Practical options for cleaning biogas prior to on-farm use at piggeries

Abstract

Interest in the use of biogas from anaerobic digestion has been increasing within the Australian pork industry in recent years, driven by a significant potential for biogas use to buffer rising energy costs and to reduce carbon emissions from individual piggeries and across the whole pork industry. A recent life cycle assessment study suggested that a 64% reduction in piggery GHG emissions could be achieved by installing biogas capture and use systems. Further Government incentives have also contributed to the growing interest in on-farm biogas.One of the major obstacles to adoption of on-farm biogas technology in the Australian pork sector is the presence of relatively high concentrations of hydrogen sulphide (H2S) in raw piggery biogas, commonly in the range of 500 to 3000 ppm. Smelling like rotten eggs, H2S is highly toxic and corrosive. Exposure to H2S, even at relatively low concentrations, can result in severe human health impacts, while corrosion and increased maintenance of biogas use equipment necessitates some form of biogas treatment to remove H2S to suitable levels.Many of the existing biogas treatment technologies used in other industries are not ideally suited for on-farm application in the Australian pork industry, because on-farm systems must be relatively simple, low-cost, safe, robust and scalable, producing minimal hazardous waste products. However, a literature review, which examined various existing biogas purification technologies, identified biological oxidation of H2S and chemisorption with iron-based solid media as potential options for piggeries, provided that some key research and development gaps could be addressed. A particular issue with regard to chemisorption was the high cost of replacing commercial chemisorption medium (accounting for up to 5% of the savings derived from biogas use). Of further interest was the observation that the active components in commercial chemisorption media were also relatively common in natural materials such as soils, and even in some agricultural and industrial waste and by-products. However, such alternative chemisorption media required targeted laboratory and on-farm testing. With regard to biological oxidation, there was a need to determine whether the treated effluent outflow from a covered anaerobic lagoon could be used as a viable nutrient source in an external packed column system. This concept required testing on-farm.(ii)To assess chemisorption options, a detailed and carefully designed laboratory study tested and compared the H2S removal capacity of a commercial iron-based medium (cg5) with that of a range of low-cost alternative media. The results of these trials indicated a far superior performance of a commercial cg5 medium, probably due to its engineered high porosity and high iron content (the active ingredient). However, a locally sourced red soil was a potentially feasible alternative medium, with reasonable chemisorption capacity and likely low cost and ready availability, depending on the piggery locality. While the pressur...

Raw Biogas Desulphurization Using the Adsorption-Absorption Technique for a Pilot Production of Agricultural Biogas from Pig Slurry in Poland

“…Activated carbon treatment could potentially be used to "polish" the biogas quality after some pretreatment step. However, it is unlikely to be widely used as a single biogas treatment step in piggeries due to the high cost of batch replacement and complexity of regeneration options [86]. By adsorption on an activated carbon bed, H2S is removed from biogas [81].…”