AWWA WQTC57149

MWRA is an unfiltered surface water wholesaler to 43 communities in the Commonwealth of Massachusetts. Current treatment includes primary disinfection with sodium hypochlorite. This is followed by soda ash, carbon dioxide and fluoride addition about 5 hours downstream. Chlorine gas is added followed by ammonia for residual disinfection about 10 hours further downstream from the soda ash addition. MWRA's source water pH and alkalinity are typically less than 7.2 and 5 mg/L as calcium carbonate, respectively. The soda ash and carbon dioxide addition was implemented for corrosion control, primarily to address the lead and copper rule. Both lead and copper levels have decreased tremendously and the 90th percentile lead level is hovering around the action level of 15 ppb. Current operating targets are pH 9.1 and alkalinity of 35 mg/L as calcium carbonate. Added benefits from this corrosion control scheme include decreases in both copper and lead levels in the wastewater bio-solids, decreases in complaints about discolored water, as well as manageable levels of nitrification. This paper focuses on the interactions between the effects of increased buffering capacity on iron release and the interaction of iron release with chloramine and pH stability, as well as chloramine stability and nitrification. The results should be applicable to other systems with low raw water alkalinity and use chloramine for residual disinfection. Includes 3 references, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2002

Number of Pages:

4

File Size:

1 file , 290 KB