Locally available agroresidues as potential sorbents: modelling, column studies and scale-up

Sawdust, cotton stalk and groundnut shell were used for removal of methylene blue from aqueous solution using batch sorption. Effect of initial dye concentration, temperature, and particle size of sorbents on methylene blue removal was investigated. Sorption capacity increases with rise in initial dye concentration and temperature. Impact of particle size on sorption of methylene blue was investigated and indicated that removal of dye increases with decrease in particle size of sorbents. Maximum sorption for sawdust, cotton stalks and groundnut shell were 9.22 mg g−1, 8.37 mg g−1 and 8.20 mg g−1 respectively; at 60 °C and 100 ppm initial dye concentration. Sorption isotherms were analyzed using fundamental Freundlich isotherm. Subsequently, sips isotherm model was employed for better fitting. Kinetic study shows that, biosorption process is pseudo-second-order in nature. During the course of this study, adsorption dynamics revealed that film diffusion was key step for biosorption. In addition, thermodynamics of sorption was studied; and it was found that Gibbs free energy (∆G°) decreases with increase in temperature. Sawdust was found to be best among all the sorbents. Therefore, column studies and breakthrough curve modelling were performed using sawdust. Furthermore, it was estimated that a scaled-up column using sawdust can treat 6672 L of wastewater in 24 h with 80% efficiency.

Solutal Convection in Layered Sorbing Porous Media

<p>We study convective instability in the vertically layered porous media saturated with mixture. The mixture consists of a carrier fluid and solid nanoparticles. The nanoparticles are considered as solute within the continuous approach. The porous media are two horizontal sublayers with different permeabilities. The solute concentration is maximal near the upper boundary and is zero near the lower boundary of the superposed sublayers. Thus, one has suitable conditions for the onset of solutal convection in the gravitational field.</p><p>The porous sublayers are reactive media, which can absorb nanoparticles. The mixture transport here is accompanied by immobilization. It is described by the mobile/immobile media model. The mobile phase is carried by fluid flow, while the immobile phase is absorbed by porous matrix. The linear kinetic equation for the mixture redistribution between the phases is applied. The Boussinesq approximation is used in the equations for convection in each of the sublayers. Numerical simulation is performed by the shooting method.</p><p>We apply a linear stability theory to find the threshold Rayleigh-Darcy number for the onset of solutal convection. This similarity criterion is determined through the average permeability and porosity of uncontaminated porous sublayers. For the first time, we introduce a solutal pore shrinkage coefficient, which is analogous to the thermal expansion coefficient for thermal natural convection. This coefficient shows that porosity decreases as the concentration of immobile phase grows in the presence of sorption. Particles in this case join the surface of pores and shrink the void space.</p><p>Firstly, we find the permeability ratios for bimodal marginal stability curves in the uncontaminated sublayers. Here, the sublayer permeabilities differ by approximately 100 times. The bimodal curves demonstrate the competition between two convective instabilities. One of them is for the local convective rolls that generate within the more permeable layer and the other is for the large-scale rolls penetrating both layers. The rolls are similar to thermal natural convection in the multi-layered porous media studied by McKibbin and O'Sullivan (1980). For sorbing porous media, the type of convective rolls strongly depends on the solutal pore shrinkage coefficient. Even a small change in its value can produce a large variation of flow streamlines from the convective rolls localized within the upper highly permeable sublayer to the rolls covering both the upper and lower sublayers. The observed sorption effect on the transition from local to large-scale convection is due to the fact that the permeability ratio depends on the solutal pore shrinkage coefficient. It is also found that sorption effect delays the onset of solutal convection.</p><p>The work was supported by the Russian Science Foundation (Grant No. 20-11-20125).</p>

Identification, Interaction and Detection of Microplastics on Fish Scales (Lutjanus Gibbus)

Background: Microplastics are found to be one of the major emerging contaminants in the environment. Various environmental occurrences cause the macro plastics to degrade slowly into microplastics. Microplastics present in the water bodies may enter into the fish’s body through ingestion of food and also get adsorbed onto the surface of their gills or skin. Objective: Microplastics of polyethylene were chosen to investigate its sorption capacity on fish scales. Dispersion of polyethylene microplastics was studied by using Total dissolved solids meter. Using this dispersion, the sorption effect was studied and it revealed that the microplastics has the sorption ability on the fish scales. Method: Polyethylene microplastics were chosen to investigate its sorption capacity on fish scales of Lutjanus gibbus. The sorption effect of microplastics on fish scales were performed by using polyethylene microplastics obtained by bath sonication and the concentration was studied using Total dissolved solids meter. Using polyethylene microplastics dispersion, the sorption effect was carried out on the scales of Lutjanus gibbus for ten days at 8 oC. Sorption of microplastics on fish scales were characterized by FE-SEM, FT-IR, and Raman spectroscopy. Results: Polymer sorption was confirmed by using optical microscopy and FE-SEM. FT-IR and Raman spectroscopy confirmed the existence of polyethylene microplastics on the fish scale. Moreover, polyethylene microplastics sorption studies were also studied in different pH, various concentrations of NaCl and at different time intervals. Conclusions: We have synthesized microplastics from the bulk polyethylene by NaCl solution. This study confirmed the successful sorption of polyethylene microplastics on the fish scale. Our study revealed that marine water may be a suitable medium to facilitate the polymer sorption on aquatic animals/organisms.

Effect of Gas Adsorption on the Application of the Pulse-Decay Technique

The permeability of coal is an indispensable parameter for predicting the coalbed methane (CBM) and enhanced CBM (ECBM) production. Considering the low permeability characteristics of coal, the permeability is usually measured by the transient technique in the laboratory. Normally, it is assumed that the calculated permeability will not greatly vary if the pulse pressure applied in the experiment is small (less than 10% of pore pressure) and previous studies have not focused on the effect of the pulse pressure on the measurement permeability. However, for sorptive rock, such as coals and shales, the sorption effect may cause different measurement results under different pulse pressures. In this study, both nonadsorbing gas (helium) and adsorbing gas (carbon dioxide) were used to investigate the adsorption effect on the gas permeability of coal measurement with the pulse-decay technique. A series of experiments under different pore pressures and pulse pressures was performed, and the carbon dioxide permeability was calculated by both Cui et al.’s and Jones’ methods. The results show that the carbon dioxide permeability calculated by Jones’ method was underestimated because the adsorption effect was not considered. In addition, by comparing the helium and carbon dioxide permeabilities under different pulse pressures, we found that the carbon dioxide permeability of coal was more sensitive to the pulse pressure due to the adsorption effect. Thus, to obtain the accurate permeability of coal, the effect of adsorption should be considered when measuring the permeability of adsorptive media with adsorbing gas by the transient technique, and more effort is required to eliminate the effect of the pulse pressure on the measured permeability.

Interactions of Fe–N–S Co-Doped Porous Carbons with Bacteria: Sorption Effect and Enzyme-Like Properties

Carbon-based (nano)materials doped with transition metals, nitrogen and other heteroatoms are considered active heterogeneous catalysts in a wide range of chemical processes. Recently they have been scrutinized as artificial enzymes since they can catalyze proton-coupled electron transfer reactions vital for living organisms. Herein, interactions between Gram-positive and Gram-negative bacteria and either metal-free N and/or S doped or metal containing Fe–N–S co-doped porous carbons are studied. The Fe- and N-co-doped porous carbons (Fe–N–C) exhibit enhanced affinity toward bacteria as they show the highest adsorption capacity. Fe–N–C materials also show the strongest influence on the bacteria viability with visible toxic effect. Both types of bacteria studied reacted to the presence of Fe-doped carbons in a similar manner, showing a decrease in dehydrogenases activity in comparison to controls. The N-coordinated iron-doped carbons (Fe–N–C) may exhibit oxidase/peroxidase-like activity and activate O2 dissolved in the solution and/or oxygen-containing species released by the bacteria (e.g., H2O2) to yield highly bactericidal reactive oxygen species. As Fe/N/ and/or S-doped carbon materials efficiently adsorb bacteria exhibiting simultaneously antibacterial properties, they can be applied, inter alia, as microbiological filters with enhanced biofouling resistance.

Insights into Kinetics of Magnesium Removal by Titain Yellow Supported on Classic Thiourea-Formaldehyde Resin

<p>It was evaluated for the adsorption behavior and the underlying kinetics of magnesium sorption on Titian yellow (TY) supported on thiourea-formaldehyde resin (TF). The results of analyzing sorption behavior showed that the sorption environment had different effects on the sorption of Mg(II) ions. It could be found that pH had the best sorption effect on Mg(II) ions, The maximum adsorption capacity of Mg was 19.45 mg g⁻¹ when it was at initial pH = 10.5. Under the optimal conditions, the maximum sorption capacities of Mg(II) ions was 19.45 mg g⁻¹. Therefore, TF-TY was found to be a most efficient adsorbent for Mg(II) removal from water.</p>

Insights into Kinetics of Magnesium Removal by Titain Yellow Supported on Classic Thiourea-Formaldehyde Resin

<p>It was evaluated for the adsorption behavior and the underlying kinetics of magnesium sorption on Titian yellow (TY) supported on thiourea-formaldehyde resin (TF). The results of analyzing sorption behavior showed that the sorption environment had different effects on the sorption of Mg(II) ions. It could be found that pH had the best sorption effect on Mg(II) ions, The maximum adsorption capacity of Mg was 19.45 mg g⁻¹ when it was at initial pH = 10.5. Under the optimal conditions, the maximum sorption capacities of Mg(II) ions was 19.45 mg g⁻¹. Therefore, TF-TY was found to be a most efficient adsorbent for Mg(II) removal from water.</p>