Date of Award

7-17-2009

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Sidney Crow

Second Advisor

George Pierce

Third Advisor

Eric Gilbert

Abstract

Acrylonitrile (AN) is a major volatile waste generated in the production of acrylamide and often associated with aromatic contaminants (toluene and styrene) in plant effluents. We examined Rhodococcus rhodochrous DAP 96622 to determine if it could be adapted to efficient biodegradation of acrylonitrile (AN) in a bioreactor. A model bioreactor with granular activated carbon (GAC) as a substratum for Rhodococcus with AN as sole carbon or in combination with toluene was established. The kinetics of AN biodegradation by immobilized and planktonic cells were evaluated and compared. Inlet load and empty retention time were varied to test the removal efficiency in fed-batch and single-pass mode reactor. In addition, the three dimensional structure and characteristics of the biofilm were followed using confocal scanning laser microscopy (CSLM) and relative software. Immobilized cells in the bioreactor, at starting concentrations of AN up to 1150 mg l-1 in the presence of Tol, had at least 13 fold higher AN degradation rates than that seen of planktonic cells. A near steady state of AN degradation was maintained at 75-85% for AN and 80%-90% for Tol within the parameter of EBRT=8 min and AN and Tol inlet loads between 50-200 mg l-1 h-1 and 200-500 mg l-1h-1, respectively. However, when the inlet load of AN was increased to more than 200mg l-1 h-1 and 500 mg l-1 h-1 for Tol, a reduction in efficiency of AN degradation was observed. Biofilms with discrete microcolonies interspersed with voids and channels were observed. Precise measurement of biofilm characteristics agreed with the assumption that the biomass and thickness of the biofilm increased along the carbon column depth. With a porous attachment material like GAC, substrate diffusion is most likely not a limiting factor for AN degradation. Rhodococcus rhodochrous DAP 96622 in a non-sterile activated charcoal column showed efficient degradation of AN in the presence of Tol. The Rhodococcus bioreactor may provide a potential practical waste gas and water treatment system.

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