Effect of chemical cleaning conditions on the flux recovery of MF membrane as pretreatment of seawater desalination

Abstract

Flux recovery through chemical cleaning was investigated using mini-module for application in desalination pretreatment using seawater as feed. This study focused on the causes of membrane fouling by evaluating the cleaning efficiency with several chemical agents at various conditions. Sodium hydroxide and sodium hypochlorite (NaOCl) as alkaline chemicals, and citric acid, nitric acid, sulfuric acid, and oxalic acid (C2H2O4) as acidic chemicals were used in the experiment. Each chemical was prepared at concentrations of 0.1, 1, 3, and 5%. The effect of chemical combination was tested with cleaning sequences of alkaline–acid–alkaline and acid–alkaline–acid. The surface characteristics of the membrane were also investigated using scanning electron microscopy and tensile strength analysis. Prior to the chemical cleaning, flux of fouled membrane was measured using artificial seawater additive humic acid and sodium alginate. Duration of chemical cleaning was set at 4 h and then the flux was checked. For the control, pure water flux was measured using virgin hollow fiber membranes. Among the chemicals, NaOCl showed the highest flux recovery rate of 27.9% at 1% concentration. For the acidic chemicals, the highest recovery rate was 79.3% at 3% C2H2O4 in humic acid fouled membrane. While for the combination chemical cleaning, 97.6% flux recovery rate was recorded. On the other hand, in the case of sodium alginate fouling membrane, NaOCl showed the highest flux recovery rate of 30.3% at 0.1% concentration. For the acidic chemicals, the highest was 68.8% recovery rate at 0.1% C2H2O4. For the series type chemical cleaning, 98.0% flux recovery rate was recorded. 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.