Preparing Old Man River for Modern Treatment: Softening Coagulation of the Mississippi River for a 70-MGD Ultrafiltration Plant

摘要

Minneapolis Water Works (MWW) has been treating Mississippi River water for over 100 years. Two water treatment facilities operated by MWW provide water to Minneapolis, Minnesota and adjacent cities. The treatment process has remained the same since the 1940’s and employs lime softening, powdered activated carbon (PAC) and ferric-based coagulation and settling prior to filtration. MWW has embarked on a program to ultrafiltration membrane filtration at both sites. The raw water characteristics reviewed in this paper include variable temperature, alkalinity and turbidity, although the pH remains fairly consistent. The temperature variation of the raw water affects plant operations in many ways including reduced treatment capacity at lower temperatures and occasional freezing of the lime softening solids. Methods have been incorporated by the Minneapolis Water Works to handle the raw water temperature variations, including operating at reduced capacity in the low raw water conditions and feeding whiting (fine calcium carbonate solids).