Cleaning effects of oxalic acid under ultrasound to the used reverse osmosis membranes with an online cleaning and monitoring system

Abstract

A new system was developed for the research on the cleanings of ultrasonic acid and alkali to the used reverse osmosis membrane (UROM). By continuously detecting the absorbance, conductivity and K+/Na+/Cl−/Ca2+ contents in the cleaning solutions with this system, the cleaning information of organic and inorganic fouling on the UROM can be obtained and their cleaning effects can be judged directly. In the research, after comparing the cleaning effects of five kinds of acid solutions to the used polyamide ROMs, it was found that the ultrasonic cleaning effect of oxalic acid is the best. Therefore the concentration and pH of the oxalic acid, the sequence of acid and alkali cleanings were investigated, the results showed that, when the pH of 0.2% oxalic acid was regulated to 2.5 by the ammonia water, the defouling rate of the UROM can be reached 91%, and if employing the acid and alkali solutions to simultaneously clean, the best cleaning effect will be obtained, in which the cleaning order should be the first acid then alkali plus the ultrasound. The results and parameters obtained in this study can be used as a reference basis for designing large-scale chemical and ultrasonic cleaning system of UROM.