Shuchi Singh

Mechanistic investigations in sono-hybrid techniques for rice straw pretreatment.

This paper reports comparative study of two chemical techniques (viz. dilute acid/alkali treatment) and two physical techniques (viz. hot water bath and autoclaving) coupled with sonication, termed as sono-hybrid techniques, for hydrolysis of rice straw. The efficacy of each sono-hybrid technique was assessed on the basis of total sugar and reducing sugar release. The system of biomass pretreatment is revealed to be mass transfer controlled. Higher sugar release is obtained during dilute acid treatment than dilute alkali treatment. Autoclaving alone was found to increase sugar release marginally as compared to hot water bath. Sonication of the biomass solution after autoclaving and stirring resulted in significant rise of sugar release, which is attributed to strong convection generated during sonication that assists effective transport of sugar molecules. Discrimination between individual contributions of ultrasound and cavitation to mass transfer enhancement reveals that contribution of ultrasound (through micro-streaming) is higher. Micro-turbulence as well as acoustic waves generated by cavitation did not contribute much to enhancing of mass transfer in the system.

Isolation, Identification, and Characterization of a Cellulolytic Bacillus amyloliquefaciens Strain SS35 from Rhinoceros Dung

Cellulose hydrolyzing bacteria were isolated from rhinoceros dung and tested for clear zone formation around the colonies on the agar plates containing the medium amended with carboxymethylcellulose as a sole carbon source. Isolates were further screened on the basis of carboxymethylcellulase production in liquid medium. Out of 36 isolates, isolate no. 35 exhibited maximum enzyme activity of 0.079 U/mL and was selected for further identification by using conventional biochemical tests and phylogenetic analyses. This was a Gram-positive, spore forming bacterium with rod-shaped cells. The isolate was identified as Bacillus amyloliquefaciens SS35 based on nucleotide homology and phylogenetic analysis using 16S rDNA and gyrase A gene sequences.

Mechanistic insight into ultrasound induced enhancement of simultaneous saccharification and fermentation of Parthenium hysterophorus for ethanol production.

This paper presents investigations into mechanism of ultrasound assisted bioethanol synthesis using Parthenium hysterophorus biomass through simultaneous saccharification and fermentation (SSF) mode. Approach of coupling experimental results to mathematical model for SSF using Genetic Algorithm based optimization has been adopted. Comparison of model parameters for experiments with mechanical shaking and sonication (10% duty cycle) give an interesting mechanistic account of influence of ultrasound on SSF system. A 4-fold rise in ethanol and cell mass productivity is seen with ultrasound. The analysis reveals following facets of influence of ultrasound on SSF: increase in Monod constant for glucose for cell growth, maximal specific growth rate and inhibition constant of cell growth by glucose and reduction in specific cell death rate. Values of inhibition constant of cell growth by ethanol (K3E), and constants for growth associated (a) and non-growth associated (b) ethanol production remained unaltered with sonication. Beneficial effects of ultrasound are attributed to enhanced cellulose hydrolysis, enhanced trans-membrane transport of substrate and products as well as dilution of the toxic substances due to micro-convection induced by ultrasound. Intrinsic physiological functioning of cells remained unaffected by ultrasound as indicated by unaltered values of K3E, a and b.

Ultrasound enhanced ethanol production from Parthenium hysterophorus: A mechanistic investigation.

This study presents mechanistic investigations in ultrasound-assisted bioethanol fermentation using Parthenium hysterophorus biomass. Ultrasound (35 kHz, 10% duty cycle) has been used for sonication. Experimental results were fitted to mathematical model; the kinetic and physiological parameters in the model were obtained using Genetic Algorithm (GA) based optimization. In control experiments (mechanical shaking), maximum ethanol titer of 10.93 g/L and cell mass concentration of 5.26 g/L was obtained after 18 h. In test experiments (mechanical shaking and intermittent sonication), ethanol titer of 12.14 g/L and cell mass concentration of 5.7 g/L was obtained in 10h. This indicated ∼ 2 × enhanced productivity of ethanol and cell mass with sonication. Trends in model parameters obtained after fitting of model to experimental data essentially revealed that beneficial influence of ultrasound on fermentation is a manifestation of enhanced trans-membrane transportation and dilution of toxic substances due to strong micro-convection induced by ultrasound.

Ultrasound enhanced enzymatic hydrolysis of Parthenium hysterophorus: A mechanistic investigation

This study has attempted to establish the mechanism of the ultrasound-induced enhancement of enzymatic hydrolysis of pretreated and delignified biomass of Parthenium hysterophorus. A dual approach of statistical optimization of hydrolysis followed by application of sonication at optimum conditions has been adopted. The kinetics of hydrolysis shows a marked 6× increase with sonication, while net sugar yield shows marginal rise of ∼ 20%. The statistical experimental design reveals the hydrolysis process to be enzyme limited. Profile of sugar yield in ultrasound-assisted enzymatic hydrolysis has been analyzed using HCH-1 model coupled with Genetic Algorithm optimization. The trends in the kinetic and physiological parameters of HCH-1 model reveal that sonication enhances enzyme/substrate affinity and reaction velocity of hydrolysis. The product inhibition of enzyme in all forms (free, adsorbed, complexed) also reduces with ultrasound. These effects are attributed to intense micro-convection induced by ultrasound and cavitation in the liquid medium.

Physical and Chemical Mechanisms of Ultrasound in Biofuel Synthesis

Physical and chemical mechanisms ultrasound-assisted processes as related to the synthesis of biofuels are reviewed. Ultrasound and its secondary effect of cavitation have physical and chemical effects on a reaction system, which can contribute to enhancement of the kinetics and yield. In this chapter, a mechanistic insight into the ultrasound assisted biofuels synthesis is given by coupling simulations of cavitation bubble dynamics with experimental data. The physical effect of ultrasound and cavitation is through intense micro-convection in the system that gives marked improvements in the mass transfer of the system. The chemical effect is through generation of highly reactive radicals through transient cavitation that induce or accelerate chemical reactions. Chemical effects include thermal decomposition of the solvent vapor molecules in the cavitation bubble resulting in generation of smaller molecular species that also affect chemistry of the process. Raising the static pressure of the reaction system above ultrasound pressure amplitude in the system helps to discriminate between physical and chemical effects of ultrasound and cavitation. Biofuels systems considered in this chapter are the pretreatment of biomass, biodiesel synthesis with acid/base and homogeneous/heterogeneous catalysts, extraction of microalgal lipids, bioconversion of crude glycerol from biodiesel industry to value added products and desulfurization of the fuel. Among the physical effects of ultrasound and cavitation, micro-streaming by ultrasound has a greater influence on reactions than shock waves generated by cavitation bubbles. In some cases, chemical effects of transient cavitation are revealed to have adverse influence on a reaction. Many biofuels systems are limited by their intrinsic characteristics that restrict the effect of ultrasound and cavitation on the reaction system.

An assessment of the potential of invasive weeds as multiple feedstocks for biofuel production

The present study assessed the feasibility of five invasive weeds, namely, Arundo donax, Saccharum spontaneum, Mikania mikrantha, Lantana camara and Eichhornia crasspies, as a feedstock for biofuels production. The yield of total fermentable sugars from the pretreatment and enzymatic hydrolysis of these biomasses was assessed. However, the pretreatment and enzymatic hydrolysis were carried out at conditions optimized for the biomass of P. hysterophorus and thus, the conditions of pretreatment/enzymatic hydrolysis were not specifically optimized for any of the invasive weeds. Despite this, it was revealed that the average yield of total fermentable (hexose + pentose) sugars from all the weeds was 43.85 g per 100 g of raw biomass, which corresponds to a theoretical yield of 27.36 g ethanol and 17.96 g butanol. These yields are comparable to bioalcohol yields from the biomass of P. hysterophorus under optimized pretreatment conditions. Characterization of the biomass was carried out using X-ray diffraction, FTIR and SEM micrographs. The high yields of fermentable sugars obtained herein from invasive weeds, even under un-optimized pretreatment conditions, clearly point towards the feasibility of biorefinery using these weeds as multiple feedstocks for the production of alcoholic biofuels.

Ultrasound-assisted bioalcohol synthesis: review and analysis

Sonication (or ultrasound irradiation) has emerged as a potential technique for the intensification of diverse physical/chemical/biological processes. In recent years, sonication has been applied in the synthesis of liquid biofuels, such as biodiesel, and bioalcohols, such as ethanol. The process of bioalcohol synthesis comprises four steps, viz. acid pretreatment, alkaline delignification, enzymatic hydrolysis and fermentation. Significant literature has been published in the last decade on the application of ultrasound for the intensification of all the steps of bioalcohol synthesis. In this paper, a critical review and analysis of the literature on ultrasound-assisted bioalcohol synthesis has been presented. This review has addressed all four steps of bioalcohol synthesis. Essentially, the literature in the areas of ultrasound-assisted biomass pretreatment, delignification and hydrolysis has been reviewed, followed by an analysis of the literature on ultrasound-assisted fermentation. Finally, the mechanistic investigations of the various steps of bioalcohol synthesis have been reviewed, highlighting the synergistic links between the physical/chemical effects of ultrasound and cavitation and the basic physical/chemical mechanisms of the steps of bioalcohol synthesis. The critical analysis of the literature in this review has not only demonstrated the efficacy of ultrasound in the intensification of all the steps of bioalcohol synthesis, but has also brought to light the underlying mechanistic issues; this could provide guidelines for the design and optimization of commercial scale bioalcohol processes.

Synthesis of Bioethanol From Invasive Weeds: Process Design, Optimization, and Intensification With Ultrasound

Abstract In this chapter, we have presented a review of literature on production of bioethanol from waste biomass in the form of highly invasive weeds such as Parthenium hysterophorus . The chapter includes all three steps of P. hysterophorus -based ethanol production, namely, pretreatment/delignification, enzymatic hydrolysis, and fermentation of the hydrolysates. Various facets of each of these steps such as various methods of pretreatment (e.g., steam explosion, dilute acid, organosolv, H 2 O 2 , and AFEX) and optimization of these methods have been dealt with. Review of literature on enzymatic hydrolysis includes optimization of treatment and intensification with techniques such as sonication. The literature review on fermentation includes different fermentation protocols (such as SHF, SSF, SSCF, and CBP) and modeling of the processes. Literature on intensification of the fermentation using sonication has also been critically reviewed. On the basis of this review, finally, some recommendations have been given for further research in this area.