Construction Of A Continuous Flow Bacterial-algal Symbiotic System And Study Of Denitrification Mechanism

Under the premise of"carbon neutrality"and"carbon peaking",municipal wastewater treatment discharge standards in China are becoming increasingly stringent.AAO（anaerobic-anoxic-aerobic）,which is the mainstream process in wastewater treatment plants,has the problems such as high energy consumption of the oxygen supply system and high treatment costs.Therefore,this paper designs an integrated AAO plant,constructs an integrated activated sludge system,and inoculates algae directly after the system is stabilized,so as to build an integrated bacterial-algal symbiotic system（ABS）.Finally,the analysis compares the removal effects of dissolved chemical oxygen demand（SCOD）,ammonia nitrogen（NH₄⁺-N）,total nitrogen（TN）,total phosphorus（TP）,and other pollutants between integrated bacterial-algal symbiotic system and integrated activated sludge system,and compares the similarities and differences of nitrogen removal pathways between them.The main conclusions obtained from this experiment are as follows:（1）The system mixed liquor suspended solids（MLSS）was stabilized at 2500–3500mg/L,the nitrification liquid reflux ratio was 300%,the sludge reflux ratio was 100%,the hydraulic retention time（HRT）was 8 h,the water temperature was 23°C,the mud age was 16 days,the dissolved oxygen（DO）in the anaerobic tank was lower than 0.1mg/L,the DO in the anoxic tank was lower than 0.2 mg/L,and the DO in the aerobic tank was maintained at 2.5 mg/L.Under the working condition of 2.5 mg/L,the discharge water quality of the integrated activated sludge system can reach the discharge requirement stably by adding 39.50 mg/L of polymeric aluminum chloride（PAC）.（2）After stabilization,the aeration volume was reduced from 0.35 L/min to 0.20 L/min,and the dissolved oxygen in the anaerobic tank was lower than 0.1 mg/L,the dissolved oxygen in the anoxic tank was lower than 0.1 mg/L,and the dissolved oxygen in the aerobic tank was 0.55 mg/L.Under the working conditions,PAC at 42.00 mg/L was added.All the effluent indexes can reach the standard.（3）There are three denitrification pathways in the integrated activated sludge system:assimilation,conventional nitrification-denitrification,and simultaneous nitrification-denitrification,contributing 47.10%,31.58%,and 21.32%,respectively.The assimilation of the integrated bacterial-algal symbiotic system contributed 55.21%to systemic denitrification and 44.79%to nitrification-denitrification.The reason for the enrichment of light-promoted bacterial genera and the enrichment of assimilatory uptake of ammonia nitrogen genes in this system is the special culture method（direct inoculation of algae by AAO）.This resulted in an integrated bacterial-algal symbiotic system with 42.86%lower aeration,100%higher resource recovery potential value and23.93%higher maximum level of nitrogen removal than the integrated activated sludge system.