Abstract: Dialysis apparatus has dilution and concentration chambers arranged alternately, which chambers each are defined by ion exchange membranes and frames each disposed therebetween. Passages for introduction of air into the dilution and concentration chambers are provided at lower portions thereof. The air introduced through the passages into the dilution and concentration chambers rises upward between the ion exchange membranes and is exhausted from upper portions thereof out of the dialysis apparatus. By the introduction of the air, solutions in the dilution and concentration chambers are driven to flow upward. Condensed phosphates are added to liquid to be treated before dialysis of the liquid.

Abstract: A system is provided for separating waste water or solution into a permea solution and a concentrated solution by feeding the waste water or solution to a reverse osmosis apparatus using a membrane.A chemical pretreating apparatus is provided to prevent hard scales contained in the waste water or solution from precipitation during the concentration in the reverse osmosis apparatus using the membrane. An apparatus for charging sponge balls is further provided to mechanically remove suspended solids and other suspended matters, that is, soft scales when deposited on the surface of membrane. The sponge balls are desirably recyclically used.