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n-Butyl levulinate (n-BL) has numerous applications in biofuel and green solvents. In this paper, we have reported mechanistic accounts of sonoenzymatic synthesis of n-BL using Novozym 435. Esterification parameters were optimized with statistical design of experiments. Application of 35 kHz sonication boosted n-BL yield from 70.9% to 92.22%. Mechanistic investigation using Ping-Pong Bi-Bi kinetics model and molecular docking simulations revealed interesting influence of sonication on esterification reaction. Exposure to sonication induced significant changes in the secondary structure of enzyme, as revealed in ATR-FTIR analysis. Sonication increased α-helix content of enzyme that increased enzyme activity by opening of flapping lid and widening the catalytic cavity. Sonication also caused unfolding of secondary structural motifs with rise in random coil content that favored formation of enzyme-ligand complexes. These effects enhanced reaction velocity and substrate affinity with reduction in inhibition and unfavorable dissociation of intermediate complexes, which ultimately enhanced n-BL yield.

Note: Please see pdf for full abstract with equations. This study investigated the in-situ chemical oxidation of the pharmaceutical compound carbamazepine (CBZ) using the combination of hydrodynamic cavitation (HC) and persulfate anion (S2O82-) and simultaneous activation of S2O82- anion by HC, UV–C irradiation and ZnO/ZnFe2O4 particles. Results show that the HC-based UV/persulfate / ZnO/ZnFe2O4 process effectively achieved 98.13 ± 1.03 % CBZ degradation. In binary oxidation system, viz. HC+UV, HC+S2O82-, HC+ZnO/ZnFe2O4, and UV+ZnO/ZnFe2O4, significantly higher 65.73% degradation was obtained using HC+S2O82- system. CBZ degradation profiles were analyzed using a mathematical kinetic model based on the reaction network. Experimental and simulated degradation profiles were matched with the initial [Fe2+]/[H2O2] ratio as a manipulation parameter. The closest match between experimental and simulated CBZ degradation profiles was obtained for the initial [Fe2+]/[H2O2] ratio = 10, which indicated enhanced leaching from the surface of ZnO/ZnFe2O4 particles. The results demonstrated that HC based persulfate oxidation system might prevent emergent pollutants like carbamazepine from polluting water.

This paper reports the degradation of the sulfadiazine (SDZ) drug with a hybrid advanced oxidation process (AOP) of heterogeneous α-Fe

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 has dealt with physical mechanism of ultrasound-assisted astaxanthin extraction from dry cell mass (DCM) of Phaffia rhodozyma. Preliminary experiments for screening of extraction solvent revealed highest extraction yield for acetone. Further experiments were performed using mixtures of DMSO and acetone with varying compositions as extraction solvent. The results were analyzed in concurrence with prediction of astaxanthin solubility using UNIFAC (Universal Quasi-Chemical Functional-Group Activity Coefficients) method and simulations of cavitation bubble dynamics. The highest astaxanthin yield of 1536 ± 3 μg/g DCM was obtained for solvent comprising 33% v/v DMSO + 67% v/v acetone. UNIFAC predicted astaxanthin solubility (1.57 g/L) was also highest for this composition, although the convection intensity predicted by bubble dynamics simulations was relatively low. Astaxanthin yield reduced with further increase in DMSO volume fraction in solvent. This result has pointed towards dominant role of solubility of solute rather than intensity of convection in extraction mixture in the extraction yield of astaxanthin.

This study has investigated ultrasound-assisted xylitol production through fermentation of dilute acid (pentose-rich) hydrolysate of sugarcane bagasse using free cells of Candida tropicalis. Sonication of fermentation mixture at optimum conditions was carried out in ultrasound bath (37 kHz and 10% duty cycle). Time profiles of substrate and product in control (mechanical shaking) and test (mechanical shaking + sonication) fermentations were fitted to kinetic model using Genetic Algorithm (GA) optimization. Max. xylitol yield of 0.56 g/g and 0.61 g/g of xylose was achieved in control and test fermentations, respectively. The biomass yield also increased marginally (∼17%) with sonication. However, kinetics of fermentation increased drastically (2.5×) with sonication with 2× rise in xylose uptake and utilization by the cells. With comparative analysis of kinetic parameters in control and test experiments, this result was attributed to enhanced permeability of cell membrane that allowed faster diffusion of nutrients, substrates and products across cell membrane, higher enzyme-substrate affinity, dilution of toxic components and reduced inhibition of intracellular enzymes by substrate.

This study has attempted to gain mechanistic insight into ultrasound assisted pretreatment of landfill leachate (prior to anaerobic digestion) by coupling experimental results with simulations of cavitation bubble dynamics. Essentially, individual roles of physical and chemical effects induced by sonication in the process have been identified. Changes in properties of leachate (such as sCOD, tCOD, NH3-N and acetate concentrations) subjected to sonication at different power levels have been studied. Sonication generated intense microconvection in system that caused faster disintegration and solubilization of biosolids. However, for high power input, where transient cavitation occurred in solution, degradation of organic matter by oxidizing radicals generated by cavitation bubbles occurred that reduced sCOD value resulting in low biogas yield in anaerobic digestion. Sonication at low to moderate power input, where stable cavitation prevailed, caused disintegration and solubilization, but not degradation, of biosolids resulting in higher sCOD value and biogas yield.

The present study has addressed carbamazepine (CBZ) degradation by hybrid advanced oxidation system of hydrodynamic cavitation (HC) assisted UV/persulfate with composite ZnO/ZnFe2O4 particles. This hybrid system is comprised of several parallel pathways for generation of both OH and SO 4 ∙ - radicals. 98.13 ± 1.03% CBZ degradation was obtained at optimum operational conditions: inlet pressure = 9 atm, pH = 4, initial concentration of CBZ = 15 mg/L, UV power = 18 W, Na2S2O8 = 500 mg/L, ZnO/ZnFe2O4 = 500 mg/L. HC alone resulted in 7.70% degradation of CBZ, while the binary HC + Na2S2O8 system resulted in markedly high degradation of 65.73%. Composite ZnO/ZnFe2O4 particles had dual characteristics, viz. photocatalytic activity and a source of Fe2+/Fe3+ ions released through surface leaching. Relative contributions of OH and SO 4 ∙ - radicals to CBZ degradation were identified through permutation-combination of different oxidation systems. Thermodynamic and kinetic behaviors of reactions of CBZ with OH and SO 4 ∙ - radicals were analyzed using density functional theory (DFT) at B3LYP/6-31 g(d) level. Single electron transfer (SET) between CBZ and SO 4 ∙ - was the primary (and thermodynamically favorable) reaction pathway in initiation of degradation. Degradation intermediates revealed ionization of CBZ through SET before hydroxylation and oxidation – which was corroboration of DFT simulations.

This paper has investigated the mechanistic issues of ultrasound-assisted transesterification process using solid Cu 2 O catalyst and mixed feedstock of non-edible oils. The optimum conditions for transesterification have been determined using statistical experimental design in packed bed catalytic reactor. The kinetic constants of different steps of transesterification process have been determined using kinetic model based on Eley-Rideal mechanism coupled to time profiles of reactants and products of transesterification in batch slurry reactors. The batch experiments have been performed at optimum conditions predicted by statistical experimental design: alcohol/oil molar ratio = 10.6, temperature = 62.5 °C, catalyst concentration = 7.25 wt% oil. It is revealed that adsorption of methanol is the slowest and rate determining step of transesterification process. Sonication enhanced the kinetics of reaction steps of transesterification process, but its effect on methanol adsorption on Cu 2 O catalyst was adverse. The activation energy of overall transesterification process was 90.14 kJ/mol; while, the sum total of activation energies of the three reaction steps of triglyceride conversion was 40.98 kJ/mol. These results essentially point to strong mass transfer influence on Cu 2 O-catalyzed transesterification process, even in presence of sonication. The adsorptive mass transfer of methanol to catalyst sites is not enhanced by microturbulence generated by sonication. Two probable causes leading to this effect are: discrete and intermittent nature of acoustic (or shock) waves generated by the transient cavitation, and secondly, the high temperature of reaction that offsets the methanol adsorption on catalyst websites.

This study presents comparative assessment of four cavitation devices (3 venturis and an orifice) in terms of cavitational yield. A 4-fold approach was adopted for assessment, viz. CFD simulations of cavitating flow, simulations of individual cavitation bubble dynamics, high speed photographs of cavitating flow and model reaction of potassium iodide oxidation. Influence of design parameters of cavitation devices on nature of cavitation produced in the flow was studied. Number density of cavitation bubbles in the flow and interactions among bubbles had critical influence on cavitation yield. Orifice gave the highest cavitational yield per unit energy dissipation in flow (despite lower working inlet pressure) due to low density of cavitation bubbles in flow. On contrary, occurrence of large cavitation bubble clouds in venturi flow had adverse effect on cavitational yield due to high interactions among cavitation bubbles resulting in inter-bubble coalescence and recombination of oxidizing radicals generated from cavitation bubbles. This article is protected by copyright. All rights reserved.

Sonication is known to enhance crystallization of lactose from aqueous solutions. This study has attempted to reveal the mechanistic features of antisolvent crystallization of lactose monohydrate from aqueous solutions. Experiments were conducted in three protocols, viz. mechanical stirring, mechanical stirring with sonication and sonication at elevated static pressure. Mechanical stirring provided macroconvection while sonication induced microconvection in the system. Other experimental parameters were initial lactose concentration and rate of antisolvent (ethanol) addition. Kinetic parameters of crystallization were coupled with simulations of bubble dynamics. The growth rate of crystals, rate of nucleation, average size of crystal crop and total lactose yield in different protocols were related to nature of convection in the medium. Macroconvection assisted nucleation but could not give high growth rate. Microconvection comprised of microstreaming due to ultrasound and acoustic (or shock) waves due to transient cavitation. Sonication at atmospheric static pressure enhanced growth rate but reduced nucleation. However, with elimination of cavitation at elevated static pressure, sonication enhanced both nucleation and growth rate resulting in almost complete lactose recovery.

Microalgae constitute relatively novel source of lipids for biodiesel production. The economy of this process can be enhanced by the recovery of β-carotenes present in the microalgal cells. The present study has addressed matter of enhancement of lipids and β-carotene production by microalgal species of Tetradesmus obliquus SGM19 with the application of sonication. As first step, the growth cycle of Tetradesmus obliquus SGM19 was optimized using statistical experimental design. Optimum parameters influencing microalgal growth were: Sodium nitrate = 1.5 g/L, ethylene diamine tetraacetic acid = 0.001 g/L, temperature = 28.5 °C, pH = 7.5, light intensity = 5120 lux, β-carotene yield = 0.67 mg/g DCW. Application of 33 kHz and 1.4 bar ultrasound at 10% duty cycle was revealed to enhance the lipid and β-carotene yields by 34.5% and 31.5%, respectively. Kinetic analysis of substrate and product profiles in control and test experiments revealed both lipid and β-carotene to be growth-associated products. The intracellular NAD(H) content during late log phase was monitored in control and test experiments as a measure of relative kinetics of intracellular metabolism. Consistently higher NAD(H) concentrations were observed for test experiments; indicating faster metabolism. Finally, the viability of ultrasound-exposed microalgal cells (assessed with flow cytometry) was >80%.

Polycyclic aromatic hydrocarbons like phenanthrene and pyrene are found ubiquitously in terrestrial and aquatic ecosystems. This study has attempted to investigate mechanistic features of simultaneous degradation of phenanthrene and pyrene by the yeast Candida tropicalis. Batch experiments comprising various combinations of initial phenanthrene and pyrene concentrations have been analyzed vis-a-vis kinetic model for cell growth that takes into account self- and cross-inhibition of both substrates. The values of interaction parameters of inhibition revealed strong competitive cross-inhibition between two substrates, due to which biomass yield with dual substrates was reduced significantly. Inhibition induced by pyrene on cell growth was higher than phenanthrene. GC-MS analysis of intermediate metabolites revealed two parallel pathways, first triggered by intracellular cytochrome P450 monooxygenase enzyme, and second initiated by dioxygenase enzymes. The former pathway yielded sulfate conjugate and dihydrodiols, while the latter resulted in acids and aldehydes that enters the TCA cycle.

This study has addressed ultrasound-assisted sulfadiazine (SDZ) degradation in heterogeneous Fenton-persulfate system and has also attempted to reveal mechanistic features. The Fenton reagent (Fe2+) was added in the form of yolk-shell nanoparticles Fe3O4@hollow@mSiO2. A kinetic model for SDZ degradation was formulated using reactions of Fenton-persulfate system. Concurrent analysis of experiments and simulations revealed faster leaching of Fe2+/Fe3+ ions from the metal core of Fe3O4@hollow@mSiO2 particles due to micro-convection generated by sonication, which enhanced SDZ degradation 4×. Inhibition effect of inorganic anions ( Cl - , NO 3 - , CO 3 2 - , SO 4 2 - ) on SDZ degradation was also studied with experiments and an extended kinetic model. CO 3 2 - and SO 4 2 - had the strongest inhibition effect due to both metal ion complexation and radical scavenging. Significant discrepancy between experimental and simulations results in the presence of anions were explained in terms of enhanced metal ion complexation and radical scavenging in the hollow core of yolk-shell particles.

This study has addressed the biodegradation of polycyclic aromatic hydrocarbon, phenanthrene using Candida tropicalis. Optimization using central composite statistical design yielded optimum experimental parameters as: pH = 6.2, temperature = 33.4 °C, mechanical shaking = 190 rpm and % inoculum = 9.26% v/v. Sonication of biodegradation mixture at 33 kHz and 10% duty cycle in log phase (12 h per day for 4 days) resulted in a 25% enhancement in phenanthrene removal. Profiles of specific growth rate (µ) and specific degradation rate (q) versus initial substrate concentration were fitted to Haldane substrate inhibition model. Both µ and q showed maxima for initial concentration of 100 mg L−1. Kinetic analysis of degradation profiles showed higher biomass yield coefficient and smaller decay coefficient in presence of sonication. Expression of total intracellular proteins in control and test experiments were analyzed using SDS–PAGE. This analysis revealed overexpression of enzyme catechol 2,3-dioxygenase (in meta route metabolism) during sonication which is involved in ring cleavage of phenanthrene. Evaluation of cell viability after sonication by flow cytometry analysis revealed > 80% live cells. These effects are attributed to enhanced cellular transport induced by intense microturbulence generated by sonication.

Sulfadiazine (SDZ) is a prominent antibiotic pollutant that appears in wastewater discharges from domestic, agricultural and pharmaceutical sectors. In this paper, we have reported studies in SDZ degradation using a novel hybrid AOP that coupled hydrodynamic cavitation with heterogeneous Fenton and persulfate. Two solid Fenton catalysts (α-Fe2O3 and Fe3O4) in the form of nanoparticles were synthesized. The composition of reaction mixture was optimized using statistical techniques. Effect of four operating parameters, viz. (1) SDZ initial concentration, (2) inlet pressure of cavitating flow, (3) pH and (4) type of heterogeneous Fenton catalyst (at optimum loading), on SDZ degradation was studied. A kinetic model for SDZ degradation was proposed based on homogeneous Fenton/persulfate system, and experimental degradation profiles were analyzed vis-a-vis simulated profiles. The highest degradation of SDZ (81%) was obtained for SDZ initial concn. = 20 ppm, pH = 4, inlet pressure = 10 atm, Na2S2O8 = 348.5 mg/L, H2O2 = 0.95 mL/L and α-Fe2O3 catalyst (181.8 mg/L). Kinetic model analysis showed best match between experimental and simulated profiles for [Fe2+]/[H2O2] initial ratio = 4. This indicated efficient catalytic activity of α-Fe2O3 nanoparticles – close to that of homogeneous catalyst. This is a consequence of high rate of mass transfer at surface of α-Fe2O3 particles due to intense turbulence and shear generated in cavitating flow in hydrodynamic cavitation reactor.

This study investigates ultrasonic enhancement of xylitol production from sugarcane bagasse using C. tropicalis MTCC 184 immobilized on PU foam. Initial xylitol yield of 0.53 g/g xylose improved to 0.65 g/g of xylose (in 36 h fermentation) after optimization of medium and fermentation parameters. Optimum values of experimental parameters for maximum xylitol were: yeast extract = 5.78 g/L, (NH4)2SO4 = 3.22 g/L, KH2PO4 = 0.58 g/L, MgSO4·7H2O = 0.57 g/L and temperature = 29.3 °C, initial pH = 6.2, agitation rate = 151 rpm and initial xylose concentration = 20.9 g/L. Application of 37 kHz sonication @10% duty cycle during fermentation at optimum conditions resulted in marked intensification of fermentation kinetics. Xylitol yield of 0.66 g/g of xylose has been obtained in ultrasound-assisted fermentation in just 15 h. Fitting of time profiles of substrates and products to kinetic model has highlighted actual physical mechanisms underlying 2-fold faster kinetics induced by sonication.

This paper reports mechanistic studies in ultrasound-assisted riboflavin production by wild strain of D. hansenii var. hansenii. Statistical optimization of fermentation resulted in riboflavin yield of 1.8 mg/g DCW. Supplementation of medium with glycine, Fe3+, cobalt and zinc further enhanced yield to 4.1 mg/g DCW. Intensification of fermentation by sonication (at 10% duty cycle) in four intervals of 12 h each (in total log phase of 48 h) was attempted. Sonication in final 12 h of log phase was most effective with the highest yield of 20 mg/g DCW. Kinetic analysis of the ultrasound-assisted fermentation revealed higher maximum specific growth rate of cells (0.30 h−1) with reduced Monod constant (5.67 g/L), indicating faster cell transport and higher substrate affinity. SDS-PAGE analysis of proteins involved in riboflavin metabolism showed overexpression of all proteins in ultrasound-assisted fermentation, which enhanced the metabolism. These results are attributed to intense microturbulence generated by sonication.