Assessment of a prototype VSP filter in a pilot plant

A novel design of cross-flow filter was supplied for testing at Harwell. This filter consisted of six cylinder perspex tubes each of which contained a coiled stainless steel wire filter element. Filtration took place from outside to inside on the filter element. The filtration gap could be adjusted by extension of the spring. Tests were carried out filtering three different liquids, mains water, ferric hydroxide floc and Harwell Low Level Waste. The filter was operated after precoating with filter aid. An optimum filter-aid concentration of 250ppm was established. Filter tests using tap water gave a steady state flux of 20m/d at 2 bar. Filtering ferric hydroxide floc at pH 9.5 gave a permeate containing < 0.5mg/l.Fe at a steady state flux of 8m/d. Processing Harwell LLW gave an α removal to less than ''approx.'' 2.5 x 10-3Bg/ml and a flux which declined from 20m/d to 2.5m/d over 40 minutes operation. The membrane could be effectively cleaned by extending the springs and backwashing with water at 4bar(g). (author)