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Enhace the Treatment Effect of Low Temperature and Low Turbidity Water by Recycling the Combined Filter Backwash Water

Author: HeLi
Tutor: CuiFuYi；XuYongPeng
School: Harbin Institute of Technology
Course: Municipal Engineering
Keywords: low temperature and low turbidity water the waste water from water treatment plant recycling enhanced coagulation mixed water
CLC: X703
Type: Master's thesis
Year: 2009
Downloads: 83
Quote: 0
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Abstract

Water treatment plant waste includes clarifier waste and filter backwash water ,which accounts for 3%~8% clean water produced by a water treatment plant.This part of waste containing a large number of inorganic particles is either directly discharged or reused before treatment. Direct emissions not only pollutes the environment but also wastes of valuable water resources.if the waste water is trented by concentration,which will increase the costs of operation and management,and is not conducive to economic feasibility.On the other hand it is difficult to deal with low temperature and low turbidity water.some measures such as increaseing dosage、added polymer coagulant aid、dosing clay in the raw water ,are adopted to improve the coagulation conditions and enhance the effect. However, the first two measures have greatly increased the operating costs; dosing clay not only increases operating costs, while its particle size distribution is also difficult to fit the raw water treatment,and increase production of wastewater,so from a technical and economic point of view, there are some unreasonable. At the same time this wastewater from water treatment plant itself contains a lot of suspended colloidal particles, if it is mixed with raw water,which will not only plays the role of clay to improve the coagulation conditions, but also solves the problem of treatment about the wastewater. The effect of this measure not only reuse of water resources, at the same time strengthen the treatment of low temperature and low turbidity.Therefore, this study centered on the enhanced effect of recycling this wastewater directly back to low temperature and low turbidity water and the optimum conditions for reuse, at the same time to insure the security to the treantment process when recycling wastewater.The results of this study in tabletest about the raw water from the M Lake, H city in the north, show that:when recycling the wastewater,it can enhance coagulation、save the dosage and exist the best conditions for recycling.There are the same law to improve the coagulation conditions when recycling clarifier sludge、filter backwash water and the two mixed-water above. But the effect and the range of turbidity to improve the coagulation about the three kand of waste water is different. For the clarifier sludge and and the two mixed-water,there is the same treantment effect,the limited value for mixed water turbidity is 30NTU and the solid content ratio is 2%;the The scope of optimal mixed water turbidity was 10~20NTU,the solid content ratio was 0.05 %~ 0.15 % ,and the dose saving rate was 25%~50%,but when recycling the filter backwash water ,the limited value for mixed water turbidity is 12NTU and the solid content ratio is 0.06%;the The scope of optimal mixed water turbidity was 5~10NTU,the solid content ratio was 0.02% ~ 0.04 % ,and the dose saving rate was 20%~30%.The mixed water tuibidity、solid content ratio and the waste water from the water treatment plant have a good correlation,we can control one of them to keep the remaining two.The study on Zeta potential and scanning electron microscopy for the waste water from the water treatment plant shows that the mechanism to enhance coagulation lies in that the Zeta potential in the clarifier sludge、filter backwash water and the two mixed-water is far greater than in raw water,which reinforces the charge neutralization and promotes the effect of the bridging and sweeps flocculation when recycling those waste water;the Zeta potential of clarifier sludge and the two mixed-water is greater than filter backwash water, so the effect and the range of turbidity to improve the coagulation for first two former are greater than the latter;at the same time the recycling waste water from the water treatment plant contains a large number of solid particles,which not only inproves the probability and the efficiency of the particle collision, adding the core of coagulation to make flocs bigger and more close-grained,but also greatly enhances the fuction of adsorption bridging and sweep flocculation because of containing more metal hydroxide particles.At the same time research shows that the recycling waste water optimum condition for the raw water is stable.when the change appears in raw water turbidity、organic content and pH,there is no significant effect for the recycling waste water optimum condition by analysis of variance, and through evaluating the settled water quality when recycling the waste water to the raw water and the change raw water influenced of various factors,the results shows that the majority difference for colourity、CODMn、ammonia nitrogen、UV254、residual aluminium residual manganese between raw water and recycling waste water experiment is greater than zero,and the point of which is above X-axis side.The statistic indicates that the measure recycling the waste water from the water treatment plant can enhanced coagulation to remove pollutants in the raw water Through the above-mentioned studies have shown that directly recycling the the waste water from the water treatment plant can enhance the coagulation、save dosage、inprove the quality of finished water comparing with the low temperature and low turbidity raw water treatment by controlling the mixed water turbidity in a propable range.This measure has significantly economic effects.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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