Effects of oxygen supply mode on linear alkylbenzene sulfonate removal during greywater treatment by oxygen-based membrane biofilm reactor.

The oxygen-based membrane biofilm reactor (O2-MBfR) has garnered increasing attention for its ability to remove linear alkylbenzene sulfonate (LAS), a widely used surfactant, from greywater for reuse while avoiding foam-related issues. However, the influence of the O2 supply mode on aerobic LAS removal remains unclear. Advancements in this area could improve O2 utilization efficiency, thereby reducing additional costs from increased aeration or advanced membrane materials. In this study, parallel and tandem O2 supply modes were compared by evaluating LAS mineralization and metabolisms in the O2-MBfR. The results demonstrated that the tandem mode achieved more efficient O2 utilization for pollutant removal. During the first 45 days, average removal ratios for chemical oxygen demand, total nitrogen and LAS were 85.8% vs. 89.2%, 68.8% vs. 83.0% and 92.9% vs. 95.3% between tandem and parallel modes, respectively. In addition, the effluent under the tandem mode exhibited improved biological stability. Mechanistic study revealed that the tandem mode increased protein and α-polysaccharide proportions in biofilms, resulting in thinner yet more compact structures with stronger resistance to hydraulic shocks. The tandem mode also promoted the growth of LAS-degrading bacteria. For instance, the abundance of the Pseudomonas genus participating in the initial steps of LAS biodegradation was 1.25-4.76 times as much as that under the parallel mode. Furthermore, statistically more LAS-degrading enzymes (e.g., acyl-CoA dehydrogenase) were enriched under the tandem mode. These findings highlight a great potential of implementing the tandem O2 supply mode in push-flow O2-MBfRs to achieve high-efficiency LAS removal while reducing costs.