Headspace micro-oxygenation as a strategy for efficient biogas desulfurization and biomethane generation in a centralized sewage sludge digestion plant

The biogas produced in a centralized digestion plant treating high-solid sewage sludge under thermophilic conditions was biologically desulfurized via in-situ headspace micro-oxygenation. The removal of hydrogen sulfide (H2S) from the produced biogas was evaluated for 84 days under decreasing injection flows of oxygen (O2), resulting in O2 doses from 0.96(±0.03) to 0.19(±0.01) NL/Nm3 biogas. A stable H2S removal efficiency of 98.2(±1.3)% was obtained with an O2 dose of 0.96(±0.03) NL/Nm3 biogas, whereas removal efficiencies of 67.4(±0.7)% were observed at the lowest O2 dose tested. The response time of the biological desulfurization system to transient oxygen conditions was evaluated through intermittent O2 injection. Headspace micro-oxygenation did not negatively impact the digestion performance, and the optimization of O2 dose allowed to reach a biogas quality complying with the specification for biomethane in terms of both O2 and H2S contents. Lentimicrobiaceae, Caldicoprobacteraceae, DTU014, Syntrophomonadaceae, and Rhodobacteraceae were the main microbial families responsible for biological H2S oxidation in digester headspace.