Abstract: A process for operating filtering membranes submerged in a tank involves, in one aspect, periodically deconcentrating the tank by partially emptying and refilling the tank with fresh water. The emptying and refilling may be performed generally simultaneously or sequentially. In another embodiment, the membrane modules are arranged in a series of filtration zones between a feed water inlet and a retentate outlet of a tank and the zone adjacent the outlet is emptied and refilled.

Abstract: A process for operating filtering membranes submerged in a tank involves, in one aspect, periodically deconcentrating the tank by at least partially emptying and refilling the tank with fresh water while permeation continues. In another aspect, long trains of membranes modules are placed in series along a flow path in the tank. In one embodiment, constant aeration is provided to prevent tank water from by-passing the membrane modules while proving controlled mixing such that the average concentration of solids in the tank is lower than the concentration of solids in the tank near an outlet for removing retentate from the tank. In another embodiment, the membrane modules are arranged in a series of filtration zones between a feed water inlet and a retentate outlet of a tank. Permeate is withdrawn from the filtration zones by separate means associated with each filtration zone.

Abstract: A process for operating filtering membranes submerged in a tank involves, in one aspect, periodically deconcentrating the tank by partially emptying and refilling the tank with fresh water. The emptying and refilling may be performed generally simultaneously or sequentially. In another embodiment, the membrane modules are arranged in a series of filtration zones between a feed water inlet and a retentate outlet of a tank and the zone adjacent the outlet is emptied and refilled.

Abstract: A process for operating filtering membranes submerged in a tank involves, in one aspect, periodically deconcentrating the tank by at least partially emptying and refilling the tank with fresh water while permeation continues. In another aspect, long trains of membranes modules are placed in series along a flow path in the tank. In one embodiment, constant aeration is provided to prevent tank water from by-passing the membrane modules while proving controlled mixing such that the average concentration of solids in the tank is lower than the concentration of solids in the tank near an outlet for removing retentate from the tank. In another embodiment, the membrane modules are arranged in a series of filtration zones between a feed water inlet and a retentate outlet of a tank. Permeate is withdrawn from the filtration zones by separate means associated with each filtration zone.

Abstract: A method of producing high purity water using weak acid cation exchange for dealkalization and a double pass reverse osmosis membrane system having enhanced membrane life.

Abstract: A method of producing high purity water using dealkalization and a double pass reverse osmosis membrane system having enhanced membrane life.

Abstract: A system of purifying water to remove at least one of natural organic matter, color, turbidity, bacteria, cysts and oocysts, viruses, arsenic compounds and insoluble impurities. The system comprises the steps of providing a body of water to be purified; controlling the pH of the body in a range of 5 to 8; and adding a coagulant to the body to provide a floc. The floc is maintained in the body in a concentration in the range of 1 to 6, for purposes of adsorbing at least one of the natural organic matter, color, turbidity and bacteria to provide treated water. Thereafter, a first portion of the treated water and floc is removed from the body of water. A submerged semi-permeable membrane is provided in the body of water for removing a second portion of the treated water. The membrane has a pore size in the range of 0.02 to 1 .mu.m to provide a permeate comprised of purified water and to provide a retentate containing the floc.