Modeling versatile and dynamic anaerobic metabolism for PAOs/GAOs competition using agent-based model and verification via single cell Raman Micro-spectroscopy

Solids retention time modulates nutrient removal in pilot-scale anaerobic-aerobic-anoxic process: Carbon allocation patterns and microbial insights

Anaerobic-aerobic-anoxic (AOA) process is a promising configuration to retrofit current wastewater treatment plants with intensified carbon utilization and nutrient removal, but lacks process optimization for scaling-up in real wastewater scenarios. Solids retention time (SRT) is a fundamental parameter of activated sludge process, but its roles in the AOA process remain vague. Here, we established a pilot-scale AOA process at different SRTs (10, 20, 30 d) to investigate the comprehensive responses and potential mechanisms. The results revealed that proper SRT extension in S20 (20 d) achieved the highest nutrient removal via enhanced nitrification, denitrification, denitrifying phosphate removal (DPR), and expanded phosphorus reservoir. Simultaneously, S20 garnered the optimized carbon conservation and allocation via efficient intracellular carbon transformation, consolidating energy foundation for nutrient removal. In contrast, excessive SRT in S30 (30 d) escalated cellular expenditure for maintenance, stimulated sludge decay with starvation stresses, triggered passive ammonia/phosphate release, and ultimately deteriorated carbon allocation and nutrient removal. Furthermore, microbial insights demonstrated that S20 has tailored habitats for autotrophic nitrifiers, and specialized denitrifying phosphate accumulating organisms (Dechloromonas) and denitrifying glycogen accumulating organisms (Thauera) featuring high carbon priority, favoring nutrient removal; while S30 accelerated exclusion of functional guilds, propagated surplus generalized ordinary heterotrophic and fermentative organisms (Saccharimonadales, Ferruginibacter, Tetrasphaera), impairing the microbial functionality. Functional analysis further corroborated the enhanced nutrient metabolism in S20, and the exacerbated sludge decay and activity attenuation in S30. These findings can advance our understanding of the interactions between SRT and C-N-P cycles in the AOA process, and underscore its significance in practical application.

Distinctive species interaction patterns under high nitrite stress shape inefficient denitrifying phosphorus removal performance

Denitrifying phosphorus removal using nitrite as an electron acceptor is an innovative, resource-efficient approach for nitrogen and phosphorus removal. However, the inhibitory effects of nitrite on anoxic phosphorus uptake and process stability are unclear. This study investigated the total phosphorus removal performance under nitrite stress and analyzed microbiome responses in 186 sludge samples. The results indicated that the total phosphorus removal rates and dominant taxon abundance were highly similar under nitrite stress. High nitrite stress induced a community-state shift, leading to unstable dynamics and decreased total phosphorus removal. This shift resulted from increased species cooperation. Notably, the shared genera OLB8 and Zoogloea under non-inhibitory nitrite stress, suggesting their vital roles in mitigating nitrite stress by enhancing carbon and energy metabolism. The response patterns of these bacterial communities to high nitrite stress can guide the design and optimization of high-nitrogen wastewater reactors.