Bioethanol can be produced from wood via acid hydrolysis, but detoxification is needed to achieve good fermentability. Overliming was investigated in a factorial designed experiment, in which pH and temperature were varied. Degradation of inhibitory furan aldehydes was more extensive compared to monosaccharides. Too harsh conditions led to massive degradation of sugars and formation of inhibiting acids and phenols. The ethanol productivity and yield after optimal overliming reached levels exceeding reference fermentations of pure glucose. A novel metric, the balanced ethanol yield, which takes both ethanol production and losses of fermentable sugars into account, was introduced and showed the optimal conditions within the investigated range. The findings allow process technical and economical considerations to govern the choice of conditions for overliming.
"Feedstocks with high content of acetylated xylan, typically agricultural residues and hardwood, give higher concentrations of aliphatic acids than softwood. The total content of aliphatic acids in softwood hydrolysates is often below 100 mM and consequently beneficial for the ethanol yield rather than harmful [48,49]. "
[Show abstract][Hide abstract] ABSTRACT: Bioconversion of lignocellulose by microbial fermentation is typically preceded by an acidic thermochemical pretreatment step designed to facilitate enzymatic hydrolysis of cellulose. Substances formed during the pretreatment of the lignocellulosic feedstock inhibit enzymatic hydrolysis as well as microbial fermentation steps. This review focuses on inhibitors from lignocellulosic feedstocks and how conditioning of slurries and hydrolysates can be used to alleviate inhibition problems. Novel developments in the area include chemical in-situ detoxification by using reducing agents, and methods that improve the performance of both enzymatic and microbial biocatalysts.
Biotechnology for Biofuels 01/2013; 6(1):16. DOI:10.1186/1754-6834-6-16 · 6.04 Impact Factor
"Detoxification of dilute acid lignocellulosic hydrolysates by treatment with Ca(OH) 2 before fermentation to ethanol, is reported by many researchers (Horváth et al. 2005; Alriksson 2006,; Mohageghi et al. 2006). Larsson et al. (1999) performed a comparison of 12 different detoxification methods for treatment of dilute acid spruce hydrolysate prior to fermentation by Saccharomyces cerevisiae, It is reported that Ca(OH) 2 treatment at pH 10 is one of the best methods with regard to improvement of ethanol productivity. "
[Show abstract][Hide abstract] ABSTRACT: Clostridium spp. produce n-butanol in the acetone/butanol/ethanol process. For sustainable industrial scale butanol production, a number of obstacles need to be addressed including choice of feedstock, the low product yield, toxicity to production strain, multiple-end products and downstream processing of alcohol mixtures. This review describes the use of lignocellulosic feedstocks, bioprocess and metabolic engineering, downstream processing and catalytic refining of n-butanol.
"While the removal of inhibitory compounds has led to more efficient product formation, the challenge of detoxification is the increased processing costs [e.g., for fermentation of a pentose-rich hydrolysate with recombinant E. coli, it was estimated that detoxification via overliming constituted 22% of the total ethanol production cost (Von Sivers and Zacchi, 1995)] and additional operations within the biorefinery that inevitably leads to loss of the valuable sugars, or even additional inhibitory compound formation. For example, overliming can result in major sugar degradation (Horváth et al., 2005), with subsequent reduction in fermentation yields. Sugar losses also were observed within an ion exchange process (26% sugar loss) and after treatment with T. reesei to degrade phenolics (35% sugar loss) (Larsson et al., 1999). "
[Show abstract][Hide abstract] ABSTRACT: Within the biorefinery paradigm, many non-monomeric sugar compounds have been shown to be inhibitory to enzymes and microbial organisms that are used for hydrolysis and fermentation. Here, two novel separation technologies, polyelectrolyte polymer adsorption and resin-wafer electrodeionization (RW-EDI), have been evaluated to detoxify a dilute acid pretreated biomass slurry. Results showed that detoxification of a dilute acid pretreated ponderosa pine slurry by sequential polyelectrolyte and RW-EDI treatments was very promising, with significant removal of acetic acid, 5-hydroxymethyl furfural, and furfural (up to 77%, 60%, and 74% removed, respectively) along with >97% removal of sulfuric acid. Removal of these compounds increased the cellulose conversion to 94% and elevated the hydrolysis rate to 0.69 g glucose/L/h. When using Saccharomyces cerevisiae D(5)A for fermentation of detoxified slurry, the process achieved 99% of the maximum theoretical ethanol yield and an ethanol production rate nearly five-times faster than untreated slurry.
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