(744a) Treatment of High-Strength Saline Phenolic Wastewater in a Chemostat Coupled With a Forward Osmotic Membrane Bioreactor

Praveen, P., National University of Singapore
Loh, K. C., National University of Singapore
Nguyen, D. T., National University of Singapore

Industrial wastewater from many sources, such as leather and petrochemical industry, contain high quantities of salts and toxic organics. Desalination of such effluents with prior removal of the organic contaminants results in the release of these pollutants in the environment at high levels. On the other hand, biodegradation of high concentration of toxic organics in saline wastewater is difficult due to the inhibitory effects these chemicals exert on the biodegrading microorganisms. A simple solution to alleviate these inhibitions is the dilution of the wastewater but it results in two problems: (1) increase in the process volume, and (2) large water requirement.

In this research, we have developed a novel bioreactor system by integrating a chemostat with a forward osmosis (FO) membrane system for treatment of phenolic wastewater at high salinity. The strategy was to dilute the wastewater to achieve non-inhibitory concentration of salts and phenol, phenol was metabolized in the chemostat and the resulting effluent was concentration and desalinated in the FO module. Water recovered through FO using was used for the dilution of the feed solution. Wastewater at phenol concentration of 1000-2000 mg/L and sodium chloride concentration of 0.5-1 M was diluted 3-5 times and pumped into the bioreactor at the dilution rate of 30-90 mL/h. Phenol was completely degraded in the chemostat within 10 h at low dilution rates, but a longer time was required to reach steady state at higher dilution rates. The specific growth rate decreased with increasing phenol concentration and at low dilution factor. The cell growth rate did not change significantly below salt concentration of 0.2 M, however, the growth rate decreased at higher concentration. In the absence of salt, the recovery of water from the chemostat effluent was simple. As the salt content of the effluent increased, a higher draw solute concentration was required for effective desalination.    

It was also observed that the water flux through the FO membranes decreased over a period of 24 h which could be due to the presence of biofilms on the membranes, and also due to concentration polarization. The biofilms could be removed from the membranes by osmotic backwash at the end of operation, which alleviating concentration polarization required thorough washing of the membranes with deionized water. These results show that the chemostat-FO system can treat saline phenolic wastewater effectively.