(108b) Comparing Multiple Oxidizers Ability to Replace a Chlorine Pre-Oxidizer Addition In a Drinking Water Filter Plant

Plant optimization testing with a state of the art mobile Pilot Plant was conducted to reduce Disinfection By-Product (DBP) formation from the reaction of Chlorine and DBP precursors in the drinking water filter plants. One approach for reducing DBP formation within a utility is maximizing the reduction of Total Organic Carbon (TOC).  Unfortunately, some alternatives such as GAC and/or enhanced coagulation, which can have a profound effect on TOC removal, are not always the optimized options. 

While Chlorine residuals are required in the distribution system for drinking water, minimizing the contact time between DBP precursors and Chlorine reduces the amount of DBP’s.  Reducing contact time led to investigations of replacing any Chlorine feed present before the final disinfection dose after the filters. The Birmingham Water Works Board (BWWB) Shades Mountain Filter Plant (SMFP) used a Chlorine Pre-Oxidant addition at the rapid mix to improve filter performance.  Since the plant was already optimized through enhanced coagulation for TOC removal a comprehensive Chlorine Pre-Oxidant replacement study was conducted. 

The testing took place in the BWWB mobile pilot plant.  The pilot plant contained two identical treatment trains that each contained a raw-water skid, a floc/sed skid, and a filter skid.  The potential Chlorine Pre-Oxidant candidates were Hydrogen Peroxide, Chlorine Dioxide, and Potassium Permanganate.  They were all evaluated against the current use of Chlorine as a pre-oxidant.  Parameters such as DBP formation, pH stability, effect on TOC levels, settled and finished turbidity, metals residuals, algal growth, filter head loss, and filter run times were evaluated.  Testing was conducted for one year in combination with various coagulants and was subjected to the same source water variations that were present at SMFP because of its testing within the mobile pilot plant. 

Each one of the before mentioned oxidizers has an advantage to its use and at least one disadvantage to its use.  This required testing several doses and sometimes combinations of oxidizers to minimize each oxidizer’s disadvantage while maximizing its advantages.