AWWA ACE58287

This paper explores the environmental, structural, work sequence, and operation considerations that have to be addressed when installing a 14 million gallons per day (mgd) low-pressure membrane process (ultrafiltration) within an existing water treatment plant (WTP) facility. To illustrate these considerations, the paper reviews the design that was performed for the rehabilitation of the existing WTP at the City of Lake Forest, Illinois. The City of Lake Forest WTP is a 12-mgd conventional granular media filtration process that uses Lake Michigan as raw water supply. The City of Lake Forest had concerns about the WTP's ability to meet existing and future water quality standards at its design capacity and to expand its capacity within the limits of the constrained site. Therefore, the City of Lake Forest decided to proceed with the rehabilitation of the existing facility. After review of the process treatment alternatives and the site constraints, low-pressure membranes appeared to be a viable alternative. Therefore, the City of Lake Forest decided to proceed with the design of a new low-pressure membrane filtration building. In order to minimize the project schedule, the first step of the design phase was to select the low-pressure membrane system. In addition to the criteria typically used for membrane selection such as full-scale experience, membrane compatibility with process chemicals, membrane certification, operation mode, and integrity testing, it appeared that installation criteria specific to the site had to be reviewed and evaluated. The main question raised during the membrane selection process was choosing between a pressure-driven system and a submerged system. The following criteria were evaluated: membrane system energy cost; installation of the new membrane system into the existing filter cells; operation of the existing treatment process during construction; minimal environmental impact of the new structure; match floor elevation between existing building and new building; maximize re-use of the existing basins; preserve the future; and, present worth analysis. Finally, a pressure-driven system was selected to match the specific constraints of the City of Lake Forest. More and more utilities are seriously considering rehabilitation of their existing facility with low-pressure membrane. Selecting the type of membrane system that addresses site and operation constraints is the key to a successful rehabilitation project. As each site is unique, the results of one study cannot be generalized for other sites. However, the same approach can be used on multiple sites. Includes 2 references, tables.