Alleviating sulfide toxicity using biochar during anaerobic treatment of sulfate-laden wastewater

This study examined the use of biochar to alleviate sulfide toxicity to methane producing archaea (MPA) and sulfate-reducing bacteria (SRB) during anaerobic treatment of sulfate-rich wastewater with concomitant sulfur recovery. At the sulfate concentration of 6000 mg SO₄^2-/L, the dissolved sulfide (DS) of 131 mg S/L resulted in total volatile fatty acids concentration of 3500 mg/L as acetic acid (HAc) and the reactors were on the verge of failure. Biochar removed >98% of H₂S_(g), 94% of DS, and 89% of unionized sulfide (H₂S_aq). 16S rRNA analysis revealed that after sulfide removal the relative abundance of MPA (Methanobacterium and Methanosaeta) increased from 0.7% to 3.7%, while the relative abundance of SRB (Desulfovibrio) decreased from 9.3% to 0.5% indicating that the reactor recovered to stable state. This study showed that biochar could effectively remove H₂S from biogas, alleviate sulfide toxicity to MPA and SRB, and promote stability of the anaerobic process.