Enhanced nitrogen removal in a micro-polluted drinking water reservoir by a new WLA-Bio® system: Mechanisms and...

The limited availability of organic carbon sources in micro-polluted water bodies restricts the efficiency of biological nitrogen removal in reservoirs. To address this limitation, a system integrating water-lifting aerators (WLAs) with inorganic electron donors was deployed to enhance the removal of nitrogen, phosphorus, and organic contaminants by indigenous microorganisms. In-situ enclosure experiments demonstrated that the WLA coupled with a biological reactor (WLA-Bio®) achieved removal efficiencies of 39.06 % for total nitrogen (TN), 65.22 % for total phosphorus (TP), and 29.03 % for chemical oxygen demand (COD_Mn). The system significantly increased the abundance of aerobic and autotrophic denitrifying bacteria by supplying essential dissolved oxygen and electron donors (e.g., Acinetobacter, Exiguobacterium, Legionella, and Flavobacterium). Co-occurrence network analysis revealed intricate microbial interactions within the system. The species abundance distribution (SAD) was well fitted by a log-normal model, while the neutral community model (NCM) indicated that stochastic processes played a dominant role in microbial community assembly, accompanied by enhanced species dispersal. Notably, the system promoted microbial metabolic activity by providing electrons required for denitrification and iron ions necessary for functional gene expression, leading to a 2.11-fold, 1.61-fold, and 1.88-fold increase in the abundance of napA, nirK, and nirS genes, respectively. These findings confirm the effectiveness of the integrated WLAs and inorganic electron donor system in contaminant removal, offering a promising strategy for in-situ remediation of micro-polluted water sources.