Mechanistic insight into assimilation capture: Implication for high-efficiency nitrogen removal from mature landfill leachate

Abstract

The AO (Anoxic/oxic) process for treating high-strength ammonia in landfill leachate requires external carbon source and alkalinity. Alternatively, the processes of partial nitrification-Anammox (PNA) and partial denitrification-Anammox (PDA) with less or no carbon source have been developed, but enabled modulation difficulty due to nitrogen valence transformation. Ammonia assimilation for nitrogen removal immobilize ammonia (NH4+-N) as organic nitrogen, without nitrogen valence conversion and reducing greenhouse gases emission. This study offers a novel approach for nitrogen removal from low chemical oxygen demand (COD) to nitrogen (C/N) ratio leachate. The nitrogen removal response of biomass to ammonia assimilation in landfill leachate was established. Results demonstrated that the nitrogen removal contribution of ammonia assimilation and organics utilization by microorganisms significantly increased with biomass. When the initial mixed liquor suspended solid (MLSS) was 11200 mg/L, the removal efficiency of total nitrogen (TN) and COD in the landfill leachate achieved 98.42 ± 0.12 % and 80.60 ± 0.35 % after 30 days of operation, respectively. The corresponding assimilation contributions for TN and COD removals were 82.00 ± 0.96 % and 52.24 ± 0.82 %, respectively. Cell protein analysis showed that higher biomass significantly increased the production of intracellular and extracellular proteins or amino acids. The enrichment of bacterial genera such as Defluviicoccus, Aequorivita, Truepera, and Proteiniphilum played a crucial role in organics removal and NH4+-N assimilation. Functional gene analysis further demonstrated that most NH4+-N and organics were removed through bacterial assimilation. This research offered a green, efficient, and economical solution for the treatment of low C/N ratio landfill leachate.