NANOFILTRATION OF HIGHLY COLORED RAW WATER FOR DRINKING-WATER PRODUCTION

Water purification with membrane technology was investigated as one of the alternatives for the future drinking water production (6,000 m(3) /d) in Nynashamn community. The selected raw water source was surface water from Lake Muskan rather than brackish water from the Baltic Sea. The lake water, without need for desalination, has a high color numbe r (up to 100 mg/l Pt) due to humic substances as web as taste and odor problems from time to time. This R&D project has been performed in tw o phases: Phase 1: Laboratory trials for membrane selection (NF/UF/MF) with and without activated carbon treatment compared with a conventio nal raw water treatment including flocculation, sedimentation, filtrat ion and activated carbon treatment. Phase 2: Pilot plant operation wit h the selected nanofiltration (NF) method for design of a full scale p lant. Phase I will be presented separately. The aim of the pilot plant operation has been to evaluate different design parameters, type of p refiltration, two tested NF-membranes, membrane cleaning procedure as well as to estimate the costs of a full-scale plant. The result of the pilot plant operation is satisfactory, implying removal of color and organic matter to undetectable levels and maintaining a higher membran e flux than expected throughout the trial period during 6 months. The membrane cleaning with a detergent (Ultrasil 10) has been repeated eve ry second day. The disposal of the NF reject into the sewage net is no t possible due to the increase of the hydraulic load. Purification of the NF-reject with ultrafiltration (UF) to a color level about the sam e as for the raw water from the lake has been suggested in combination with disposal of the UF reject by irrigation of a nearby golf course. The membrane alternative is according to the cost calculation competi tive with other alternatives. The water price will be a little higher (about 0.17 USD/m(3) higher) than conventional treatment including act ivated carbon, but the drinking water quality will be improved and mor e consistent. The membrane application above is unique in Sweden but a t the same time in accordance with the present trend in several other countries to utilize membrane technology without chemicals instead of conventional raw water treatment for drinking water production.