Pretreatment Of Thiophanate-Methyl Production Wastewater By Light Induced Photocatalytic Oxidization

Pesticide wastewater has the properties of high concentration,deep chrominance, high toxicity and complex components and is difficult to be degraded by microorganism.TiO₂ is wildly used in multiphase photocatalytic oxidation owing to its innocuity,high photocatalytic activity,strong oxidation ability and good stability.As to the method discussed in this paper,pure TiO₂ and Fe³⁺,Cu²⁺,Ag⁺ doped powders were prepared in sol-gel method with Ti(OC₄H₉)₄ as its precursor,and the powders were calcined under 500℃for 2 hours.XRD analysis showed that all powders were anatase,with their grain diameters varying from 11.2nm to 49.8nm, specific surface areas varying from 51.24 to 102.13 m²Â·g^-1。Thiophanate-methyl industrial wastewater was treated by photocatalytic oxidation under UV-light with prepared TiO₂ powder.According to the relationship between time and concentration of COD_Crin wastewater,the powders are categorized into three types:pure TiO₂ and 1.5%Cu²⁺(n:n)doped TiO₂ made COD_Crin wastewater decreased with the passing of time;0.5%Fe³⁺,0.5%Cu²⁺and 1.0%Ag⁺ doped TiO₂ made COD_Crin wastewater decreased in the first 2 hours,then increased,and the final COD_Crvalue was lower than the initial ones;other TiO₂ powders made COD_Cr increased.Fe³⁺,0.5%Cu²⁺,1.5%Cu²⁺and 0.5%Ag⁺ doped TiO₂ made contents of NH₃-N in wastewater increased at first,then decreased;pure and 1.0%Cu²⁺,1.0% Ag⁺,and1.5%Ag⁺ doped TiO₂ also made contents of NH₃-N in wastewater decreased at first,then increased;photocatalytic oxidation made bioavailability of wastewater increased by 3.5 to 4.3 times,and BOD₅/COD_Cr＞0.3.After treating for 8 hours,the bioavailability of wastewater was presented in the following order:1.5%Fe＞1.0%Cu＞1.5%Ag≈0.5%Cu≈1.0%Fe＞0.5%Fe＞1.0%Ag＞1.5%Cu＞0.5%Ag＞TiO₂.Treating wastewater under solar light with prepared TiO₂ powders,and its results showed that:pure TiO₂ and 0.5%Fe³⁺doped TiO₂ made COD_Crin wastewater decreased at first,then increased;other TiO₂ powders made COD_Crincreased.After treating for 8 hours,the COD_Crin wastewater was presented in the following order: 1.5%Cu＞0.5%Cu＞1.0%Ag＞0.5%Fe＞1.5%Ag＞1.0%Cu＞1.5%Fe＞1.0%Fe＞0.5%Ag＞TiO₂.Pure TiO₂ made contents of NH₃-N in wastewater increased at first,then decreased;%0.5Fe,1.0%Cu,0.5%Ag and 1.5%Ag doped TiO₂ made contents of NH₃-N in wastewater decreased at first,then increased;other TiO₂ powders made content of NH₃-N in wastewater increased.Photocatalytic oxidation made bioavailability of wastewater increased by 2.5 to 3.6 times.After treating for 8 hours, the bioavailability of wastewater was presented in the following order:1.5%Fe＞1.0%Fe＞1.5%Cu＞0.5%Cu＞1.5%Ag＞0.5%Fe＞1.0%Ag≈1.0%Cu＞0.5%Ag＞TiO₂.Comparison between the UV-light and solar light as to their photocatalytic oxidation efficiency showed that:After treating for 8 hours,COD_Crin wastewater treated under UV-light were higher than that treated under solar light.Difference of contents of NH₃-Nin wastewater decreased at first,and then increased while treated wastewater with pure and 1.0%Ag doped TiO₂.Difference of contents of NH₃-N of other powders treated wastewater increased at first,then decreased.Difference of bioavailability between UV-light and solar light treated wastewater were positive,and theΔBOD₅/COD_Crincreased at first,then decreased.