Membrane fouling and cleaning in ultrafiltration of wastewater from banknote printing works

The hollow fiber blend membrane, fouled by plant wastewater from banknote printing works, was characterized with SEM and the fouling elements were investigated by EDX. Based on analysis results, fouling process in ultrafiltration was simulated by using the model substances, which exist in the wastewater from banknote printing works, such as Turkey red oil, sodium hydroxide and calcium ion. It is observed that the reaction between Turkey red oil and calcium ion forms sediments, which leads to the beginning of membrane fouling. Furthermore, a four-step cleaning method, including de-ionized water cleaning, hydrochloric acid (0.1N) aqueous solution cleaning, second de-ionized water cleaning and sodium hydroxide (1 wt.%) aqueous solution cleaning, was used to clean the seriously fouled membrane in both lab and plant scale (membrane areas were 0.0157 and 80 m2, respectively) experiments. The results show that the cleaning method is effective. The membrane surface after cleaning was also analyzed by SEM/EDX and the foulants in the cleaning solutions were identified by TOC and ICP. According to these experimental results, the mechanisms of membrane fouling and cleaning were proposed. The four-step cleaning method has been widely used in the ultrafiltration of wastewater from banknote printing works.