Anoxic desulfurization of biogas rich in hydrogen sulfide through feedback control using biotrickling filters: Operational limits and multi-omics analysis

Biodesulfurization is crucial for sustainable biogas purification from hydrogen sulfide (H₂S). This study investigates the operational limits of anoxic biotrickling filters (BTFs) for treating biogas with high H₂S concentrations (up to 20,000 ppm_v) using nitrite, along with simulated interruptions in H₂S supply. The BTF achieved a maximum elimination capacity of 312 g S-H₂S m^-3 h^-1 with an H₂S removal efficiency of 98 % at an empty bed residence time of 284 s. A proportional-integral-derivative (PID) feedback control system was successfully employed to maintain an H₂S outlet concentration close to the requisite setpoint (100 and 500 ppm_v) by adjusting the nitrite flow rate, thereby minimizing its accumulation. Continuous nitrite feeding after interruptions in H₂S supply was essential to avoid H₂S release due to sulfate-reducing bacteria. Multi-omics analyses, combining metagenomics and proteomics, revealed Sulfurimonas as the dominant sulfur-oxidizing bacteria, which downregulates most enzyme genes involved in nitrogen and sulfur metabolism in response to substrate starvation. These findings underscore the resilience of BTFs under extreme conditions and the value of multi-omics approaches in understanding microbial population dynamics, positioning BTFs as a robust solution for large-scale biogas purification.