Volume 67, Issue 9

The highest yields of biosurfactants were obtained by: (i) Pseudozyma antarctica (107.2 g L−1) cultivated in a medium containing post-refining waste; (ii) Pseudozyma aphidis (77.7 g L−1); and (iii) Starmerella bombicola (93.8 g L−1) both cultivated in a medium with soapstock; (iv)Pichia jadinii (67.3 g L−1) cultivated in a medium supplemented with waste frying oil. It was found that the biosurfactant synthesis yield increased in all strains when the cell surface hydrophobicity reached 70–80 %, enabling the microbial cells to make good contact with hydrophobic substrates. The lowest surface tension of the post-cultivation medium was from 32.0 mN m−1 to 37.8 mN m−1. However, this parameter (which was also determined by a drop collapse assay) was of limited use in monitoring biosurfactant synthesis in this study. The crude glycerol was not a good substrate for biosurfactant synthesis although, in the case of P. aphidis, 67.4 g L−1 of biosurfactants were obtained after cultivation in the medium supplemented with glycerol fraction (GF2). In a low-cost medium containing soapstock and whey permeate or molasses, about 90 g L−1 of mannosylerythritol lipids were synthesised by P. aphidis and approximately 40 g L−1 by P. antarctica.

Kinetics of the reaction of CO2 and ethylethanolamine (EMEA) in aqueous solutions has been studied using the stopped-flow technique with conductivity detection. Measurements were performed at 288 K, 293 K, 298 K, and 303 K. Amine concentration ranged from 10 mol m−3 to 37.5 mol m−3. The termolecular mechanism was applied to interpret the kinetic data. In this mechanism, carbamate formation occurs in a single-step reaction without the formation of a zwitterion intermediate. An original method of analyzing the experimental data was proposed allowing the derivation of pseudo second order rate constants from the measured kinetic traces. Based on these values, the third order rate constants $$\left( {k_{H_2 O} } \right)$$ of the reaction of CO2, water, and EMEA were derived and correlated by the Arrhenius equation.

This work studies the influence of the alkali pre-treatment of Sorghum Moench — a representative of energy crops used in biogas production. Solutions containing various concentrations of sodium hydroxide were used to achieve the highest degradation of lignocellulosic structures. The results obtained after chemical pre-treatment indicate that the use of NaOH leads to the removal of almost all lignin (over 99 % in the case of 5 mass % NaOH) from the biomass, which is a prerequisite for efficient anaerobic digestion. Several parameters, such as chemical oxygen demand, total organic carbon, total phenolic content, volatile fatty acids, and general nitrogen were determined in the hydrolysates thus obtained in order to define the most favourable conditions. The best results were obtained for the Sorghum treated with 5 mass % NaOH at 121°C for 30 min The hydrolysate thus achieved consisted of high total phenolic compounds concentration (ca. 4.7 g L−1) and chemical oxygen demand value (ca. 45 g L−1). Although single alkali hydrolysis causes total degradation of glucose, a combined chemical and enzymatic pre-treatment of Sorghum leads to the release of large amounts of this monosaccharide into the supernatant. This indicates that alkali pre-treatment does not lead to complete cellulose destruction. The high degradation of lignin structure in the first step of the pre-treatment rendered the remainder of the biomass available for enzymatic action. A comparison of the efficiency of biogas production from untreated Sorghum and Sorghum treated with the use of NaOH and enzymes shows that chemical hydrolysis improves the anaerobic digestion effectiveness and the combined pre-treatment could have great potential for methane generation.

This paper presents a kinetic analysis of the biodegradation of organic pollutants in a batch bioreactor and investigates the kinetic properties of activated sludge using different mathematical models. The treatment was conducted for different initial concentrations of leachate from 500 mg dm−3 to 5000 mg dm−3 and initial concentrations of activated sludge from 1.84 g dm−3 to 6.62 g dm−3 over 48 h. Four different kinetic models were applied to the data. The kinetic analysis was performed with the traditional Monod model, the modified Monod model with endogenous metabolism, the Haldane model, and the Haldane model extended to include endogenous metabolic consumption and known as the Endo-Haldane model. Kinetic parameters for each model were determined using differential analysis and the Nelder-Mead method of non-linear regression. The lowest deviations and very good matches with the experimental data were achieved using the Endo-Haldane model. This indicated that this model best described the process of biodegradation of leachate from tobacco waste composting. This is due to this model incorporating the effects both of inhibition and endogenous metabolism.

The paper addresses an approach to robust stabilization of chemical continuous stirred tank reactors. State feedback was used for the stabilization and the feedback controller was designed using the robust model-based predictive control algorithm in which the symmetric constraints on input and output variables are taken into account. The known strategy was modified by adding integral action to the controller. Parameters of robust feedback controllers with and without integral action were found as solutions of a constrained optimization problem solved on the infinite prediction horizon. The possibility to stabilize chemical reactors with uncertainty using the robust model-based predictive control has been verified by simulations and compared with the optimal linear quadratic control and the model-based predictive control. The obtained results confirm that the robust model-based predictive control provides better results than other approaches.

The decomposition of meta-phenylphenol (m-PP) and para-phenylphenol (p-PP) in a heterogeneous gas-liquid system using ozone was investigated. The influence of different reaction parameters such as ozone and PP isomers concentration as well as pH and temperature of the reaction mixture on the PP decay rate was determined. The second-order rate constants for the direct reaction of molecular ozone, determined in a homogeneous system, were (5.85 ± 0.35) × 102 M−1 s−1 and (8.90 ± 0.33) × 102 M−1 s−1 for m-PP and p-PP, respectively. The rate constants for the reaction of m-PP and p-PP with ozone increased with increasing pH. The reaction rate constants with ozone were found to be (1.75 ± 0.02) × 109 M−1 s−1 and (1.86 ± 0.02) × 109 M−1 s−1 for m-PP and p-PP anions, respectively.

Production of bioproducts is associated with the generation of considerable amounts of effluents from the bioreactors used. Application of the nanofiltration process was proposed for the treatment of these effluents in order to separate both inorganic and organic solutes. Composition of the fermentation broth precludes the utilization of traditional spiral-wound modules (high turbidity) for the solutes separation in the NF process. The tubular module with AFC30 membranes applied in this work enables such a possibility. Transport and separation characteristics of the NF membrane were determined for the reference solutions containing components present in the effluents generated during the fermentation of glycerol with the use of bacteria.

The gaseous byproducts produced during the composting of different kinds of solid waste are carbon dioxide (CO2) and ammonia (NH3). CO2 is a greenhouse gas and NH3 is a toxic and corrosive air pollutant so, they must be removed from exhaust gases prior to release into the atmosphere. The purpose of this work was to investigate the sorption of CO2 and NH3, evolved during composting, on zeolite and potting soil. The composting of the mixture of grape waste (GW) and tobacco waste (TW) in the mass ratio GW: TW = 55: 45 (dry mass basis) was carried out under forced aeration (0.645 L min−1 kg−1) in a column reactor (10 L) under adiabatic conditions over 21 days. Adsorption of the gases evolved was carried out in the fixed-bed column reactor (0.166 L). The most important physical-chemical characteristics of the composting mass and adsorbents and the evolved CO2 and NH3 were closely monitored. The highest CO2 and NH3 concentrations were measured at the thermophilic stage and the cooling stage of composting, respectively. The results showed that zeolite and potting soil were good adsorbents for the sorption of CO2 and NH3. The zeolite adsorbed 31 % of the evolved CO2 and the entire concentration of ammonia, whilst the potting soil adsorbed 3 % of CO2 and 49 % of NH3 from the exhaust gases.

The main objective of this work was to verify the mixed solvent electrolyte (MSE) thermodynamic model for the prediction of the liquid-solid equilibrium in the soda system. The full quaternary system NaCl-NaHCO3-Na2CO3-H2O and its three subsystems were considered. Validation of the thermodynamic model was based on experimental data from literature. Phase diagrams for the soda system are plotted for isotherms of 45°C. Good agreement of the MSE results with those from experiments was found at 45°C. Similar phase diagrams for other temperature levels can be constructed based on the validated MSE model.

The main purpose of the present paper was to apply the Laser Doppler Anemometry (LDA) technique to measure turbulent liquid flow in a Kenics static mixer. The LDA set-up was a one-channel backscatter system with argon-ion laser. Measurements in the static mixer were carried out for three values of the Reynolds number: 5000, 10000, and 18000. Water was used as the process liquid. Values of the axial and tangential components of the local, mean, and root mean square velocities were measured inside the static mixer. It was observed that the shape of the velocity profile depends strongly on the Reynolds number, Re, as well as on the axial, h, and radial, α, position of the measurement point. Strong dependence of the velocity fluctuations on the Reynolds number was found in the investigated range of Re and the measurement point position. Furthermore, one-dimensional energy spectra of the velocity fluctuations were also obtained by means of the Fast Fourier Transform. Fluctuation spectra of the axial and tangential velocities provided information about the energy density of velocity fluctuations in the observed range of Reynolds numbers. A study of the energy spectra led to the conclusion that the energy density increases with the increasing radial distance from the mixer walls at constant values of h, Re, and α. Minor variations in the mean value of the energy density, E, were observed together with variations of the measurement point angular position, α. In addition, it was observed that an increase of the Reynolds number causes significant increase of the power spectral density.

The separation of diluted ethanol solutions and fermentation broths by membrane distillation was investigated. The influence of stream flow-rate on the ethanol flux was studied. An evaluation of the process conditions on the separation degree of ethanol was performed with the application of hydrophobic capillary membranes composed of polypropylene. By removing the alcohol via membrane distillation, it is possible to achieve a higher content of ethanol in the permeate than that in the broth. The enrichment coefficient amounted to 4–6.5, and decreased with an increase of the ethanol concentration in the broth. It was found that the flow-rate affects the value of the enrichment coefficient. A positive influence of carbon dioxide on the ethanol transport through the capillary membrane was observed. The evolution of CO2 bubbles from the broth increases the stream turbulence, probably enhancing the alcohol concentration in the layer adjacent to the membrane surface.

Microwave radiation was used in the acquisition of aluminium ammonium calcium phosphates. The substrates such as CaCO3, H3PO4, aqueous ammonia were reagent grade, whereas Al(OH)3 was prepared afresh. The influence of process parameters (pH 6 ± 2, molar ratios of Al3+: Ca2+: PO43− in the substrates, respectively 0.31: 0.62: 1; 0.5: 0.5: 1; 0.72: 0.36: 1) on the phase composition and the product properties was determined. Statistical software STATISTICA 10 was used for planning and evaluation of the experiments. The process parameters making it possible to acquire the material with the anticipated physicochemical properties were determined based on statistical evaluation of the planned research by the plan fractional factorial design at three levels 3(k−p). The phase composition of the samples was studied using XRD analysis. The specific surface area was calculated using the BET method and the particle size was determined by LSM. Materials with a molar ratio of Al3+: Ca2+ and Al3+: NH4+ in the range of 0.07–0.76 and 0.75–3.4, respectively, with an absorption oil number of 36–56 g per 100 g, S BET within 8.2–73 m2 g−1, and particle size in the range of 156–252 nm were obtained.

The influence of pre-reactor and reactor temperatures on the conversion of 1,3-dichloropropan-2-ol and the selectivity of its transformation to epichlorohydrin in continuous dehydrochlorination for two modes of the reaction product collection was studied. The dehydrochlorination process and mechanism of diglycidyl ether formation are described.

Plasmonic nanoparticles such as those of gold or silver have been recently investigated as a possible way to improve light absorption in thin film solar cells. Here, a simple method for the preparation of spherical plasmonic gold nanoparticles in the form of a colloidal solution is presented. The nanoparticle diameter is controlled in the range from several nm to tens of nm depending on the synthesis parameters with the size dispersion down to 14 %. The synthesis is based on thermal decomposition and reduction of the chloroauric acid in the presence of a stabilizing capping agent (surfactant) that is very slowly injected into the hot solvent. The surfactant prevents uncontrolled nanoparticle aggregation during the growth process. The nanoparticle size and shape depend on the type of the stabilizing agent. Surfactants with different lengths of the hydrocarbon chains such as Z-octa-9-decenylamine (oleylamine) with AgNO3 and polyvinylpyrrolidone with AgNO3 were used for the steric stabilization. Hydrodynamic diameter of the gold nanoparticles in the colloidal solution was determined by dynamic light scattering while the size of the nanoparticle metallic core was found by small-angle X-ray scattering. The UV-VIS-NIR spectrophotometer measurements revealed a plasmon resonance absorption in the 500–600 nm range. Self-assembled nanoparticle arrays on a silicon substrate were prepared by drop casting followed by spontaneous evaporation of the solvent and by a modified Langmuir-Blodgett deposition. The degree of perfection of the self-assembled arrays was analyzed by scanning electron microscopy and grazing-incidence small-angle X-ray scattering. Homogeneous close-packed hexagonal ordering of the nanoparticles stretching over large areas was evidenced. These results document the viability of the proposed nanoparticle synthesis for the preparation of high-quality plasmonic templates for thin film solar cells with enhanced power conversion efficiency, surface enhanced Raman scattering, and other applications.

Three new compounds based on carbazole planar skeleton were synthesised. Among them there is a new ligand and a potential DNA intercalator which contains a benzothiazolium moiety connected to the carbazole ring by a vinyl bridge. The absorption and emission spectral properties of this new ligand have been studied by spectroscopic methods.

This work deals with catalytic activity of tetrabutylammonium decatungstate(VI) in the oxidation of selected alcohols with hydrogen peroxide as an oxidant using 1,2-dichloroethane/water or acetonitrile/water as a solvent system. Different forms of heating were compared. The highest conversions of substrates were achieved in the two phase system acetonitrile/water using microwave irradiation combined with elevated pressure. Finally, optimum parameters for these reactions in a microwave pressurised reactor were established and discussed.

Results of numerical calculations of dynamic shape and wall correction factors for the flow of a Newtonian fluid over a vertically oriented cylindrical particle in a cylindrical tube are reported. Mathematical model of the flow was solved using the finite element method by means of the COMSOL Multiphysics software. Dependences of the shape factor on the cylinder aspect ratio and of the wall correction factor, F W, on the ratio of the cylindrical particle diameter to the tube diameter, and on the aspect ratio were obtained. Numerical dependences were approximated by simple relationships suitable for dynamic shape and wall correction factors prediction.

In this work we present a simple and non-invasive approach to the preparation of semi-conducting single-walled carbon nanotubes (SWCNTs) through selective destruction of the metallic counterparts present in the starting material. Most separation techniques require chemical treatment, the application of ultrasound, or the addition of auxiliary molecules, which lead to the introduction of defects and impurities. In this contribution, laser ablation SWCNTs were selectively oxidised via long-term heating leading to the enrichment of semi-conductive nanotubes. Spectroscopic analysis demonstrates that the selective character of oxidation occurs only in the optimal temperature range, determined by thermo-gravimetric analysis. By tuning the process parameters, one can obtain a sample exhibiting different purity (up to 95 % of semi-conducting nanotubes) and separation efficiency. The samples’ quality and yield of separation were determined by UV-VIS-NIR spectroscopy, Raman spectroscopy, and TG analysis. The approach presented is readily scaleable.