On-farm trials of practical options for hydrogen sulphide removal from piggery biogas

Manure-derived biogas is increasingly used at Australian piggeries to produce heat and generate electricity. However, high concentrations of hydrogen sulphide (H2S) in piggery biogas is discouraging further use, because of a lack of practical, cost-effective H2S removal options. To address this issue, on-farm trials were conducted at two piggeries. One trial tested H2S oxidation; adding small amounts of air to biogas, upstream of a low-cost enhanced surface treatment vessel which was fabricated on-farm with intrinsic safety measures. Covered anaerobic pond (CAP) effluent provided a convenient, low-cost nutrient source for the biofilm of naturally-occurring microorganisms in the packed column. This treatment was effective, removing over 90% of the H2S in a single pass and reducing H2S concentrations from 4000 ppm to <400 ppm. Another trial tested chemisorption performance of natural, iron-rich red soil, mixed with a ground sugar cane mulch bulking agent, in comparison with cg5 commercial media (iron-oxide pellets). The red soil removed H2S, but had a substantially lower capacity (∼2 g S/kg red soil) than the cg5 (∼200 g S/kg media). Accordingly, red soil is unlikely to be feasible as a primary treatment medium, but may be useful for final polishing after an oxidation step has removed most of the H2S.