Biotechnology Group, Department of Chemical Engineering, Faculty of Engineering, Tarbiat Modares University, P.O. Box 14115-143 Tehran, I.R. IRAN
A dissolved methane sensor based on silicone tube was designed, constructed and optimized.The silicone tube diameter, silicone tube length and helium flow rate (as the carrier gas(were considered as process parameters to be optimized.A continuous stream of helium (50 mL/min) was directed through the tubing, sweeping out the dissolved methane which diffused through the walls of the tubing from the fermentation broth. The probe was made of silicone rubber tubing, 10 cm in length with inner and outer diameters of 0.25 cm and 0.35 cm, respectively (Detakta Company; NO. 02502). A semi-conductor methane gas sensor (Figaro TGS 2611) - which is highly sensitive and selective to methane gas - was used to measure the dissolved methane continuously. Henry’s law along with a special circuit experimental method was applied for calibration. The output concentration was displayed in mg/l (or ppm) of dissolved gas. The accuracy and response time of this system are ± 2 % and 2 minutes, respectively. Moreover, a control system was installed for recycling methane gas during fermentation
 Coty, V. F., A Critical Review of the Methane Utilization of Methane, Biotechnol. Bioeng., Symposium, 1, 105 (1969).
 Kosaric, N. and Zajic, J. E., Microbial Oxidation of Methane and Methanol, Adv. Biochem. Eng., 3, 89 (1974).
 Trotsenko, Y. A., Metabolic Features of Methane-Methanol-Utilizing Bacteria, Acta Biotechnological, 3, 269 (1983).
 Hanson, R. S. and Hanson, T. E., Methanotrophic Bacteria, Microbiol. Rev., 60, 439 (1996).
 Shafiee, P., Shojaosadati, S.A.and Chakhabi A.H., Biodegradation of Polycyclic Aromatic Hydro-carbons by Aerobic Mixed Bacterial Culture Isolated from Hydrocarbon Polluted Soils, Iranian J. Chem. Chem. Eng., 25, 73 (2006).
 Yazdian, F., Hajizadeh, S., Shojaosadati, S. A., Khalilzadeh, R., Jahanshahi, M. and Nosrati, M., Production of Single Cell Protein from Natural Gas: Parameter Optimization and RNA Evaluation, Iran. J. Biotech., 3, 235 (2005).
 Beland, M., Sterilisable Probe for Extraction of Volatile Compounds in Liquids and Their Quantitative Determination, W.O. 03/069314 A1 (2002).
 Phillips, Donalhd H. and Johns, Marvin VIN J., Measurement of Dissolved Oxygen in Fermentations, J. Biochem. Microbiol Technol. Eng., III, p. 261 (1961).
 Sheehan, Brain T. and Johnson, Marvin, J., Production of Bacterial Cells from Methane, Appl. Microbiol., 21, 511 (1971).
 Béland, M., Bourque, D., Perrier M. and Miguez, C. B., On-Line Estimation of Stoichiometric Growth Parameters for Methylobacterium extorquens, Computer Applications in Biotechnology (2004). Elsevier, March (2005).
 Yinghao, Y., Ramsay, Juliana A. and Ramsay, Bruce A., On-Line Estimation of Dissolved Methane Concentration During Methanotrophic Fermen-tations, Biotech. Bioeng., 95, 788 (2006).
 Jordan, S. M. and Koros, W. J., Permeability of Pure and Mixed Gases in Silicone Rubber at Elevated Pressures, J. Poly. Sci., B: Poly. Phys.,28, 795 (1990).
 Crank, J., “The Mathematics of Diffusion”, 2nd Ed., Clarendon Press, Oxford, (1975).