Study On Denitrifying Bacteria In Recycled Seawater

In recent years,China's recirculating marine aquaculture industry has developed rapidly and its product varieties and production have increased year by year.Experts predict that nearly two-thirds of the world's edible aquatic products will come from farming fishery by 2030.However,the ecological environment has also deteriorated with the development of the recycling marine aquaculture industry,triggering a series of increasingly serious environmental problems.The performance of the seawater aquaculture industry is over-intensive farming and feeding a lot of bait to increase production,which seriously pollutes the water environment.As one of the world's largest seawater aquaculture aquaculture countries,China has found that the wastewater discharged from recirculating marine aquaculture has the characteristics of large water volume,low pollutant concentration,low water temperature and high salinity through the detection and management of the recirculating marine aquaculture industry when compared with ordinary city sewage.Its pollution to the environment is mainly manifested in the following two aspects:On the one hand,there are too many artificial feeds and water pollution caused by fishery drugs in the breeding process.On the other hand,the pollution caused by non-compliance of aquaculture wastewater discharge has relatively high diffusibility and will rapidly spread to the surrounding water bodies.The water pollution caused by the above two aspects contains excessive nitrogen and phosphorus elements,which will cause eutrophication of the water body.Therefore,biofilm reactors with strong bioretention capacity have been used in engineering to treat such wastewater,and good results have been achieved.However,higher seawater salinity is still a critical factor that restricts the efficiency of biological treatment.Scholars at home and abroad all hope to solve this problem by obtaining salt-tolerant nitrifying bacteria,denitrifying bacteria and other denitrifying bacteria.In this study,two salt-tolerant denitrifying bacteria were isolated from the water purification unit of the seawater recirculating aquaculture system and the metabolic characteristics of nitrogen were ascertained.Further,the reactor was set up and activated at the outlet of the water purification unit to perform simultaneous nitrification and denitrification and its processing conditions were explored.The denitrifying bacterial culture medium supplemented with seawater was used in this study.Two strains of denitrifying bacteria were isolated and separated by serial dilution and plate streaking,and their morphological and molecular biological characteristics were identified.In addition,their denitrification activity was measured under different environmental conditions and nutritional conditions.Regarding the erection of start-up reactors,aeration biological filter reactor was used to treat circulating aquaculture wastewater and its treatment effect was measured.The simultaneous nitrification and denitrification performance was measured at different hydraulic retention times,aeration rates and reactor heights.Two strains of denitrifying bacteria were successfully isolated.One strain was moderate halophilic denitrifying bacteria and the other was low temperature moderately halophilic denitrifying bacteria.The best environmental conditions and nutritional conditions for their metabolism were ascertained,and simultaneous nitrification and denitrification reactors were successfully started.Moderate halophilic denitrifying bacteria were gram-negative bacilli.It was closest to Halomonas sp.,which reached 98%.It was initially determined that it belonged to the genus Halomonas.The optimal metabolic conditions were temperature 30°C,salinity 10%,pH7.5-8.5 and C/N?mass ratio?4:1.Low-temperature moderate halophilic denitrifying bacteria were gram-negative bacilli.It was closest to Halomonas sp.,which reached 98%.It was initially determined that it belonged to the genus Halomonas.Its optimal metabolic conditions were temperature 41°C,salinity 15%,pH 7.5-8.5 and C/N?mass ratio?4:1.The effluent NH₄⁺-N concentration in the reactor was lower than 1 mg/L,the average removal rate was higher than50%and the effluent was free of NO₂^--N;the average removal rate of NO₃^--N reached 55%and the total nitrogen removal rate reached 50%.The simultaneous nitrification and denitrification effect was best when the reactor had a hydraulic retention time of 1.67 d and aeration volume of0.15 L/min.