Effect of bacteria-algae ratio on treatment of anaerobic digested wastewater by symbiotic coupling of bacteria and algae under the background of carbon neutralization

Environmental pollution is a growing concern, particularly the impact of sewage treatment gas on the atmosphere's greenhouse effect. Efficient sewage resource recycling is crucial to achieving carbon neutrality. The bacteria-algae symbiotic sewage treatment system combines wastewater treatment, carbon dioxide fixation, and biomass energy recovery to achieve the goal of carbon neutrality, environmental protection, and the transformation of high-value added products. This paper presents the construction of a sequencing batch photobiological reaction system that utilizes a microbial-algae symbiotic relationship. The system was used to analyze the degradation effects of sCOD, TN, AN, and TP in anaerobic digestion wastewater by varying the microbial-algae ratios. Additionally, changes in the microbial community were analyzed to explore the system's potential for reducing carbon emissions. The study's findings indicate that: 1)When the ratio of bacteria to algae was 2:3, the removal rates of TN, AN, sCOD, and TP were 81.38%, 94.28%, 75.33%, and 96.56%. 2)Changing the ratio of bacteria to algae would affect the bacterial concentration in the mixed system, but not the bacterial community structure. The results indicate that a ratio of 2:3 enhances the removal of pollutants by bacteria and algae symbionts.3) Under the context of carbon neutralization, this paper investigates the reduction of carbon emissions in ADE treated by bacteria-algae symbiosis at the optimal bacteria to algae ratio. The experimental process can reduce 177.03 mg CO2 compared to complete nutrient consumption treatment, which is equivalent to a reduction of 355.08 g CO2 per 1 m3 of ADE. For full anaerobic treatment, this experimental process can reduce 228.35 mg of CO2 equivalent CH4, which translates to a reduction of 456.71 g of CO2 equivalent CH4 per 1 m3 of ADE.