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This study has put forth the concept of “control through utilization” for invasive weeds, which cause severe damage to ecosystem and biodiversity. The study comprised of extraction of lignin and pretreatment of spent biomass of four invasive weeds. Lignin was extracted from native biomass using 1,4–dioxane as solvent. Lignin yield of all biomass varied in the range 8.61 − 11.14% w/w with the solvent recovery of 75.56–78.88% v/v. Extracted lignin was characterized using FTIR, TGA, and GPC. Lignin from Mikania micrantha had the highest thermal stability (T50% = 490 °C) and molecular weight (Mw = 5537 g/mol). The spent biomass was subjected to dilute acid pretreatment for synthesis of total reducing sugars (TRS). TRS yields from different entities were as follows: non-extracted biomass = 94.18 − 221.81 mg/g, warm water wash = 8.74 − 15.66 mg/g, and raw biomass = 115.9 − 391.27 mg/g raw biomass. Biomass of Saccharum spontaneum gave the highest TRS yield.

Invasive weeds ubiquitously found in terrestrial and aquatic ecosystems form potential feedstock for lignocellulosic ethanol production. The present study has reported a bioprocess for production of ethanol using mixed feedstock of 8 invasive weeds found in India. The feedstock was subjected to pretreatment comprising dilute acid hydrolysis (for hydrolysis of hemicellulosic fraction), alkaline delignification and enzymatic hydrolysis of cellulosic fraction. Pentose-rich and hexose-rich hydrolyzates obtained from pretreatment were fermented separately using microbial cultures of S. cerevisiae and C. shehatae. Fermentation mixture was sonicated at 35 kHz at 10% duty cycle. The time profiles of total reducing sugars, ethanol and biomass was fitted to a kinetic model using Genetic Algorithm. Sonication boosted the kinetics of fermentation 2-fold. The net bioethanol yield of the process was ∼220 g/kg raw biomass (with contributions of 86.8 and 133 g/kg raw biomass from pentose and hexose fermentations, respectively). Comparative evaluation of parameters of kinetic model under control and test conditions revealed several beneficial influences of sonication on both pentose and hexose fermentation systems such as faster transport of nutrients, substrate and products across cell membrane, rise in Monod saturation constant for substrate with concurrent reduction in substrate inhibition, and reduction of energy requirements for cell maintenance. Flow cytometry analysis of native and ultrasound-treated cells revealed no adverse influence of sonication on cell viability.

Growing concern about the rapid depletion of fossil fuels, current environmental conditions, energy challenges and new environmental regulations has encouraged the researchers worldwide for new environmentally compatible alternatives from natural resources. In this context, biogas produced from anaerobic digestion of organic resources may be considered as a significant bioenergy with the potential to address these concerns. Biogas is a mixture of methane and carbon dioxide as the major constituents with other trace components like water vapor, hydrogen sulfide, ammonia, carbon monoxide and nitrogen. Uses of biogas can be seen in heating, cooking, lighting and power production. However, cleaning of biogas from its impurities, mainly CO2 and H2S, can extend its scope of applications. There are numerous physico-chemical (viz. cryogenic, adsorption, membrane separations and absorption) and biological (in situ and ex situ) technologies for biogas upgradation. These operations are aimed at enriching the methane content of biogas above 90% and thereby enhancing the calorific value up to 35.3 MJ/m3. The purpose behind such upgrading is generally focused to meet the fuel standards to be used in vehicles, for injection in the natural gas grid, and to be used as substrate for the production of chemicals or for fuel cell applications. Enriched biogas is compressed and stocked in gas cylinder and transported to the desired location for utilization. Additionally, use of enriched biogas reduces greenhouse gas emissions. This chapter aims at meticulously evaluating the existing and emerging biogas production and upgradation technologies and confers the outlook for overcoming the challenges associated with them.

In the present study, lignin was extracted from debarked bamboo waste of paper industry by soxhlet extraction method with 1,4–Dioxane as main solvent (along with small quantities of catalyst and water). 10 g of biomass results in 1.5 g of lignin through soxhlet process. The purity of extracted lignin was determined, followed by structural and thermal properties using FTIR and TGA. The elemental composition and mass of lignin was determined by elemental analyser and gel permeation chromatography (GPC). The extracted lignin was found to be highly pure, with very low (0.42% w/w) ash and negligible carbohydrate content. The solubility of extracted lignin in various organic solvents like dioxane, THF, DMF, etc. makes it advantageous over lignin derived from other processes. Pyrolytic oil and char were also obtained through pyrolysis of extracted lignin. The composition of bio-oil and biochar was analysed. The results showed that pyrolytic oil was rich in aromatic content and biochar was high in carbon content.

This study reports an ultrasound-assisted Acetone-Butanol-Ethanol (ABE) fermentation process using Clostridium acetobutylicum MTCC 11,274 and mixed feedstock consisting of eight highly invasive weeds. Composite (pentose + hexose) hydrolyzate was fermented with sonication at 35 kHz and 10% duty cycle (test) and mechanical agitation at 150 rpm (control). Net solvent yield with sonication was 0.288 g/g raw biomass in 92 h against yield of 0.168 g/g raw biomass in 120 h with mechanical agitation. Butanol yield in test and control fermentation was 0.233 and 0.149 g/g total fermentable sugar, respectively. Substrate and metabolites profiles in test and control fermentation were analyzed using biokinetic model. Sonication enhanced kinetics of metabolic reactions with rise in substrate affinity of enzymes (reduced saturation constants) and greater resistance to substrate inhibition. Flow cytometry analysis of cells exposed to sonication revealed high cell viability with no adverse effect on physiology.

This study reports synthesis of biodegradable poly(3-hydroxybutyrate) (PHB) polymer from two invasive weeds, viz. P. hysterophorus and E. crassipes. The pentose and hexose-rich hydrolyzates obtained from acid pretreatment and enzymatic hydrolysis of two biomasses were separately fermented using Ralstonia eutropha MTCC 8320 sp. PHB was extracted using sonication and was characterized using FTIR, 1H and 13C NMR and XRD. PHB content of dry cell mass was 8.1-21.6% w/w, and the PHB yield was 6.85×10-3-36.41×10-3% w/w raw biomass. Thermal properties of PHB were determined by TGA, DTG and DSC analysis. PHB obtained from pentose-hydrolyzate had glass transition temperatures of 6°-9°C, while PHB from hexose-rich hydrolyzate had maximum thermal degradation temperatures of 370°-389°C. These thermal properties were comparable to the properties of commercial PHB. Probable causes leading to differences in thermal properties of pentose and hexose-derived PHB are: extent of crystallinity and presence of impurity in the polymer matrix.

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.

This study has assessed four invasive weeds, viz. Saccharum spontaneum (SS), Mikania micrantha (MM), Lantana camara (LC) and Eichhornia crassipes (EC) for enzymatic hydrolysis prior to bioalcohol fermentation. Enzymatic hydrolysis of pretreated biomasses of weeds has been conducted with mechanical agitation and sonication under constant (non-optimum) conditions. Profiles of total reducible sugar release have been fitted to HCH-1 model of enzymatic hydrolysis using Genetic Algorithm. Trends in parameters of this model reveal physical mechanism of ultrasound-induced enhancement of enzymatic hydrolysis. Sonication accelerates hydrolysis kinetics by ∼10-fold. This effect is contributed by several causes, attributed to intense micro-convection generated during sonication: (1) increase in reaction velocity, (2) increase in enzyme-substrate affinity, (3) reduction in product inhibition, and (4) enhancement of enzyme activity due to conformational changes in its secondary structure. Enhancement effect of sonication is revealed to be independent of conditions of enzymatic hydrolysis - whether optimum or non-optimum.

This study has attempted to gain physical insight into ultrasound-assisted enzymatic desulfurization using system comprising horseradish peroxidase enzyme and dibenzothiophene (DBT). Desulfurization pathway (comprising DBT-sulfoxide and DBT-sulfone as intermediates and 4-methoxy benzoic acid as final product) has been established with GC–MS analysis. Intrinsic fluorescence and circular dichroism spectra of ultrasound-treated enzyme reveal conformational changes in secondary structure (reduction in α-helix and β-conformations and increase in random coil content) leading to enhancement in activity. Concurrent analysis of desulfurization profiles, Arrhenius and thermodynamic parameters, and simulations of cavitation bubble dynamics reveal that strong micro-convection generated by sonication enhances enzyme activity and desulfurization kinetics. Parallel oxidation of DBT by radicals generated from transient cavitation gives further boost to desulfurization kinetics. However, random motion of enzyme molecules induced by shock waves reduces frequency factor and limits the ultrasonic enhancement of enzymatic desulfurization.