| Most reservoirs located above 30° north latitude of China will have water frozen in winter,and the water quality will be characterized by low temperature and low turbidity.The water intake of the Plant A originates from the Reservoir A,which is in the northeastern region.It has an ice period of 4 to 5 months every year.The Plant A is currently using a conventional water purification process,which has some difficulties to treat the low temperature and low turbidity raw water in this period.Therefore,Plant A increased the dosage of coagulant to strengthen the coagulation process.However,the increase in the amount of coagulant has a marginal effect,and the operation cost of the water plant is greatly increased.At the same time,due to the long water supply network of the Plant A,in order to ensure that the residual chlorine at the end of the pipe network meets the standard,the amount of disinfectant is high,so the disinfection by-product chloral hydrate(CH)in the effluent water has a higher risk of exceeding the standard.This paper is aimed at the practical problems of the Plant A.The low temperature and low turbidity raw water of the Reservoir A during the ice period was used as the experimental water,and potassium permanganate,potassium ferrate,sodium hypochlorite and chlorine dioxide were used as oxidants to systematically explore the efficiency of coagulation strengthening and CH control of low temperature and low turbidity water under the conventional water purification process.It is proposed that at a low coagulant dosage,it can effectively enhance the coagulation and the control risk of CH exceeding the standard.Firstly,through the study of the pre-oxidation process of the above four oxidants,it is found that under the appropriate dosage and reaction time,the single pre-oxidation process has a certain enhancement of the removal rate of each index of coagulation performance,and can control the amount of CH.Among them,the pre-oxidation of Na Cl O has the best strengthening effect on each index of coagulation efficiency;the preoxidation of chlorine dioxide has the best control effect on the production of CH.Furthermore,a systematic study was conducted on the combined pre-oxidation process of the above four oxidants in pairs.Through the central part of the analysis experiment,the efficiency of each process' s enhanced the coagulation and the effect of controlling CH were systematically analyzed.The research proves that each composite pre-oxidation process model has a synergistic effect on certain responses,and at the same time discusses the applicability of each process to solve practical engineering problems,and selects potassium permanganate combined with sodium hypochlorite that has a synergistic effect on each response index of the model.Therefore,the Response Surface Methodology was carried out on the potassium permanganate combined with sodium hypochlorite pre-oxidation process,and the process parameters were optimized using Entropy Weight Method: the dosage of potassium permanganate is 0.2070mg/L,the dosage of sodium hypochlorite is 0.7737mg/L and the reaction time of sodium hypochlorite is 10 min.The chroma and CH removal rate obtained by the verification experiment differed from the predicted values by 2.08% and 1.68%,respectively,which proved the high accuracy of the model and the effectiveness of optimization.Finally,the efficiency of this to process to Plant A was studied,and it was found that the dosage of coagulant can be reduced by 10% under the premise of ensuring the coagulation effect,increasing the removal rate of CH by 21.5%.An economic analysis of the Plan A was carried out.It was proved that this process can save 942,800 RMB during the period of low temperature and low turbidity of each year(based on daily supply of 900,000 tons of purified water and on 4 months of use),which only calculate the cost of the medicament. |
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