Why would a water plant want to use ferrous instead of ferric coagulants?
There are a number of advantages of using ferrous instead of ferric ion coagulants. First, ferrous can be purchased in equivalent % iron content as ferric at a lower price. If the water plant process has an oxidant residual of chlorite or chlorine in pretreatment, then the plant can save coagulant cost by reducing or substituting the ferric coagulant dose with ferrous. Second, the water plant may use the less expensive ferrous to offset part or all of the cost of chlorine dioxide. Third, the ferrous ion could reduce or eliminate the chlorite byproduct level from chlorine dioxide dosages in excess of 1.4 mg/L. Fourth, when the ferrous ion eliminates the chlorite byproduct level prior to the distribution system that uses free chlorine, the possibility of “cat urine” odors at the tap is also eliminated. 15. How can we lower the TTHMs in the drinking water? There are six causes of higher TTHMs in drinking water. They are higher: 1. TOC levels, 2. chlorine doses, 3. pH levels, 4. temperatur
