Establishing mainstream nitrite shunt process in membrane aerated biofilm reactors: Impact of organic carbon and biofilm scouring intensity

Abstract

Establishing one-stage short-cut nitrogen removal processes for carbon captured wastewater has been a challenge. This paper characterizes implementation of a nitrite shunt process in an intermittently aerated membrane aerated biofilm reactor (MABR). The unique characteristics of MABR showed the development of a diverse microbial population facilitating a multi-population coexistence approach to establish the nitrite shunt process. This study also evaluates the impact of soluble COD (sCOD):N ratio and scouring intensity on ammonia and total nitrogen removal efficiencies. Two sCOD:N ratio levels and three scouring modes, including aggressive, normal, and no scouring, were examined in six junior MABR pilots. The pilots were fed chemically enhanced primary treated wastewater with an ammonia concentration of 20 mg/L. The results showed that under intermittent aeration and sCOD:N ratio of 2.5, denitrifiers could out-compete nitrite-oxidizing bacteria (NOB), and a successful nitrite shunt pathway was achieved. However, when wastewater with an sCOD:N ratio of 1.2 was introduced, NOB was the dominant active species. The results also indicated that MABRs with no scouring achieved significantly higher total nitrogen removal, 0.80 g/m 2/d, than the aggressively and normally-scoured MABRs, 0.34 g/m 2 /d, and 0.59 g/m 2/d, respectively. In terms of ammonia removal, the MABRs under normal scouring showed the highest removal of 1.58 g/m 2/d, whereas the MABRs scoured aggressively showed no notable performance either in total nitrogen removal or in ammonia removal. The microbial analysis revealed a higher relative abundance of nitrifiers and denitrifiers in normally-scoured and non-scoured MABRs, respectively.