Denitrification Incorporating Microporous Membranes

A microbial system for removal of nitrate from drinking water in which the denitrification reactions are physically separated from the water being treated by a microporous membrane was studied. The experimental system was composed of two equal-volume cells separated by a 0.02 μm pore size polytetrafluoroethylene membrane. No pressure difference existed across the membrane, and nitrate ions were transported through the membrane by diffusion. Results of experiments with biofilm denitrification and suspended-culture systems are presented. Deoxygenation by N 2 stripping and by SO-2 produced equivalent results. Removal rates with the suspended culture systems were greater than those with biofilms. Effective membrane diffusivities calculated for suspended-culture systems were approximately the same as for sterile systems, indicating that resistance to transport was not changed by the addition of the suspended microbial culture. The methanol requirement observed in the experiments was 1.4 g total organic carbon (TOC) per g NO--N removed. Removal rates followed first-order pseudotransport controlled models for both the biofilm and suspended-culture systems. A prototype continuous-flow system is presented.