Calorimetric investigation of anaerobic digestion: Biomass adaptation and temperature effect

A high-resolution bench-scale calorimeter (Bio-RC1), specially suited for microbiological studies, has been used to investigate the response of an anaerobic granular sludge to repetitive glucose additions at various temperatures. Through the analysis of heat-evolution profiles resulting from substrate degradation, significant biological events have been identified: the feeble net heat uptake related to aceticlastic methanogenesis has been evaluated, and the detrimental effect of a nutrient deficiency, which led up to 75% decrease in heat production rate, has been detected. After several glucose pulses under non-limiting nutrient conditions, a reliable and reproducible reference thermal response, which is an important condition for the application of calorimetric measurements to detect inhibitory effects, was finally obtained. Afterward, glucose additions were repeated at various temperatures, and 57% biomass activity reduction, with respect to the reference value at 35 degrees C, was observed when temperature was fixed at 20 degrees C. Additionally, a preliminary toxicity test was also performed by exposing the biomass to increasing formaldehyde concentrations.