The utility chose the latter because it wouldn't require any new building, thus reducing costs, and because it would incorporate the existing piping. It also offers the greatest flexibility for meeting future regulations and the ability to be easily automated. After conducting side-by-side tests with products from two manufacturers, the utility chose the Memcor CS submerged system from Siemens Water Technologies because it offered the lowest 20-year lifecycle cost.
To use submerged membranes in place of the existing filter system, the utility:
- Installed submerged membranes in the existing filter basins
- Increased the pretreatment capacity from 7.5 mgd to 15 mgd without a parallel treatment train
- Installed a new rapid-mix basin
- Converted the ozone contact basin and the first third of the sedimentation basins into flocculation basins
- Added plate settlers to the remaining portions of the sedimentation basin
- Used the waste wash water reclamation building to house the ancillary membrane equipment and the wash water plate settler
- Upgraded the waste wash water basin for year-round use
- Increased the intake and high service pump station capacities to 15 mgd
- Switched disinfection from chlorine gas to bulk sodium hypochlorite
- Eliminated ozone by using powdered activated carbon and potassium permanganate for taste and odor control.
The upgrade had to be done during the winter when the plant wasn't in use, so speedy installation was critical. Construction began August 2004 and the plant was on line by April 2005. Since then, it's met its capacity and performance needs. Should the plant need to be expanded again, new modules may be added to the membrane basins quickly and fairly inexpensively.
Manitowoc and Kennewick are just two utilities whose need to expand capacity in a limited space, timeframe, and budget made low-pressure membrane filtration a viable option. Outstanding water quality and the ability to adapt to rapidly changing raw water conditions are the icing on the cake.
— Gallagher is director of global process technology for Siemens Water Technologies, Shrewsbury, Mass.Environmentally friendly filtration
Mississippi's state capital spares 40 acres of wetlands.
In 1914, when Jackson, Miss., built its first drinking water treatment plant, it was standard operating procedure to discharge untreated residuals into local waterways. A second plant, built in 1992, did the same until a residuals handling facility was added in 1997.
By 2006, the Mississippi Department of Environmental Quality was threatening to fine the city $25,000/day for using the Pearl River as an effluent filter, demand was close to overwhelming the plants' combined 67-mgd capacity, and neither could meet the EPA's Long Term 2 (LT2) Enhanced Surface Water Treatment Rule.