A COMPARATIVE-STUDY OF GEL ENTRAPPED AND MEMBRANE ATTACHED MICROBIAL REACTORS FOR BIODEGRADING PHENOL

A comparative study between two reactors, one using microorganisms entrapped in calcium alginate gel, and the other using microorganisms attached on the surface of a membrane (polymeric microporous sheeting, MPS(TM)) to biodegrade phenol is performed. Results indicate that the alginate bead bioreactor is efficient at higher phenol concentrations while the membrane bioreactor shows better performance at lower phenol concentrations. This unique response is primarily attributed to the different techniques by which the microorganisms are immobilized in the two reactors. In batch mode, below a starting concentration of 100 ppm phenol, biodegradation rates in the membrane bioreactor are (7.58 to 12.02 mg phenol/h . g dry biomass) atleast 10 times the rates in alginate bead bioreactor (0.74 to 1.32 mg phenol/h . g dry biomass). Biodegradation rates for the two reactors match at a starting concentration of 250 ppm phenol. Above 500 ppm phenol, the rates in the alginate bead bioreactor are (7.3 to 8.1 mg phenol/h . g dry biomass) on an average 5.5 times the corresponding rates in the membrane bioreactor (2.18 to 1.03 mg phenol/h . g dry biomass). In continuous feed mode the steady state degradation rates in the membrane bioreactor are one to two orders of magnitude higher than the alginate bead bioreactor below 150 ppm inlet phenol concentration. At an inlet concentration around 250 ppm phenol the rates are comparable. Above 500 ppm of phenol the rates in the alginate bioreactor are an order of magnitude high than the membrane bioreactor. Due to substrate inhibition, and its inability to sustain a high biomass concentration, the membrane bioreactor shows poor efficiencies at phenol concentrations above 250 ppm. At low phenol concentrations the apparent reaction rates in the alginate bead bioreactor decrease due to the diffusional resistance of the gel matrix, while biodegradation rates in the membrane bioreactor remain high due to essentially no external diffusional resistance. Results indicate that a combined reactor system can be more effective for bioremediation than either separate or attached microbial reactors.