Application of an anaerobic reactor for the treatment of sulfide-rich wastewater using biogas for H₂S removal

Anaerobic treatment of sulfur-rich wastewater is challenging because sulfide greatly inhibits the activity of anaerobic microorganisms, especially methanogenic archaea. We developed an internal phase-separated reactor (IPSR) that removed sulfide prior to methanogenesis by gas stripping using biogas produced in the reactor. The IPSR was fed with synthetic wastewater containing a very high sulfide concentration of up to 6,000 mg S L^-1 with a chemical oxygen demand (COD) of 30,000 mg L^-1. The IPSR was operated at an organic loading rate of 5-12 kg COD m^-3 day^-1 at 35 °C. The results show that the sulfide concentration was reduced from 6,000 mg S L^-1 in the influent to <700 mg S L^-1 in the first-stage effluent. The second-stage effluent contained <400 mg S L^-1. As a result of effective sulfide removal by its gas stripping function, the IPSR had a COD removal efficiency of >90% over the entire experimental period. High-throughput 16S rRNA gene sequencing revealed that the major anaerobic archaea were Methanobacterium and Methanosaeta, which are frequently found in high-rate anaerobic reactors. Thus, the IPSR maintains these microorganisms and achieves high-process performance even when fed wastewater with very high sulfide concentrations.