Bioremediation of ethanol in air using a gas-fluidized bioreactor

A gas-fluidized bed bioreactor was developed in this research as a new method for treating polluted air. The fluidization characteristics of selected packing materials were investigated. Then, bioremediation was tested using two types of packing in a fluidized bioreactor, as well as in a comparable packed bed. Microorganisms on the particles biodegrade contaminants in the polluted air, which flows up through the bed. At high flowrates, the polluted air fluidizes the particles, while at low velocities the operation is in packed bed mode.Initially, sawdust was selected for use as a packing material. Due to the poor fluidization properties of sawdust, glass spheres were added. A mixture of sawdust and glass spheres remained well mixed during fluidization. In the mixture, interparticle forces increased with increasing moisture in the sawdust, eventually causing defluidization of the bed. In the absence of bioremediation, mass transfer was studied between ethanol-contaminated air and sawdust/glass sphere packing, and found to be higher in the fluidized versus packed mode. In bioremediation experiments, ethanol removal efficiencies were as high as 95% in both operating modes. The maximum elimination capacities (EC) of ethanol were 75 and 225 g m^-3 sawdust h^-1 in the fluidized and packed beds respectively.The packing of the fluidized bed bioreactor was optimized in order to boost bioremediation rates. Experiments showed that peat granules fluidized well in a bubbling regime, likely due to their relatively high density and sphericity. In peat bioremediation trials, the fluidized mode outperformed the packed bed; the maximum ECs were 1520 and 530 g m^-3 peat h^-1, respectively. Removal efficiency in the fluidized mode decreased with velocity, because the size and amount of large bubbles increased.A steady-state model of the fluidized bioreactor was developed. By taking account of bubble properties during fluidization, the model helps to explain how bubble size, microbial properties and bioreactor residence time affect removal efficiency and elimination capacity of the bioreactor.A peat gas-fluidized bioreactor shows promise as an efficient, low-cost technology for air treatment. Particle mixing in the fluidized bed may prevent operating problems associated with the packed bed bioreactor. Fluidized bioreactors are ideal for the treatment of high volume, low concentration air emissions