Effect of Zn2+ on the Performances and Methanogenic Community Shifts of UASB Reactor During the Treatment of Swine Wastewater

Abstract

Zn2+ was added to one of the two identical bench-scale upflow anaerobic sludge blanket (UASB) reactors in steady-state period treating swine wastewater to evaluate the effects of Zn2+ on performance and methanogenic population. Real-time quantitative PCR (QPCR) was used to quantify the 16S rRNA gene concentrations of the four methanogenic orders. In both reactors, the hydraulic retention time (HRT) was sustained at 48 h and the inner temperature was kept at 35 °C. Both promotion and inhibition of Zn2+ on chemical oxygen demand (COD) removal, methane production and methanogens community were observed in accordance with different Zn2+ dosages. COD removal rate and methane production reacted in the same way as methanogens, suggesting that the impact of Zn2+ on the methanogenic community was the critical reason that caused the changes of UASB performance in treating swine wastewater with unstable Zn2+ concentration. Among the methanogenic community, Methanomicrobiales (MMB) was the dominant group which got visibly impacted by the dosed Zn2+. Overall, lower concentration of Zn2+, e.g., less than 17.8 mg/L, was supposed to be advisable for a stable and high efficient treatment of swine wastewater by UASB reactor in practice.