Abstract
Since 1999 a UF plant with a mean throughput of 1,3 ML/d is in operation treating surface water from a reservoir and spring water for drinking water supply. A three year DVGW (German Gas and Water Works Association) research project accompa-nied the operation in order to gather data of the membranes life time, their opera-tional efficiency, the dependence of transmembrane pressure on raw water quality (e.g. turbidity, particle count, concentrations of algae, natural organic matter) and the waste water demand.

During operation TMP increased with increasing raw water turbidity and algae con-tent and decreasing temperature as expected. Waste water demand has been mini-mized by decreasing the backwash frequency down to 6 %. Detailed observation of TMP data versus time showed that hydrogen peroxide had not much positive influ-ence on backwash efficiency. Backwashes with filtrate and chlorine showed better cleaning efficiency. However, the use of this chemical should be minimized because of the formation of disinfection-by-products in the backwash water causing problems with their discharge. Therefore alternating backwashes with acid and base were in-troduced in the last step of the research project resulting in a decrease of TMP. Whether these rather low values can be kept constant for longer periods of time will be recorded in an upcoming research project that has been proposed for approval.

Filtrate from the UF-plant always fulfilled the requirements of the standard for drinking water in Germany. Bubble test for integrity showed that almost all membranes were still integer.

The competence for this project is at the department of Technology.