Augmented hydrolysis of acid pretreated sugarcane bagasse by PEG 6000 addition: a case study of Cellic CTec2 with recycling and reuse

In an integrated lignocellulosic biorefinery, the cost associated with the “cellulases” and “longer duration of cellulose hydrolysis” represents the two most important bottlenecks. Thus, to overcome these barriers, the present study aimed towards augmented hydrolysis of acid pretreated sugarcane bagasse within a short span of 16 h using Cellic CTec2 by addition of PEG 6000. Addition of this surfactant not only enhanced glucose release by twofold within stipulated time, but aided in recovery of Cellic CTec2 which was further recycled and reused for second round of saccharification. During first round of hydrolysis, when Cellic CTec2 was loaded at 25 mg protein/g cellulose content, it resulted in 76.24 ± 2.18% saccharification with a protein recovery of 58.4 ± 1.09%. Filtration through 50KDa PES membrane retained ~ 89% protein in 4.5-fold concentrated form and leads to simultaneous fractionation of ~ 70% glucose in the permeate. Later, the saccharification potential of recycled Cellic CTec2 was assessed for the second round of saccharification using two different approaches. Unfortified enzyme effectively hydrolysed 67% cellulose, whereas 72% glucose release was observed with Cellic CTec2 fortified with 25% fresh protein top-up. Incorporating the use of the recycled enzyme in two-stage hydrolysis could effectively reduce the Cellic CTec2 loading from 25 to 16.8 mg protein/g cellulose. Furthermore, 80% ethanol conversion efficiencies were achieved when glucose-rich permeate obtained after the first and second rounds of saccharification were evaluated using Saccharomyces cerevisiae MTCC 180

Expeditious production of concentrated glucose-rich hydrolysate from sugarcane bagasse and its fermentation to lactic acid with high productivity

Sugarcane bagasse (SCB) is anticipated to emerge as a potential threat to waste management in India on account of cheap surplus energy options and lower incentives through its co-generation. Through biotechnological intervention, the efficient utilization of SCB is seen as an opportunity. The present study aimed towards expeditious production of concentrated glucose-rich hydrolysate from SCB. Alkali pretreated biomass was chosen for hydrolysis with a new generation cellulase cocktail, Cellic CTec2 dosed at 25 mg g−1 glucan content. A two-step (9% + 9%) substrate feeding strategy was adopted with a gap of an hour, and saccharification was terminated in three different ways. Irrespective of the methods employed for termination, ∼84.5% cellulose was hydrolyzed releasing ≥100 g L−1 glucose from 18% biomass. Direct use of glucose-rich filtrates yielded 69.2 ± 2.5 g L−1 of L (+) lactic acid (LA) using thermophilic Bacillus coagulans NCIM 5648. The best-attained glucose and LA productivities during separate hydrolysis and fermentation (SHF) in the present study were 5.27 and 2.88 g L−1 h−1, respectively. A green and sustainable process is demonstrated for the production of industrially relevant sugars from SCB at high productivity and its valorization to bio-based LA

Conclusive selection of optimal parameters for cellulase production by <i>Talaromyces verruculosus</i> IIPC 324 under SSF via saccharification of acid-pretreated sugarcane bagasse

<p>Cellulase production studies were conducted with <i>Talaromyces verruculosus</i> IIPC 324 under solid state fermentation (SSF), and optimal parameters were conclusively selected via saccharification of acid-pretreated sugarcane bagasse. Various physicochemical parameters affecting cellulase production under SSF were optimized. Endoglucanase and cellobiase production responded differently under individual growth conditions. Maximum endoglucanase and cellobiase activity of ≥ 250 U/g and ≥ 45 U/g respectively was obtained when the strain was grown at 24°C for 4 days with an initial moisture content of 62.5% on wheat bran supplemented with 1.62% ammonium chloride. The enzyme cocktail obtained from these optimized growth conditions yielded 8.37 ± 0.75 g L⁻¹ reducing sugar from acid-pretreated sugarcane bagasse after 72 h at 60°C and pH 4.0. With the addition of Avicel PH-101 at 5% concentration in wheat bran, the cellulase cocktail of <i>Talaromyces verruculosus</i> IIPC 324 released 9.17 ± 0.60 g L⁻¹ and 7.82 ± 0.06 g L⁻¹ of total reducing sugars and glucose respectively at 60°C (pH 4.0) after 72 h. The addition of glucose and other simple sugars did not repress the cellulase production under SSF conditions, making <i>Talaromyces verruculosus</i> IIPC 324 an attractive candidate for cellulase production and its application for biofuel production from lignocellulosic biomass.</p

Salting-out assisted solvent extraction of L (+) lactic acid obtained after fermentation of sugarcane bagasse hydrolysate

Lactic acid is among the twelve platform chemicals produced from inexpensive and renewable feedstocks such as lignocellulosic biomass. The present study illustrates salting-out assisted solvent extraction of L (+) lactic acid, derived from sugarcane bagasse hydrolysate. Screening studies with various extractants and diluents revealed that a combination of tri-n-butyl phosphate and ethyl acetate yielded the best results and extracted 59.63 ± 1.28% lactic acid from the dilute fermentation broth adjusted to a pH of 1.6 ± 0.2. Various inorganic salts were screened to enhance extraction efficiency further. The addition of 60% (w/v) ammonium sulfate improved the lactic acid extraction by 36.17%. This salt concentration successfully extracted 85.95 ± 0.44% lactic acid to the organic phase under optimized conditions from the fermentation broth at a pH of ~ 2.5 containing 40–100 g L−1 lactic acid. Recovery of > 80% salt is also shown using chilled acetone, which upon reuse showed a nominal decline of 3.3% during extraction. Thus an eco-friendly approach using a green solvent like ethyl acetate with mild operating conditions is demonstrated in the present study