Insights into photosynthetic bacteria-bioaugmented wastewater treatment systems: Low-carbon performance and microbial...

Photosynthetic bacteria (PSB) are regarded as promising bioaugmentation agents to assist the conventional activated sludge (CAS) wastewater treatment process in achieving low-carbon benefits, but the performance and microbial mechanisms remain poorly understood. This study selected Rhodopseudomonas palustris to develop bioaugmented (PSB-CAS) systems, evaluated their low-carbon potential under different operational conditions, and elucidated the underlying microbial mechanisms. The results indicated that the PSB-CAS system exhibited the optimal low-carbon performance under light and micro-aerobic conditions. The removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), and total phosphorus (TP) reached 93.7%, 98.8%, and 89.4%, respectively, accompanied by 31.5% reduction in carbon emissions and 123.9% increase in the proportion of the carbon sequestered in sludge. Under the regulation of R. palustris, interactions within the microbial community were optimized, leading to enhanced metabolic activity. A synergistic metabolic relationship was established in the PSB-CAS system: interspecies electron transfer with electroactive microorganisms and the oxidation of organic substrates by R. palustris provided electron donors for the Calvin-Benson-Bassham (CBB) cycle, enabling R. palustris to fix CO₂ produced by heterotrophic microorganisms via the tricarboxylic acid (TCA) cycle. Correspondingly, the inoculated R. palustris optimized microbially driven carbon transformation and promoted the sequestration of organic carbon from wastewater in sludge. Overall, this study demonstrates that the PSB bioaugmentation strategy facilitates the low-carbon performance during wastewater treatment by establishing efficient interspecies cooperation, which provides critical insights for its practical application and development.