Fixed-bed fermentation of rice straw and chicken manure using a mixed culture of marine mesophilic microorganisms

A mixture of rice straw (80%) and chicken manure (20%) was pretreated and fermented to carboxylic acids by using a mixed culture of marine mesophilic microorganisms. Two sets of four fermentors, built from PVC pipes, were used for both biomass pretreatment and fermentation. Four 1 L fermentors (F1–F4) were arranged in series, where liquid fermentation products were transferred from one fermentor to the other, to form a train. A liquid volume of 10 mL and 15 mL were transferred every four days for Trains A and B, respectively. The maximum total acid concentration for F1 in Train A was 34.2 g/L and the maximum acid concentration in F2–F4 was 44 g/L. The maximum total acid concentration in F1 in Train B was 30.5 g/L and the maximum acid concentration in F2–F4 was 48 g/L. The conversion in each of the fermentors in Train A varied from 0.821 to 0.879 g VS digested/g VS fed and the yield was in the range 0.489–0.609 g total acids/g VS fed. The conversion and yield in Train B were 0.741–0.914 g VS digested/g VS fed and 0.563–0.669 g total acids/g VS fed, respectively. The continuum particle distribution model (CPDM) predicted acid concentrations and retention times in the fixed-bed fermentation system with R2 of 0.67–0.84 in Trains A and B.