DYNAMIC DETERMINATION OF ANAEROBIC ACETATE KINETICS USING MEMBRANE MASS-SPECTROMETRY

A small, stirred, 14.4-mL tank reactor was designed to serve as a meas urement cell for short-term investigation of microbial kinetics. A mas s spectrometer membrane probe allowed the measurement of the dissolved gases of hydrogen, methane, oxygen, and carbon dioxide, pH was measur ed by an electrode and controlled by addition of acid or alkali. The h ighly sensitive measurement of gases with low solubility allowed rapid measurements at very low conversion. In kinetic experiments, a stepwi se increase of substrate concentration (method A) and continuous feed of substrate (method B) were used, allowing quick estimation of substr ate kinetics. Acetate conversion in mixed culture biofilms from a flui dized bed reactor was investigated. Substrate inhibition was found to be negligible in the concentration range studied. Experiments at vario us pH values showed that the undissociated acid form was the kinetic d eterminant. Kinetic parameters for Haldane kinetics of protons were K- SH = 1.3 x 10(-5) mol m(3) and K-IH 8.1 x 10(-3) mol m(-3). With free acid (HAc) as the rate determining species, the kinetic parameters for method A were K-SHAc = 0.005 mol m(-3) and K-IHAc 100 mol m(-3) and f or method B were K-SHAc 0.2 mol m(-3) and K-IHAc 50 mol m(-3). The max imum biomass activity occurred at around pH 6.5. Acetate was exclusive ly converted to methane and CO2 at pH > 6. (C) 1998 John Wiley & Sons, Inc.