Full-scale recycling of backwash water from sand filters using dead-end membrane filtration

In 1995 and 1996 laboratory tests and pilot scale tests have indicated that backwash water from sand filters can be recovered by dead-end membrane filtration treatment. These test results showed that the heavily contaminated water, containing suspended solids from 100–1,000 mg/l consisting of mainly iron hydroxides and manganese oxides, can be purified into drinking water in one treatment step. In order to prove that this technology is also suitable for the recovery of backwash water on practical scale, a full-scale dead-end membrane filtration installation has been designed and built at the Eindhoven production plant of the Water Utility Company East Brabant1 in The Netherlands (operational since January 1997). The design was based on a flux of 170 l/m2 h bar and a maximum capacity of 120 m3/h. Although for the time being the installation has not been operated at maximum capacity, investigation into its performance during a longer period shows that the used method proved beyond any doubt to be very appropriate in terms of purification performance, energy and chemical consumption, productivity, recovery and costs. After more than one year, the full-scale plant still operates at a flux of 160 l/m2 h bar. The energy consumption turned out to be even lower than expected and amounts to 0.15 kWh/m3. The recovery was found to be 93%. The exploitation costs amounts to 0.43 NLG/m3.