A Preliminary Study On Wastewater Treatment And Lipid Accumulation By Algae-Bacteria Symbiotic System

With the continuous development of social economy and the increasing shortage of resources and energy,microalgae biotechnology plays a more and more important role in the sustainable development of sewage treatment.Taking advantage of the fact that algae can utilize the nutrients in sewage and convert them into high-value-added products,the cost of microalgae cultivation can be reduced and the recycling of resources can be realized by combining wastewater treatment based on microalgae with biodiesel production.However,in the large-scale application of this technology,it is extremely difficult to ensure complete sterility of the system.Interestingly,the presence of some bacteria has been proved to strengthen the advantages of microalgae in biomass accumulation and lipid production.In this paper,microalgae were cultured in synthetic wastewater,and the algal-bacterial symbiosis system were constructed to further explore the interaction between algae and bacteria.The optimum co-culture systems were screened to provide theoretical basis for the pervasive application of algae-bacteria symbiotic wastewater treatment technology.The results of bibliometric analysis indicated that the coupling technology of wastewater treatment and lipid production by using algal-bacterial symbiosis is indeed a cutting-edge trend in this field.The microalgae-Pseudomonas putida and microalgae-Bacillus licheniformis co-culture system were constructed respectively.Results showed that the comprehensive performance of Scenedesmus sp.336+Pseudomonas putida system with the inoculum ratio of 5:1（algae/bacteria）was the best.The total biomass dry weight and lipid content of this system reached 910.33mg/L and 25.51%respectively.The complete removal of NO₃^--N and PO₄^3--P were achieved and the removal efficiencies of NH₄⁺-N and COD were 98.65%and 98.06%,respectively.All of the above effects were significantly better than the pure culture system of microalgae.In addition,the ability of Scenedesmus sp.336,Chlorella sp.1602 and activated sludge（AS）alone or in combination（at the algae-activated sludge ratio of 1:1）to remove nutrients and accumulate lipid in artificial municipal wastewater under light/dark conditions was studied.The symbiotic systems showed greater advantages than the sterile systems.Scenedesmus sp.336+AS system obtained the highest lipid productivity after seven days of cultivation in light,while the NO₃^--N and COD were completely absorbed and utilized,as well as the removal rate of PO₄^3--P and NH₄⁺-N were 99.82%and 87.13%,respectively.Total superoxide dismutase（SOD）activity was measured to demonstrate the relationship between oxidative stress and lipid accumulation.Besides,the results of microbial analysis showed that some dominant plant growth-promoting bacteria could secrete indole-3-acetic acid（IAA）to enhance the interaction between algae and bacteria,and the denitrifying bacteria that could coexist with microalgae also improved the efficiency of wastewater treatment in the symbiotic systems.