2.4. Batch and continuous fermentation–PV coupled process
The compositions of cassava flour are shown in Table S1 (see Supplementary material). Batch fermentation kinetics was studied first using 70 g/L cassava flour (equivalent of 61.6 g/L glucose) as the carbon source. The fermentation medium was autoclaved at 121 C for 120 min followed by cooling to 37 C under an O2-free N2 atmosphere. The bioreactor was inoculated with 10% inoculate volume without pH control. Broth samples were taken from the bioreactor at intervals until all glucose was consumed. The experimental setup for the pervaporation of the model solution of ABE and the fermentation–PV coupled process was the same as that described in previous work (Li et al., 2014). In brief, it consisted
of two parts: a 2 L Multigen reactor (New Brunswick Scientific, Edison, NJ) with 1 L working volume, a pervaporation system with a membrane module, a peristaltic pump and two cold traps. The fermentation experiment was allowed to run until the butanol concentration reached the toxicity level to the organisms. Then in situ ABE removing process was started by coupling ABE fermentation with pervaporation. The gas stream containing volatile compounds, including mainly acetone, butanol and ethanol, was then cooled. The permeate solution was collected at the bottom of the cold trap at intervals to measure its volume and analyze the ABE contents. Simultaneously, samples were taken from the bioreactor
for analysis of sugar and product concentrations throughout the whole operation. Concentrated liquid cassava mash was continuously fed into the bioreactor to maintain the volume of bioreactor. The product yield and productivity were estimated based on total sugar consumption and products present in the fermentation broth and the permeate solution collected from cold trap