Effect of chemical cleaning conditions on the flux recovery of fouled membrane

Flux recovery through chemical cleaning was investigated using small-sized membrane modules for application in drinking water treatment using river water as feed. This study focused on the causes of membrane fouling by evaluating the cleaning efficiency with several chemical agents at various conditions. Sodium hypochlorite and sodium hydroxide as basic chemicals, and citric acid, nitric acid, oxalic acid, and sulfuric acid as acidic chemicals were used in the experiment. Each chemical was prepared at concentrations of 0.1, 1, 3, and 5%. The mini-module was made of four strings of polyvinylidene fluoride hollow fibers with pore diameter of 0.038 μm. Flux was tested at constant pressure of 0.5 bar. The experiment was operated at the temperature range of 18.1–25.3°C. To compare the effect of water temperature, cleaning test was performed at the range of 0–5°C. Also, the effect of combination of chemicals was tested with cleaning sequences of base–acid–base and acid–base–acid. The surface characteristics of the membrane were also investigated using Scanning electron microscopy and tensile strength analyses. Prior to the chemical cleaning, flux of fouled membrane was measured using deionized water. Duration of chemical cleaning was set at 30 min, 1, 2, and 4 h, and then, the flux was checked. For the control, pure water flux was measured using virgin hollow fiber membranes. Among the chemicals, sodium hypochlorite showed the highest flux recovery rate of 44.0% at 1% concentration. On the other hand, for the acidic chemicals, the highest was only 38.1% recovery rate at 1% oxalic acid. Recovery efficiency increased as the concentration of chemicals and cleaning time increased. Organic or biofilm was considered as the main foulant as observed from the experimental results. In addition, the cleaning efficiency was better in basic than acidic.