AWWA MTC57588

AWWA MTC57588 Solving Morro Bay's Seawater Reverse Osmosis Plant's Iron Problem
Conference Proceeding by American Water Works Association, 03/05/2003

Kartinen, Ernest, Jr.; Martin, Christopher

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The City of Morro Bay is located on the central coast of California about midway between Los Angelesand San Francisco. In the late 1980s and early 1990s, California suffered a drought. The Cityconstructed a 0.58 MGD desalting plant. The water supply for the desalting plant comes from wellslocated on the beach fronting the Pacific Ocean. The plant began operation in early 1993. The desalteroperated for several months and was then shutdown following the "miracle March" rains.In 1995, there was again a shortage of rainfall and the desalter was returned to service. However, highprecipitated iron concentrations in the well water supplied to the desalter required changing the cartridgefilter elements at intervals of about 1/2 hour. It was impractical to operate the desalter because of thecost of changing the filter elements and also because there was insufficient cartridge filter capacity tomaintain feedwater flow to the RO equipment because the filter elements were having to be changed toofrequently.The City received notice that the supply of imported water from the California State Water Project wasto be interrupted for at least one month beginning about November 1, 2002, so that maintenance of Statefacilities can be accomplished. Less than normal rainfall and contamination of some of the City's wellwater limited the City's other water supplies. It was determined, therefore, to use the desalter to meet theCity's water needs.However, it was first necessary to reduce the iron problem. Boyle Engineering was retained torecommend a method to solve the iron problem. Two solutions were pilot tested for a short period oftime that included:addition of chemicals (acid and a reducing agent) in an attempt to redissolve the iron thataccumulates in the cartridge filters; and,filtration to remove the iron ahead of the RO system.The pilot tests indicated that installing an iron filter to treat the incoming well water would be the mosteconomical, reliable means of solving the iron problem. Accordingly, in late summer of 2002, the Citydetermined to install such a filter. Due to the approaching shutdown of the State water supply, the Cityadopted a "fast-track" approach to designing and installing the filter. Includes tables, figures.