AWWA WQTC62416

The Philadelphia WaterDepartment (PWD) conducted pilot studies focusing on how long manganese control may be maintainedin the event of a chlorine loss. The main variables were pH and temperature, although the influentmanganese concentration did vary slightly as well. PWD also investigated the use of oxidation-reductionpotential (ORP), presented as E_H, as a predictive tool for manganese breakthrough.Testing was performed at the Baxter and Belmont Pilot Plants. Two sets of experiments (one in thespring and one in the fall) were performed. The primary objective was to evaluate how long it wouldtake before manganese breakthrough after a sudden loss of chlorine occurred. A secondary objectivewas to determine whether ORP could be used to predict filter effluent manganese breakthrough.Breakthrough was defined as filter effluent containing more than 0.015 mg/L total manganese.Conventional treatment at coagulation pH 6.5 was employed, with two manganese oxide-coated dualmedia filters in operation at each plant. Filtration pH of 6.5, 7.5 and 8.5 were tested. Sodiumhypochlorite (NaOCl) was applied to the influent of each filter with the goal of achieving a 0.5 mg/Lfree chlorine residual at filter effluent. Raw, settled and filter manganese were sampled after steadystate conditions were achieved (but just prior to chlorine shutoff) to establish a baseline. Filter effluenttotal and dissolved manganese and ORP were sampled just prior to chlorine shutoff, and at definedintervals after chlorine shutoff until the filter run terminated. If time permitted, the filters werebackwashed and restarted (without chlorination) for a subsequent filter run. The filter effluentmanganese and ORP data were plotted against a triple-axis of actual sample date/time, elapsed filter runtime, and elapsed time since chlorine shutoff.Results from both the Baxter and Belmont pilot plants indicated that the filters held manganese longer athigher pH and in warmer water. Manganese breakthrough was not, however, dependent on influentmanganese concentration at the low levels used in these experiments (50-100 µg/L). The Belmont plantoperated with higher manganese loading yet controlled manganese for as long or longer than the Baxterfilters. ORP dropped significantly within the first hour after chlorine termination and became essentiallyconstant after that. ORP did not appear to be a predictive tool for manganese breakthrough from the data collected. Includes 3 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2005

Number of Pages:

23

File Size:

1 file , 980 KB