Study On The Performance Of Bacteria-algae Symbiosis-Dynamic Membrane Bioreactor For Domestic Sewage Treatment

Algae has great potential in sewage treatment.Compared with traditional sewage treatment methods,algae treatment of sewage does not require the use of chemical agents,has good biological nitrogen and phosphorus removal efficiency,and can also convert carbon dioxide into organic matter to achieve carbon sink effect.However,due to the small particle size of microalgae,it is easy to float up and lose with water,causing secondary pollution,which hinders the application of microalgae in the field of water treatment.With the concept of carbon neutrality,the requirements for energy saving and consumption reduction in sewage treatment plants have been further improved.In this case,dynamic membrane filtration(DMF)has become a new choice to improve the energy efficiency and resource recovery of urban sewage treatment plants.In this study,microalgae were inoculated into the activated sludge autochthonous dynamic membrane system,and the stainless steel mesh with a pore size of 500 mesh(25μm)was used as the membrane substrate to filter the mixture of bacteria and algae.The removal efficiency of pollutants in simulated domestic sewage and the retention effect of chlorella by dynamic membrane bioreactor(DMBR)under the condition of bacteria-algae symbiosis were investigated.The key technical problems such as operation stability and membrane fouling of bacteria-algae symbiosis-DMBR were investigated.Firstly,the symbiotic conditions of bacteria and algae were optimized.Taking the three factors of light intensity,light cycle and the proportion of bacteria and algae as variables,the optimal operating conditions of the dynamic membrane reactor were selected as light intensity 4000 lux,light 12h/dark 12 h,and the proportion of bacteria and algae 5:1.Then,the bacteria-algae symbiosis-DMBR system was operated for a long time under the determined optimal conditions.The pure sludge SBR system and the bacteria-algae symbiosis SBR system were used as controls to explore the efficiency of the bacteria-algae symbiosis-DMBR system in treating domestic sewage.By comparing the operation of bacteria-algae symbiotic-DMBR and pure sludge-DMBR systems,the effects of bacteria-algae symbiotic sludge mixture on dynamic membrane filtration and membrane fouling were studied.The results showed that the symbiotic environment of bacteria and algae could improve the degradation of pollutants.Compared with the pure sludge SBR system,the COD removal rate of the symbiotic SBR system increased by 22.9 %,and the removal rates of ammonia nitrogen,total nitrogen and total phosphorus increased by7.39 %,12.02 % and 8.01 %,respectively.The symbiotic-DMBR further improved the COD,total nitrogen and total phosphorus removal rates of the symbiotic SBR system,which were 18.92 %,3.02 % and 4.39 %,respectively.The removal effect of ammonia nitrogen was flat.The concentration of chlorophyll a in the effluent of the dynamic membrane was stable at about 400μg,and the retention rate of microalgae was up to 88.2 %,with an average of 86.3 %,which effectively alleviated the loss of algae.The MLVSS/MLSS ratio of bacteria-algae symbiosis-DMBR was between70-77 %.The microbial content in the reactor was high and the activity was strong.The average ratio of chlorophyll a concentration to MLVSS was 1.55(μg/mg).Compared with the pure sludge-DMBR,the membrane fouling cycle of the algal-bacterial symbiosis-DMBR system was prolonged by 113.3 %.The bacteria-algae symbiont changed the properties of the mixed liquid sludge.The physical and chemical properties of the sludge were strongly correlated with the changes of EPS content and composition.The change of EPS properties was the key factor affecting the performance of the dynamic membrane reactor.Finally,the physical brushing method was used to clean the polluted membrane layer.The brushing could remove most of the polluted mud cake layer,and the membrane flux was restored to 92.4 % of the new membrane.However,there were residual pollutants,resulting in a decrease in the pore size of the stainless steel mesh and a shortened membrane fouling cycle of the regenerated membrane.In summary,the bacteria-algae symbiosis-DMBR system achieved efficient and high-quality effluent and reduced membrane fouling,providing a reference for the combination of bacteria-algae system and dynamic membrane process.