Experimental Study On Advanced Treatment Of Tail Water From Wastewater Treatment Plant By Aeration Enhanced Constructed Wetland

In recent years,a large number of urban sewage treatment plants and sewage treatment facilities have been built in China,and the sewage treatment capacity has increased significantly.However,with the increasingly stringent requirements for various water quality in China,the effluent quality of sewage treatment plants can no longer meet the requirements,and the nitrogen and phosphorus content in the effluent is still high,At the same time,it is also an important way for emerging pollutants drugs and personal care products(PPCPs)to migrate to the water environment.A large amount of tail water discharge will lead to water eutrophication and significant ecological toxicity.As a typical spectrum antibiotic,tetracycline(TC)is widely used because it can inhibit most Gram-positive and Gram-negative bacteria,Rickettsia,trachomavirus and so on.Due to the limited removal effect of conventional process in wastewater treatment plant,it is constantly detected in natural water.Therefore,it is of great significance to carry out advanced treatment of tail water of sewage treatment plant to improve water environment in China.According to the present situation of the tail water of the sewage treatment plant,combined with the characteristics of insufficient oxygen supply and poor oxygen transfer capacity of the constructed wetland,the enhanced process of "aeration enhanced vertical subsurface flow constructed wetland" is proposed.This paper studies the adsorption effect of wetland substrate on ammonia nitrogen,explores the start-up and optimal operation parameters of the process,the removal effect of the system on TC,and the correlation between the removal rate of TC and conventional indicators,so as to provide reference for the advanced treatment of wastewater treatment plant tail water and the application of constructed wetland technology.The results are as follows:(1)The experiment of ammonia nitrogen adsorption on three kinds of substrates(zeolite,ceramsite and slag)in a small column device shows that zeolite has a good removal effect on NH4+-N.The average removal rate of NH4+-N by zeolite is 48.31%,and that by ceramsite and slag is 43.64%and 35.03%.Therefore,the addition of zeolite as the substrate can effectively remove NH4+-N in the effluent of sewage treatment plant.(2)The method of continuous cultivation after inoculating activated sludge was used to start the biofilm formation of constructed wetland,which lasted for 31 days.At the start of the experiment,the removal rates of CODcr and ammonia nitrogen were about 27%and 21%After stable operation,the removal rates of CODcr and NH4+-N increased gradually,and the removal rates of CODcr and NH4+-N reached more than 70%respectively.(3)After the constructed wetland runs stably,the main factors affecting the pollutant removal efficiency of the system are aeration position,aeration intensity and hydraulic load The optimal parameters of the system operation were determined through experiments.The system has good treatment effect when the aeration position is 1/2 of the constructed wetland,the aeration intensity is 2.55m3/m2·h,and the hydraulic load is 0.48m3/m2·d.at this time,the average removal rate of pollutants in the tail water can reach CODCr was 70.95%,NH4+-N was 80.21%,TN was 47.70%and TP was 30.78%.The average effluent concentrationcan reach 11.74mg/L for CODCr,0.85mg/L for NH4+-N,7.16mg/L for TN and 0.303mg/L for TP.(4)In this experiment,tetracycline(TC)was selected as the target PPCPs.Through the adsorption kinetics of zeolite,ceramsite and slag,it was found that the slag had the best adsorption effect on TC,followed by ceramsite and zeolite.The results showed that the adsorption of TC on the three substrates reached a balance in about 12 h.The process of adsorption of TC on the substrates conformed to the pseudo first-order and pseudo second-order kinetic models,but not to the intra particle diffusion model.The adsorption of TC on the substrates depended on the physicochemical properties of the substrates.The results show that the adsorption effect of the substrate on TC increases with the increase of TC content,and the isothermal adsorption process includes physical and chemical action(5)when the aeration position is 1/2 of the constructed wetland,the aeration intensity is 2.55m3/m2·h,and the hydraulic load is 0.48m3/m2·d,the removal efficiency of different influent concentrations of TC by the constructed wetland system is investigated.When the influent concentration of TC was 50μg/L、100μg/L、200μg/L、400μg/L、600μg/L 和 800μg/L,the average removal rate of TC was 93.38%、95.47%、97.36%、95.89%、86.22%和 81.73%.and the average effluent concentration of TC was 3.31μg/L、4.53μg/L、5.28μg/L、16.44μg/L、82.68μg/L 和146.16μg/L.The results show that the removal rate of TC in constructed wetland system first increases and then decreases.The influent concentration of TC is 200μg/L,and the constructed wetland system has a good removal effect(6)By analyzing the relationship between the removal rate of TC and the conventional indexes,it was found that the removal rate of TC was significantly positively correlated with the removal rates of CODcr and TN,indicating that the biodegradation of TC mainly depended on aerobic microorganisms.