Ultrafiltration for the reuse of spent filter backwash water from drinking water treatment

During most water treatment processes, spent filter backwash water (SFBW) is generated. Reuse of SFBW is of concern because of the possible recycling of heavy metals, precursors for disinfection by-products and microorganisms. Innovations in membrane technology, especially in micro- and ultrafiltration processes, offer a suitable treatment for SFBW in order to guarantee a water quality necessary for reuse. Results from a pilot-scale ultrafiltration plant with submerged membranes are presented. Experiments were performed with SFBW from a full-scale water treatment plant. The plant was operated with high fluxes of more than 40 L/(m2·h) using clarified and non-clarified SFBW. Best membrane performance was obtained using non-clarified SFBW. As a result, no space- and timeconsuming sedimentation processes are necessary. The presence of powdered activated carbon in the SFBW did not have a negative impact on flux and TMP. Results confirmed that the filtrate can be used as an additional and safe water source. When a continuous maintenance disinfection was provided, filtrate was free of microbial contamination and could be reused without any safety concerns.