Effect of [zn.sup.2+] on the performances and methanogenic community shifts of UASB reactor during the treatment of swine wastewater

[Zn.sup.2+] 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 [Zn.sup.2+] 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 [Zn.sup.2+] on chemical oxygen demand (COD) removal, methane production and methanogens community were observed in accordance with different [Zn.sup.2+] dosages. COD removal rate and methane production reacted in the same way as methanogens, suggesting that the impact of [Zn.sup.2+] on the methanogenic community was the critical reason that caused the changes of UASB performance in treating swine wastewater with unstable [Zn.sup.2+] concentration. Among the methanogenic community, Methanomicrobiales (MMB) was the dominant group which got visibly impacted by the dosed [Zn.sup.2+]. Overall, lower concentration of [Zn.sup.2+], 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. Keywords 16S rRNA gene * Granular sludge * Methanogenic population * UASB * [Zn.sup.2+]