The Kenosha, Wisc., Water Utilities recently put a new $29.5 million microfiltration water treatment plant into operation at a 40 percent lower cost than originally expected. The 20-mgd microfiltration plant is the largest of its kind in the U.S., according to one of the project designers, Montgomery-Watson.
The new microfiltration plant and the already existing rapid sand filtration plant can be run by one operator.
Kenosha conducted a ribbon cutting ceremony in June for the O. Fred Nelson Water Production Plant. It was actually an upgrade of the 40-mgd existing plant, which consisted of the ?West Plant? treatment facilities (finished in 1951) and the ?East Plant? rapid sand filtration plant (constructed in 1963).
Kenosha contracted Montgomery-Watson and General Contractor-Riley Construction in the fall of 1995 to design a conventional treatment plant with ozonation. The utility had considered building a microfiltration plant, but balked at the estimated cost of more than $50 million.
Halfway through preliminary design, however, the cost of the USFilter Memcor CMF microfiltration system decreased significantly, with membrane filtration costs decreasing to an estimated $1 per thousand gallons. The designer suggested looking at switching to this newer technology.
A pilot plant study was done to test the performance of membrane filtration on cold Lake Michigan waters. The study met goals and resulted in the construction of a new 20-mgd membrane microfiltration treatment plant and modifications to the existing ?East Plant,? a 20-mgd rapid sand filtration plant. The plant would have an ultimate capacity of 40 mgd. The project also involved new low-lift and high-lift pumping facilities, a 2.5 million-gallon reservoir/CT tank, and a new SCADA/Control System from Mauell Corporation.
The microfiltration portion of the plant has 16 Memcor CMF membrane units.
Memcor CMF Microfiltration differs from sand and other media filters by physically preventing inorganic or organic contaminants greater than 0.2 microns from penetrating and passing through the CMF barrier membrane. A low pressure feed water system drives water from outside the membrane to inside, where filtered water exits. The membrane units are completely skidded and modular and the plant is designed to add an additional 8 units in the future.
After the filtration process, the water flows to a 2.5 MG finished water reservoir and chlorine contact tank. A closely controlled residual of chlorine is maintained to ensure continuous sterile water in the distribution system. The high-pressure pump station pumps directly from the finished water reservoir into the distribution system at a pressure of approximately 90 psi. The high-pressure pump station consists of six vertical turbine pumps with a combined capacity of 48 mgd.
The plant is controlled by three Mosaic Mapboards from Mauell, which serve as a ?watchdog? to continuously monitor status, flow and filtration for the Kenosha system.
The first mapboard dynamically displays flow rates and the status of the filtration systems in the treatment plant, while the second mapboard, also dynamic, depicts the plant water distribution system. Data for flow rates, pump status, pressures, and reservoir levels also is shown on the boards.
Using the mosaic technology at the new facility enhances traditional desktop CRTs and man-machine interfaces with a big picture overview normally hidden by the limitations of the CRT screen size.
The mapboard display panel indicators are driven by Mauell?s I/O controllers, interfaced to Allen-Bradley PLCs. LEDs and digital readouts integrated into the panels indicate ?on,? ?standby,? and ?failure? of the pumps and provide water pressure readings.
The system also has an operator console designed to house the third mapboard directly in the console. This custom console will monitor the membrane filtration process.
On Dec. 19, 1998, the plant was given conditional approval by the Wisconsin DNR to begin delivery of treated water to customers. The membrane plant was put to the test on Jan. 1 when the storm that shut down Chicago?s O?Hare Airport slammed the beaches of Lake Michigan, pinning the influent turbidity meter at 1,000 NTU. The microfiltration plant never stopped running.
?We selected the microfiltration system for its ability to handle changing turbidity without the need for changing chemical dosages,? said Ed St. Peter, Assistant General Manager of the plant. ?We ran the system through the new year and we had turbidity peaks that we had never experienced before. The filtrate quality of the Memcor CMF units never changed; turbidity and particle count values were extremely low.?
The new microfiltration plant puts Kenosha ahead of expected regulatory requirements concerning surface water and disinfection byproducts without the use of pretreatment chemicals.
On June 19th. , one day before the opening session of the AWWA convention the O. Fred Nelson Water Production Plant opened as the largest operating microfiltration drinking water plant in North America. Within 5 days the plant gave tours to over 700 people. The plant tours were self-guided to 17 different stations. ?We came up with the idea originally for the residents. We wanted to show them what we built and that their plant is the safest drinking water plant available,? St. Peter said. Then USFilter and Montgomery Watson asked us to make the tour a permanent part of our plant available to their customers and then provided us with the creative and financial resources. The response has been fantastic, one resident said after her tour ?Now I don?t mind the increase in my water bill.? To date the plant has had over 2000 people visit, including persons form New Zealand, and China. For more information or to arrange a tour please contact the Assistant General Manager, Ed St. Peter by email at [email protected].
The Memcor CMF-S (Submerged) membrane units, which also were unveiled at the June AWWA show in Chicago, can treat upto 5.2 MGD with 576 modules in a single filter cell.
As engineers and owners gain microfiltration experience, and the cost of membranes drop, the future trend is to design bigger and bigger microfiltration plants. This signaled USFilter to create a new Microfiltration system, the Memcor CMF-S unveiled in June. The Memcor CMF-S system addresses the problem of multiple-skidded units for larger installations by offering a pre-engineered modular membrane system designed to be submerged into built on-site rectangular concrete tanks.
Performance
The CMF-S uses a membrane with a 0.2-micron nominal pore size and demonstrates up to 6 log removal of Giardia and Cryptosporidium. A vacuum pump draws water through the membrane fibers of sub-modules submerged in the open top filter tanks. The fibers are the same polypropylene material as those used in the conventional CMF process, but the Memcor CMF-S operates under vacuum, so maximum driving pressure is only 85Pa. This lower pressure limit is not the disadvantage it first appears because filter cake characteristics improve at lower pressures. Compared against earlier versions of CMF, operation of the Memcor CMF-S system shows:
Performance
- Fluxes 80-95% of CMF for the same time between chemical cleans.
- Lower plant footprints.
- Approximately 80% reduction in valves and seals per membrane area.
- Much simplified process
- The same Backwash efficiency and Backwash intervals
- The same Cleaning efficiency and CIP intervals
- The same Membrane Integrity
- Lower capital and operating costs per volume of water treated for large plants
Performance
The lower flux results from a lower maximum operating pressure for CMF-S vs CMF (12 PSI vs 22 PSI). But the lower fluxes are more than offset by the reduction in capital cost.Integrity testing
The Memcor CMF-S uses the same membrane integrity testing system as USFilter uses for conventional Memcor CMF. Membrane integrity testing gives automatic feedback of membrane condition. Plant operators and service technicians use membrane integrity in the field to ensure consistent filtrate quality. The integrity test involves the filtrate side of the sub-modules being pressurized with air to 100kPa. At this pressure, air cannot overcome the membrane?s bubble point (except for a small amount of air that flows through diffusion). The rate of pressure decay is measured over a period of time. If this rate is low, the cell is proven integral. If it is over a threshold value, it indicates that membrane integrity is suspect. Damaged fibers (which can be repaired through pinning) or leaking O-rings are the most common causes of integrity problems. These repairs are typically carried out during the yearly maintenance, such is the robustness of the CMF and CMF-S systems.
