Advanced Treatment Of Municipal Sewage Secondary Biochemical Tailwater By Heterogeneous Catalytic Ozonation

The problem of DOM and POPs residue in municipal sewage is gradually being taken seriously,which will endanger the safety of water resources and human health.Conventional sewage treatment process cannot completely degrade the residual organic matter of municipal sewage,it is urgent to seek an economical and efficient advanced treatment method.In this paper,MnOx-CeOx composite metal oxide catalysts were prepared to deeply treat municipal wastewater secondary biochemical tailwater.The contants of this article includes:optimization of catalyst preparation,exploration of optimal system operating parameters,degradation process and mechanism of organic pollutants.The main conclusions are as follows:1.The activity of the catalyst was determined by carrier type(ceramsite,spherical/γ-Al2O3,raschig ring/γ-Al2O3),calcination temperature,heating rate and heating method(one-step heating,multi-step heating).The removal rate of the target oganic(Ofloxacin)showed that the optimization preparation process parameters of MnOx-CeOx catalyst are as follows:the carrier was raschig ring/γ-Al2O3,the sintering temperature was 600℃,the roasting heating rate was 5℃·min-1.The heating process was multistep gradient heating,keep temperature at 250℃ and 450℃ for 90 minutes respectively.Under the optimum preparation parameters,the degradation efficiency of Ofloxacin reached 91.80%.The SEM,XRD,XPS and BET results showed that the catalyst prepared by optimized processes has larger surface area and more active Mn3+.2.Municipal wastewater secondary biochemical tailwater was treated by heterogeneous catalytic ozonation technology,combined with MnOx-CeOx/γ-Al2O3 catalyst.According to the removal of COD,the optimal experimental parameters of the system are obtained:the contact time was 20 minutes,the ozone gas flow was 0.2 L·min-1.Under optimal operating parameters,the COD of ozone-catalyzed effluent was 16.58 mg·L-1,the Chroma was 20 times and the TOC was 12.2 mg·L-1 when ozone dosage was 30 mg·L-1,the effluent index was better than A standard(COD=20 mg·L-1)of Discharge Standard of Water Pollutants for Municipal Wastewater Treatment Plants(DB11/890-2012)3.Aromatic Protein,Humic acid-like,Soluble microbial by-product-like and Fulvic acid-like were detected in secondary biochemical tailwater.Kinetic analysis showed that ozone preferentially oxidized electron-donating groups,and the degradation order of various organic compounds was:Aromatic Protein>Soluble microbial by-product-like>Humic acid-like>Fulvic acid-like.When ozone dosage was 30 mg·L-1,the removal rate of all kinds of organic matter above 88%.4.After ozone-catalyzed advanced treatment,the Mw of organic matter was reduced from 3523 Da to 1502 Da,and the Mn of organic matter was reduced from 1389 Da to 883 Da.A variety of organic pollutants were detected in municipal wastewater secondary biochemical tailwater,among which the Vinyl laurate with a highest concentration of 65.94 mg·L-1.Ozone-catalyzed effluent contained only trace amounts of environmental pollutants,with concentrations below 0.70 mg·L-1,the removal rate of 9 kinds of POPs including Butyl octyl phthalate exceeds 90%.The degradation products of POPs in secondary biochemical tailwater are nontoxic and easily decomposed by nature.The main product of organic degradation was Ethyl acetate,with a concentration of 33.62 mg·L-1,which accounted for 62.30%of the total organic content in ozone-catalyzed effluent.