| dc.description.abstract | The MixAlco® process, an example of the carboxylate platform, converts lignocellulosic biomass to hydrocarbon fuels and chemicals using mixing cultures. The performance of mixed-culture fermentation depends on various factors, such as the energy source, nutrient source, and the resulting C/N ratio. It has been proven that co-digestion of two or more substrates has higher acid yields than either substrate fermented on its own. Countercurrent fermentation is employed to increase reaction rates and enhance acid yields and substrate conversion. However, it is time-consuming and labor intensive; it takes months to reach a single steady-state data point for a given liquid retention time (LRT) and volatile solids loading rates (VSLR). To overcome this challenge, the Continuum Particle Distribution Model (CPDM) is a technique that predicts the performance of countercurrent fermentation through mathematical methods using data from batch fermentations conducted at different substrate loadings.
Effects of nutrients were studied using chicken manure (fresh, air-dried, and oven-dried) or sewage sludge (fresh and air-dried) as nutrient sources. Among all chicken manures, the CPDM map showed reduced conversion and acid concentration for oven-dried treatments, which suggests that the drying process damages the nutrient source. At high VSLR, air-dried nutrients have higher acid concentrations than fresh; however, the conversion is low, which adversely affects process economics. In mixed-culture fermentation, fresh nutrients are preferred. At the same conditions, fresh chicken manure and sewage sludge have similar acid concentration; however, in fermentations using sewage sludge, there is a larger portion of caproic acid. At 300 g solids/L liquid, the CPDM map predicts that high acid concentrations (48.2 g/L) and conversions (0.79 g NAVSdigested/g NAVSfeed) are obtained at low VSLR (4 g/(L·day)) and high LRT (35 days). | en |
