Enhancing performance of ultrafiltration with inline dosing of coagulant and powdered activated carbon

Abstract

In this study simultaneous and continuous inline dosing of PAC and coagulant in UF was investigated. Surface water was directly treated with PAC-UF and performance of the system was assessed by looking at membrane fouling and organic micropollutants removal. Combining adsorption and membrane processes in one technique, hybrid membrane processes, enhances performance of OMP removal by membrane processes. Powdered activated carbon (PAC) combined with coagulation and ultrafiltration (UF) is a possible treatment technique for surface water.
Permeability in UF-membranes remains steady, when dosing coagulant. Only a small increase in irreversible fouling of 0.2-0.7*109 m-1h-1 is visible. However, absence of coagulant dosing causes irreversible fouling to increase to 8.7*1010 m-1h-1 and can not be easily reversed with a chemically enhanced backwash (CEB). Inline dosing of PAC alone causes an irreversible fouling of 11.4*1010 m-1h-1 and highest increase in reversible fouling of 11.7*1010 m-1h-1. Addition of coagulant (1.2 mg/l) lowers reversible fouling compared to no dosing, on the other hand addition of PAC to coagulant shows no clear increase or decrease in reversible fouling. Coagulation has a negative effect on capillary blocking, an increase of 4-8% compared to no coagulant or adsorbent. PAC and no dosing did not influence pore blocking.
Highest removal of low to good adsorbable OMP was 10-63% for continuous and simultaneous dosing of 12 mg PAC/l and 1.2 mg FeCl3/l. Increasing filtration time (30 to 60 min) showed highest removal efficiency of 75% of Sotalol and 5-Methyl-1H-Benzotriazole, both good adsorbable OMP. Removal of PFAS varies between a few percent and 37%. Continuous dosing of coagulant (1.2 mg/l) with PAC (10 mg/l) has a negative impact on OMP adsorption including PFAS. With a higher PAC dose (15 mg/l) removal efficiency was not affected.
Addition of coagulant with PAC-UF showed to be effective to prevent irreversible fouling, with direct surface water treatment. However, coagulation is responsible for blocking of capillaries even resulting in a small decrease of permeability. Removal of OMP including PFAS was much lower compared to other PAC-UF systems and therefore PAC-UF with simultaneous and continuous inline dosing of PAC is not a good set-up. Adjustments in set-up should be made in order to make this configuration work. Possible improvements are increase of filtration time between backwash and dosing sequence of PAC and coagulant.