Mass transfer of carbon dioxide in anaerobic reactors under dynamic substrate loading conditions

Abstract

The objectives of the present investigations were (1) to discuss the dominant factors influencing mass transfer of carbon dioxide (CO 2) and methane (CH 4) in anaerobic reactors, (2) to survey theoretical approaches to estimate mass transfer coefficients k L a and (3) to provide experimental data in order to verify the proposed k L a-correlation which was then used in mathematical modelling of the anaerobic digestion process. CO 2 mass transfer was found to be governed by the liquid phase resistance with the volumetric mass transfer coefficient k L a being a function of the actual biogas production rate. From measurements of the HCO 3 −-concentration and the pH in the liquid phase, the partial pressure of CO 2 in the gas phase and the CO 2-production rate under dynamic substrate loading conditions, the proposed correlation between k L a and upflow gas velocity was experimentally verified for three different wastewaters. Measured k L a-values for CO 2-mass transfer in anaerobic reactors differed by a factor of 2–3 from steady-state to dynamic loading conditions. The experimental results matched with previously reported values and provided a significantly better simulation of CO 2- and CH 4-production in anaerobic reactors under dynamic substrate loading conditions.