Nashville, TN — The water treatment plant Barge, Waggoner, Sumner, and Cannon, Inc. (BWSC) designed for the Sewanee Utility District has received industry attention as the cover story of the March/April 2011 issue of Tennessee Public Works, a publication of the Tennessee Chapter of the American Public Works Association.
The project posed several challenges for BWSC designers, the first of which was to introduce as much modern technology as possible to a small water treatment plant while still controlling costs. BWSC proposed a design that would not only incorporate a microfiltration membrane unit, but would also make overall plant maintenance easier and less costly.
To help save costs, BWSC embarked on a program of bench-scale testing of raw feed water conditions in order to define conditions and identify the best option for membrane selection. The raw water was of high quality allowing use of in-pipe micro-flocculation, which achieved a significant cost savings over conventional pre-filtration sedimentation.
The use of in-pipe micro-flocculation supported the goal of ease of maintenance, too. Rather than requiring expensive external basins, a simple metal building was sufficient to shelter the process equipment inside. With far less equipment exposed to the environment, maintenance costs should be lowered. Further supporting ease of maintenance was design of secondary containment of chemical feed within the building. No chemical line or injection point is located outside the secondary containment and all secondary containment structures were built to be easily washed down if a leak occurs.
The membrane itself is an out-in pressure microfiltration membrane made of Polyvinylidene fluoride (PVDF) and manufactured by the Pall Company. The effective filtration range is up to 0.1 micron diameter. The membrane filtration system virtually eliminates all bacteria or higher life forms such as Cryptosporidium as well as a large percentage of pathogenic viruses. Membrane replacement cycle ranges from ten to fifteen years. To date, the plant has exceeded all water quality standards and has reduced disinfection by product (DBP) formation over that of the previous conventional plant.
BWSC also designed the new building for the WTP, relocated the raw water feed pump station, and designed all instrumentation and chemical feed systems. Construction costs including the membranes came in at $2.7 million and the project construction spanned 15 months.
The article notes “The Sewanee project demonstrated that relatively small utilities can afford the benefits and reduced risk available in the implementation of technologically up-to-date process equipment.” BWSC is excited to have provided the client with a cost-effective, environmentally sensitive solution that meets and exceeds their expectations. |
