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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. [ABSTRACT FROM AUTHOR]

Currently, there are challenges with proper disposal of cassava processing wastewater, and a need for sustainable energy in the cassava industry. This study investigated the impact of co-digestion of cassava wastewater (CW) with livestock manure (poultry litter (PL) and dairy manure (DM)), and porous adsorbents (biochar (B-Char) and zeolite (ZEO)) on energy production and treatment efficiency. Batch anaerobic digestion experiments were conducted, with 16 treatments of CW combined with manure and/or porous adsorbents using triplicate reactors for 48 days. The results showed that CW combined with ZEO (3 g/g total solids (TS)) produced the highest cumulative CH4 (653 mL CH4/g VS), while CW:PL (1:1) produced the most CH4 on a mass basis (17.9 mL CH4/g substrate). The largest reduction in lag phase was observed in the mixture containing CW (1:1), PL (1:1), and B-Char (3 g/g TS), yielding 400 mL CH4/g volatile solids (VS) after 15 days of digestion, which was 84.8% of the total cumulative CH4 from the 48-day trial. Co-digesting CW with ZEO, B-Char, or PL provided the necessary buffer needed for digestion of CW, which improved the process stability and resulted in a significant reduction in chemical oxygen demand (COD). Co-digestion could provide a sustainable strategy for treating and valorizing CW. Scale-up calculations showed that a CW input of 1000–2000 L/d co-digested with PL (1:1) could produce 9403 m3 CH4/yr using a 50 m3 digester, equivalent to 373,327 MJ/yr or 24.9 tons of firewood/year. This system would have a profit of $5642/yr and a $47,805 net present value. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) is a corrosive trace gas present in biogas produced from anaerobic digestion systems that should be removed to reduce engine-generator set maintenance costs. This study was conducted to provide a more complete understanding of two H2S scrubbers in terms of efficiency, operational and maintenance parameters, capital and operational costs, and the effect of scrubber management on sustained H2S reduction potential. For this work, biogas H2S, CO2, O2, and CH4 concentrations were quantified for two existing H2S scrubbing systems (iron-oxide scrubber, and biological oxidation using air injection) located on two rural dairy farms. In the micro-aerated digester, the variability in biogas H2S concentration (average: 1938 ± 65 ppm) correlated with the O2 concentration (average: 0.030 ± 0.004%). For the iron-oxide scrubber, there was no significant difference in the H2S concentrations in the pre-scrubbed (450 ± 42 ppm) and post-scrubbed (430 ± 41 ppm) biogas due to the use of scrap iron and steel wool instead of proprietary iron oxide-based adsorbents often used for biogas desulfurization. Even though the capital and operating costs for the two scrubbing systems were low (<$1500/year), the lack of dedicated operators led to inefficient performance for the two scrubbing systems. [ABSTRACT FROM AUTHOR]

Co-digestion of dairy manure with waste organic substrates has been shown to increase the methane (CH4) yield of farm-scale anaerobic digestion (AD). A gummy vitamin waste (GVW) product was evaluated as an AD co-digestion substrate using batch AD testing. The GVW product was added at four inclusion levels (0%, 5%, 9%, and 23% on a wet mass basis) to a co-digestion substrate mixture of dairy manure (DM), food-waste (FW), and grease-waste (GW) and compared to mono-digestion of the GVW, DM, FW, and GW substrates. All GVW co-digestion treatments significantly increased CH4 yield by 126–151% (336–374 mL CH4/g volatile solids (VS)) compared to DM-only treatment (149 mL CH4/g VS). The GVW co-digestion treatments also significantly decreased the hydrogen sulfide (H2S) content in the biogas by 66–83% (35.1–71.9 mL H2S/kg VS) compared to DM-only (212 mL H2S/kg VS) due to the low sulfur (S) content in GVW waste. The study showed that GVW is a potentially valuable co-digestion substrate for dairy manure. The high density of VS and low moisture and S content of GVW resulted in higher CH4 yields and lower H2S concentrations, which could be economically beneficial for dairy farmers. [ABSTRACT FROM AUTHOR]