Hybrid membrane bioreactor-filler system enables efficient nitrogen removal from semiconductor wastewater through engineered microbial niche differentiation: Process optimization, biofilm-enhanced kinetics, and multi-omics insights.

Qidong Yin, Jingjing Sun, Qianyuan Wu, Wen-Long Wang, Yuntao Guan

Nitrogen removal from semiconductor wastewater is challenged by low carbon-to-nitrogen (C/N) ratios and the need for specialized microbial guilds to degrade organoamines including tetramethylammonium hydroxide (TMAH), N-methyl-2-pyrrolidone (NMP), and monoethanolamine (MEA). We hypothesized that creating distinct ecological niches within a single treatment system would shift microbial community assembly from stochastic to deterministic processes, selectively enriching specialized functional guilds and improving nitrogen removal without external carbon addition. To test this, we developed a hybrid system integrating a multi-stage anoxic-oxic (AOAO) process with a long sludge retention time (SRT) membrane bioreactor (MBR) and polyurethane fillers, creating three distinct ecological niches (suspended sludge, filler biofilm, and MBR biomass). Following process optimization with back-loaded hydraulic retention time (HRT) allocation and 150% internal recycle, the system achieved stable total nitrogen (TN) removal of 73% (effluent TN 7-9 mg L-1) without external carbon addition. Normalized stochasticity ratio (NST) analysis confirmed that the anoxic microenvironment within fillers shifted community assembly toward deterministic processes (NST = 37% vs. 76% in suspended sludge). This shift enriched Methanomethylovorans (5.1-fold) for anaerobic TMAH demethylation and Hyphomicrobium for methylotrophic denitrification. Untargeted metabolomics identified tryptophan and succinate depletion in filler biofilm, with strong metabolite-gene correlations (tryptophan-norB, r = 0.90; succinate-dmmA, r = 0.83) linking organoamine catabolism to respiratory denitrification. Co-occurrence network analysis confirmed tightly coupled anaerobic demethylation and denitrification modules in filler biofilm (216 edges, density 0.53). This work demonstrates that engineered niche differentiation can overcome carbon limitation in organoamine-rich industrial wastewater, providing a transferable design paradigm for carbon-efficient biological nitrogen removal.