Of the four wells that supplied water to the town of Littleton, Mass., back in the early 1990s, the Spectacle Pond well had the highest yield and caused the most headaches. Manganese was present in the water at 0.70 mg/l, and iron concentrations were around 0.30 mg/l. Complaints were being received from consumers about ugly brown stains on laundered clothing and bathroom fixtures.
A solution to the well water problem would need to account for the fact that the town had no sewer system and that the residents did not want to see truck traffic in their neighborhood hauling away waste.
The primary goals were to meet the current requirements of the Safe Drinking Water Act. This included reducing iron, manganese, and corrosivity, eliminating coliform bacteria and minimizing trihalomethane formation. Given that the well is under the influence of surface water, secondary goals were established to meet the anticipated requirements of the Surface Water Treatment Rule and the Enhanced Surface Water Treatment Rule.
The ultrafiltration system the town purchased was supplied by Koch Membrane Systems, Inc., and it incorporates ozone to oxidize the dissolved manganese and iron. The oxides of manganese and iron are insoluble and precipitate out of the water as brown particles that turn water the color of weak tea.
These particles are large enough to be filtered out of the water as it passes through the hollow fibers.
The effluent from the ozonation process is pumped to four parallel skids of hollow fiber cartridges. Ninety-five percent of the feedwater passes through the membranes and becomes permeate. The remaining 5% contain the retained manganese and iron oxides and are bled away from the filters to a collection tank where it is later treated by a secondary ultrafiltration system.
An important design objective was to minimize waste disposal requirements. The secondary ultrafiltration system consisting of a skid containing 20 cartridges accomplishes this by batch treating the waste stored in the collection tank. Nearly all the waste from all five skids is concentrated in this tank. It is periodically drained to drying beds, from where the water is filtered through sand and gravel and is sent to Spectacle Pond, leaving behind a fine deposit of manganese and iron oxides. As a result, the system recovers 99.9% of the feedwater as product, and there is very little waste. It has been operating virtually trouble free since start-up in 1997.
RSS: WWD Articles
.gif)
