Initial rates technique as a procedure to predict the anaerobic digester operation

Abstract In this study a novel and practical procedure was developed, that involves: initial methane production rate measurement in batch tests, kinetic parameters determination and modeling application in a continuous digester. The procedure was evaluated with three experimental conditions: raw sludge as substrate incubated at 35 °C and 55 °C and thermal pretreated sludge incubated at 35 °C. The initial specific methane production rate was fitted with the Monod type equation in order to calculate the kinetic parameters. The values obtained for the maximum specific methane production rate were 0.043, 0.143 and 0.052 gCH 4  gVS I −1  d −1 for each experimental condition, aforementioned. The substantial increment of this parameter at thermophilic condition shows the differences in the specific maximum growth rate between thermophilic and mesophilic populations. The affinity constant values were 3.842, 4.790 and 4.623 g L −1 for each experimental condition; however, a significant uncertainty was obtained due to some identification problems. A preliminary validation of the procedure was applied for predicting the operation of a continuous digester treating raw sewage sludge. The overall behavior of the system was represented by the model, although it slightly underestimates the experimental values, by approximately 20%. The results achieved, indicate that the procedure may be used as a tool in a real scale operation; however, further research must be performed.