Bench-Scale Liquid-Phase Microaeration and Iron Dosing Comparison for In Situ Biogas Desulfurization and Antibiotic Resistance Management in Mesophilic Anaerobic Digestion

Abstract

Microaeration and iron dosing are promising in situ desulfurization methods for anaerobic digestion (AD). However, limited reports exist on their systematic comparison. Consequently, this study investigated liquid-phase microaeration (60–106 mL air/Lreactor/d) and ferric chloride (250–650 mg FeCl3/L) dosages in mesophilic AD of sewage sludge operated at a solid residence time of 20 days. Both methods provided up to 88% H2S removal and moderate siloxane removal (30–37%) but had no apparent impact on mercaptan removal from biogas. However, the control and test reactors demonstrated equivalent AD performance in terms of biomethane yields, chemical oxygen demand, and total/volatile solids degradation efficiencies, indicating that air and iron dosages were primarily utilized for biogas desulfurization. Still, both methods resulted in substantial changes in microbial community composition. Notably, the indication of syntrophy between facultative microbes and hydrogenotrophic methanogens was intensified by both methods. For both methods, antibiotic resistance gene (ARG) and mobile genetic element (MGE) abundances in digestate decreased considerably due to the decrease in the abundance of potential ARG hosts. Compared to iron dosing, MGE removal was slightly higher in the microaeration reactor. These findings provide valuable insights into the efficacy of these two approaches in desulfurization and the reduction of antibiotic resistance in AD.