Cleaning of ultrafiltration membranes after the treatment of surface water: static–dynamic test

Abstract

Access to safe drinkable water is a basic human right and an international development goal. AQUAPOT international project, created by Chemical and Nuclear Engineering Department of the Polytechnic University of Valencia, has been focused on research and development of low-cost and effective water treatment technologies based on membrane technology able to be used in developing countries. After several years of intensive laboratory and field research, Aquapot's ultrafiltration (UF) plants have been settled in different locations of Ecuador (province of Azuay) and Mozambique (province of Maputo). At present, most of the installed plants work successfully, producing drinking water suitable for human consumption and even for industrial use. However, installation of the designed UF-drinking water treatment facilities has shown that cleaning standard protocol of ultrafiltration membranes is not effective. This fact could affect microbiological quality and volume of the pure water produced and also life of the membrane and the UF-plant. In order to develop optimized cleaning protocols based on the use of common and accessible chemicals, Aquapot started an applied research studying several cleaning methods. Previous studies have been focused in applying different types of cleaning: chemical cleaning (by means of static tests and dynamic tests) and physico-chemical cleaning (combining chemical reagents with the hydrodynamic action of air bubbles). This work describes the experimental procedure performed in static-dynamic cleaning test, which combines soaking with dynamic circulation of cleaning solutions. Sodium hypochlorite and hydrogen peroxide at 25 degrees C performed the best results, recovering permeate flux from 10 to 12 times, respectively, compared with fouled membranes. Main results obtained for the different chemical solutions tested at 25 and 40 degrees C were also compared with previous chemical (static and dynamic test) and physicochemical cleaning. Results showed that the tested cleaning protocol improves the effectiveness of the cleaning and recovers UF membrane performance even until 30 times, when sequence of cleaning is done by sodium hypochlorite followed by hydrogen peroxide.