Ruchi Agrawal

Pilot scale study on steam explosion and mass balance for higher sugar recovery from rice straw.

Pretreatment of rice straw on pilot scale steam explosion has been attempted to achieve maximum sugar recovery. Three different reaction media viz. water, sulfuric acid and phosphoric acid (0.5%, w/w) were explored for pretreatment by varying operating temperature (160, 180 and 200°C) and reaction time (5 and 10min). Using water and 0.5% SA showed almost similar sugar recovery (∼87%) at 200 and 180°C respectively. However, detailed studies showed that the former caused higher production of oligomeric sugars (13.56g/L) than the later (3.34g/L). Monomeric sugar, followed the reverse trend (7.83 and 11.62g/L respectively). Higher oligomers have a pronounced effect in reducing enzymatic sugar yield as observed in case of water. Mass balance studies for water and SA assisted SE gave total saccharification yield as 81.8% and 77.1% respectively. However, techno-economical viability will have a trade-off between these advantages and disadvantages offered by the pretreatment medium.

Untreated wheat straw: potential source for diverse cellulolytic enzyme secretion by Penicillium janthinellum EMS-UV-8 mutant.

Study describes the production of cellulases by Penicillium janthinellum EMS-UV-8 using untreated wheat straw (WS), treated WS (acid, alkali, steam exploded, organo-solv) and pure cellulosic substrates (avicel, cellulose-II and carboxymethyl cellulose). Severely pretreated WS and cellulose-II produced more cellulolytic enzymes than untreated samples. XRD and FTIR analysis revels that the increase in the amorphous structure of pretreated WS/cellulose increases enzyme production. Enzyme samples prepared using different substrates were used for the hydrolysis of dilute acid treated wheat straw (DATWS), steam exploded wheat straw (SEWS) and avicel. The enzyme prepared using untreated WS gave more hydrolysis of DATWS and SEWS than the enzyme prepared using pretreated WS or pure cellulosic substrates. This revels that more diverse/potential enzymes were secreted by P. janthinellum EMS-UV-8 mutant using untreated WS. This study may contribute in production of efficient enzyme mixture/cocktail by single fungal strain for economic conversion of biomass to sugars.

Improved saccharification of pilot-scale acid pretreated wheat straw by exploiting the synergistic behavior of lignocellulose degrading enzymes

Requirement of high enzyme dosage for lignocellulosic biomass hydrolysis is one of the challenges for the viability of the second generation bioethanol technology. Here, an optimal enzyme mixture was developed by partially replacing the cellulase proportion with accessory enzymes (β-glucosidase, xylanase, pectinase, laccase) and its hydrolytic performance was compared with different commercial counterparts for the saccharification of pretreated wheat straw (PWS) using a 250 kg per day continuous pilot plant. Maximum degree of synergism was observed with xylanase followed by pectinase, laccase, and β-glucosidase. The statistically optimized enzyme mixture enhanced hydrolysis by 51.23% and 40.66% in 6 h and 24 h, respectively. This study elucidates that presence of even small amount of oligomers and cellobiose pose a strong inhibition for the enzymes. Therefore, development of an optimal enzyme formulation is a sustainable approach to reduce overall enzyme loading for biomass saccharification.

Pilot scale dilute acid pretreatment of rice straw and fermentable sugar recovery at high solid loadings

The aim of this work was to study the dilute acid pretreatment of rice straw (RS) and fermentable sugar recovery at high solid loadings at pilot scale. A series of pretreatment experiments were performed on RS resulting in >25wt% solids followed by enzymatic hydrolysis without solid-liquid separation at 20 and 25wt% using 10FPU/g of the pretreated residue. The overall sugar recovery including the sugars released in pretreatment and enzymatic hydrolysis was calculated along with a mass balance. Accordingly, the optimized conditions, i.e. 0.35wt% acid, 162°C and 10min were identified. The final glucose and xylose concentrations obtained were 83.3 and 31.9g/L respectively resulting in total concentration of 115.2g/L, with a potential to produce >50g/L of ethanol. This is the first report on pilot scale study on acid pretreatment of RS in a screw feeder horizontal reactor followed by enzymatic hydrolysis at high solid loadings.

Investigating the enzyme-lignin binding with surfactants for improved saccharification of pilot scale pretreated wheat straw

In this study, commercial surfactants have been investigated at economically viable dosage to enhance the enzymatic saccharification of pretreated wheat straw at high solid loadings. Twenty one surfactants were evaluated with pilot scale pretreated wheat straw and mechanism of surfactant action has been elucidated. One surfactant has improved the saccharification of dilute acid wheat straw (DAWS) by 26.4% after 24h and 23.1% after 48h while, steam exploded wheat straw (SEWS) saccharification was increased by 51.2% after 24h and 36.4% after 48h at 10% solid loading. At 20% solid loading, about 31% increase in yield was obtained on DAWS and about 55% on SEWS after 48h. Further, lignin was isolated from pretreated wheat straws and characterized which revealed that SEWS derived lignin was more hydrophobic than DAWS lignin. This investigation suggests that surfactant supplementation during saccharification is an effective strategy to achieve higher saccharification yield.

Evaluation of recalcitrant features impacting enzymatic saccharification of diverse agricultural residues treated by steam explosion and dilute acid

Exploring agricultural biomass for biofuel production necessitates pretreatment as a prerequisite step. However, due the variability in recalcitrance among biomasses, choosing an optimum pretreatment methodology suitable for multiple feedstocks is challenging. To assess which parameters of pretreated biomass may serve as useful indicators of potential subsequent enzymatic saccharification, an insight into the structural alteration during pretreatment and its impact on the downstream process is essential. In this study, two pretreatment methods, dilute acid (DA) and steam explosion (SE) have been employed on three different biomasses viz. rice straw (RS), cotton stalk (CS) and mustard stalk (MS). The alteration in recalcitrant features of the pretreated residues was measured by chemical analysis, XRD, BET and FT-IR. FT-IR proved useful to measure the cellulose related properties viz. lateral order index (LOI) and hydrogen bond index (HBI) besides lignin related features, i.e. cross-linked lignin (CLL), lignin/cellulose (L/C) and syringyl/guaiacyl (S/G) ratio. The results show that S/G ratio, specific surface area and HBI of the pretreated residues had a positive correlation with enzymatic saccharification across different biomasses and pretreatment methodologies employed. On the other hand, lignin content, CLL, L/C ratio and LOI showed a negative correlation. However, the extent of xylan removal showed a positive correlation with the enzymatic saccharification only when a single pretreatment method was applied to different biomasses. The structure-activity correlation presented here would help to assess and predict the enzymatic saccharification while applying DA or SE pretreatment methods on different biomasses. This correlation could provide assistance in designing an optimum technology.

Second generation bioethanol production at high gravity of pilot-scale pretreated wheat straw employing newly isolated thermotolerant yeast Kluyveromyces marxianus DBTIOC-35

Second-generation bioethanol production by a newly isolated thermotolerant yeast strain was studied at 42 °C and above using pilot-scale dilute acid pretreated wheat straw (WS) as feedstock. This strain was identified as Kluyveromyces marxianus DBTIOC-35 by biochemical characterization as well as molecular phylogenetic analysis of the ITS-5.8S rRNA gene and D1/D2 domain of the 26S rRNA gene after PCR amplification and sequencing. Simultaneous saccharification and fermentation (SSF) at 42 °C and 45 °C using 10% biomass loading resulted in ethanol titers of 29.0 and 16.1 g L−1, respectively. At 42 °C ethanol productivity was higher during SSF (0.92 g L−1 h−1) than separate hydrolysis and fermentation (SHF) (0.49 g L−1 h−1) at 20% biomass loading. The results indicated that at 20% biomass loading, SSF without pre-saccharification led to more ethanol production (66.2 g L−1 with 83.3% yield) at a faster rate than SSF with pre-saccharification (PSSF) which produced an ethanol titer of 61.8 g L−1, 77.7% yield and productivity of 0.86 g L−1 h−1. Based on these findings, application of newly isolated yeast K. marxianus DBTIOC-35 in SSF of lignocellulosic biomass can eliminate the pre-saccharification step which is a novel advantage of thermotolerant yeasts in terms of cutting down the overall biomass to bioethanol process time and enhancing bioethanol titer, yields and productivities.

Induction of cellulases by disaccharides or their derivatives in Penicillium janthinellum EMS-UV-8 mutant

ABSTRACT Disaccharides or their derivatives were analyzed for the induction of cellulases by Penicillium janthinellum EMS-UV-8 mutant. Among seven (Crocin, Gentiobiose, Cellobiose, α-D-Cellobiose octaacetate, Trehalose, Melibiose, Turanose) different compounds tested, α-D-Cellobiose octaacetate (COA) was found to be promising for induction of cellulases. The maximum of 0.8 IU/mL filter paper units, 4.7 IU/mL β–glucosidase and 1.0 mg/mL protein were produced using 0.1% (weight/volume) COA as an inducer and 1% glucose as a carbon source for growth. Next to COA the gentiobiose, trehalose, melibiose and turanose also induce cellulase but at a low level. The induction of cellulase was also analyzed in the presence and absence of light and it was found that the absence of light supports more growth and less cellulase induction, while in the presence of light mycelial growth was restricted but more cellulases were induced. The knowledge of cellulase induction by COA and light could be beneficial for large-scale cellulase production for conversion of cellulosic biomass to biofuels.

Indian Biofuel Progress, GHG Emission and GHG Savings by Biofuels: Comparative Assessment with World

Indian biofuel research and development is increasing day by day. Indian government made a plan to make 20% ethanol/biofuel blending by 2020. Few companies are already working on the biodiesel/lignocellulosic ethanol research and production, but they are not yet commercially working. The ethanol from molasses is available only for making 5% blending with gasoline, and appropriate policies are necessary to increase the ethanol production not only from one source but from other various renewable resources. Research institutions are working to make lignocellulosic biofuels available at lower price. The production and use of biofuel not only helps India at economic level but also may help to reduce some greenhouse gas emissions. At present, India is one of the most CO2-emitting countries but behind the USA and China. The recent report indicates the slowdown of global CO2 emission and that may be because of several reasons, but it is a good beginning.