Simultaneous and Efficient Removal of Linear Alkylbenzenesulfonate and Nitrogen in a Membrane Biofilm Reactor under Low Dissolved Oxygen Conditions

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.

Carbon Source in Tertiary Denitrification Regulates Dissolved Organic Nitrogen in Wastewater Effluent

“…The lower C/N in anoxic reactors compared with aerobic reactors has been demonstrated to inhibit the yield of heterotrophic microorganisms. 57 Due to the requirement of oxygen as an electron acceptor in ammonification, 58 the ability of microorganisms in the anoxic process to degrade produced DON is thus also restricted in this study. External carbon sources could be converted to organic nitrogenous matter during biological activity such as the serine cycle.…”

Mass Flow and Metabolic Pathway of Nonaeration Greywater Treatment in an Oxygenic Microalgal–Bacterial Biofilm

“…In the symbiotic biofilm, the C in LAS was aerobically biodegraded into CO 2 by the bacteria, , but CO 2 was fixed into biomass during microalgae photosynthesis . The produced O 2 in microalgae photosynthesis was utilized as the electron acceptor during LAS aerobic mineralization. , Increasing the organic loading led to continuous microalgae growth, contributing to the improved C fixation by microalgae in both regions. Compared with downstream region 2, relatively high organics and low microalgae biomass concentrations in upstream region 1 led to higher organics removal through CO 2 emission.…”

“…As summarized in Figure , the symbiotic biofilm achieved efficient C (>94%) and N (>95%) removals in a steady state for each stage, and the removals were mostly from assimilation, with only minor parts contributed by CO 2 (2.2–4.4%) and N 2 (1.7–3.5%) emissions. Compared with bacteria, microalgae assimilation was predominant in the fixing of C and N. For organics metabolism, part of the C was converted into new biomass through bacteria assimilation, but most of the C in LAS (>60%) was mineralized into CO 2 by aerobic respiration, , with a minor flow through denitrification. , The produced CO 2 during organics aerobic mineralization was converted into new microalgal biomass . Most of the N was fixed into microalgae and bacteria by assimilation processes, and only a minor flow of N was to N 2 through nitrification and denitrification (Figure ).…”