NANOFILTRERING AV HUMUSRIKT YTVATTEN FÖR DRICKSVATTENPRODUKTION / Nanofiltration of surface water rich in humus for drinking water production

Water purification with membrane technology was investigated as one of the alternatives for the rurure drinking water production (6,000 m^/d) in Nynäshamn 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 colour number (up to 100 mg/1 Pt) due to humic substances as well as taste and odour problems rrom time to time. This R&D project has been performed in two phases:
– Laboratory trials for membrane selection (MF/UF/NF) compared with conventional raw water treatment (phase 1).
– Pilot plant operation with the selected nanofiltration (NF) method for design of a full scale plant (phase 2).
The aim of the pilot plant operation has been to evaluate different design parameters, type of prefiltration, 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 excellent, implying removal of colour and organic matter to undetectable levels. The membrane cleaning with a detergent (Ultrasil 10) has been repeated every second day. Further con-centration of the NF-reject with ultrafiltration (LJF) and disposal of the L)F reject by irrigation or a nearby golf course has been recommended from a hygienic and environmental point or view. The membrane alternative is according to the cost calculation competitive with other alternatives. The membrane application above is unique in Sweden but at 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.