Abstract
In a conventional syngas fermentation process, gas was released into the fermentation broth through a single orifice or multiple orifices, except the hollow fiber membrane reactor. Consequently, a simplified bioreactor has been developed employing an innovative gas supply and effluent extraction systems. A continuous stirred tank bioreactor (CSTBR) has been developed by incorporating an innovative gas supply and effluent extraction system to ferment syngas into ethanol. The working volume of the bioreactor was controlled to 2 L. The CO gas was fermented in the developed bioreactor by using a microorganism (Clostridium ljungdahlii) with different gas (5–15 mL/min), media, and effluent flow rates (0.25–0.75 mL/min) and stirrer speed (300–500 rpm). Gas was diffused into the fermenting broth through an aqueous aeration tube commonly used in the small household aquarium, placed at the bottom layer throughout the periphery. The effluent was extracted from the top layer of the broth by using a membrane separator. Ethanol and acetic acid concentrations were varied from 0.17–1.17 and 8.50–23.68 g/L-effluent, respectively. It seems that the performance of CSTBR can be enhanced with an innovative gas supply system, which may reduce the gas bubble size and result in higher lateral velocity at the releasing point, especially, throughout the periphery instead of the center of the reactor through a single or multiple orifice.
Highlights
In a conventional syngas fermentation process, gas was released into the fermentation broth through a single orifice or multiple orifices, except the hollow fiber membrane reactor
Till to date in a conventional syngas fermentation process gas was released into the fermentation broth through a single orifice or multiple orifices (Mohammadi et al 2012; Cotter et al 2009; Younesi et al 2006) in both the batch and continuous process, except for a few examples, especially, the hollow fiber membrane reactor (Shen et al 2014; Richter et al 2013)
The low-cost gas diffuser was placed in the bottom layer and on the periphery of the fermentation broth, and an in situ cell retention filter was placed on the upper layer of the broth, which were the innovative ideas in this reactor development
Summary
In a conventional syngas fermentation process, gas was released into the fermentation broth through a single orifice or multiple orifices, except the hollow fiber membrane reactor. A simplified bioreactor has been developed employing an innovative gas supply and effluent extraction systems. Production and utilization of lignocellulosic ethanol (hereafter referred to ethanol) have been emphasized because it does not compete with food crops. Ethanol has been produced from lignocellulosic biomass (hereafter referred to biomass) by both biochemical and thermochemical conversion technologies. Each process has its advantages and disadvantages in ethanol production from biomass, biochemical dominates over the thermochemical process (Subramani and Gangwal 2008). The biochemical conversion process requires higher pretreatment and enzyme costs, has low fermentability of the mixed sugar stream (C5), and Ethanol can be produced from syngas through a catalytic or bio-synthesis thermochemical conversion.
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