H₂S and volatile fatty acids elimination by biofiltration: Clean-up process for biogas potential use

In the present work, the main objective was to evaluate a biofiltration system for removing hydrogen sulfide (H₂S) and volatile fatty acids (VFAs) contained in a gaseous stream from an anaerobic digestor (AD). The elimination of these compounds allowed the potential use of biogas while maintaining the methane (CH₄) content throughout the process. The biodegradation of H₂S was determined in the lava rock biofilter under two different empty bed residence times (EBRT). Inlet loadings lower than 200 g/m³ h at an EBRT of 81 s yielded a complete removal, attaining an elimination capacity (EC) of 142 g/m³ h, whereas at an EBRT of 31 s, a critical EC of 200 g/m³ h was reached and the EC obtained exhibited a maximum value of 232 g/m³ h. For 1500 ppmv of H₂S, 99% removal was maintained during 90 days and complete biodegradation of VFAs was observed. A recovery of 60% as sulfate was obtained due to the constant excess of O₂ concentration in the system. Acetic and propionic acids as a sole source of carbon were also evaluated in the bioreactor at different inlet loadings (0-120 g/m³ h) obtaining a complete removal (99%) for both. Microcosms biodegradation experiments conducted with VFAs demonstrated that acetic acid provided the highest biodegradation rate.