Pilot-scale biogas desulfurization through anoxic biofiltration

In this study, the performance of a pilot-scale biotrickling filter (BTF) for anoxic hydrogen sulfide (H₂S) removal from real biogas was evaluated over 226 days. The BTF, inoculated with activated sludge from a nearby wastewater treatment plant, operated in an industrial environment with raw biogas from an anaerobic digester fed with municipal solid waste. The operating strategy was based on controlling nitrate consumption by sulfur-oxidizing nitrate-reducing (SO-NR) bacteria. H₂S-inlet loads (H₂S-IL) ranged from 0.43 to 61.73 g S-H₂S m³ h⁻¹ , with biogas flow rates between 0.25 and 3.5 m³ h⁻¹ and H₂S concentration peaks of 11,000 ppm_v. The pH was maintained at 7.0 using a 25 %v·v⁻¹ NaOH solution. The H₂S removal efficiency (H₂S-RE) exceeded 93.9 % for most of the period, with a maximum elimination capacity of 35.17 g S-H₂S m⁻³ h⁻¹ at an IL of 37.20 g S-H₂S m⁻³ h⁻¹ (H₂S-RE > 95 %). Sulfate selectivity was over 85 % during normal operation. High H₂S-IL led to excessive elemental sulfur accumulation without nitrate, which was later oxidized to sulfate during low H₂S-IL periods, preventing maintenance shutdowns. Overall, the results demonstrate the efficacy of anoxic BTFs in removing H₂S under variable biogas conditions at a pilot scale.