This paper deals with two recent developments made by the authors about the hybrid membrane systems applicable to the water purification. The performance of a hybrid MF membrane system with circulating powdered activated carbon and condensed sludge has been studied using a pilot plant. The powdered activated carbon was intermittently dosed to the system for adsorbing mainly the humic substances. Manganese ions and ammonia nitrogen were biologically oxidized by the iron-oxidizing bacteria and ammonia oxidizing bacteria inhibiting the condensed sludge. In the hybrid MF membrane system, decreasing rate of the permeability was much less than that of a conventional MF membrane process. This may result from the reduced organic loading to the membrane due to the adsorption of humic substances onto the powdered activated carbons. A novel UF membrane process was also developed, where the nitrifying bacteria are fixed on the surface of the rotating disk membranes. With this membrane process, the simultaneous performance of the strict solid-liquid separation and the biological ammonia oxidation are possible. In order to increase the washing efficiency, a small quantity of the sponge particles were introduced into the membrane chamber and then the disk rotational speed was increased. This membrane washing method using sponge particles was so effective that the filtration resistance due to the accumulated cake was completely cancelled.

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