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.

Organic solvent production plants emit waste gases containing volatile organic compounds (VOCs) which are usually harmful to the environments and public healths. Plant managers are obligated to control the VOC emission to meet regulations at reasonable costs. A solvent plant located in southern Taiwan emits VOC-containing gas streams from some distillation columns and storage vessels with a total ventilation gas flow rate of 2.6-3.6 m3/min which contains VOCs with concentrations of less than 1,000 mg C/m3. Due to a concern of plant¡¦s safety, the plant managers constructed a full-scale biofilter for eliminating a part of the VOCs and the associated odors in the waste gas. This study aimed to investigate the effects of operation parameters such as EBRT (empty bed retention time) of the gas through the biofiltration media and organic loading to the media on the VOC removal efficiency. The biofilter is constructed of RC (reinforced concrete) with outer dimensions of 8.45 mL ¡Ñ 3.30 mW ¡Ñ 3.00 mH. The filter was also instrumented with inverters for control of speed of induced fans, and with thermometers, hygrometers, and wind speed meters. Fern chips with a total packing volume of 36 m3 was used as the biofiltration media. After inoculation with suitable microorganisms, the waste gas was introduced to the filter for VOC elimination. Nutrients (urea, milk, and a phosphate salt) and water were supplemented to the media on a daily basis. The investigation period is July, 2008 to May, 2010. In the period, THC (total hydrocarbon) concentrations for the influent and effluent gases to and from the reactor were daily measured. In addition, on a weekly basis, compositions of the VOCs in gas samples were detected by a gas chromatography equipped with a flame ionization dector (FID). On the same time basis, pH, COD (chemical oxygen demand), SS (suspended solids) in a sample of the trickled liquid from the media was analyzed. Media pH and moisture content were also analyzed for understanding the environmental conditions around the microorganisms for the VOC degradation. Results indicated that the media was in conditions of pH = 4.5-7.0, moisture = 11-61 % in the experimental phase. Trickled liquid had low COD and SS contents which can be easily treated by the existing wastewater unit in the plant, or be recycled to the media. Avarage THC, NMHC (nonmethane hydrocarbon), and VOCs were 71, 73, and 79%, respectively, with gas EBRTs of 4.2-6.3 min. With media pH of 4-5 and moisture contents 51-57%, over 90% of the influent VOCs coulb be eliminated. However, nearly dried media (moisture around 10%) had VOC removal efficiencies of lower than 30%. Nutrition tests indicate that the VOC removal efficiency was nearly proportional to milk supplementation rate. Removal of ethnaol and acetic could easily be removed with an efficiency of over 97% while 2-pentane was only 74%. Odor intensities of the treated gas could be controlled to <1,000 (dilutions to threshold) according to 3 test data.

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