(691b) Removal and Prevention of Biofouling in Forward Osmosis Membrane Bioreactors

Authors: 
Satterfield, D. J., University of Nevada, Reno
Hiibel, S. R., University of Nevada Reno
With increasing populations and declining clean water supplies, treatment of municipal wastewater for reuse is becoming more viable. Membrane treatment processes will be an integral part in reuse treatment, however membrane fouling results in decreased process efficiencies. Forward osmosis (FO) is a membrane-based separation process that uses the osmotic pressure resulting from a salt gradient rather than a hydraulic pressure as the driving force, resulting in energy savings over traditional membrane treatment processes. The objectives of this project were to 1) design and build a submerged FO membrane bioreactor (MBR) with three independent membrane loops, and 2) to evaluate alternative membrane cleaning mechanisms to improve and maintain flux performance.

As part of the first objective, the hardware and programming logic code for the FO MBR system were developed and integrated to create a system that was able to measure and compare membrane flux over time for three independent FO membrane cassettes where all three were exposed to the same biological fouling conditions. The MBR contained E. coli JW3818 ΔrfaH grown in LB broth with 50 mg/L kanamyacin, and half strength LB with kanamycin was used to replace volume lost from the MBR through the FO membrane. As part of the second objective, various thermal osmotic backwashing methods were evaluated for flux recovery and propensity for re-fouling. It was found that osmotic backwashing at 70 ° C for 30 min resulted in 15% greater flux recovery compared to the baseline case of 60 min at ambient temperature. During this process, the hot water removes the adhered biofilm allowing for increased flux recovery. It is hypothesized that the elevated temperature of the thermal backwash results in cell death at the membrane surface, thereby enhancing the osmotic backwashing efficiency. Confocal Scanning Laser Microscopy (CSLM) confirmed that less biofilm was present after thermal backwashing than with ambient backwashing. Based on these preliminary results, hot osmotic backwashing is a promising membrane cleaning technique to remove and decrease reoccurrence rate of biofouling in FO MBR operations.