| In this study,we studied the treatment ability of marine aquaculture tailwater by constructing two sets of composite vertical flow constructed wetland systems with different scales.The two systems were small-scale test system and pilot test system.The small-scale test system was used to study the effect of hydraulic load and operation period on the concentration change of pollutants in the system,and to reveal the effect of hydraulic state on pollutants.Under different hydraulic loads and treatment time,explored the effect of the the pilot test system on the major pollutants in the treatment of aquaculture tailwater.The optimal inlet hydraulic load and operating time were obtained under actual operating conditions.Based on the differences in the structure of the microbial flora in the root system and the substrate of the two systems,the reasons for the formation of the treatment and the impact on the treatment of the tailwater were analyzed.Provide data support for the promotion and application of composite vertical flow constructed wetlands in marine aquaculture tailwater treatment.The main results were as follows:(1)In the small-scale test system,the removal effect of COD was not good,and the highest removal rate was only 45.59%,the hydraulic load and operation time had little effect on the change of COD concentration in the system.The removal effect of TP is good.Under different hydraulic load and treatment time,the removal rate of TP was more than 50%.The adsorption of TP by the matrix would affect by the state of hydraulic load.The higher the hydraulic load was,the later the adsorbed matrix layer was.The removal effect of TN was susceptible to the influence of hydraulic load and operating time,high hydraulic load affected the denitrification capacity of the downflow unit,which led to the increase of TN concentration in the upflow unit and affects the final effluent quality.(2)In the pilot treatment system,the operation time had a great influence on the removal rate of pollutants under high hydraulic load.Under the hydraulic load of 12.57m/d,the removal rate of COD was 9.83%,the removal rate of TN was 24.75%,and the removal rate of TP was 61.54% when the system was operated for 1.5h;when the operation time was 3.0h,COD removal rate was 23.50%,TN removal rate was 62.46%,TP removal rate was 75.90%;the removal rates of COD,TP and TN were 32.12%,87.84% and 59.53% respectively.According to calculation and analysis,the optimal inlet load of the composite vertical flow constructed wetland system was 10~11m/d,and the optimal operation time was 3.0h,which could obtain the maximum pollutant removal amount considering the best treatment effect of TN and TP pollutants.(3)Based on the distribution of microorganisms in the two systems,plant roots were most suitable for microbial growth activities.The cinder layer was not suitable for the life of microorganisms,which tend to accumulated in the gravel layer and filter sand layer in the matrix.Excessive hydraulic loading results in the migration of microbial accumulation points to the system rear.The denitrification of microorganism will change the p H environment inside the system,which will affect the quality of effluent.Under the influence of hydraulic factors and microbial metabolism,denitrification dominated in the downflow unit while nitrifying bacteria were more active in the upflow unit.The upflow unit was affected by the hydraulic factors and the activities of microorganisms,which made the concentration of various pollutants fluctuate obviously and affected the effluent quality... |
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