agricultural fertilizers. However, the high-water content in digestate and the associated low nutrient concentration increase the cost of its storage and transport. Dewatering of fermented material could help reduce these costs. The main part of this work included the design of an integration of the selected dewatering technology into the biogas plant – its placement in a process, an addition of necessary appliances, the influence on material and energy flows. In this case, the fermentation residues are processed in two phases. First, a separation of the solid and the liquid fraction by a screw press. The second step is to thicken the liquid digestate by evaporation in a multistage evaporator. Evaluation of the design of a dewatering technology, including its impact on the economy of the biogas plant, is also part of the diploma thesis.

<p>Today the use of anaerobic digestion technique emerges as an alternative to the conventional treatment method of pig slurry to the pig producers in Brazil because of the energy demanding intensive pig production and the negative environmental impact that arises during storage and use. The end products of AD technique are biogas as an energy source and digestate that can be used as a fertilizer.</p><p>The study took place at two pig producers in southern Brazil in order to evaluate the biogas production in the area, its applications and environmental impact. The visited pig producers run a confined animal production system where the slurry that is used in the anaerobic digesters is diluted.</p><p>The studied digesters are covered with an air tight flexible plastic membrane that takes the shape of a balloon where each digester has the volume of 620 m3. Sedimentation occurs inside each reactor where the temperature also fluctuates. The produced biogas is conveyed to a torch where</p><p>the biogas is combusted.</p><p>The results of this study show that the digesters are working properly but there is a need for mixing and constant temperature in order to optimize the process. Biogas is primarily suited for heat production and the digestate can be used as a fertilizer. Biogas production is considered to have a positive environmental impact if the biogas is used or combusted in a torch. There is also a need to apply a cover over the digestate during the storage time to avoid ammonia emissions.</p><p>The approximated biogas potential for Rio Grande do Sul is nearly 100 GWh/year. For an</p><p>approximated biogas potential of more consideration it is found that further studies of the housing systems in Rio Grande do Sul are needed. This is due to a greatly varying amount of degradable materials in the pig slurry from one ranch to another.</p>

Today the use of anaerobic digestion technique emerges as an alternative to the conventional treatment method of pig slurry to the pig producers in Brazil because of the energy demanding intensive pig production and the negative environmental impact that arises during storage and use. The end products of AD technique are biogas as an energy source and digestate that can be used as a fertilizer. The study took place at two pig producers in southern Brazil in order to evaluate the biogas production in the area, its applications and environmental impact. The visited pig producers run a confined animal production system where the slurry that is used in the anaerobic digesters is diluted. The studied digesters are covered with an air tight flexible plastic membrane that takes the shape of a balloon where each digester has the volume of 620 m3. Sedimentation occurs inside each reactor where the temperature also fluctuates. The produced biogas is conveyed to a torch where the biogas is combusted. The results of this study show that the digesters are working properly but there is a need for mixing and constant temperature in order to optimize the process. Biogas is primarily suited for heat production and the digestate can be used as a fertilizer. Biogas production is considered to have a positive environmental impact if the biogas is used or combusted in a torch. There is also a need to apply a cover over the digestate during the storage time to avoid ammonia emissions. The approximated biogas potential for Rio Grande do Sul is nearly 100 GWh/year. For an approximated biogas potential of more consideration it is found that further studies of the housing systems in Rio Grande do Sul are needed. This is due to a greatly varying amount of degradable materials in the pig slurry from one ranch to another.

The production of biogas through the anaerobic digestion of cattle manure and its subsequent use in the generation of electricity on large Ontario farms is currently economically attractive. While larger farms have advantages of scale, there are substantially more small farms for which individually designed and engineered biogas systems are prohibitively expensive. Although biogas has numerous benefits, it contains hydrogen sulfide, an odourous, poisonous and corrosive gas, which emits sulfur oxides upon combustion. Larger systems can afford to use specialized biogas engines which tolerate some levels of hydrogen sulfide. For smaller scale systems to be financially attractive the hydrogen sulfide needs to be removed inexpensively, allowing for more flexibility in engine choice for electricity generation. In this work, the solid by-products from the anaerobic digestion process were used to create activated carbon, which has a high capacity for hydrogen sulfide. Not only does the carbon adsorb hydrogen sulfide, it allows for the surface oxidation of hydrogen sulfide to elemental sulfur and sulfate. Since the sulfur is in a beneficial form for fertilizer use, and there are no chemicals added to create the carbon, the spent sulfur-containing carbon can be land applied, eliminating any spent carbon disposal costs.

The production of biogas through the anaerobic digestion of cattle manure and its subsequent use in the generation of electricity on large Ontario farms is currently economically attractive. While larger farms have advantages of scale, there are substantially more small farms for which individually designed and engineered biogas systems are prohibitively expensive. Although biogas has numerous benefits, it contains hydrogen sulfide, an odourous, poisonous and corrosive gas, which emits sulfur oxides upon combustion. Larger systems can afford to use specialized biogas engines which tolerate some levels of hydrogen sulfide. For smaller scale systems to be financially attractive the hydrogen sulfide needs to be removed inexpensively, allowing for more flexibility in engine choice for electricity generation. In this work, the solid by-products from the anaerobic digestion process were used to create activated carbon, which has a high capacity for hydrogen sulfide. Not only does the carbon adsorb hydrogen sulfide, it allows for the surface oxidation of hydrogen sulfide to elemental sulfur and sulfate. Since the sulfur is in a beneficial form for fertilizer use, and there are no chemicals added to create the carbon, the spent sulfur-containing carbon can be land applied, eliminating any spent carbon disposal costs.

The aim of the work was to examine microalgae growth and nutrient elimination in various diluted digestates in the first trial, then to study CO2 removal from a simulated biogas mixture by the same strain in the second trial. Scenedesmus SCCP K-1826 was cultivated in the digestate from Sundet biogas plant diluted 10, 20 and 30 times. The cultures were open-air with occasional CO2 injections to control pH. On day 15, the best growth was obtained in the 10 times diluted sample. COD, TN and TP removal efficiencies were similar in each bottle as the strain didn’t perform better in any specific dilution. The control proved that additional mechanisms other than photosynthesis contributed to digestate cleaning. Using the 10 times diluted sludge, Scenedesmus was grown in sealed flasks filled with simulated biogas (35.3 % CO2 + 32.3 % CH4 + 32.3 % N2). More algal biomass was produced in this batch culture. Nutrient removal efficiencies were close to the ones reached in the open-air flasks. After 10 days, 96 % of carbon dioxide was reduced. Methane content was depleted as well, possibly due to undesirable methane oxidizing bacteria which infiltrated the medium.

The aim of this thesis was to compare several biogas plants in the South and Central Bohemia in several respects. Overall, it was also beneficial to see how these biogas plants solve or not solve the pretreatment of the substrate, as well as the use of ancillary benefits, such as the use of heat or residual digestate. Part of this thesis is a literature search, mapping the possibilities of increasing the efficiency of agricultural biogas plants.

The Ontario biogas industry is relatively young and the overall objective of this research was to help support the growth of the industry with investigating the use of co-substrates and reactor design to enhance biogas production, recommend guidelines on the operation of full scale systems to optimize performance and characterize digestate quality. Laboratory studies evaluated the use of various substrates in the co-digestion with liquid dairy manure. These studies were used to establish ultimate biogas yields, % volatile solids (VS) reduction and minimum hydraulic retention times (HRTs). Box-Wilson Central Composite design models for corn thin stillage and waste grease (as co-substrates with dairy manure) suggest methane yields optimize with increasing proportion of the feed VS from co-substrates (constant total VS in all assays) and increasing temperatures; however, temperature had a great effect. Bench scale studies were conducted to determine a change in digester design to optimize biogas yields and increase digestate stability. A two-phase digestion system was implemented for co-digestion systems using thin stillage and waste grease with dairy manure, and methane yields showed to increase by over 22% when compared with single-phase systems. Based on current FIT contracts of 18 to 20¢/kWhe, the increased electricity and heat production could make the two-phase system economically attractive for producers. Organic loading rates (OLRs) over 4.4 g VS/L led to digester upset and OLRs of over 4.2 g VS/L·day are not recommended. On-farm anaerobic digester systems were studied for digester performance and digestate quality. Residual biogas potential (RBP) yields were effective at evaluating the stability of digestate and the U.K. PAS 110:2014 limit of 0.45 L biogas/g VS (28 days incubation) was assessed too lenient for the Ontario systems studied. A limit of 0.25 L biogas/g VS after 28 days of incubation or 0.45 L biogas/g VS after 60 days of incubation are recommended. VS reductions ranged from 56 to 76% and easily achieved the O. Reg. 267/03 regulated 50% VS reduction. E.coli and Salmonella were typically 1 to 3 logs CFU/100 mL lower than raw manure and increased HRT did not demonstrate a significant impact on the bacterial log reductions. Intermediate alkalinity (IA)/partial alkalinity (PA) proved to be a valuable tool in determining potential digester upset and has been recommended as a standard performance parameter for on-farm systems.

The focus of this thesis is the posibility of obtaining phosphorus from liquid digestate. The theoretical part of the thesis is focused on summarizing the current situation regarding phosphorus recovery. The research summarizes the essential information about the method of struvite precipitation, by which phoshphorus is obtained in the form of struvite, which can be further used as a fertilizer. Based on the process information, an experimental device was designed to obtain phosphorus in the form of struvite, corresponding to industry standards. It is a cylindrical vessel with a conical bottom, in which the liquid digestate with the chemicals is mixed with a stirrer. The functionality of the device was tested experimentally on the created device. The results of the experiment were analyzed by XPS method, which confirmed the formation of struvite. For future operation, modifications of the device and pre-treatment of the liquid digestate were proposed, which could improve the whole process and its results.