Abstract
Lignocellulosic biomass is a renewable source with great potential for biofuels and bioproducts. However, the cost of cellulolytic enzymes limits the utilization of the low-cost bioresource. This study aimed to develop a consolidated bioprocessing without the need of supplementary cellulase for butyric acid production from lignocellulosic biomass. A stirred-tank reactor with a working volume of 21 L was constructed and operated in batch and semi-continuous fermentation modes with a cellulolytic butyrate-producing microbial community. The semi-continuous fermentation with intermittent discharging of the culture broth and replenishment with fresh medium achieved the highest butyric acid productivity of 2.69 g/(L· d). In semi-continuous operation mode, the butyric acid and total carboxylic acid concentrations of 16.2 and 28.9 g/L, respectively, were achieved. Over the 21-day fermentation period, their cumulative yields reached 1189 and 2048 g, respectively, corresponding to 41 and 74% of the maximum theoretical yields based on the amount of NaOH pretreated rice straw fed in. This study demonstrated that an undefined mixed culture-based consolidated bioprocessing for butyric acid production can completely eliminate the cost of supplementary cellulolytic enzymes.
Highlights
Butyric acid is a widely applied material in the chemical, textile, food and pharmaceutical industries (Zhang et al, 2009) with potential application in the production of biofuel butanol (Richter et al, 2012; Lee et al, 2014) and biodegradable plastics (Albuquerque et al, 2011)
Similar to the degradation of rice straw, the carboxylic acids and hydrogen production increased from the second day and leveled off from the sixth day onwards
In the three runs of butyric acid fermentation, the amounts of pretreated rice straw fed in the reactor were 1839, 1814, and 6779 g and the actual yields of butyric acid were 294, 317, and 1189 g, respectively, corresponding to 37 to 41% of the maximum theoretical yield based on the amount of rice straw fed into the reactor
Summary
Butyric acid is a widely applied material in the chemical, textile, food and pharmaceutical industries (Zhang et al, 2009) with potential application in the production of biofuel butanol (Richter et al, 2012; Lee et al, 2014) and biodegradable plastics (Albuquerque et al, 2011). Butyric acid fermentation from renewable biomass may provide a reasonable alternative. Using lignocellulosic biomass as the fermentation feedstock provides environmental and cost benefits, the benefits gained from the low feedstock cost is completely counteracted by the cost of cellulolytic enzymes. The best-known biorefinery platform, cellulolytic enzymes are required to break down lignocelluloses into five- and six-carbon sugars that are further converted to desired chemicals, for example, ethanol (Agler et al, 2011). By contrast, purified cellulolytic enzymes are not necessary for lignocellulose conversion through a carboxylate platform, another biorefinery platform.
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