Methanogenic and non-methanogenic activity tests. Theoretical basis and experimental set up

Abstract The theoretical basis of the methods allowing to determine and calculate methanogenic and non-methanogenic sludge activities in anaerobic digesters are examined and, accordingly, proper experimental conditions are established. Some operational parameters of batch experiments like initial substrate concentration and inoculum size can be estimated from the expected kinetic constants. Methods based on the theoretical considerations are proposed and employed in order to evaluate: (a) the maximum methanogenic activity of anaerobic digester sludges, (b) the maximum hydrolytic and acidogenic activities and (c) the kinetic parameters corresponding to methanogenic, acidogenic and hydrolytic steps. Results show that maximum methanogenic activity of sludges from anaerobic reactors may be determined accurately by using small vials connected to Mariotte flasks with an alkaline fluid. A different procedure based on head space gas chromatographic analysis was also evaluated. This method is suitable to determine very low methane productions and may be applied to the methanogenic activities determination at substrate concentrations lower than the half-saturation constant. The activity tests were advisable to determine either the specific microbial activity, expressed by a sole parameter (i.e. maximum specific activity); or the kinetic of substrate consumption, that implies data adjustment to the Monod or the Andrews Model for the calculation of maximum specific activity and half saturation constant. The developed methods were applied to characterize the biomass of a lab-scale mesophilic anaerobic filter.