Simultaneous and Efficient Removal of Linear Alkylbenzenesulfonate and Nitrogen in a Membrane Biofilm Reactor under Low Dissolved Oxygen Conditions
Xiaocai Cui, Beibei Wu, Ying Liu, Qingqing Ren, Tian Ren, Yun Zhou
Abstract
This work focused on revealing the removal mechanisms of linear alkylbenzenesulfonate (LAS) and nitrogen under low dissolved oxygen (DO) conditions in a membrane biofilm reactor (MBfR) during greywater treatment. High ammonium led to net accumulation of protein-enriched extracellular polymeric substances (EPS). The biofilms with more protein-EPS had faster kinetics for the removal of LAS, ammonium, and total nitrogen, based on zero-order or first-order kinetics. High protein-EPS alleviated LAS toxicity to microbial physiological functions and achieved stable and efficient removal of LAS and nitrogen under low DO conditions. With DO concentrations of 0.6 mg/L, all the biofilm samples achieved efficient ammonia oxidation and LAS mineralization. When DO decreased to 0.3 mg/L, enriching the biofilms with more ammonium led to increased accumulation of LAS biodegradation-related genus and enzymes, nitrifiers and ammonium monooxygenases (AMO), and denitrification-related heterotrophs and reductases, all of which allowed the unaffected removal of LAS and nitrogen under low DO conditions. Two metabolic LAS removal mechanisms under low DO conditions were that LAS can be mineralized in the presence of AMO and LAS oxidase, and LAS can be removed in the denitrification process as the electron donor. Our results provided key information for the practical application of O2-MBfR in low-energy-input wastewater treatment.