AWWA ACE63033

This slide presentation outlines the identification and resolution of a distribution system water quality event for discolored or yellowed tap water in New Jersey's Monmouth County. Numerous flushings were performed andone sample at an interconnectionwas yellow and contained >2 mg/Lmanganese but low iron.However, combined filter effluentsamples collected every 4 hoursshowed low (<0.04 mg/L) Mn levels. The local treatment plant practices included: water is ozonated, coagulated with PACl, and then split to sixpurification Units (upflow sludge blanket clarifier/filters);chlorine, fluoride, zinc orthophosphate, and caustic are addedbefore water enters clearwell;ozone added at 2-3 mg/L; noresidual leaves the contact basin; and,finished water at pH 7.5 and1 mg/L orthophosphate. The investigation is outlined as follows: examined plant records for raw, filtered, and CFE for turbidity,TOC, iron and manganese;examined distribution system samplerecords for color, orthophosphate, iron,manganese and HPC; and,collected sludge blanket samples,found low levels of manganese ininterstitial water but when sampleswere digested in hydrochloric acid,manganese levels were greater than 10 mg/L. The hypothesis included:increase in water temperature and algae combined withpreozonation resulted in increase biodegradable organiccarbon in sludge blankets;blanket(s) became anoxic leading to manganese release for ashort period of time (several hours at most); and,dissolved manganese passed through filters and reacted withpost-filter chlorine and slowly precipitated causing yellow water. The resolution included:plant had been upgraded to discontinue prefilter chlorination toavoid making disinfection byproducts (DBPs) so plant staff wanted to discontinuechlorination;preliminary tests showed that the granular activated carbon (GAC) filters could remove atleast 0.5 mg/L permanganate; and,began sodium permanganatefeed, increasing level until pinkwater was observed above filters. Includes figures.

Product Details

Edition:

Vol. - No.

Published:

06/01/2006

Number of Pages:

23

File Size:

1 file , 4.5 MB