Monitoring of microbial activity in soil using biological oxygen demand measurement and indirect impedancemetry

This paper describes a technique that allows one to monitor simultaneously oxygen consumption and carbon dioxide production in order to better characterize microbial activity in soil. The experimental methodology is based on biodegradation tests in biometric flasks filled with soil and equipped with a CO2 trap (KOH solution) and OxiTop® measuring heads (used for Biological Oxygen Demand [BOD] determination). CO2 was measured using both indirect impedancemetry and acid/base titration. First, results showed that the concentration of the KOH solution concentration is a key design parameter for the sensitivity of the method. Second, respiratory quotient was calculated during the biodegradation tests in microcosms. Biomass evolution was also monitored to study the possible correlation between the respiratory quotient and biodegradation phases. As a conclusion, it is stated that on-line monitoring of the respiratory quotient can provide relevant information concerning in situ soil microbial activity.