Process performance and microbial community structures in three ANAMMOX-mediated systems with different mixing conditions.

Anaerobic ammonium oxidation (ANAMMOX) represents an efficient, cost-effective, but sensitive nitrogen removal process for wastewater treatment. Different reactor configurations have been used in full-scale applications but each configuration has unique characteristics, which could influence process performance and community dynamics. The objective of this study is thus to analyze the impact of mixing conditions on nitrogen removal and community structures in a hybrid up-flow anaerobic sludge blanket reactor (H-UASB), moving bed biofilm reactor (MBBR) and gas-lift reactor (GLR). Community dynamics were studied through shotgun sequencing, while concentrations of NH 4 ⁺, NO 3 ^- and NO 2 ^- were determined colorimetrically. During the study, MBBR displayed the highest average nitrogen removal efficiency (NRE) (67%) followed by H-UASB (63%), and then GLR (54%). The relative abundance of AMX in the suspended biomass was consistently higher in H-UASB than in MBBR and GLR, while that of nitrite-oxidizing bacteria (NOB) and complete ammonia-oxidizing bacteria (CMX) was higher in MBBR than in GLR and H-UASB. It was observed that the relative abundance of ammonia-oxidizing bacteria (AOB) in the suspended biomass fluctuated across the reactors. The relative abundance of CMX and Nitrospira in the biofilms in H-UASB and GLR was higher than in the suspended biomass, while comparable abundance was observed in MBBR. On the contrary, the relative abundance of AMX in the suspended biomass in H-UASB and MBBR was higher than in the biofilms, whereas it was comparable in the GLR. It was thus concluded that the mixing conditions in the three reactors influenced process performance and community dynamics. [Display omitted] • MBBR showed better nitrogen removal than H-UASB and GLR. • Growth of AMX was favored in suspended biomass in H-UASB and MBBR. • Growth of Nitrospira spp. and CMX was favored in biofilms in H-UASB and GLR. • Comparable growth of nitrifying bacteria in biofilms and suspended biomass in MBBR. • Comparable growth of AMX in biofilms and suspended biomass in GLR. [ABSTRACT FROM AUTHOR]