Sheer enormity of lignocellulosics makes them potential feedstock for biofuel production but, their conversion into fermentable sugars is a major hurdle. They have to be pretreated physically, chemically, or biologically to be used by fermenting organisms for production of ethanol. Each lignocellulosic substrate is a complex mix of cellulose, hemicellulose and lignin, bound in a matrix. While cellulose and hemicellulose yield fermentable sugars, lignin is the most recalcitrant polymer, consisting of phenyl-propanoid units. Many microorganisms in nature are able to attack and degrade lignin, thus making access to cellulose easy. Such organisms are abundantly found in forest leaf litter/composts and especially include the wood rotting fungi, actinomycetes and bacteria. These microorganisms possess enzyme systems to attack, depolymerize and degrade the polymers in lignocellulosic substrates. Current pretreatment research is targeted towards developing processes which are mild, economical and environment friendly facilitating subsequent saccharification of cellulose and its fermentation to ethanol. Besides being the critical step, pretreatment is also cost intensive. Biological treatments with white rot fungi and Streptomyces have been studied for delignification of pulp, increasing digestibility of lignocellulosics for animal feed and for bioremediation of paper mill effluents. Such lignocellulolytic organisms can prove extremely useful in production of bioethanol when used for removal of lignin from lignocellulosic substrate and also for cellulase production. Our studies on treatment of hardwood and softwood residues with Streptomyces griseus isolated from leaf litter showed that it enhanced the mild alkaline solubilisation of lignins and also produced high levels of the cellulase complex when growing on wood substrates. Lignin loss (Klason lignin) observed was 10.5 and 23.5% in case of soft wood and hard wood, respectively. Thus, biological pretreatment process for lignocellulosic substrate using lignolytic organisms such as actinomycetes and white rot fungi can be developed for facilitating efficient enzymatic digestibility of cellulose.
The unstable and uncertain availability of petroleum sources as well as rising cost of fuels have shifted global efforts to utilize renewable resources for the production of greener energy and a replacement which can also meet the high energy demand of the world. Bioenergy routes suggest that atmospheric carbon can be cycled through biofuels in carefully designed systems for sustainability. Significant potential exists for bioconversion of biomass, the most abundant and also the most renewable biomaterial on our planet. However, the requirements of enzyme complexes which act synergistically to unlock and saccharify polysaccharides from the lignocellulose complex to fermentable sugars incur major costs in the overall process and present a great challenge. Currently available cellulase preparations are subject to tight induction and regulation systems and also suffer inhibition from various end products. Therefore, more potent and efficient enzyme preparations need to be developed for the enzymatic saccharification process to be more economical. Approaches like enzyme engineering, reconstitution of enzyme mixtures and bioprospecting for superior enzymes are gaining importance. The current scenario, however, also warrants the need for research and development of integrated biomass production and conversion systems.
Azolla, an aquatic fern is ideal candidate for exploitation in constructed wetlands for treating metal-contaminated wastewaters. This study demonstrates the potential of Azolla spp. namely A. microphylla, A. pinnata and A. filiculoides to tolerate Cr ions in the growth environment and bioconcentrate them. These species could grow in presence of up to 10 lg ml )1 Cr and showed biomass production 30-70% as compared to controls. Nitrogenase activity was not affected at 1-5 lg ml )1 but at higher concentrations it diminished. There was no growth at higher concentrations of chromium. However, the necrosed biomass harvested from treatments containing higher concentrations of chromium, accumulated Cr to the levels 5000-15,000 lg g )1 . At increased levels of Cr, the metal was accumulated in higher amount in dry biomass. Bioconcentration Factor (BCF) ranged between 243 and 4617 for the three species. A. microphylla showed highest bioconcentration potential. Thus, these Azolla spp. can be exploited for treatment of tannery and other Cr contaminated wastewaters.
Parthenium sp. is a noxious weed which threatens the environment and biodiversity due to its rapid invasion. This lignocellulosic weed was investigated for its potential in biofuel production by subjecting it to mild alkali pretreatment followed by enzymatic saccharification which resulted in significant amount of fermentable sugar yield (76.6%). Optimization of enzymatic hydrolysis variables such as temperature, pH, enzyme, and substrate loading was carried out using central composite design (CCD) in response to surface methodology (RSM) to achieve the maximum saccharification yield. Data obtained from RSM was validated using ANOVA. After the optimization process, a model was proposed with predicted value of 80.08% saccharification yield under optimum conditions which was confirmed by the experimental value of 85.80%. This illustrated a good agreement between predicted and experimental response (saccharification yield). The saccharification yield was enhanced by enzyme loading and reduced by temperature and substrate loading. This study reveals that under optimized condition, sugar yield was significantly increased which was higher than earlier reports and promises the use of Parthenium sp. biomass as a feedstock for bioethanol production.
Background The objective of this study was to develop a consortium of effective microorganisms to hasten the composting process and to reduce the composting period. Results An efficient microorganism (EM) consortium was developed using Candida tropicalis (Y6), Phanerochaete chrysosporium (VV18), Streptomyces globisporous (C3), Lactobacillus sp. and enriched photosynthetic bacterial inoculum for rapid composting of paddy straw. Paddy straw was amended with poultry droppings to narrow down its C:N ratio for faster degradation. Composting was carried out in open pits with EM consortium and compared with compost inoculant (CI) consisting of Aspergillus nidulans (ITCC 2011), Trichoderma viride (ITCC 2211), Phanerochaete chrysosporium (NCIM 1073) and A. awamori (F-18). Changes in biochemical and physiochemical parameters like C:N ratio, pH, EC and humus were studied over a period of 60 days to test compost maturity and stability along with microbial and extracellular hydrolytic enzyme activities. Paddy straw amended with EM and CI hasten the composting process by bringing C:N ratio down to 15:1 and achieving a total humus content of 4.82 % within 60 days. High activity of hydrolytic enzyme carboxymethyl cellulase (CMCase) (0.43 IU/g) and microbial activity in terms of dehydrogenase (158.64 lg TPF/g/day) was observed in this treatment. The activity of xylanase was positively correlated (r = 0.987) with alkali-soluble carbon.Conclusion This study illustrates the importance of microbial bioaugmentation to hasten the composting process of paddy straw to produce quality compost.
Biomass pretreatment often leads to the formation of compounds that are inhibitory to enzymatic hydrolysis. To remove inhibitory compounds prior to enzymatic hydrolysis, pretreated biomass is washed with at least 3 volumes of water. However, this washing step would be difficult to manage in commercial operations because of the unsustainable water consumption. This study reports on the effects of formic acid and furfural on Accellerase 1500 with cellulose powder and dilute acid-pretreated poplar as substrates. Using cellulose powder as the substrate for enzymatic hydrolysis with the addition of 5 or 10 mg/mL formic acid, glucose recovery was reduced by 34% and 81%, respectively, in comparison to the control. The addition of furfural, at 2 or 5 mg/mL, to the enzymatic system reduced glucose recovery by 5% and 9%, respectively. When 5 mg/mL of formic acid was combined with 5 mg/mL of furfural, glucose recovery in the cellulose powder enzymatic system was reduced by 59%. Inhibition of sugar recovery was more pronounced when dilute acid-pretreated poplar was used as a substrate for enzymatic hydrolysis. At 24 h incubation, recovery reductions were 94%, 97%, and 93% in the presence of 5 or 10 mg/mL formic acid or the 5 mg/mL combination.
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