Study On The Effect And Mechanism Of Bacteria-Algal Symbiotic System On Sewage Treatment

Compared with the traditional biological treatment method,the use of bacteria-algal symbiosis system to treat wastewater can make up the deficiency of activated sludge and microalgae process.The combination of bacteria and algae can accelerate the flocculation and sedimentation of microalgae,reduce the cost of separation in the later stage of wastewater treatment by microalgae process,help to break the bottleneck of the downstream resource product chain of microalgae.Meanwhile,it can also be conducive to solve the problems of large area occupied by activated sludge process and excess sludge disposal.However,there are few studies on the effects of bacterial-algal mixing ratio and environmental factors on the removal of pollutants and bacteria-algal structure in the bacterial-algal system,and the changes of the bacterial community and the recycling of resources in the symbiosis process of the bacterial-algal system need to be further studied.Chlorella pyrenoidosa which is common in fresh water is employed as raw material to treat artificial wastewater by mixing with activated sludge in different proportions.The specific experiments and conclusions are as follows:1)At the same biomass,three systems(pure bacteria,pure alga group,and bacteria-alga ratio group)were set to investigate the effects of nitrogen and phosphorus removal,COD removal and the growth of Chlorenella.The bacteria-algal system had the best treatment effect on nitrate nitrogen,the removal effect of phosphorus was better than that of pure bacteria system,and the removal effect of COD was better than that of pure algae system.The bacteria-algae system has a good effect on the growth of Chlorella.Compared with pure algae system,the bacteria-algae system can greatly reduce the settling time.To further explore the effect of bacteria-algae group on nitrogen and phosphorus removal,high activated sludge was mixed with different proportion of Chlorella,and high Chlorella was mixed with different sludge.The results of the two experiments showed that the removal of phosphate in the symbiotic system was mainly Chlorella,and the removal of nitrate nitrogen was related to the total biomass.2)The effects of environmental factors on the removal of pollutants and the growth of Chlorella by the bacterial-algal system were investigated by setting different pH,light and dark and aeration conditions.Under different pH value conditions,the neutral bacteria-alga group had the best removal effect on nitrogen,phosphorus and COD,and the growth of Chlorenella was also the best.The acidic state and alkaline state had a great effect on the phosphorus removal and bacteria-alga structure.Under light and dark conditions,the bacteria-algae light treatment of nitrogen,phosphorus,COD effect was the best.The removal of pollutants and the promotion of Chlorella growth in the bacteria-algal light group were better than that in the pure algal light group.In the dark condition,the nitrogen removal effect of the bacteria-algal dark group was better than that of the pure algal dark group,and the phosphorus removal effect of both groups was poor.Compared with the growth of the pure algal dark group,the dark condition had a greater impact on the growth of the pure algal dark group.In view of the phosphorus release phenomenon in the bacteria-alga group before,by setting different aeration rate conditions,the nitrogen and phosphorus removal effect of the bacteria-alga group was better with the increase of aeration rate,and the nitrogen and phosphorus removal difference between the unaerated group and the aerated group was great.At the same time,aeration rate can promote the growth of Chlorella to some extent.3)On the basis of the optimized experimental conditions,the removal of pollutants by three systems(pure algae,pure bacteria and bacteria-algae system)was further investigated,and the change of microbial community structure during the formation of bacteria algae symbiotic system and the advantages of recycling wastewater by bacteria algae system were analyzed.Under the optimal conditions,the removal of nitrogen,phosphorus and COD was the best in the bacteria-alga group.The results of high-throughput sequencing shows that the bacteria species and abundance of the bacteria-algae group changed greatly before and after the experiment.Alphaproteobacteria,which was dominant in abundance,was beneficial to the initiation and maintenance of the bacteria-algae symbiosis.The abundance of Chloroplasts increased,indicating that Chloroplasts with fungal-algal structure can grow well.Rhizobiales with the largest proportion of abundance can promote EPS production and improve the sedimentation performance of bacteria and algae.Compared with the pure bacterial system,the fungal flora of the bacteria algae system is more stable,in which Rhodotorula glutinosa and Chlorella can form a fungus Chlorella symbiosis.The bacteria-algal system can remove certain harmful bacteria in the wastewater,and the microflora is in favor of the formation of the symbiotic system.Fatty acid determination results showed that oleic acid(C18:1)is the dominant fatty acid in the bacteria-algal system,which indicates that the application of bacteria-algal system for wastewater treatment and recycling has certain advantages.