Development of a foamed emulsion bioreactor for air pollution control.

摘要

The thesis reported here describes the development of an innovative bioreactor for air pollution control that overcomes some of the shortcomings of the current gas phase bioreactors. The new reactor was called the foamed emulsion bioreactor (FEBR), and experimental investigations proved that it was able to reach extremely high elimination capacities (280 g m -3 h-1 with 95% removal, up to 408 g m -3 h-1 when the air stream was supplemented with oxygen) when toluene vapors were used as model pollutant. A conceptual mathematical model for the FEBR was developed and was validated with experimental results. The model described or predicted the phenomena of mass transfer and biodegradation in the FEBR. Simulation of the FEBR performance at various operating conditions provided guidance on selecting the optimum conditions for high elimination capacity of toluene. Model parametric sensitivity studies revealed that the maximum biodegradation rate and the diffusion coefficient were highly sensitive parameters. Detailed experiments with FEBRs identified interesting biokinetic phenomena not widely reported by others. Cells attached to the organic phase exhibited a 2 to 5 times higher toluene-degrading activity than cells suspended in the bulk phase of the emulsion. This is one of the possible causes for the effective biodegradation of low concentrations of pollutants in the FEBR. When the effects of batch and continuous operation of the FEBR on the performance of the FEBR were examined, continuous operation with feeding nutrients and partial wasting of cells was the best operating strategy. It resulted in sustained and high toluene removal (89--94%) and high cell activity (>6 INTF mmol g-1protein ) over 360 hours. The same strategy proved to be effective for the treatment of lower toluene concentrations and to overcome 48 h of toluene starvation. A paper scale-up of the laboratory data was conducted to evaluate the applicability of a potential full-scale FEBR. Because the FEBR could be built smaller than a biofilter or a biotrickling filter, its projected capital cost was lower. Operating costs were slightly higher so that the total treatment costs were similar to the costs of biofiltration or biotrickling filtration. Biotreatment costs were much lower than those for thermal or catalytic oxidation. Finally, when cometabolic degradation of trichloroethylene (TCE) with toluene was attempted in the FEBR, high treatment performance (82--96% removal, TCE elimination capacity of 14--28 gTCE m-3 h -1) was obtained, suggesting that the FEBR concept could be successfully applied to other key environmental applications.