Application of out—in MF/UF-systems for drinking water treatment with air supported backwash — three case studies☆

Membrane filtration is increasingly accepted as a treatment process for drinking water supply in Germany as it guarantees an effective particle removal. However, there is still research and development required for the regular backwash and cleaning of the membrane systems. In this paper three case studies will be shown where MF/UF-systems with minimized chemical demand were operated. These systems use air-water-mixtures on the feed side of the membrane during regular backwash of the membranes with filtrate and thereby causing a mechanical cleaning of the membrane surfaces. The investigations showed that regular backwash with filtrate supported by air flush on the feed side is a very effective method to keep TMP low and minimize its increase. The use of air supported backwash helps minimizing the demand for wastewater. As for the regular backwash with filtrate no chemicals are required, the backwash waters may be discharged to the recipient or the sewer without any restrictions. The investigations showed also, that there still is the need for chemical cleaning, because some irreversible fouling always remains. The frequency of chemical cleaning however is very much dependent on the raw water quality. A specific throughput has been calculated which should help to compare different systems with each other.