Traditional Water Treatment Process Optimization Of Pilot Study Under The Condition Of The Water Quality Change

This thesis has focused on the raw water from one of the water plant in Northwest China. Through pilot study between dissolved air flotation（DAF） and sedimentation, we not only analysed the optimal running parameters of DAF and sedimentation, but also the processing effect of conventional water quality indicators and the processing effect of disinfection by-products during different periods of the raw water such as low turbidity and low temperature、normal turbidity and normal temperature、high turbidity and high temperature. The main results are as follows:（1）Through the experiment during the period of raw water in low temperature and low turbidity treated by DAF in pilot scale in Northwest China, this thesis has explored the optimal operation parameters of dissolved air flotation（DAF） process, such as the dosage of coagulant, hydraulic gradient, recycle rate, scum period, etc. It was found that to the raw water, coagulant ployaluminum ferric chloride（PAFC）do better than FeCl3·6H2O in treatment process. The dosage of coagulant impacted the various pollutants removal rates directly. The more the recycle rate is, the higher the removal rate of turbidity, ammonia nitrogen, COD_Mn, UV₂₅₄, DOC by DAF process. Hydraulic gradient has a little influence on the removal of COD_Mn、UV₂₅₄、DOC. The DAF treating effect was under the best condition while the average hydraulic gradient（G）value was 70s-1,recycle rate was 9.25%, scum period was 2h.（2）The pilot treatment effects between coagulation-sedimentation process and coagulation-dissolved air flotation（DAF） process for the low temperature and low turbidity raw water and high temperature and high turbidity in Northwest China were compared. The experiment results showed that for turbidity removal, DAF was more effective than sedimentation process. The dosage of coagulant by DAF was 40 percentage less than that by sedimentation process. In winter and spring, the removal of ammonia nitrogen in coagulation dissolved air floatation process and coagulation sedimentation process efficiency are relatively poor under the condition of the same dosage of coagulant; For the removal of the organic matter, coagulation dissolved air floatation process was better than coagulation sedimentation process. In summer and autumn, when the dosage of coagulant was the same, the treatment effect of dissolved air floatation process for raw water was better than the sedimentation process. In Northwest China, when we need to improve the existing water treatment plant under the condition of low temperature and low turbidity of the raw water, we can give priority to the dissolved air flotation process.（3） In order to optimize the pre-chlorination conditions and control the formation of disinfection by-products, the pre-chlorination process safely enhanced by potassium permanganate for treating surface water traditionally in Northwest China was carried out,the results showed that for the traditional treating process, the pre-chlorination process safely enhanced by potassium permanganate can effectively remove turbidity and COD_Mn and also control the other water quality indicators to ensure water quality; When the percentage of potassium permanganate in coagulant aid was low, the CH in water samples of filter water after 72 h chlorination increased when the pre-chlorine dosage increased; When the percentage of potassium permanganate in coagulant aid was high, the CH in water samples of filter water after 72 h chlorination decreased when the pre-chlorine dosage increased; Considering the formation of CH and the other water-quality indexes being controlled, optimal operating conditions and parameters were determined: the best dosage of chlorine in pre-chlorination was 0.4 mg/L, the optimal ratio of potassium permanganate in coagulant aid was 1.0%.Uder this condition we can control chloral hydrate and relatively more economically and effectively. CH formation could be controlled while the other water quality indicators. also could be better control at the same time.