Date of Award
Doctor of Engineering Science in Chemical Engineering
Chemical Engineering, Chemistry and Environmental Science
Samir S. Sofer
Piero M. Armenante
Richard B. Trattner
Hsin Neng Hsieh
A comparative study has been performed between two bioreactors treating phenol, one using calcium alginate entrapped microorganisms, and the other using microorganisms attached on the surface of a polymeric membrane. Laboratory experiments conducted in batch recirculation mode, as well as a continuous feed mode, showed that the calcium alginate bio-bead reactor is more efficient in treating high feed concentrations of phenol, while the membrane bioreactor is more effective in the lower concentration regime (less than 150 ppm). In batch recirculation mode, the reaction rates (expressed as mg phenol/hr*gm dry cells) in the membrane reactor are an order of magnitude higher at feed concentrations of phenol below 100 ppm. Biodegradation rates for the two reactors match at around 250 ppm phenol concentration, and at about 1000 ppm phenol concentration the reaction rates in the calcium alginate bioreactor are 7.5 times the corresponding rates in the membrane reactor.
In continuous feed mode the alginate reactor requires 5.5 times more volume than the membrane bioreactor for close to 90% degradation of a feed stream containing 50 ppm phenol. At 1000 ppm feed concentration of phenol, the membrane reactor requires 3.4 times larger volume than the alginate bioreactor for the same degradation.
Due to substrate inhibition, and an inability to sustain a high biomass concentration, the membrane reactor shows poor efficiencies at high phenol concentrations. At low phenol concentrations, the apparent reaction rates in the alginate bioreactor decrease due to diffusional resistance of the gel matrix, while reaction rates in the membrane bioreactor remain high from essentially no internal diffusional resistance.
At high phenol concentrations (above 250 ppm), the degradation rates in the alginate reactor show strong dependence on dissolved oxygen levels, indicating a DO limited operating regime. The degradation rates in the membrane bioreactor also show oxygen dependency, not due to intrinsic kinetics, but more due to the transport effects.
Results indicate that a combined reactor system (employing both reactor types) can be more effective over a wide range of phenol concentrations than those where only entrapped or attached microbial reactors are used for bioremediation.
Lakhwala, Fayaz Saifuddin, "A combined gel entrapped and membrane attached microbial process for biodegrading organic compounds" (1991). Dissertations. 1144.