Abstract
With the increasing demand for renewable energy and sustainable waste treatment, biogas production is expanding. Approximately four billion litres of bio-ethanol are produced annually for vehicle fuel in Europe, resulting in the production of large amounts of stillage residues. This stillage is energy-rich and can be used for biogas production, but is a challenging substrate due to its high levels of nitrogen and sulphate. At the full-scale biogas production plant in Norrköping, Sweden (Svensk Biogas i Linköping AB), thin grain stillage is used as a biogas substrate. This paper describes the plant operation and strategies that have been implemented to digest thin stillage successfully. High ammonia concentrations in the digester have resulted in syntrophic acetate oxidation (SAO) becoming the major pathway for acetate degradation. Therefore, a long hydraulic retention time (HRT) (40–60 days) is used to allow the syntrophic acetate-oxidising bacteria time to grow. The high sulphate levels in thin stillage result in high levels of hydrogen sulphide following degradation of protein and the activity of sulphate-reducing bacteria (SRB), the presence of which has been confirmed by quantitative polymerase chain reaction (qPCR) analysis. To optimise biogas production and maintain a stable process, the substrate is diluted with tap water and co-digested with grain residues and glycerine to keep the ammonium nitrogen (NH4-N) concentration below 6 g L−1. Combined addition of iron, hydrochloric acid and cobalt successfully precipitates sulphides, reduces ammonia toxicity and supplies microorganisms with trace element. Mesophilic temperature (38 °C) is employed to further avoid ammonia toxicity. Together, these measures and doubling the digester volume have made it possible to increase annual biogas production from 27.7 TJ to 69.1 TJ.
Highlights
Anaerobic digestion is the microbiological degradation of organic material in the absence of oxygen.The product from this degradation is biogas, which mainly consists of bio-methane and carbon dioxide.Organic wastes from industry, wastewater treatment plants or households can be treated in biogas plants to produce energy-rich bio-methane, which may be used to produce vehicle fuel or electricity and heat
This paper describes results and experiences from a full-scale operation using thin grain stillage as the dominant substrate at an industrial biogas plant in Norrköping, Sweden run by Svensk Biogas i Linköping AB, a subsidiary company of the public municipal company Tekniska verken i Linköping AB (Linköping, Sweden)
Despite the challenges involved in using thin stillage as a substrate for biogas production, experiences show that large-scale gas production from this material is possible
Summary
Anaerobic digestion is the microbiological degradation of organic material in the absence of oxygen. As a consequence of the increased demand for renewable energy and sustainable waste treatment, the number of full-scale biogas production plants in Europe is increasing [2,3] and these require a supply of substrate, e.g., energy-rich industrial residues The high protein content in thin stillage results in the release of organic sulphur as sulphides, which have various negative effects on the industrial biogas production process These include corrosion, precipitation of trace elements, inhibition of microorganisms and consumption of organic material [mainly alcohols, volatile fatty acids (VFA) and hydrogen] that would otherwise be used for methane production [11,18,19,20]. Major challenges and the solutions devised to cope with these are discussed and on-going work to optimise gas production efficiency is described
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