Impact Of Pre–oxidation On Removal And Transformation Of Atrazine During Drinking Water Treatment

With the rapid development of China's economy and society and the impact of human activities,surface water pollution has become increasingly prominent.In order to increase crop yields,people began to use a lot of pesticides since the reform and opening up,while most of the pesticides can enter the water body through various channels,causing water pollution.Atrazine as a triazine herbicide is cheap,efficient and widely used.It has a high detection rate in water and can cause harm to human health through the effects of biological enrichment.At present,the conventional drinking water treatment process has a low removal rate of dissolved organic matter.It is difficult to treat it to meet the requirements of drinking water quality standards using conventional water treatment processes when the water source is organically polluted.In order to ensure the quality of the water supply,it is necessary to upgrade the traditional water treatment process,and on this basis,add pretreatment and advanced treatment processes.Chemical oxidation and GAC adsorption may effectively remove organic pollutants in the raw water,so we set the"pre-oxidation+conventional treatment process+GAC adsorption"process to treat the water containing atrazine,and in-depth research.The removal efficiency and migration and transformation rules in each unit process determine the optimal operating process parameters and reliable control strategies.With a view to providing basic data for actual drinking water treatment plant operation management and water quality health risk assessment.?1?Atrazine has the characteristics of stable molecular structure and difficult to degrade.and only 4 kinds of degradation products were screened out after the oxidation reaction.According to the obtained mass spectrum and mass spectrometry analysis principles,its possible molecular structure and degradation pathway were proposed.In this process,dechlorination-hydroxylation and dealkylation reactions mainly occur.?2?Sodium hypochlorite?NaClO?and potassium permanganate?KMnO₄?were used in the pre-oxidation experiment.The results show that the removal rate of atrazine is lower in this process,and its degradation rate before the 30 minutes is fast,consistent with the quasi-first-order degradation kinetic model.Furthermore,its degradation rate gradually decreased with the oxidation time extended.The gradual increase of the dosage of oxidant cannot quickly increase the degradation rate of atrazine.The atrazine removal effect in the solution increases slowly when the concentration of oxidant is?10 mg/L.Substrate concentration has an effect on the removal of atrazine in water samples.The removal efficiency of low-concentration atrazine solution is slightly higher than that of high-concentration solution.Changing the pH of the solution will not significantly remove the effect of atrazine.?3?In this experiment,three coagulants?polyaluminum chloride,aluminum sulfate and ferric chloride?were used to study the removal effect of atrazine in the solution under different conditions.The experimental results show that under the same conditions,the coagulation effect of the three coagulants is polyaluminum chloride>aluminum sulfate>ferric chloride.The increase of the dosage of coagulant has little effect on the removal rate of atrazine in water.Under different pH conditions,polyaluminum chloride will have different chemical properties and reaction mechanism,pH change has little effect on the coagulation effect.However,it can significantly change the surface ionic properties of activated carbon to affect the adsorption effect of GAC.Generally,the adsorption effect under acidic conditions is higher than that under alkaline conditions,and the effect is worst under neutral conditions.The addition of KMnO₄ can significantly change the color of the solution and increase the UV₂₅₄.In addition,its oxidation reaction to produce manganese dioxide that is not easily soluble in water is also one of the reasons for the increase in solution turbidity.?4?Water samples with different water quality conditions were prepared by adding humic acid and kaolin to the water inorder to change the TOC and turbidity of the solution.As a polymer electrolyte,humic acid could competes with Atrazine as a coagulant,resulting in poor coagulation.The increased turbidity of the solution increases the probability of collisions between the particles,causing part of the atrazine in the solution to be adsorbed on the surface of the flocs and separated from the water with it.Based on the self-provisioned water sample,we collected the actual water samples from the Guangdang River and the Sanyuan Lake for comparison.The removal effect is better than that of pure water,which may be due to the presence of abundant organic matter and ions in the actual water sample,which promotes the reaction.