Biodegradation of Phenol in Saline Solutions Using a Chemostat-Forward Osmosis Hybrid Process

Industrial effluents from petroleum, textile and leather industries generate large quantities of saline wastewater with high content of organic compounds. Membrane processes such as forward osmosis (FO) can effectively desalinate the wastewater, but these increase the organic content of the concentrate. This problem aggravates when the wastewater contains toxic aromatic compounds such as phenol which exert drastic effects when released into the environment. Biodegradation, which is commonly used for removal of phenol from wastewater, is ineffective in these conditions as both salt and toxic organics inhibit cell growth and metabolism at high concentrations. One approach to mitigate substrate inhibition is the dilution of the wastewater but this requires huge supply of water and results in a large process volume.

The objective of this research was to design a coupled chemostat-FO process to facilitate wastewater dilution, phenol biodegradation and subsequent recovery of water. The strategy was to dilute saline phenolic wastewater to sub-inhibitory concentrations of salt and phenol, enabling biodegrading microorganisms to metabolize phenol. The use of a chemostat kept the process volume constant while ensuring complete biodegradation, whereas FO concentrated the effluent and facilitated desalination and water recovery. Biodegradation of 1000-2000 mg/L phenol at 0.5-1 M sodium chloride could be achieved within 12 h of operation at 3-5 times dilution. The high specific growth rate of the microorganisms at lower effective concentration of salt and phenol facilitated high dilution rates in the chemostat. The bioreactor could be operated at the dilution rate of 90 mL/h without observing any cell wash out. Water used for dilution was easily recovered and reused using magnesium chloride as the draw solute and cellulose acetate FO membranes. The water flux could be further improved by increasing the concentration and the flow rate of the draw solute. It was also demonstrated that the setup could be used for desalination of wastewater by adjusting the operating conditions. These results indicate that the chemostat-FO system can achieve biodegradation of toxic pollutants prior to desalination and can be promising in treatment of saline wastewater with high organic content.