Roles of sulfite and internal recirculation on organic compound removal and the microbial community structure of a sulfur cycle-driven biological wastewater treatment process

A sulfur cycle-driven bioprocess was developed for co-treatment wet flue gas desulfurization wastes with municipal sewage, as a result of sludge minimization. In this process, organics removal (one of the main objectives in sewage treatment) is closely associated with biological sulfate/sulfite reduction (BSR). In the previous studies, both the pros and corns of sulfite (SO₃²⁻) in microbial activities were demonstrated. In this study, we are motivated to unveil the detailed role of SO₃²⁻ in organic compound removal in the sulfur conversion-associated process. In addition, the effect of internal recirculation (IR) of UASB reactor was also explored. The results demonstrated that sulfite does inhibit the organic removal rate via depressing the acetate oxidation to inorganic carbon. And the inhibition is reversible when influent sulfite concentration decreased from 400 to 132 mg S/L, corresponding to the relative sulfate/sulfite-reducing genera increased from 18.66 to 38.62%. And the fermenting-related bacteria significantly decreased when an internal recirculation was employed for the UASB reactor. The results of this study could shed light on the understanding of the roles of sulfite and IR in organic compound removal performance and microbial community structures in BSR, which could be in turn beneficial to optimize the organic removal capacity of the sulfur bionconversion-concerning sewage treatment technology.