Control strategies with variable air arrangements, forcefully aerated in single circular tray solid state bioreactors with modified Gompertz model and analysis of a distributed parameter gas balance

Aspergillus awamori and Aspergillus oryzae were cultivated on wheat bran in newly designed single circular tray solid state bioreactor (SSB) systems. The effect of aeration arrangements on moisture content, oxygen (O-2) supply, carbon dioxide (CO2) evolution during solid state fermentation (SSF) was investigated. The purpose was to study the effect on oxygen uptake rate (OUR) and carbon dioxide evolution rate (CER), of operating variables, fermentation on the perforated base tray and internal moist air circulation under natural and forced aeration. Temperature, O-2 and CO2 were measured continuously on-line. Final moisture content was also measured. A direct technique of establishing a correlation among fungal growth, CER and OUR were proven successful in this work. The information obtained from CER and OUR led to the estimation of respiratory quotient (RQ). RQ describes the state of the fungal population in the tray SSB and gives an indication of fungal metabolic behaviour. RQ values <1 were obtained from 14 experiments using single circular tray SSB system for the two fungi. A Gompertz model was used to fit the integrated CO2 data and predict the quantity of CO2 evolution in all experiments. A correlation was found between the RQ and CO2 evolution. The aeration strategies and arrangements applied in these studies exceeded the optimum requirements and allowed accurate measurements of gas composition, temperature, moisture content and fungal biomass gradients. The model system developed in this study may provide an excellent system for further investigations of mass transfer and possibly for large scale operation.