Biogas upgrading and ammonium removal from anaerobic digestate using a hydrogen sulfide-tolerant microalgae consortium without pH control

Biogas containing up to 5,000 ppmv H2S was effectively upgraded using a microalgae-bacteria consortium without pH control, enabling simultaneous CO2 -to-O2 conversion and ammonium removal. Under H2S stress, microalgae showed increased O2 production per cell but reduced nitrogen removal. Although 10,000 ppmv H2S initally supressed microbial growth, partial recoverry occurred after acclimation, with lower overall performance. H2S altered microbial community structure, with Parachlorella dominating the microalgae and specific sulfide-tolerant bacteria (e.g., Fuscovulum, Mucilaginibacter, Paraburkholderia, Sphingomonas) emerging under high H2S.