Emission and reduction of non-CH4-trace gases in a compost-based biofilter receiving gas from a pig manure storage tank.

Manure gas consists of methane (CH4) and trace gases such as hydrogen sulphide (H2S) and ammonia (NH3), which contributes to global climate change and impacts local surroundings due to odour and eutrophication. A compost-based biofilter was established at a pig farm to reduce CH4 emissions from gas produced in a manure storage tank. This study evaluated the efficiency of the biofilter in reducing H2S and NH3 emissions. In addition, nitrous oxide (N2O) produced by the compost material was quantified, and its potential climate change impact was assessed. The average CH4 oxidation efficiency was reported to be 93 ± 6.5 % in a previous study on the biofilter. This study shows that the biofilter in addition to CH4 significantly reduced H2S and NH3 trace gas emissions by 86% and 84% on average, respectively. The production and emission of N2O from the biofilter surface was very low (2.8% compared to CH4 removal (g CO2-eq m-2h-1)) and did not hamper the mitigation effect of reducing CH4 emissions by the biofilter. In summary, the study demonstrated that biofilter technology is highly effective not only in removing CH4 emissions from covered manure storage tanks, but also in significantly reducing NH3 and H2S emissions.