Biocarrier with layer-specific structure enhanced the microalgae-partial nitrification-anammox system performance: Insights into microbial aggregation behavior by FT-ICR-MS and XDLVO analysis

Microalgae-partial nitrification-anammox (MPNA) can simultaneously address the technical bottlenecks of nitrite source and phosphate removal of anammox bacteria, but biomass loss and unclear aggregation mechanisms remain challenges. In this work, the biocarrier with layer-specific structure was applied in MPNA to encapsulate the biomass for modulating the cooperative nitrogen and phosphorus metabolism among microorganisms. In MPNA with biocarrier, the alteration of the microenvironment enriched AnAOB and AOB as well as inhibited the NOB, and more biodegradable organics participated in substrate exchange between microalgae and bacteria, assisting nitrogen metabolism. Thus, the total nitrogen and phosphorus removal efficiency reached 89.7% and 79.2%, increased by 17.4% and 16.3% compared to MPNA, respectively. By combining molecular spectrum and FT-ICR-MS analysis, the biocarrier with layer-specific structure was proven to induce microorganism to produce more hydrophobic substances like lignin, carbohydrates, condensed aromatic structures for improving Lewis acid-base free energy, microbial aggregation and sludge mechanical strength. Lastly, the genes associated with EPS synthesis and nitrogen cycle were dissected. This work sheds light on strategy development of biomass retention and granule aggregation in engineered application of microalgae-partial nitrification-anammox system.