Study On Treatment Of Municipal Wastewater By Coupling Microalgae And Activated Sludge Process

To date,the environmental problem has become a global problem,the water environment problem is widely concerned.In particular,although China is rich in water resources,the per capita consumption of water resources in China belongs to the country in shortage of water resources due to the large population base.Sewage treatment and recycling is an important way to solve the shortage of water resources.As a common method of urban sewage treatment in China,activated sludge process plays an important role in protecting human health and ecological environment.However,activated sludge process has some disadvantages,such as high energy consumption,in which aeration accounts for about 50%of the total power consumption.Therefore,reducing aeration energy consumption is an important method to reduce energy consumption of activated sludge method.At present,the methods to reduce aeration mainly include the control of the aeration process and the improvement of the aeration efficiency.However,these methods can not fundamentally solve the problem of aeration energy consumption and require a large amount of data regulation.In this experiment,the coupling reaction system of microalgae and activated sludge was constructed,and microalgae was used to provide oxygen to activated sludge,so as to reduce the aeration energy consumption.Moreover,microalgae can effectively absorb nitrogen and phosphorus and other elements to achieve the goal of sewage purification with lower energy consumption.The research contents are as follows:The coupling reaction system of microalgae/activated sludge was constructed and placed in outdoor etheric sunlight as the light source.The feasibility of long-term stable operation of the system and the removal efficiency of pollutants were investigated.The experimental results showed that when the total suspended solid concentration of the coupling system was more than 2500 mg/L,the light transmittance of the reaction system decreased,which further affected the photosynthesis of microalgae,resulting in a significant decrease in the dissolved oxygen in the system,and finally resulted in a decrease in the treatment effect of various pollutants.When the TSS content was less than 2500 mg/L,the coupling system could effectively remove pollutants such as COD,ammonia nitrogen and phosphorus.In the stable operation stage,the COD in the effluent was stable at about 50 mg/L,the total nitrogen concentration was stable at about 5 mg/L,and the phosphorus was stable at about 1 mg/L,basically reaching the first-level standard for pollutant discharge of urban sewage treatment plants.In this process,no traditional aeration was needed,which greatly saved the operating cost of the system.The microalgae/activated sludge coupling system was constructed to treat municipal wastewater under the condition of built-in light source.LED light was used as the light source in the system.The feasibility of stable operation of the system under the condition of indoor built-in light source and the removal of pollutants were investigated.The results showed that pH was one of the important factors affecting the removal of pollutants.In addition,when the continuous illumination time was too long,the temperature inside the reactor wloud rise to about 50℃,which was not conducive to the growth and metabolism of microorganisms.When the light-dark ratio was 2 h:2 h,it could not only meet the illumination demand of microalgae and achieve a better pollutant treatment effect,but also avoided the phenomenon of excessive temperature in the reactor.When a certain amount of Na₂CO₃ is added to stabilize pH value and the light-dark time ratio was 2 h:2 h,the coupling system could operate steadily and effectively remove pollutants such as COD,ammonia nitrogen and phosphorus.In the stable operation stage,the COD in the effluent was stable at about 50 mg/L,the concentration of ammonia nitrogen was stable at about 5 mg/L,and the concentration of phosphorus was stable at about 1 mg/L,basically reaching the first-level standard for pollutant discharge of urban sewage treatment plants.The experimental results of gas detection showed that nitrous oxide was produced and the gas content was 0.29 mL/h,which indicated that nitrification or denitrification was carried out in the nitrogen metabolism at the reaction stage,but no methane gas was detected.