Research On Enhanced Coagulation Of Source Water Of A Northern City With Low Temperature And Turbidity Containing High Organic Matter

City A is located in the northeast of China.Its water source comes from a reservoir which is constructed in an earlier time,and the reservoir is surrounded by the farmland surrounding vegetation,the water in these reservoirs have been in a high color and high organic state,its annual average PI is 10.48 mg/L,and the PI will rise to 12 mg/L in the period of low temperature and low turbidity.This phenomenon directly conduct to the PI of water yield in the reservoir is not reach the standard,and greatly exceeded 3mg/L quality control specification which water supply group must abide and 5mg/L in the current national standard limit value.In order to solve the problems in the water treatment plant of city A,this subject was background for the most unfavorable situation（0-2 ℃,0-2 NTU,PI≥12 mg/L）of the actual production in winter,and aim to make the PI lower than 3mg/L,a systematic study was carried out on the raw water of city A which has treated by the enhanced coagulation process.this study was prepared PSAF coagulant and chitosan modified kaolin coagulant,and then optimize and characterize these two reagents.And in the next,this study determinate the optimal element ratio（Si:Al:Fe=5:7:7）which aim at the PASF coagulant of city A water resource,and determinate the optimal preparation parameters（Skraeling=1:1,ωHCl=5%,ωCTS=2%）of chitosan modified kaolin coagulant in a standard of Zeta potential modification,and use a variety of characterization methods to proved the preparation process of two reagents is reasonable and effective.In addition,this study also improve the traditional Ferron complexation timed spectrophotometric method to make it measure the aluminum and iron mixture at the same time or in a same assignment.Via the new method,study research the hydrolysis rules and influence factors of Fe/Al in which the PSAF prepared by use optimized parameters.In subsequent studies of enhanced coagulation treatment of city A,the influence factors of raw water was investigated,and prove that the PASF prepared in research have obviously advantage than PI which was used in waterworks（Save 40% at the same condition）.And using the optimized preparation of PASF in a dosage of 100 mg/L compound with 5 mg/L and 20 mg/L chitosan modified kaolin coagulant respectively,this study exploration out the way of enhance coagulation which dispose the PI of raw water of city A to under 3 mg/L in the most unfavorable conditions.Aimed at the enhance coagulation method produce the turbidity,pH and the rest of Al when make the PI reach the standard,study solve the problem in a way of addition a little PSi and Na₂CO₃.In a case of 100 mg/L PASF compound with 5 mg/L Ca O in low temperature and low turbidity,it is feasible that addition 5 mg/L PSi after 2min when coagulation start,and addition 5 mg/L Na₂CO₃ in the water which have been filtration will make the PH and the concentration of the rest of Al reach 7 and 0.064mg/L respectively,therefore it will conform to the national standard.According to the treatment method which reach the standard and the characteristics of water of city A in different seasons,this study worked out the production and application plan which reach the standard in the period of icebound in winter,the period of snow melting in spring and the normal turbidity period in summer or autumn respectively.And based on the technical economic analysis of the preparation cost of the coagulants,the costs of the enhanced coagulation program was obtained,The cost of water preparation under the most adverse conditions of the icebound period in winter is 0.1739 yuan/t,which is at a economical leve.It demonstrate that the coagulants and the enhance coagulation program which is developed in this study could achieve expected purpose,it is also able to solve the existing problems of the water plant in the range of acceptable cost and has the practical significance to apply it to the production of the water treatment plant in city A.