The Biodynamic Research Institute in Järna developed an on-farm biogas plant integrated within the highly self-supporting farm organism, Skilleby-Yttereneby, one of the farms studied in the BERAS project. The biogas plant digests dairy cattle manure and organic residues originating from the farm and the surrounding food processing units

Evers, Lars

Granstedt, Artur

Schäfer, Winfried

English

Organic Eprints

E K O L O G I S K T   L A N T B R U K   N R   4 6   •  D E C E M B E R   2 0 0 5ENVIRONMENTALIMPACTS OF ECO-LOCAL FOOD SYSTEMS– final report fromBERAS Work Package 2Artur Granstedt, Olof Thomssonand Thomas Schneider (eds.)Centrum för uthålligt lantbrukBaltic Ecological Recycling Agriculture and Society (BERAS) Nr. 5105C H A P T E R   VIIWinfried Schäfer, AgriculturalEngineering Research (VAKOLA),MTT, FinlandArtur Granstedt and Lars Evers,Swedish Biodynamic ResearchInstitute, Järna SwedenBiogas plant in JärnaThe Biodynamic Research Institute in Järna developed an on-farm bio-gas plant integrated within the highly self-supporting farm organism,Skilleby-Yttereneby, one of the farms studied in the BERAS project. Thebiogas plant digests dairy cattle manure and organic residues origina-ting from the farm and the surrounding food processing units. The in-put of stable manure and food residues contain 17.7 to 19.6 % total sol-ids. This recently developed technology is in the process of testing andrefinement.  In a two-phase process the hydrolysis reactor is conti-nuously filled and discharged. The output from the hydrolysis reactoris separated into a solid and liquid fraction. The solid fraction is com-posted. The liquid fraction is further digested in a methane reactor andthe effluent is used as liquid fertiliser. Initial results show that anaerobicdigestion followed by aerobic composting of the solid fraction improvesthe nutrient balance of the farm compared to when mere aerobic com-posting is used.MethodologyManure from 65 adult bovine units kept in a dairy stanchion stall isshifted by an hydraulic powered scraper into the feeder channel of thehydrolysis reactor. The urine is separated in the stall via a perforatedscraper floor. The manure is a mixture of faeces, straw and oat husks.From the feeder channel the manure is pressed via a 400 mm wide feederpipe to the top of the 30° inclined hydrolysis reactor of 53 m3 capacity.Gravitation slowly pulls the manure down mixing it with the substrate.After a hydraulic retention time of about 22 to 25 days at 38°C, thesubstrate is discharged through a bottomless drawer in the lower partof the reactor into the transport screw beneath. Every drawer cycleremoves about 100 l substrate from the hydrolysis reactor. From thetransport screw the major part of the substrate partly drops into a downcrossing extruder screw where it is separated into solid and liquidfractions. The remaining material in the transport screw is conveyedback to the feeder channel and inoculated into the fresh manure. Thesolid fraction from the extruder screw is stored in the dung yard forcomposting. The liquid fraction is collected in a buffer container andfrom there pumped into the methane reactor with a 17.6 m3 capacity.Liquid from the container and from the methane reactor partly returnsinto the feeder pipe (to the hydrolysis reactor) to improve the flowability. After an hydraulic retention time of 15–16 days at 38°C theeffluent is pumped into a slurry store covered by a floating canvas. Thegas generated in both reactors is collected and stored in a sack and fedby a compressor to the process heater and the furnace of the estate forheating purposes. The anaerobic digestion of manure (including theliquid phase) and the following aerobic composting of the solid fractionare referred to as process A in Results.For the compost trials (10.5.2004–13.8.2004 and 27.10.2004–16.3.2005) samples of 50 l manure and 50 l solid fraction from the106     E K O L O G I S K T   L A N T B R U K   N R   4 6   •   D E C E M B E R   2 0 0 5C H A P T E R   VIIhydrolysis reactor were aerobically digested (composted) at 15°C and20°C respectively in the climate chamber of MTT/Vakola. Compost ofmanure is referred to as process B in ResultsResultsThe results concerning the nutrient contents are presented in more detailin a separate report. (Schäfer et al. 2005).During the anaerobic digestion in process A, 14.6–15.4 % of thecarbon was found in the biogas. During the aerobic composting in pro-cess A, 26–31 % of the input carbon of the solid fraction escaped. Inprocess B 58-60 % of the carbon escaped during aerobic composting.Even if the biogas yield were to be increased by threefold, there wouldstill be 41–42.5 % of carbon available for composting of the solid fraction.This confirms the hypothesis that biogas production before compostinghas a minimal negative impact on the humus balance (Möller, 2003),and much less than aerobic composting.Total nitrogen losses ranged between 19 % and 29 % in process Aand between 30 % and 48 % in process B. Similar values were found forammonium (NH4): up to 6% losses in process A compared to 96 % inprocess B. Potassium and phosphorus losses were higher (how much?)in process A than process B. The results confirm the calculations ofMöller (2003) that biogas production increases recycling of NH4 andreduces overall nitrogen losses compared to mere aerobic composting.The two-phase prototype biogas plant in Järna is suitable for di-gestion of organic residues of the farm and the nearby food processingunits. The prototype put many recent research results into practice.However there is still a lack of appropriate technical solutions for hand-ling of organic material of high dry matter content and for processoptimisation. The innovative continuously feeding and dischargingtechnique is appropriate for the consistency and the dry matter contentof the organic residues of the farm. It is probably not suitable for largerquantities of un-chopped straw or green cut.DiscussionAnaerobic digestion of manure and organic residues followed bycomposting the dry fraction of the hydrolysis reactor improves theenergy and nutrient balance compared to mere aerobic composting sinceit achieves both the production of methane gas (that can be used forheating, electricity production or vehicle fuel) and the conservation ofnutrients. Appropriate new technology such as the prototype biogasplant in Järna is a key factor in making this possible.More measurements are required to see if the results cited abovecan be confirmed. The optimisation of the plant in respect to hydraulicretention time and load rate may lead to higher gas generation but thiswould require an improved measuring technique. In addition aneconomic evaluation is necessary to assess the competitiveness of thenew technology. The benefits of an on-farm biogas plant may be more107C H A P T E R   VIIevident if the nutrient balance evaluation considers not only the biogasplant but also the nutrient cycle of the farm organism over a wholecrop rotation period. Not only the quantity but also the quality of thenutrients affects soil fertility, fodder quality and animal health and bothneed to be taken into considerationTiina Lehto, South Savo RegionalEnvironment Centre, Finland, andArtur Granstedt, SwedishBiodynamic Research Institute,Järna, SwedenPossibilities for developing combined recycling andrenewable energy production in Juva and JärnaThe plant nutrients in food stuffs from agriculture end up in slaughter-house wastes, domestic wastes (wastes from household and foodindustry) and sewage wastes. These three fractions contain 4, 3 and 2kg N per capita and year and 2, 0.5 and 1 kg P per capita and year(Calculated from Magid et al. 2002). About 60 % of the nitrogen and45% of the phosphorus are in the liquid wastes residues mainly in thehuman urine fraction. Of the total phosphorus taken up by plants (20kg P per ha) about 75 % can be recycled within the farming system onecological recycling agriculture (ERA) farms if nutrients in manure areoptimally utilized. However, 15 % of the P is found in the sewage fractionfrom human consumption. This could be re-circulated for use in agri-culture through urine separation if the hygienic aspects can be takencare of in a secure way. Another 10 % of the P is found in slaughterwastes which could also be an important resource for the sustainableagriculture.Two ways of local recycling of the solid fraction of biowaste, oneof which is combined with the production of biogas, have been studiedwithin the BERAS-project. Their goal is the safe recycling of nutrients,reduced emissions of greenhouse gases and reduced emissions ofreactive nitrogen. One way is the central recycling at community leveldescribed above for Juva that often is combined with production ofbiogas and other energy recovering systems. However, centralisedbiowaste treatment raises problems with quality control and with thehigh risk of contamination from heavy metals, medicaments, and ani-mal (including human) pathogens. For these reasons these nutrientsare not allowed to be used on soil for food production.The second option is to have a smaller-scale system with betteropportunities to choose and control the material treated. An exampleof this is the recycling of food residues introduced in the small-scalebiogas plant on Yttereneby farm in Järna described above. This small-scale biogas plant for use at farm level may be a better solution forrecycling of nutrients from human food (local processors, ecologicalpublic kitchens and consumers) as it provides opportunities for effectivecontrol against contamination from pathogens and harmful substances.This technology was established as an essential link in the local ecologicalrecycling system that at the same time reduces emissions of greenhouse

Biogas plant in Järna

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