| 1. |
- Larsson, Madeleine, 1984-, et al.
(författare)
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Towards a more circular biobased economy and nutrient use on Gotland : finding suitable locations for biogas plants
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this study we have investigated the role of biogas solutions to support increased resource efficiency on the island Gotland, including recovery and redistribution of nitrogen (N) and phosphorus (P) within the agricultural sector. First, we analyzed the potential for expanding energy and nutrient recovery from organic residues using biogas solutions. Our findings suggest that the biogas production could expand to 165 GWh, from the current 36 GWh (2020), with manure accounting for a potential 110 GWh biogas annually if all were digested. Comparing the nutrients contained in organic feedstock with the crop nutrient demand on Gotland showed that for N the demand is 2.4 times higher than the supply. In contrast, the calculations showed a 137 tonnes P surplus, with distinct excess areas in the center and southern part of the island.We then compared scenarios with different numbers (3 - 15) of biogas plants with respect to efficient nutrient redistribution and transport costs. Spatial constraints for new plants, e.g. need for roads with a certain capacity and permit issues, were accounted for by adding local information to a national data set. We identified 104 potential locations (1 km$^2$ grid cells) and used an optimization model to identify the most suitable locations for minimized transport costs. Optimal (meeting the crop demand with no excess) redistribution of all nutrients contained in the feedstock, as raw digestate from biogas plants, would result in an export of 127 tonnes of P from the island. The model results indicated that if all potential feedstock would be digested in three additional biogas plants and nutrients redistributed for optimal reuse, the total transport cost would be 2.6 million SEK annually, excluding the costs for nutrient export from the island (3.7 million SEK). If instead 10 or 15 smaller plants would be built, the transport cost would drop to 1.8 million SEK, with the same amount of P being exported. Comparing the scenarios with different number of biogas plants (3 - 15), showed that some locations are more suitable than others in terms of distance to feedstock andto fields with fertilizer demands. Finally, a preliminary analysis of the amount of crop residues indicated that this type of feedstock could add a substantial amount of biogas production, but more extensive analyses are needed to assess the feasibility to realize part of that potential.
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| 2. |
- Karlsson, Anna, et al.
(författare)
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Improvement of the Biogas Production Process : Explorative project (EP1)
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- There are several ways to improve biogas production in anaerobic digestion processes and a number of strategies may be chosen. Increased organic loading in existing plants will in most cases demand the introduction of new substrate types. However, to substantially increase the Swedish biogas production new, large-scale biogas plants digesting new substrate types need to be established.Better utilization of existing digester volumes can be linked to: Increase of organic loading rates and/or reduced hydraulic retention timeOptimizing the anaerobic microbial degradation by identifying rate-limitations, its causes and possible remedies such as:Nutrient and trace element balancesNeeds and availability of trace elementProcess design aiming at an increase of the active biomass (e.g. recirculation of reactor material, two stage processes)Process inhibition (enzymatically regulated product inhibition and toxicity)Improved pre-treatment to increase degradation rates and VS-reductionMixing and rheologyBetter monitoring and controlCo-digestion with more high-potential substratesThe present report reviews a number of fields that are linked to improvements in the biogas production process as based on the bullets above.A well-working, active biomass is a prerequisite for efficient biogas production processes, why factors affecting microbial growth are crucial to obtain stable processes at the highest possible organic load/lowest possible hydraulic retention time.The microorganisms need nutrients, i.e. carbon, nitrogen, phosphorus, calcium, potassium, magnesium and iron as well as trace elements such as cobalt, nickel, manganese, molybdenum, selenium and tungsten for growth. The need of nutrients and trace elements varies with the substrate digested, the organic loading rate, the process design (e.g. the reactor configuration, the degree of recirculation etc). In addition, the complexity of the chemical reactions controlling the bioavailability of the trace metals is wide, why optimal addition strategies for trace elements needs to be developed.Substrates as food wastes, sewage sludge, cattle manure, certain energy crops and algae are good bases to obtain processes with good nutrient- and trace element balances. These kinds of substrates can often be implemented for “mono-substrate” digestion, while substrates dominated by carbohydrates or fats needs to be co-digested or digested in processes modified by e.g. nutrient- and trace element additions, sludge recirculation, etc. Protein-rich substrates often include enough nutrients, but can give other process problems (see below).Iron, cobalt and nickel are the nutrients/trace elements given most attention so far. However, molybdenum, selenium and tungsten have also, among others, been shown effective in different AD applications. The effects have, however, mainly been shown on turnover of VFAs and hydrogen (resulting in increased methane formation), while just a few studies have addressed their direct effect on rates of hydrolysis, protein-, fat- and carbohydrate degradation. Selenium- and cobalt-containing enzymes are known to be involved in amino acid degradation, while selenium and tungsten are needed in fat- and long chain fatty acid degradation. Enzymes active in hydrolysis of cellulose have been shown to be positively affected by cobalt, cupper, manganese, magnesium and calcium. This implies that trace element levels and availability will directly affect the hydrolysis rates as well as rates and degradation pathways for digestion of amino acids, long chain fatty acids and carbohydrates. However, their effect on hydrolysis seems neglected, why studies are needed to map the metals present in active sites and co-factors of enzymes mediating these primary reactions in AD. Further investigations are then needed to elucidate the importance of the identified metals on the different degradation steps of AD aiming at increased degradation rates of polymeric and complex substrates. It should also be noted that the degradation routes for amino acid degradation in AD-processes, factors governing their metabolic pathways, and how ATP is gained in the different pathways seem unknown. The different routes may result in different degradation efficiencies, why a deeper knowledge within this field is called for.Trace metals added to biogas reactors have positive effects on the process only if they are present in chemical species suitable for microbial uptake. Interaction of biogenic sulfide with trace metals has been identified as the main regulator of trace metal speciation during AD. Fe, Co and Ni instantaneously form strong sulfide precipitates in biogas reactors but at the same time show very different chemical speciation features. The soluble fraction of Co widely exceeded the levels theoretically possible in equilibrium with inorganic sulfide. The high level of soluble Co is likely due to association with dissolved organic compounds of microbial origin. Fe and Ni speciation demonstrated a different pattern dominated by low solubility products of inorganic metal sulfide minerals, where their solubility was controlled mainly by the interactions with different dissolved sulfide and organic ligands. To our knowledge, the information about chemical speciation of other trace metals (Se, Mo, and W among others) and its effects on the bioavailability in anaerobic digestion environments is rare. Providing information on the metal requirements by processes linked to their bioavailability in biogas reactors is identified as a key knowledge needed for maximizing the effect of metals added to biogas reactors. Further research is also needed for development and design of proper metal additive solutions for application in full scale biogas plants. A practical approach is to supplement trace metals in specific chemical forms, which are either suitable for direct bio-uptake or will hamper undesirable and bio-uptake-limiting reactions (e.g. mineral precipitation).Recirculation of reactor material as a way to enrich and maintain an active microbial biomass (and, thus, an increase in the substrate turnover rate) in tank reactors has been tested for digestion of fat within BRCs project DP6. The methane yield increased from 70 to 90% of the theoretical potential at a fat-loading rate of 1.5 g VS/L and day. The same strategy has been successful during digestion of fiber sludge from the pulp and paper industry, i.e. the recirculation has been crucial in establishment of low hydraulic retention times. Also degradation of sewage sludge (SS) would likely be improved by recirculation as the retention time of the solid SS is prolonged in such a system. However, this remains to be tested. The recirculation concept also needs to be evaluated in larger scale reactors to form a base to include extra costs and energy consumption vs. the benefits from increased yields.To divide the anaerobic digestion process into two phases, where the hydrolytic/acidogenic and the syntrophic/methanogenic stages of anaerobic digestion are separated, might be a way to enhance degradation of lignocellulosic materials as the hydrolysis of these compounds may be inhibited by the release of soluble sugars. It should be noted that the natural AD of ruminates is phase-separated and improvements in AD can likely be achieved using these natural systems as a starting point. Also the degradation of aromatic and chlorinated species is likely enhanced by phase separation. One way to obtain such systems is to combine a leached bed for hydrolysis of insoluble material with a methanogenic reactor treating the leachate. Plug flow reactors might be another possibility as well as membrane reactors, which physically separates the hydrolyzing and methanogenic phases.Inhibition caused by toxic levels of ammonia (protein- and ammonia rich substrates), fat-rich substrates and long chain fatty acids (LCFAs), aromatic compounds, salts etc. have been reported in many cases and some remedies are suggested. Ammonia can be stripped off as a measure to overcome too high levels. Another option is to adjust pH of the reactor liquid by addition of acid shifting the ammonia-ammonium balance in the system towards less free ammonia. A decrease in alkalinity by acid addition might also affect the availability of trace elements as solubility of trace metal mineral phases is generally higher at lower pH. LCFA degradation has been shown to benefit from periodic additions of fat and is, thus, an effective strategy to minimize inhibition by the release of the LCFA. Adsorption to zeolites has also been shown to abate the inhibition by LCFA. The best way to avoid inhibition is, however, to keep the processes nutritionally well balanced and using concepts suitable for the actual substrate mix digested (i.e. sludge recirculation, phase separation etc.) in order to obtain the highest possible degradation rate for problematic compounds, thus, avoiding accumulation of inhibitory components such as LCFA and aromatics. High ammonia and salt levels can often be regulated by the substrate mix.The hydrolysis is often reported as rate limiting in digestion of complex polymers in balanced anaerobic digestion systems, while the methanogensis is regarded as rate-limiting for more easily degraded substrates. As mentioned above the effect on methane formation rates by the addition of trace elements have been shown in numerous studies, while their effect on the hydrolysis and acidogenic AD steps are much less studied. Thus, the effects of the trace elements on the early steps in the AD-chain need to be investigated further.To obtain high-rate hydrolysis, effective and energy efficient pre-treatment methods are crucial for a large number of substrates. The rate of hydrolysis is to a large extent dependent on the properties of the organic compounds in the substrate e.g. carbohydrates, proteins, fat or lignocellulosic material as well as particle size and pre-treatment methods applied.
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| 3. |
- Karlsson, Magnus, et al.
(författare)
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Final report for BRC EP3 (New industries)
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In BRC EP3 focus has been on new industries. The goal has been to find some new industries where biogas production is a resource‐efficient way to take advantage of material flows that are not used today. From this goal seven activities were formulated and are in short: (A1) Present biogas solutions, (A2) Overview of new industrial sectors in Sweden regarding biogas production, (A3) Possibilities and impossibilities process‐wise, (A4) Energy and environmental impacts, (A5) Societal aspects, (A6) Selection of case studies, and (A7) Case study design. These activities needed different angles of approach and therefore a variety of methods were used in the project, e.g. literature studies, calculations, measurements, interviews and workshops. The results from the activities are presented in short below.A1: International comparison of biogas production at industrial sites, for example, is impossible to carry out as different classifications are used in different countries. In A1 a way to categorize biogas plants is proposed and discussed.A2: By screening and geographically pin‐pointing the food industry, eight clusters were chosen for deeper studies. A mapping of biogas potential was thereafter carried out in these clusters. The activity shows great potentials for some of the clusters regarding biogas production.A3: Process‐related feasibility for opportunities for the clusters studied in A2 is targeted. The general conclusion is that there are no severe aspects that imply that one should not continue working with a specific cluster or a specific substrate found in those clusters, regarding biogas production.A4: Each cluster found in A2 is assessed in terms of environmental aspects (climate, acidification and eutrophication), energy balance and economy, which were found being the most important assessment criteria when it comes to efficient biogas solutions. The results show, for example, that even though some of the clusters hold a large potential for biogas production some of these clusters do not imply profitable solutions or environmental advantages compared to the present situation of using the substrates. Moreover, the study shows that the end use of the biogas (electricity, heat and vehicle fuel) has significant influence on the results. It is shown that each cluster has a unique combination of substrates and unique alternatives for use of both substrates and produced biogas, implying different beneficial solutions. Sometimes the beneficial solutions differ dependent on what assessment criterion used.A5: Societal aspects were explored for each cluster found in A2. It is shown that there are differences between the clusters regarding institutional and organizational prerequisites. Important areas have been identified on both a national level (e.g. taxes) and regional level (e.g. cooperation between public and private sectors).A6: When selecting case studies it is found that the following aspects needs to be considered: (1) biogas potential, (2) character of substrates and other materials, (3) environmental aspects (climate, acidification and eutrophication), (4) influence on energy balances (5) economy, (6) use of biogas, and (7) societal aspects.A7: When designing case studies the same aspects as for A6 applies. However, when designing the case study it is also vital to consider where to put the system border and also consider the localization of the production unit (e.g. internal at a company or detached).Moreover, integration of biogas solutions with other types of material or energy flows has to be considered.All the stated parts in “Motivation and aim” are addressed in the project. Consequently, the target of the project is achieved.
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| 4. |
- Lindfors, Axel, 1993-, et al.
(författare)
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The current Nordic biogas and biofertilizer potential : An inventory of established feedstock and current technology
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Biogas solutions in the Nordics is undergoing rapid developments and the demand for biogas is ever increasing because of the Russian war on Ukraine and the transition to fossil free industry and transportation. Furthermore, with the introduction of several multi-national companies into the biogas sector in the Nordics and with more and more biomethane being traded across national borders, it becomes increasingly important to view biogas solutions in the Nordics as a whole and to go beyond the confines of each individual nation. Since the transition and the current energy crisis require a quick response, understanding what could be done with current technologies and established substrates is important to guide decision-making in the short-term. This study aims to do just that by presenting the current biogas potential for the Nordics, including Denmark, Finland, Iceland, Norway, and Sweden. The potential was estimated for eight categories: food waste, manure, food industry waste, sludge from wastewater treatment, landscaping waste, straw, agricultural residues, and crops with negligible indirect land use effects (such as ley crops and intermediary crops). Two categories were excluded due to a lack of appropriate estimation procedures and time to develop such procedures, and these were marine substrates and forest industry waste. Furthermore, several categories are somewhat incomplete due to lack of data on the availability of substrates and their biogas characteristics. These include, for example, crops grown on Ecological focus areas, excess ley silage, damaged crops, and certain types of food industries. The specifics of each category is further detailed in Section 2 of the report.In the report, the biogas potential includes the biomethane potential, the nutrient potential, and the carbon dioxide production potential, capturing all outputs of a biogas plant. The results of the potential study show that the current biomethane potential for the Nordics is about 39 TWh (140 PJ) per year when considering the included biomass categories in the short-term perspective. In relation to current production, realizing this potential would mean a roughly fourfold increase in yearly production, meaning that a significant unexploited potential remains. On the nutrient side, the biogas system in the Nordics would, given the realization of the estimated potential, be of roughly the same size as current mineral fertilizer use (about 75 percent for nitrogen and 160 percent for phosphorous). While this represents the management of a significant portion of nutrients used in agriculture, the potential to replace or reduce mineral fertilizer use through biogas expansion remains unexplored in this study since a significant portion of nutrients come from biomass that is already used as fertilizer (e.g., manure). Finally, on the carbon dioxide side, about 4.2 million tonnes of carbon dioxide would be produced, which could be either captured and stored or captured and utilized, thereby further increasing the positive environmental effects associated with biogas solutions. In conclusion, there remains a large unexploited biogas potential in the Nordics, even when only considering current technologies and established feedstock that could be realized in the short-term (the theoretical potential is much larger since many substrate categories are excluded and the potential is limited to established technologies). Such a realization would bring large increases to biomethane production but would also mean that a significant amount of nutrients would be recirculated through the biogas system. This means that the biogas system has a key role to play in increasing both the food and energy security in the Nordic countries, in addition to its many positive environmental effects.
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