AWWA MTC93060

A series of pilot tests and experiences from three full scale plants are summed up in this paper. It is evident that treatment of water with high content of humic substances are difficult because of long term fouling. A significant layer of gel-like matter will build up on to the membrane during 1000 to 2000 hours of operation with no cleaning of the membrane. Fine absolute filtration below 50 um seems to protect better from fouling than deep bed media filters. Cleaning should be done at least once a week, depending on solution strength, with dedicated agents. This way a flux level of 12-20 l/m2.h can be achieved with water temperatures below 10C. Proper choice of membrane for soft raw waters will be those with pore sizes of 1-2 nm and highly hydrophilic surface. Thus the operating pressure could be kept to a minimum (3-6 bars) to avoid excessive compression of the fouling layer, and still maintain a color removal of about 90%.