| Xiangjiaba water plant lies in the Jinsha River downstream on that junction of Shuifu county of Yunnan province and Yibin city of Sichuan province, relying Xiangjiaba hydropower station which is the last stage of Jinsha River hydropower base. Since the actual operation, due to water closure and impoundment of station, raw water conditions are good, and qualities of effluent water are stable that meets the relevant requirements. However, a lot of water users were found out calculus when medical examination, presumably due to the hardness of the water quality is likely to be so high that affects their health. Meanwhile, the high water hardness may be potentially harmful for the safe operation of the hydropower unit. Therefore, in order to optimize the water quality further to protect the safety of water and health of water users, it is necessary for the study of water quality(mainly considering hardness) after the impoundment, to adapt to the increasing trend of requirements of drinking water quality, ensure water security of the Three Gorges hydropower units and guide the entire water treatment technologies, management and operation in the Jinsha River area.Combined with the actual water quality and operation of Xiangjiaba water plant, pharmacy softening is selected as the subject of water softening way by the method selection. Univariate tests investigated the factors affecting pharmacy softening, combined with practice, considering influence of stirring intensity, reaction time, and coagulant effect are not obvious on the hardness part, while the dosage is an important factor, and the figures of total hardness, calcium hardness and p H value indicators changes with dosage were received.The orthogonal experiment is taken that based on the univariate experiments, and finally take the Ca(OH)2 dosage and Na2CO3 dosage as two factors that will not consider the mutual influence between factors after full consideration. Ca(OH)2 dosage(mg/L) has 4 levels of K1(40), K2(80), K3(120) and K4(160), Na2CO3 dosage(mg/L) has 4 levels of K1(10), K2(20), K3(30) and K4(40). Considering the best effects of total hardness removal, test results consistent with that in the winter and summer, Ca(OH)2 dosage should be appropriate of 80mg/L~120 mg/L, then take the best effects of carbonate hardness removal(temporary hardness) into consideration, the optimal dosage of Ca(OH)2 is 80 or 120 mg/L, and the optimal dosage of Na2CO3 is 40 mg/L; but in this situation the p H value is in excess of the standard requirements, so the consideration is needed to add acid to a p H correction.Orthogonal test actually just provides an optimum range of values, in order to find out a more accurate optimal dosage figure and take into verified, software Design-Expert 8.05.b is used to do Box-benhnken(BBD) test for response surface analysis. Combined with previous results of experiments, to input date in the range of lime 80~120mg / L, soda ash 30~40 mg/L and coagulant 5~9 mg/L, the desired test conditions were given and there come with response results of total hardness, turbidity and p H value. It is proven that the fitted regression equation is relatively comply with the actual situation, this model can be used to analyze and predict the total hardness; and the model can well reflect the true value of the test which means higher reliability of the test. When considering the total hardness and turbidity, the optimal value on analysis: lime 94.53mg/L, soda ash 40 mg/L and coagulant 8.81mg/L, after treatment total hardness and turbidity is 61.098mg/L(of Ca CO3)(its removal rate is 55.0%) and 5.74432 NTU. Results of verification test basically reached the goal 60 mg/L(of Ca CO3). Since the p H value of 10.57 has been higher than the national standard value(of 6.5 to 8.5) on this situation, it is required to add the subsequent acidification step. When considering the total hardness, turbidity and p H value, the optimal value on analysis: lime 82.60mg/L, soda ash 40 mg/L and coagulant 9.00mg/L, after treatment total hardness turbidity and p H value is 62.3539mg/L(of Ca CO3)(its removal rate is 54.1%), 5.62396 NTU and 10.2006. Results of verification test basically reached the goal 60 mg/L(of Ca CO3). Since the p H value of 10.57 has been higher than the national standard value(of 6.5 to 8.5) on this situation, it is required to add the subsequent acidification step.Finally, through the type and quantity of pharmacy dosing variation, combined with the existing market price, the price of Lime(Ca(OH)2) is counted by 400 yuan/t, of soda ash(Na2CO3) is counted by 1000 yuan/t, and the cost on softening water to some certain total hardness in Xiangjiaba water plant is obtained on the existing basis, which including acidification costs on two cases that due to that in or not in the consideration of which the p H value is exceeded.(Among them, lime and soda ash dosage is taken by the minimum dosage needed that can achieve some level.) This provides a good economic basis for future production test. |
PDF Full Text Request