Effect Of Metal Ions On The Byproducts Precursor Of Chlorination Disinfection In Coagulation

With the development of social industry,the concentration of all kinds of metal ions in natural water gradually increases.The presence of metal ions affected the reaction process between coagulation（or disinfectant）reagents and natural organic pollutants in water by complexation or catalysis.In this paper,two kinds of fulvic acid（FA）from different sources were used as substrates,aluminum sulfate and polyaluminium chloride（PAC）were used as coagulants to investigate the influence of the Pb²⁺and Mn²⁺on the coagulation process.The UV-Vis,FTIR,3DEEM and other methods were employed to explore the relevant mechanism.The main contents and results of this paper were as follows:Fulvic acid from different sources has distinct properties.There is fluorescence peaks of fulvic acid,tryptophan like and complexane like substances in FA1’3DEEM.The protein fluorescence peak also was found in FA2,indicating that there were more complex and more aromatic in FA2 than in FA1.The optimal p H,dosage of aluminum sulfate and PAC for removal of THMs prescuors were 7,12mg/L and 8mg/L during coagulation.The tryptophan and fulvic acid like substances were removed more effectively than tyrosine like substance.Coagulation can diminished THMs prescuors by removing the unsaturated aromatic structure in FA.The presence of Pb²⁺can affected the removal rate of THMs prescuors.During coagulation,Pb²⁺has more positive removal effect on THMs prescuors under acidic condition and negative effect under alkaline condition.The effect of Pb²⁺on FA2 was larger than on FA1,resulting in the complexation of Pb²⁺and hydrophilic substances in FA.During coagulation,Pb²⁺can effectively improved the removal effect of-OH structure,C=C and N-H structure in aromatic structure,C-O structure of OCH₃ alcohol and carbohydrates of FA under alkaline condition.Pb²⁺-FA2 complex makes the flocs more dense and leads to the high concentration of Pb²⁺in the effluent under neutral and acid conditions.Then,the formation of THMs was promoted by the high concentration of Pb²⁺in effluent’chlorination process.The presence of Mn²⁺in FA can promote the removal of THMs prescuors during coagulation and inhibite the formation of THMs in chlorination.The unsaturated structures was removed by coagulation in presence of Mn²⁺.The relative content of oxygen-containing functional groups such as ester,hydroxyl,carboxyl and carbonyl increased,and the relative concentration of fatty chain decreased in coagulation effluent with Mn²⁺.After coagulation,the fluorescence peak intensity of tryptophan,tyrosine and fulvic acid like substance of effluent with Mn²⁺were weaker than that of effluent without Mn²⁺.The effect of Mn²⁺in the coagulation process was weaker than that of Pb²⁺.These phenomena indicats that complexation of mental ions was closely related to its effect on the removal of THMs prescuors during coagulation.