MODELING OF ANAEROBIC FORMATE KINETICS IN MIXED BIOFILM CULTURE USINGDYNAMIC MEMBRANE MASS-SPECTROMETRIC MEASUREMENT

The dynamics of the anaerobic conversion of formate in a microbial mix ed culture taken from an anaerobic fluidized bed reactor was studied u sing a new stirred micro reactor equipped with a membrane mass spectro meter. The microreactor with a toroidally shaped bottom and pitched bl ade turbine and a cylindrical flow guide was thermostated and addition ally equipped with a pH electrode and pH control. During fed-batch exp eriments using formate, the dissolved gases (methane, hydrogen, and ca rbon dioxide), as well as the acid consumption rates for pH control we re monitored continuously. Initially and at the end of each experiment , organic acids were analyzed using ion chromatography (IC). It was fo und that about 50% of the formate was converted to methane via hydroge n and carbon dioxide, 40% gave methane either directly or via acetate. This was calculated from experiments using (HCO3-)-C-13 pulses and me asurement of (CH4)-C-12 and (CH4)-C-13 production rates. About 10% of the formate was converted to lactate, acetate, and propionate, thereby increasing the measured CO2/CH4 production ratio. The nondissociated formic acid was shown to be rate determining. From the relatively high K-S value of 2.5 mmol m(-3), it was concluded that formate cannot pla y an important role in electron transfer. During dynamic feeding of fo rmate, hydrogen concentration always increased to a maximum before dec reasing again. This peak was found to be very discriminative during mo deling. From the various models set up, only those with two-stage degr adation and double Monod kinetics, both for CO2 and hydrogen, were abl e to describe the experimental data adequately. Additional discriminat ion was possible with the IC measurement of organic acids. (C) 1995 Jo hn Wiley and Sons, Inc.