Online Monitoring of Solid-State Fermentation Using Respirometry

Solid-state fermentation (SSF) is characterized by its complexity and heterogeneity. Use of agro-industrial residues as substrate avoids accurate measurement of biomass and substrates during the SSF process. Exhaust gas analysis has been used to indirectly estimate the biomass growth; however, these devices don't allow simultaneous measurements from different experimental units or bioreactors and they don't allow accurate simultaneous measurement of CO2, O2, and air-flow rate. A respirometry system based on CO2, O2, and air-flow measurement detectors fed by a system of 15 solenoid valves controlled by a programmable logic controller and a data logger was developed and evaluated during the growth of Rhizomucor pusillus in SSF. The respirometry system was compared to a classical chromatographic respirometer. Accurate measurements of CO2, O2, and air-flow rate allow precise and instantaneous estimation of some kinetic parameters associated with the respiration of the culture such as the specific CO2 production rate and the respiratory quotient. The respirometry system herein described allows online measurements of the microbial process allowing control procedures to be set in SSF processes.