Study On The Application Of Symbiosis Of Bacteria And Algae And Filtration Of Predatory Aquatic Animals In The Treatment Of Aquaculture Wastewater

In recent years,China’s aquaculture industry has developed rapidly,but the aquaculture industry is still generally extensive cultivation.During the period of clearing ponds,a large amount of nitrogen and phosphorus-rich aquaculture wastewater will be discharged into the surrounding water environment at one time,bringing the surrounding water environment Impact pollution.The project group undertaken the"Aquaculture Industry Wastewater Purification and Reuse Technology Integration and Application Demonstration"National Water Special Sub-project proposed a new aquatic product of"aquaculture wastewater-fungus and algae symbiosis unit-aquatic animal unit-subsurface flow constructed wetland-breeding new water"Aquaculture water recycling mode to achieve zero discharge of aquaculture wastewater.The fungal-algal symbiosis unit is responsible for converting the dissolved nitrogen and phosphorus in the aquaculture water into granular algae,and then through the filtering action of the filter-feeding aquatic animal in the aquatic animal unit,and the subsequent further filtering effect of the subsurface flow constructed wetland to remove the converted algae to achieve The ecological treatment of organic matter in the aquaculture water and the orderly conversion and utilization of nitrogen and phosphorus can achieve the purpose of recycling aquaculture water.This thesis is responsible for the research on the"symbiotic unit-aquatic animal unit"in this model,to study the effects and optimal operating conditions of the two purification units in purifying aquaculture wastewater,and to build a demonstration project.The research results of this paper can be summarized as follows:1、Research on the optimization of the operating conditions of the bacterial-algae symbiosis unit system.Using chlorella and activated sludge to build a symbiotic system of bacteria and algae,to explore the growth of algae and the removal effect of pollutants in aquaculture wastewater under the conditions of different algal bacteria inoculation ratio and hydraulic retention time in different temperature ranges.And study the conversion of nitrogen.The experimental results showed that the algae production rate was the highest in the symbiotic system of algae inoculation at a temperature of 30°C and a ratio of 5:1.The chlorophyll a reached 753.18μg/L,DCOD_Cr,TDP,TDN after 7 days of experiment,The removal rates of NH₄⁺-N and NO₃^--N were 68.90%,90.83%,87.18%,99.97%and 98.11%,respectively.Algae assimilation is the main phosphorus removal mechanism.Microbial denitrification and algae assimilation are the main nitrogen removal mechanisms,accounting for 51.1%and 48.5%of the total removal rate,respectively.When the water temperature is in the range of 20℃～30℃,the hydraulic retention time of 4 days should be used,which can get better algae growth and pollutant removal efficiency.The experiment lasted 21 days,and the chlorophyll a concentration in the system was stable at 835.1μg/L Around,the removal rates of COD_Cr,TDN and TDP were 50.6%,63.4%and 96.6%,respectively.When the temperature range is10℃～20℃,the 8d hydraulic retention time purification effect and algae growth are the best.At the end of the experiment,the chlorophyll a concentration is 571.0μg/L,and the removal rates of COD_Cr,TDN,and TDP are 46.2%,50.0%,and 94.8%.2.Algae filter feeding test for aquatic animals.Comparing the water filtration rate of three common filter-feeding aquatic animals,such as Triangle salamander,Corona snail,and Clam,the operating conditions such as breeding density and hydraulic retention time are optimized to obtain higher algae removal efficiency and water quality purification effect.The experimental results show that the water filtration rates of Triangle mussel,Culex serrata and Clam are 1.00±0.41 L/（kg·min）,0.44±0.15 L/（kg·min）and 1.51±0.82 L/（kg·min）.Considering comprehensively the water filtration capacity and the ability to endure hypoxia,the parasitoid was further tested.Comparing the changes of chlorophyll a content under the three culture density gradient conditions of 0.3 g/L,0.5 g/L and0.7 g/L,the experiment showed that the algae elimination effect was the best under the culture density of 0.5 g/L,and the chlorophyll was obtained after 24h a Removal rate reached 88.3%.Further examining the effect of hydraulic retention time,the experiment showed that the algae removal effect was the best under the condition of 1.0 d hydraulic retention time,and the removal rate of chlorophyll a was 77.2%at the end of the experiment.COD_Cr,TN,TP,NH₄⁺-N,NO₂^--N and NO₃^--N can all achieve higher removal rates,respectively 55.4%,68.1%,95.0%,92.1%and 62.3%.3.Established aquaculture water recycling model demonstration project of"aquaculture wastewater-fungus-algal symbiosis pond-aquatic animal pond-subsurface flow constructed wetland-breeding new water",and investigated the"bacteria-algae symbiosis unit-aquatic animal unit"studied in this paper"The purification effect in the actual project,after four months of operation and commissioning,the results show that:the average total removal rate of COD_Cr,TDP,TDN,NH₄⁺-N and NO₃^--N by the bacteria and algae symbiosis purification unit and aquatic animal purification unit 44.7%,22.0%,40.3%,45.0%and 22.4%,the average removal rate of algae by the aquatic animal purification unit is 54.6%,and can achieve a win-win situation of environmental and economic benefits.