Filter cartridges reduce contaminants in desalination system

Problem: A private club on the Atlantic Ocean in Rhode Island relied on desalination for drinking water. Northeast Water Solutions Inc. (NWSI) helped during startup of the initial RO system. The source water contained elevated TDS, iron and manganese. The system ran for 15 minutes before it automatically shut down due to terminal pressure drop across the RO membranes. The prefiltration plan was inadequate given the quality of the water and the strict limitations imposed by the state Department of Environmental Management.

Solution: NWSI installed a new treatment system consisting of 5-micron bag filters followed by 25 1-micron dual-gradient cartridge filters and then a 2,000-gallon atmospheric storage tank. After repressurization to 40 psi, the water stream is directed through duplex parallel NanoCeram 4.5- by 20-inch pleated filters from Argonide Corp. Flow is then directed through 1-micron final prefilters before a 7,500 gpd RO system. The recovered water flows into a 1,000-gallon atmospheric storage tank followed by UV disinfection before entering the water distribution pump station feeding the resort. The reject water is discharged to an ocean outfall. A remote maintenance system monitors pressure drop across each step in the filtration process.

Result: The filter cartridges have decreased the frequency of membrane cleaning by reducing iron and manganese in the feedwater. Monitoring provides the client with worry-free service and plentiful drinking water. The system is now in compliance with state regulations. 407/322-2500; www.argonide.com.

Underdrains retrofitted into compact footprint

Problem: In an upgrade of its drinking water plant to eliminate taste and odor complaints, the town of Palmer, Mass., needed a 6-foot bed of granular activated carbon (GAC). However, the plant’s layout limited the maximum dimensions of the tank that could be retrofitted to the site.

Solution: By installing low-profile Triton underdrains and a slightly deeper filtration tank, the town was able to accommodate a full 6-foot-deep GAC bed. The Vee-Wire Technology from Bilfinger Water Technologies in the underdrains has wedge wire elements placed 0.005 inch apart to create an upper surface that holds granular media without a traditional gravel bed. That allows systems to accommodate more media, enabling greater depth filtration and more contaminant removal. It maintains a 6 percent open area, minimizing headloss and plugging. During backwash, the narrowing profile between each pair of wires acts like a nozzle, accelerating the flow of air and water to backwash and agitate the media, creating a uniform, fluidized cleaning action.

Result: The water treatment plant is running with high efficiency and minimal operating cost in its existing footprint. 800/833-9473; www.water.bilfinger.com.

Air strippers remove vinyl chloride contamination

Problem: A South Florida municipality had three drinking water wells contaminated with vinyl chloride from an unknown source. The wells were needed to meet water demand and could not be taken out of service. The community needed a quick and economical solution for the short and long term.

Solution: Within six weeks of notification, Carbonair Environmental Systems supplied two rental STAT 720 low-profile air strippers to remove the vinyl chloride. For a permanent solution, the city bought the two rental units and one additional STAT 720. Carbonair assisted with the design of the permanent system and supplied a system-control package integrated with the city’s SCADA system.

Result: The resulting system routinely reduces vinyl chloride from an average of 13.1 ug/L to less than 0.5 ug/L, saving the city significant money and avoiding a short-term water shortage. 800/526-4999; www.carbonair.com.