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There are several ways to change the concentration of lime in raw water through lime feeder, such as the dosage of lime, the operation time, lime feeder velocities, lime feeder effluent pH etc. Technically, the effluent pH of lime feeder should be kept at around 12, that is the lime saturate pH, our assupmtion is that with a continously flow comes from a distribution of raw water into lime feeder the previously dissolved lime would be consumed, it result in more washed out and provide the effluent pH at around 12, it follows more and more settled lime become dissolvable in water, and with a proper combination of lime dosage and flow rate the effluent pH could be kept constantrate this function could be kept until all the settled lime dissolve in water and come out with effluent water, thus provide us the constant effluent pH for a relatively long time, we hope it can achieve 12 hours for routine opertation.
Since the effluent pH should be constant based on our assumption, the way we can change the lime concentration in raw water is depend on the flow rate of lime feeder, it also create convenience for the operator to use the apparetus changing pH and AlK in raw water. The flow rate should be in certain range which could provide the pH environment in the tank between 6.5 to 7.5, it is the range coagulation will be most efficient. <Water Quality and Treatment by Letter 1999>
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