A method for producing ultra high purity liquid oxygen from standard grade liquid oxygen which integrates the oxygen purification process with a nitrogen purification process by utilizing the condensing duty of liquid nitrogen, thereby causing the nitrogen to vaporize which is desirable prior to delivery to a nitrogen purification unit.A water purifier comprises a negative plate (E) arranged on the floor of a water stream and positive plates (A, B) arranged above and opposed to the negative plate (E). Floats (F) are arranged left and right sides and/or upstream and downstream in the direction ($g(a)) of the flow so that the positive plates (A, B) can sink under the surface of the water stream. The purifier further comprises means (h) for moving the positive plates (A, B) vertically and means (C) for collecting gas, as required. The positive plates (A, B) and the negative plate (E) cooperate to create an electric field, and high-intensity field pulses oxidize or decompose pollutant, such as nitrogen and phosphorus, contained in the stream of water.
