On-Line Measurement of Dissolved Methane Concentration During Methane Fermentation in a Loop Bioreactor

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.