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Microaeration reduces hydrogen sulfide in biogas

Walter Mulbry, Stephanie Lansing, Craig Coker
Biocycle 2017 v.58 no.1 pp. 57-59
aeration, air, anaerobic digesters, anaerobic digestion, bacteria, biogas, chemical treatment, dairy manure, emissions, equipment design, feedstocks, headspace analysis, hydrogen sulfide, oxidation, oxygen, pumps, sensors (equipment), sludge, sulfur
Although there are a variety of biological and chemical treatments for removal of hydrogen sulfide (H(2)S) from biogas, all require some level of chemical or water inputs and maintenance. In practice, managing biogas H(2)S remains a significant challenge for agricultural digesters where labor and operational funds are very limited compared to municipal and industrial digesters. As an alternative treatment for H(2)S, relatively low volumes of oxygen or air can be injected into the digester headspace. Under the resulting micro-aerobic conditions, sulfide-oxidizing bacteria in the manure feedstock will convert dissolved sulfide into elemental sulfur. Although the feasibility of sulfide oxidation under micro-aerobic conditions has been demonstrated in small scale experiments and sludge digesters, further research is improve this approach for use on small agricultural digesters. The objective of this study was to determine the effect of different aeration rates on hydrogen sulfide emissions during anaerobic digestion of dairy manure. Duplicate plug flow field-scale digesters were operated at different levels of aeration or without aeration. Results showed that hydrogen sulfide levels decreased rapidly from 3500 ppmv to less than 100 ppmv when oxygen levels in the digesters were 0.4% or higher. Control of aeration rates using simple pumps coupled to inexpensive oxygen sensors may lead to improved use of microaeration in both large and small digester operations.