Rapid decomposition of rice straw by application of a novel microbial consortium and study its microbial community dynamics.

Rice straw decomposition is an attractive solution to open-field burning but the traditional method has slow kinetics and takes 60-90 days to obtain mature compost. In this study, we propose to boost up the decomposition process by addition of a novel microbial consortium rich in lignocellulolytic microbes. C: N ratio of the compost reached 11.69% and degradation efficiency of cellulose and hemicellulose was found to be 64 and 87% respectively within 25 days. Lignocellulolytic activity of the microbial consortium was confirmed by plate and activity assay. These parameters clearly indicated that a mature compost was obtained in 25 days. The 16S rRNA gene amplicon sequencing and functional analysis of predicted genes indicated amino acid and carbohydrate metabolism as the major metabolic pathway during composting. The tertiary level of functional analysis revealed the major metabolic pathways in the bacterial communities as pentose phosphate pathway, glycolysis and tricarboxylic acid cycle.

Enhanced enzymatic hydrolysis of mild alkali pre-treated rice straw at high-solid loadings using in-house cellulases in a bench scale system.

In the present study, scale-up systems for cellulase production and enzymatic hydrolysis of pre-treated rice straw at high-solid loadings were designed, fabricated and tested in the laboratory. Cellulase production was carried out using tray fermentation at 45 °C by Aspergillus terreus in a temperature-controlled humidity chamber. Enzymatic hydrolysis studies were performed in a horizontal rotary drum reactor at 50 °C with 25 % (w/v) solid loading and 9 FPU g(-1) substrate enzyme load using in-house as well commercial cellulases. Highly concentrated fermentable sugars up to 20 % were obtained at 40 h with an increased saccharification efficiency of 76 % compared to laboratory findings (69.2 %). These findings demonstrate that we developed a simple and less energy intensive bench scale system for efficient high-solid saccharification. External supplementation of commercial ß-glucosidase and hemicellulase ensured better hydrolysis and further increased the saccharification efficiency by 14.5 and 20 %, respectively. An attempt was also made to recover cellulolytic enzymes using ultrafiltration module and nearly 79-84 % of the cellulases and more than 90 % of the sugars were recovered from the saccharification mixture.

Valorization of microalgae biomass into bioproducts promoting circular bioeconomy: a holistic approach of bioremediation and biorefinery.

The need for alternative source of fuel has demanded the cultivation of 3rd generation feedstock which includes microalgae, seaweed and cyanobacteria. These phototrophic organisms are unique in a sense that they utilise natural sources like sunlight, water and CO2 for their growth and metabolism thereby producing diverse products that can be processed to produce biofuel, biochemical, nutraceuticals, feed, biofertilizer and other value added products. But due to low biomass productivity and high harvesting cost, microalgae-based production have not received much attention. Therefore, this review provides the state of the art of the microalgae based biorefinery approach to define an economical and sustainable process. The three major segments that need to be considered for economic microalgae biorefinery is low cost nutrient source, efficient harvesting methods and production of by-products with high market value. This review has outlined the use of various wastewater as nutrient source for simultaneous biomass production and bioremediation. Further, it has highlighted the common harvesting methods used for microalgae and also described various products from both raw biomass and delipidified microalgae residues in order to establish a sustainable, economical microalgae biorefinery with a touch of circular bioeconomy. This review has also discussed various challenges to be considered followed by a techno-economic analysis of the microalgae based biorefinery model.

Black liquor: A potential moistening agent for production of cost-effective hydrolytic enzymes by a newly isolated cellulo-xylano fungal strain Aspergillus tubingensis and its role in higher saccharification efficiency.

In the present study, black liquor generated during mild alkali pre-treatment was evaluated as a moistening agent to produce cost effective hydrolytic enzymes using novel cellulo-xylano fungal strain Aspergillus tubingensis M7. The fungus competently produced 21.90 and 22.46 filter paper, 1004 and 1369 endoglucanase, 117 and 142 ß-glucosidase and 8188 and 7981 U/g xylanase activity by using modified Mandel & weber's and black liquor medium, respectively. The crude hydrolytic enzymes from black liquor were evaluated for saccharification of pre-treated biomass. Reducing sugar yields (mg/g substrate) and the corresponding saccharification efficiency (%) from rice straw, corncob, sugarcane bagasse and banana stem were 745.50 (86.02; 18 h); 596 (74.50; 24 h); 358.15 (42.98; 24 h) and 245.70 (33.00; 24 h), respectively. Residual biomass compositional analysis revealed that reduced onset temperature, increased activation energy and pre-exponential factor in saccharified biomass as compared to pre-treated and untreated biomass, suggesting their utilization for pyrolysis to obtain value added products.

Structural insight into the fungal ß-glucosidases and their interactions with organics.

Fungal ß-glucosidases (BGLs) have unceasingly utilized for industrial applications and recently, they possess a crucial role in bioethanol production. To engineer the BGLs, understanding their structures, intermolecular interactions and molecular docking is requisite, which is carried out in this work based on the glycosyl hydrolase (GH) family. Among 12 BGLs, protein sequence, structure, and conserved sites of GH1 BGLs are evidently diverged to GH3 BGLs. Even biophysical and chemical features of GH1 BGLs are utterly varied from GH3 BGLs, wherein pI, instability index, aliphatic index, surface & buried area, thermostability and thermodynamics are included. On the contrary, aromatic, charged, polar, and hydrophobic residues are significantly higher in GH1 BGLs as compared to that of GH3 BGLs. Moreover, molecular docking of BGLs with 12 substrates and 5 inhibitors revealed that the GH3 BGLs efficiently bound with laminaribose, gentibiose, aryl- and cello-substrates than GH1 BGLs; however, GH3 BGLs are noticeably inhibited by glucose, glucono-δ-lactone, methanetriamine. So, structural insight of BGLs provides an explicit knowledge regarding the catalytic residues, biophysical chemistry and notable binding ligands, which are most important factors for enzyme engineering.

Enhanced biogas production from rice straw by selective micronutrients under solid state anaerobic digestion.

Biomethanation of rice straw (RS) was studied in a batch mode at high total solid content (TSC) of 25% in outdoor pilot scale digesters. Performance was monitored for over six months by supplementing Nickel and Cobalt 15 and 10mgkg(-1) RS to each of mesophilic and thermophilic digesters for 35 and 21days retention time (RT), respectively. The average biogas production from mesophilic and thermophilic digesters were found varying 310 and 396Lkg(-1)TS, respectively. The corresponding figures for the control digesters were 225 and 270Lkg(-1)TS. Around 37 and 46% higher biogas production was recorded by supplementing the micronutrients in mesophilic and thermophilic digesters, respectively. Methane content in biogas was 57-59%. Matured compost had nitrogen, phosphorus and potassium contents of 1.0-1.2, 1.3-2.2, and 1.2-2.1%, respectively. The results demonstrated that the present process is faster, requires less than 85% water and produces green energy in addition to manure in less time compared to conventional process.

Utilization of solid and liquid waste generated during ethanol fermentation process for production of gaseous fuel through anaerobic digestion--a zero waste approach.

Preliminary investigations were performed in the laboratory using batch reactors at 10% solid concentration for the assessment of the biogas production at thermophilic and mesophilic temperatures using solid residues generated during ethanol fermentation process. One kg of solid residues (left after enzyme extraction and enzymatic hydrolysis) from thermophilic reactors (TR1 and TR2) produced around 131 and 84L of biogas, respectively, whereas biogas production from mesophilic reactors (MR1 and MR2) was 86 and 62L, respectively. After 20 and 35days of retention time, the TS and VS reductions from TR1, TR2 and MR1, MR2 were found to be 39.2% and 35.0%, 67.3% and 61.0%, 21.0% and 18.0%, 34.7% and 27.8%, respectively. Whereas the liquid waste was treated using four laboratory anaerobic hybrid reactors (AHRs) with two different natural and synthetic packing media at 15-3days HRTs. AHRs packed with natural media showed better COD removal efficiency and methane yield.

Simultaneous saccharification and fermentation of delignified lignocellulosic biomass at high solid loadings by a newly isolated thermotolerant Kluyveromyces sp. for ethanol production.

Simultaneous saccharification and fermentation studies were carried out using thermotolerant newly isolated Kluyveromyces sp. with three different delignified lignocellulosic biomass viz. rice straw, wheat straw and sugarcane bagasse at 5-15% solid loading and 6-12 FPU g(-1) substrate enzyme loading for different time intervals 0-72 h at 42°C. Maximum ethanol achieved from rice straw, wheat straw and sugarcane bagasse with in-house crude cellulases from Aspergillus terreus was 23.23, 18.29 and 17.91 mg mL(-1) at 60 h with 10% solid load and 9 FPU g(-1) substrate enzyme loading. Tween 80 1% (v/v) enhanced the ethanol yield by 8.39%, 9.26% and 8.14% in rice straw, wheat straw and sugarcane bagasse, respectively. External supplementation of ß-glucosidase to the crude as well commercial cellulases produced maximum theoretical ethanol yield of 71.76%, 63.77%, 57.15% and 84.56%, 72.47%, 70.55% from rice straw, wheat straw and sugarcane bagasse, respectively.

Performance evaluation of anaerobic hybrid reactors with different packing media for treating wastewater of mild alkali treated rice straw in ethanol fermentation process.

Four anaerobic hybrid reactors with different packing media viz. gravel (R1), pumice stone (R2), polypropylene saddles (R3) and ceramic saddles (R4) were operated in semi-continuous mode. Biomethanation potential of the wastewater generated during alkali-treatment of rice straw in ethanol production process was investigated at ambient conditions. The reactors were operated with varying organic loading rates (0.861-4.313 g COD l(-1) d(-1)) and hydraulic retention time (3-15 days). Higher COD removal efficiency (69.2%) and methane yield (0.153 l CH4 g(-1) CODadded) were achieved in reactor R2 at 15 days HRT. Modified Stover-Kincannon model was applied to estimate the bio-kinetic coefficients and fitness of the model was checked by the regression coefficient for all the reactors. The model showed an excellent correlation between the experimental and predicted values. The present study demonstrated the treatment of wastewater from alkali treated rice straw for production of biogas.

Production of cellulases by solid state fermentation with Aspergillus terreus and enzymatic hydrolysis of mild alkali-treated rice straw.

Rice straw was used as substrate for cellulase production by solid state fermentation with Aspergillus terreus. Substrate concentration, moisture ratio, inoculum size and initial pH were optimized using response surface methodology involving Box-Behnken design. The predicted filter paper activity under optimized parameters was 9.73 U/g and the validated filter paper activity was 10.96 U/g. Hydrolysis of the biomass pretreated with 0.125% to 1% NaOH for 24h at room temperature was performed using crude cellulase preparation. Treatment with 0.5% NaOH at room temperature for 24h was the most efficient treatment method for saccharification. Under the optimized conditions, rice straw yielded 676 mg reducing sugars per gram of substrate at a cellulase loading of 9 FPU g(-1) substrate. The present study establishes the possibility of using mild alkali pretreated rice straw for the production of fermentable sugars with 74.19% efficiency which can be further utilized for the production of ethanol.