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The lime dosage we want should be able to increase the pH of water to the degree we want, while neutralizing the effect of the alum that will be shortly added to it. By calculating the alkalinity under the orginial pH we can find the total carbonate eg.CT in the system, and then we can find the relationship between the target ANC and the desired pH we want(see figure 1). The total lime dose required in tank is the sum of the amount using to neutralize the alum and to raise the raw water to the desired pH(see equation 1 below).
After we get the required lime dose demand in raw water, we want to find the lime feeder flow rate to satisfy this dosage, under the assumption that the effluent pH of lime feeder keeps at 12.4, and the plant flow rate keeps at 50 L/min, we get the required flow in limefeeder. Based on equation 1, we can go further to get the ratio between flow rate in lime feeder and the plant with the pH requirement in raw water, this relationship shows in figure 2.
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