Water recovery and treatment of spent filter backwash from drinking water using chemical reactor-ultrafiltration process

Abstract

During routine operations of water treatment plant (WTP), production of spent filter backwash water (SFBW) is inevitable that imposes high operation and maintenance costs. The study investigates treatment and water recovery from SFBW from WTP via combined chemical reactor-ultrafiltration (CR-UF) process. The daily generated SFBW from full-scale treatment plants were treated by the pilot pant of CR-UF process, which is comprised of a primary sedimentation basin, coagulation and flocculation tank immersed UF membrane module. The optimum conditions for CR process were pH 7.5 and FeCl3 dose 20 mg/L, which led to significant removal of turbidity, color, and UV254 that are equal to 97.11 ± 0.10 %, 63.31 ± 1.98 %, and 30.74 ± 0.72 %, respectively. The CR-UF produced permeate with very low turbidity (0.3 ± 0.01 NTU and 93.0 ± 1.1 % removal) has met the water standard of 5 NTU. During the continuous operation of CR-UF process and after three consecutive cycles of UF backwashing, initial flux slightly declined from 8.57 L/m2.h in the 1st cycle to 8.20 L/m2.h in the 3rd cycle, demonstrating the irreversible fouling due to nanoparticle blocking. In four proposed blending of SFBW, the amount of UV254 and TOC did not change significantly (<1 % increase), and additional coagulant was not needed. The hazard index (HI) values for all the population groups were <1, suggesting a minimal adverse health risk regarding the consumption of treated SFBW by the CR-UF process. Overall, the permeate stream of CR-UF process can be reused as a source of raw water for drinking water treatment plant.