Membrane filtration of high turbidity sources

Membrane filtration processes have become widely used for low turbidity water sources that require particle removal and disinfection. In cases where the feed water contains high turbidity levels or high fouling tendencies, pre-treatment has been required to allow the membranes to operate efficiently. Submersion membranes have allowed direct treatment on many of these water supplies but operate under vacuum. This presents limitations on operating flux and design conditions for incorporating into existing facilities. The treatment unit designs are also very expensive to implement for small water treatment applications. A recently developed pressure driven ultrafiltration (UF) membrane is being tested on several different water sources and has demonstrated exceptional operation on high turbidity feed water sources. The module design includes a single potted end with the membrane fibers looped on the bottom to allow draining of solids from the module. The UF membrane filters outside to inside and has been operated on feed water turbidity levels up to 200 ntu. The availability of a pressure driven hollow fiber membrane that can efficiently filter high suspended solids water sources can provide a cost effective solution for many small to medium sized water supplies. Conditioning the feed water with a coagulant or direct filtration of high turbidity feed water can be used depending on the organic material present without settling or other clarification process. This eliminates the need for additional structural pretreatment and reduces overall system cost and size. Current limitations include the module size that makes this cost prohibitive for very large systems. Larger membrane systems where high-suspended solids are present in the feed water have been utilizing immersion membrane technologies more and more over the past few years. These systems typically operate under a vacuum and can be used for large water treatment plants as their design allows large filtration modules such as Memcor's CMFS filter block at 880 m³/hr. This allows significant capital cost reductions and allows membrane filtration to be competitive to conventional filtration technologies for virtually all filtration applications. This paper will review the economics and performance of both pressure driven and immersion membrane systems for small to large water supply systems on feed water containing high-suspended solid levels. Actual testing data for the new pressure driven hollow fiber UF membrane and immersion membrane systems will be provided on different water supplies including unconditioned surface water, filter backwash water and coagulated surface water.