Novel Respirometry Measurement and Comparison of Monod Kinetic Constants and Methanogen Concentrations for 27 Full-Scale Anaerobic Bioreactors.

Monod kinetic coefficient values (k_m and K_s) as well as methanogen concentrations (X_ac and X_h2) for various anaerobic bioreactors are required to gain a deeper understanding of anaerobic biotechnology. However, there are no existing, practical methods to measure or estimate these parameters or variables in typical anaerobic digester biomass that contains mixed cultures with inert organic solids. Current measurement methods rely on pure cultures developed in the laboratory. In this work, a novel respirometric method was developed and used to determine methanogen Monod parameters and active biomass concentration for samples from 27 full-scale anaerobic reactors. Differences (one to three orders of magnitude) were observed among acetate and H₂ k_m values and active biomass fractions for the different biomass microbial communities. Average k_m values for acetate and H₂ were 14.6- and 48-g COD/g COD_x-d, whereas average K_s values were 21.9- and 0.32-mg COD/L, respectively. Average X_ac as a fraction of total VSS was 0.80% and ranged from 0.02% to 2.49%, whereas average X_h2 was 1.16% and ranged from 0.04% to 8.23%. Granular biomass k_m values were approximately three times greater than flocculant biomass values, indicating significant fundamental differences ostensibly exist in methanogenesis between the two process configurations. In the future, relationships may be developed to predict kinetic constant values based on microbial community composition.