Hideo Iwahashi

The effect of heavy metal ions on the oxidation of cellulose triacetate membranes

Abstract Cellulose triacetate (CTA) membranes have strong resistance to chlorine. The effect of the concentration of chlorine and temperature on the resistance performance was studied. However, the effect of heavy metal ion and pH on it has not been studied well. We studied the effect of various kinds of heavy metal ion, concentration of chlorine, temperature and pH. We measured the reverse osmosis (RO performance, acetylation degree (combined acetic acid content) and molecular weight of CTA. From the experiments it is seen that some heavy metal ions such as copper and cobalt strongly affect the oxidation of CTA by chlorine; and it was also found that the oxidation degree depends on temperature, pH and concentration of chlorine. Furthermore, we investigated the masking agents which reduce the effect of heavy metal ion, and we found some effective masking agents.

Performance change formula of cellulose triacetate hollow fiber RO membranes due to oxidation and hydrolysis

Abstract The changes of salt permeability coefficients, B-values, with time were investigated on cellulose triacetate hollow fiber RO membranes having oxidation and hydrolysis. The increasing rate constants of B-values and K-values were obtained, and the prediction formula on K-values was derived. Calculated K-values are in fair agreement with experimental values. Since the K-value in hydrolysis, KH, and that in oxidation, KO, can be calculated independently, this formula is expected to be applied to the prediction of performance changes with time, including the period of suspension in RO plant operation.

Test result of the intermittent chlorine injection method in Jeddah 1 plant

Abstract This test was performed in order to confirm safe operation without biological trouble at the Jeddah site by using intermittent chlorine injection (IC) operation as follows: dechlorination by injecting sodium bisulphite for 7 h/shift and keeping chlorinated feed seawater for 1 h/shift. We have confirmed the following: There is no increase of bacteria, and conditions of productivity and salt rejection are stable. So far it can be concluded that safe operation without biological trouble was confirmed at the Jeddah site by using the ICI operation.

The behavior of an oxidizing/reducing agent in seawater

Abstract The behavior of oxidizing/reducing agents in seawater are investigated. Br − is oxidized to BrO − by ClO − when the raw seawater and chlorinated seawater are in contact. In the chlorinated seawater Br − is oxidized to BrO − 3 via BrO − . The sodium bisulfite generates some oxidizing agents in the case of coexistence of heavy metal such as Cu and Co, chloride ion and dissolved oxygen in the solution whose pH is neutral. In the design of the sterilizing system of the RO plant, it is very important to know the heavy metal concentration of feed water and to select the materials for the plant.

The study of environmentally friendly pretreatment system

Abstract The Mitsubishi Heavy industries, Ltd. has been challenging the development of a chemical-free pretreatment. In this paper, we will present our experience of the field tests. The test results turned out to be very successful and proved that the chemical-free pretreatment is applicable for reverse osmosis seawater desalination. Chemical-free rapid sand filtration especially is the most promising process, which has been applied as a pretreatment system of salt manufacturing works in Japan and worked in condition for more than 40 years. Although the exact mechanism has not been identified, the performance of this system seems to be related to the microbial activity. It is hoped that this pretreatment system will solve the environmental problem that is caused by a seawater desalination plant.