Application of a combined UF/RO system for the reuse of filter backwash water from treated swimming pool water

Results from the full-scale application of a combined ultrafiltration (UF) and reverse osmosis (RO) treatment process for the reuse of spent filter backwash water (SFBW) from treated swimming pool water are presented. Ultrafiltration treatment showed a significant reduction of particulate matter. Turbidity decreased from values between 5 and 25 FNU in the feed (SFBW) to values below 0.02 FNU. At the plant investigated in this study, filtration periods up to 90 min were achieved. With this configuration, efficiencies of more than 97% for the UF plant were obtained. In order to avoid an increasing concentration of salts and dissolved compounds, up to one-third of the UF filtrate was directed to the RO plant. As a result, no deterioration of the swimming pool water quality was observed, and especially the concentration of disinfection by-products did not increase. A cost comparison showed annual savings depending on the expected useful life of the membranes. If the expected useful life of the membranes exceeded 7 years, annual savings of more than 4,300 would be possible. With regard to threshold values for the direct discharge of the concentrate, the concentration of suspended solids, adsorbable organic halides as well as the chemical oxygen demand are of special interest.