Abstract
Biological desulfurization of biogas from a field-scale anaerobic digester in Peru was tested using air injection (microaeration) in separate duplicate vessels and chemical desulfurization using duplicate iron filters to compare hydrogen sulfide (H2S) reduction, feasibility, and cost. Microaeration was tested after biogas retention times of 2 and 4 h after a single injection of ambient air at 2 L/min. The microaeration vessels contained digester sludge to seed sulfur-oxidizing bacteria and facilitate H2S removal. The average H2S removal efficiency using iron filters was 32.91%, with a maximum of 70.21%. The average H2S removal efficiency by iron filters was significantly lower than microaeration after 2 and 4 h retention times (91.5% and 99.8%, respectively). The longer retention time (4 h) resulted in a higher average removal efficiency (99.8%) compared to 2 h (91.5%). The sulfur concentration in the microaeration treatment vessel was 493% higher after 50 days of treatments, indicating that the bacterial community present in the liquid phase of the vessels effectively sequestered the sulfur compounds from the biogas. The H2S removal cost for microaeration (2 h: $29/m3 H2S removed; and 4 h: $27/m3 H2S removed) was an order of magnitude lower than for the iron filter ($382/m3 H2S removed). In the small-scale anaerobic digestion system in Peru, microaeration was more efficient and cost effective for desulfurizing the biogas than the use of iron filters.
Highlights
Anaerobic digestion (AD) reduces organic pollution while creating renewable energy in the form of methane (CH4 )-enriched biogas
The introduction of small amounts of ambient air (1–3%) into biogas storage allowed for the removal of more than 3000 ppm hydrogen sulfide (H2 S) daily from the produced biogas, often reaching a H2 S concentration lower than the detection level (1 ppm)
Microaeration H2 S removal remained stable during the 50 day experiment, while the iron filter treatment efficiency decreased over time
Summary
Anaerobic digestion (AD) reduces organic pollution while creating renewable energy in the form of methane (CH4 )-enriched biogas. The hydrogen sulfide (H2 S) concentration in biogas can be high, ranging from 100 to 30,000 ppm [1,2]. Sulfate-rich feedstocks, such as swine manure, can produce biogas with high H2 S concentrations, which affects the use of the biogas after digestion [3]. H2 S is originated by the microbial breakdown of organic material during the anaerobic digestion [4]. The presence of H2 S can compromise the functions of EGS, produce odor prior to biogas utilization, and is toxic at high concentrations [7]. According to the US Occupational Safety and Health Administration (OSHA), 0.01–1.5 ppm H2 S is the odor threshold (characteristic rotten egg smell), while 2–5 ppm H2 S may cause nausea and headaches, and 1000–2000 ppm H2 S can cause death, depending on the length of exposure
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