Study On Degradation Of Tetracycline-containing Wastewater By Composite Moving Bed Biofilm Reactor

Pharmaceutical and personal care products（PPCPs）in surface waters has become one of the new pollutants that are currently of wide concern.Among them is the widely used tetracycline drug,which has been detected in several water systems in China with multiple frequencies.Trace amounts of PPCPs-like contaminants contained in wastewater treatment plant effluent are reported to be one of the major sources of surface water pollution.Traditional wastewater treatment processes are relatively ineffective in removing tetracyclines,so new water treatment processes and equipment are needed to enhance the removal efficiency of such pollutants.Moving bed biofilm reactor（MBBR）treatment reactors as a combination of activated sludge method and biofilm method are considered as a class of purification reactors for effective removal of hard-to-degrade pollutants.Among them,the performance of biofilm carriers is a key factor in the efficacy of MBBR reactors.In order to improve the MBBR reactor and enhance the degradation efficiency of tetracycline type pollutants,the suspended graphite carbon material was selected as a negative carrier for microorganisms and photocatalysts to construct a composite MBBR reactor for the degradation study of tetracycline-containing wastewater and to investigate the degradation effect of the new MBBR reactor on tetracycline.The details of the study are as follows.（1）Degradation of tetracycline in a suspended graphite carbon carrier-loaded biofilm MBBR reactorTwo parallel MBBR reactors were constructed with suspended graphite charcoal and HDPE carriers,and the efficiency of film hanging and degradation of low concentration of tetracycline were investigated under the conditions of filler dosing ratio of 30%,HRT of 8h and temperature of 15～20°C.The results showed that the suspended graphite charcoal carriers had a faster film hanging rate and better degradation efficiency than HDPE carriers.In the 45-day experiment,the loading of microorganisms on the suspended graphite charcoal carrier was 3.4 times higher than that on the HDPE carrier.When the influent tetracycline concentration was 10 mg/L,the removal rates of suspended graphite carbon carriers were71.85%,89.95%,74.49%,63.91%and 85.47%for tetracycline,COD,TP,TN and NH4+-N,respectively.The suspended graphite carbon carriers significantly increased the relative abundance of nitrifying and denitrifying bacteria as well as tetracycline-degrading bacteria.（2）Photo-oxidative degradation of tetracycline by suspended graphite carbon loaded with TiO₂in a photocatalytic MBBR reactorA composite photocatalyst was prepared using suspended graphite carbon as a carrier loaded with TiO₂to construct a photocatalytic MBBR reactor,and the tetracycline removal rate of 50 mg/L in the influent water was studied under the reaction conditions of HRT of 3hours,1 g/L of the composite photocatalyst,water temperature of 30°C and p H of 6 after optimizing the photodegradation conditions under the irradiation of light source with a xenon lamp simulating sunlight.The results showed that the maximum degradation rate was up to99.32%.（3）Study on the treatment of tetracycline wastewater by constructing a composite MBBR reactor with tandem biofilm and photocatalysisA biofilm MBBR reactor and a photocatalytic MBBR reactor were connected in series to build a composite MBBR reactor for a wastewater with a feed water of 3 mg/L of tetracycline.The biofilm MBBR was operated for 273 days to optimize the working conditions to maximize the performance of the MBBR.Then,during the 11 days of operation of the composite MBBR reactor,the feed water concentration of tetracycline 3mg/L was maintained,and the final measured removal rates of tetracycline,COD,TP,TN and NH₄⁺-N were 92.25%,87.43%,87.49%,66.81%and 95.72%,respectively,and the composite MBBR reactor achieved good treatment effect on the wastewater containing tetracycline.