Nutrient removal performance and microbiome of an energy-efficient reciprocation MLE-MBR operated under hypoxic conditions

Abstract

A critical challenge in the application of membrane bioreactors (MBR) for domestic wastewater treatment is its high energy consumption caused by continuous aeration for biofouling control. To reduce energy consumption and mitigate fouling in membranes, alternative configurations using dynamic shear-enhanced filtration by membrane reciprocation, rotation, and vibration to mechanically impose shear on membrane surfaces have been recently introduced. However, although these methods are effective at lowering energy usage, the nutrient removal efficiencies and microbial community compositions of these systems have not been well studied. In this study, a lab-scale no-aeration reciprocation membrane bioreactor was used to characterize the microbial composition, functional profile and nutrient removal of the reciprocation MBR system operated under hypoxic conditions. Microbial community analysis showed Proteobacteria (35%) and Saccharibacteria (27%) to be the most abundant phyla in the sludge and the biofilm samples, respectively. Nitrogen and phosphorus removal efficiencies were observed at 70% and 50% while the chemical oxygen demand concentration had about a 99% decrease in the effluent. Quantitative PCR of nutrient-removing genes revealed the presence of complete ammonia-oxidizing organisms (comammox) with a mean abundance of 1.88 × 10⁴ gene copies/g sludge, which explains the high ammonia removal despite a low abundance of canonical ammonia-oxidizing bacteria (AOB). Fluorescence in-situ hybridization showed a prevalence of nitrite-oxidizing bacteria (NOB) with clusters that are distant from other nutrient-removing communities, suggesting that their metabolism is not dependent on ammonia oxidizers. The reciprocation MBR configuration may be a suitable, more energy-efficient alternative to conventional air-scouring systems because of its biofouling mitigation and promising nutrient removal performed by the diverse microbial communities in its system.

Keywords: Comammox; Membrane bioreactor; Nutrient removal; Reciprocation.