Insights into sulfate removal by batch cultures of sulfate reducing bacteria and photosynthetic bacteria: bioreduction of high-concentration sulfate

Sulfate-containing wastewater treatment is important for decreasing industrial pollution. This study investigated the operation of upflow anaerobic sludge blanket (UASB) in removing sulfate at high loading rates under light and dark environments, respectively. Then, sulfate reducing bacteria (SRB) and photosynthetic bacteria (PSB) were isolated from reactors and cultivated at different oxygen and illumination conditions to explore their sulfate removal performance. In UASB systems, photoreactors maintained approximately 60% sulfate removal at a COD concentration of 10,000 mg/L, whereas non-photoreactors exhibited a near-complete loss of sulfate removal under the same conditions due to sulfide toxicity. SRB survived in both aerobic and anaerobic environments; however, exposure to light slightly inhibited sulfate removal with a reduction of 7.72%. Besides, PSB exhibited 20% faster growth under anaerobic conditions. Natural light further enhanced sulfide removal efficiency, achieving 50% removal at 300 mg/L sulfide, compared to less than 40% under compact fluorescent light. Batch inoculation of domesticated SRB and PSB into photoreactors resulted in sulfate removal efficiencies of 85.14% and 91.10%, respectively, which is significantly higher than the corresponding 72.55% and 63.48% achieved in non-photoreactors. This study not only provided a clean pathway to sulfate removal but also helped fully understand the properties of sulfate removal <i>via</i> SRB and PSB, providing a precondition for their practical application. Sulfate removal by UASB was studied in light and dark conditions at high COD loading. Effects of oxygen and illumination on SRB and PSB cultivation were explored. Integrating SRB with PSB potentially achieved a clean pathway for sulfate removal.