Study on wastewater treatment characteristics and microbial ecosystem of bacteria-algae symbiosis coupling under carbon neutralization background

At present, environmental pollution is becoming more and more serious, the sustainable development of human society is facing severe challenges. As a crucial nexus for pollutant discharge and greenhouse gas emissions, the establishment of carbon-neutral wastewater treatment processes in wastewater treatment plants, aiming to achieve coordinated development of pollution reduction and carbon mitigation, constitutes a pivotal pathway for environmental governance in the new era. The bacteria-algae symbiotic culture system, based on microalgae biological treatment technology, integrates wastewater treatment, carbon fixation, and biomass energy recovery. It represents a green, low-carbon, economical, and sustainable integrated sewage treatment technology, aligning with the requirements of carbon neutrality. This study constructed an algae-assisted sequencing batch photobioreactor (A-SBPBR) and individual microalgal systems to compare the degradation efficiencies of soluble chemical oxygen demand (sCOD), ammonia nitrogen (AN), and total phosphorus (TP) in high-strength food waste anaerobic digestion effluent (ADE), with high-throughput sequencing conducted to analyze bacterial community dynamics and microbial ecological shifts, coupled with carbon accounting model integration to quantify system-specific carbon emission reduction capacities. Experimental results demonstrated that the bacteria-algae symbiotic system achieved removal efficiencies of 58.89 %, 91.94 %, and 78.89 % for sCOD, AN, and TP, respectively, when treating ADE. Notably, the sCOD degradation rate was approximately 8 % higher than that of the pure algal system. At the phylum level, the bacterial community structure within the symbiotic system exhibited greater diversity and balanced phylum distribution. At the class level, the relative abundances of Gammaproteobacteria, Anaerolineae, and Microgenomatia increased by 5-12 %, 11-14 %, and 2-6 %, respectively, compared to the pure algal system. Carbon footprint analysis revealed that treating 1 m³ of ADE with the symbiotic system reduced CO₂ emissions by 51.2 g compared to conventional aerobic processes and lowered CH₄ emissions (expressed as CO₂ equivalents) by 111.94 g relative to anaerobic processes. These findings indicate that the bacteria-algae symbiotic technology synergistically combines high-efficiency pollutant removal with carbon sequestration capabilities, providing a viable solution for wastewater treatment aligned with carbon neutrality objectives.