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 and
one sample at an interconnection
was yellow and contained >2 mg/L
manganese but low iron.
However, combined filter effluent
samples collected every 4 hours
showed low (<0.04 mg/L) Mn levels. The local treatment plant practices included:
water is ozonated, coagulated with PACl, and then split to six
purification Units (upflow sludge blanket clarifier/filters);
chlorine, fluoride, zinc orthophosphate, and caustic are added
before water enters clearwell;
ozone added at 2-3 mg/L; no
residual leaves the contact basin; and,
finished water at pH 7.5 and
1 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 sample
records for color, orthophosphate, iron,
manganese and HPC; and,
collected sludge blanket samples,
found low levels of manganese in
interstitial water but when samples
were digested in hydrochloric acid,
manganese levels were greater than 10 mg/L. The hypothesis included:
increase in water temperature and algae combined with
preozonation resulted in increase biodegradable organic
carbon in sludge blankets;
blanket(s) became anoxic leading to manganese release for a
short period of time (several hours at most); and,
dissolved manganese passed through filters and reacted with
post-filter chlorine and slowly precipitated causing yellow water. The resolution included:
plant had been upgraded to discontinue prefilter chlorination to
avoid making disinfection byproducts (DBPs) so plant staff wanted to discontinue
chlorination;
preliminary tests showed that the granular activated carbon (GAC) filters could remove at
least 0.5 mg/L permanganate; and,
began sodium permanganate
feed, increasing level until pink
water was observed above filters. Includes figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 4.5 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 23 |
| Published : | 06/01/2006 |
