Removal of geosmin and 2-methylisoboneol (2-MIB) by membrane system combined with powdered activated carbon (PAC) for drinking water treatment

Abstract

Adsorption kinetic tests and step-feeding tests were performed to evaluate adsorption characteristics of geosmin and 2-methylisoborneol (2-MIB). Removal efficiencies of each unit process in powdered activated carbon (PAC) membrane hybrid system were evaluated as well. The hybrid system consists of two unit processes; a coarse powder activated carbon (C-PAC) contactor and a submerged membrane tank. A pilot plant having a capacity of 500m3day−1 was installed in W municipal drinking water treatment plant. C-PAC contactor has C-PAC (80–150 mesh) slurry blanket with a high concentration of 30,000mgL−1 and the blanket is maintained in the contactor without loss. After the adsorption capacity of the C-PAC was exhausted, C-PAC turned into a biological activated carbon. In step feeding tests, 2-MIB and geosmin were continuously injected to the raw water as a concentration of 50ngL−1 for 2-MIB and 200ngL−1 for geosmin. Addition of fresh PAC of 15mgL−1 and 5mgL−1 was required to reduce the concentration of 2-MIB or geosmin below odor threshold concentration, respectively. These values are less than half of required dose from kinetic tests. The removal of Geosmin and 2-MIB by the bio-film formed on the C-PAC in the contactor was accounted for approximately up to 25% of the overall removal. As the raw water temperature increased from 5 to 20°C, the biological removal efficiency was almost doubled. The operating pressure of membrane had been stable when the flux was maintained below 33Lm−2h−1 with recovery rate of 98% for three months. The recovery cleaning is expected every 6 months for the long term operation.