AWWA MTC57623

A dynamic model was developed to describe the competitive adsorption of trace organic compounds by powdered activated carbon (PAC) in a PAC/membrane filtration system. Two major competitive mechanisms caused by natural organic matter (NOM), direct competition for sites and pore blockage were considered. The model accurately predicted atrazine removal in the presence of 1,4-dichlorobenzene (p-DCB) and poly(styrene sulfonate) (PSS), which represented the strongly competing and the pore blocking NOM fractions, respectively. The model was applied to investigate the effects of important design and operating parameters such as the length of membrane cleaning interval, manner of membrane cleaning (backwash or hydraulic flushing), PAC type, dose, and dosing scenarios on the removal of trace organic compounds. Atrazine removal was found to be affected by the membrane cleaning interval (MCI) more than by the hydraulic retention time (HRT). It was also found that a long MCI was not necessarily beneficial for the adsorption of trace organic compounds when low PAC doses were used. The optimal membrane backwash interval for trace organic compound removal should be determined based on the NOM characteristics of the influent water, the PAC dose and the backwash or hydraulic flushing water quality. The type of adsorbent was also very important. It should be selected based on the NOM characteristics of the influent water. Includes 10 references, tables, figures.