Floating polypropylene covers are installed on each filtration pond to help control algae growth. Click here to enlarge imageEssex and Suffolk Water installed floating covers on each of the 18 ponds to combat the problem and contain costs. Filter beds must be accessed occasionally so the floating covers had to be capable of being completely removed. Additionally, the material had to meet the requirements of the UK Drinking Water Inspectorate (DWI).
The water company selected the tan 1.14-mm reinforced polypropylene geomembrane manufactured by Stevens Geomembranes of Holyoke, Massachusetts, USA. The membrane was manufactured in the company's state-of-the-art calendering facility located in Westfield, North Carolina. Bulk rolls of 1.94-metre-wide x 275-metre-long were shipped to a fabrication facility in the UK where individual floating covers were made for each of the 18 filter beds.
A moving gantry spanning the full width of the tanks and running on rails parallel to the tank sides was installed to remove the floating covers and gain access to the filter beds. The membrane is rolled onto the gantry as the mechanism is rolled down the tract when the membrane is removed from an individual tank. A series of straps and ties holds the membrane securely in place while on the gantry.
This type of algae control, using a polypropylene floating cover to restrict algae development is the first of its kind in the UK, if not in Europe, according to Stevens Geomembranes. The combination of a lightweight floating cover made of a DWI-approved material and an efficient means of deployment and removal for access solves a difficult problem for Essex and Suffolk Water. The company only has to drain the ponds and clean the sand once each year instead of several times each year. In addition, chlorine use decreased significantly due to the reduction of algae growth.
Author's note
Vincent McPartland is the vice president of sales and marketing for Stevens Geomembranes, based in Holyoke, Massachusetts, USA. Stevens Geomembranes manufactures polypropylene-based geomembranes for many applications, including reservoir liners, floating covers and wastewater treatment liners. For more information, visit Stevens' website: www.stevensgeomembranes.com.