Dual-function of nitrogen removal and autoinducer-2 quorum quenching improves MBR performance in treating...

Semiconductor wastewater contains high concentrations of nitrogen and toxic organic compounds, posing significant environmental and operational challenges for biological treatment systems. In this study, we isolated the dual-function bacterium Enterobacter sp. XB1, which primarily removes nitrogen through dissimilatory nitrate reduction to ammonium (DNRA) and assimilatory nitrate reduction (ANR), and also exhibits autoinducer-2 (AI-2) quorum quenching (QQ) activity. XB1 was immobilized in polymeric beads and employed in a membrane bioreactor (MBR) to enhance nitrogen removal and mitigate biofouling. The strain exhibited robust performance under tetramethylammonium hydroxide (TMAH, up to 400 mg/L) stress, achieving ammonium and total nitrogen (TN) removal rates of 12.1 mg/L/h and 14.5 ± 0.53 mg/L/h, respectively. While DNRA facilitates rapid nitrate-to-ammonium conversion, true TN removal is achieved primarily through ANR-driven biomass assimilation, which results in actual nitrogen elimination when combined with sludge wasting under SRT-controlled MBR operation. Membrane biofouling in the MBR was delayed by a 2.6-fold due to AI-2 signal disruption. In real semiconductor wastewater, XB1 achieved a TN removal rate of 92.1 ± 0.22 % and a reduction in total organic carbon (TOC) of 74.3 ± 0.61 % within 6 h. Transcriptomic analysis revealed the presence of genes associated with dissimilatory and assimilatory nitrate reduction, as well as AI-2 uptake. These findings demonstrate the feasibility of integrating XB1 into MBR systems for efficient nitrogen and organic pollutant removal, while simultaneously reducing membrane fouling. This study thus presents a promising strategy for sustainable semiconductor wastewater treatment.