Anaerobic respirometry as a tool to evaluate the effect of pretreatment on anaerobic digestion efficiency
Abstract
This study aims to evaluate the impact of pretreatment on the anaerobic digestion of wheat straw and other lignocellulosic materials. For that, an original procedure named “Anaerobic Respirometry” is used as a tool to monitor the Methane Production Rate (MPR) of treated and untreated materials, allowing determining the impact of pretreatment in terms of CH4 production and degradation kinetics. Results from various grinding technologies, namely impacts mill, knife mill, air-jet mill, ball mill illustrate this procedure. The MPR experimental curves obtained for pretreated substrates show two distinct peaks in the methane production rate. This can result from an accumulation of acetate which is then consumed and gives rise to the second peak. A second hypothesis can also involve a phenomenon of bacteria colonization on the cellulose delaying methane production. Although this double peak complicated the results interpretation, CH4 production over the 10 days period was determined from the MPR in order to evaluate the impact of the mechanical pretreatment on the anaerobic digestion efficiency. The results demonstrate an increase up to 44% in CH4 production from 122 for the knife mill sample up to 175 NLCH4/kgVS for samples grinded by ball mill.