A novel flux enhancing method for membrane bioreactor (MBR) process using polymer

Abstract

Pilot- and full-scale experiments were performed to elucidate the feasibility of using a modified cationic polymer for capital and operational cost savings. This membrane performance enhancing product is referred to as MPE50™. Since the low flux caused by low water temperature is one of the most important hurdles in reducing capital costs, the extent of short-term and long-term flux improvements by MPE50 was tested at low temperatures (10–13°C). Though membrane fouling rates should be exponentially proportional to the flux when the critical flux is exceeded, it was found that membrane fouling rates were almost constant during MPE50 treatment, irrespective of the flux, if the flux was moderately higher than the critical flux. As a consequence, with 400 ppm MPE50, a full-scale municipal MBR plant (2,300 m 3 /d) could be operated at an average flux of 47.25 LMH, which is 39% above the critical flux (34LMH), for one day without significant permeability loss. On the other hand, without MPE50, flux could be maintained at 35 LMH, which was 35% above the critical flux (26 LMH), for only 2–3 h. Additional pilot tests were performed at a low temperature (10°C), to test for long-term flux increase. During treatment with 200 ppm MPE50, the flux duration increased from 22 days to more than 30 days, and a 50% higher flux (from 17 LMH to 25 LMH) could be maintained. MPE50 was also tested at a problematic site (50 m 3 /d) where membrane fouling hydrophobic waxes were present in the influent. At this site, the long-term flux increased from 10 LMH to 25 LMH by using 300 ppm MPE50, which was a 150% increase. Finally, membrane and aeration savings by MPE50 were estimated. When the flux increased 50–150%, membrane and aeration savings were expected to be 33–60% and 22–40%, respectively.