Treatment of aqueous effluents of the leather industry by membrane processes

A multi-scale assessment of the impact of salinity on the desorption of chromate from hematite: Sea level rise implications

The solubility and transport of Cr(VI) is primarily controlled by adsorption-desorption reactions at the surfaces of soil minerals such as iron oxides. Environmental properties such as pH, ionic strength, and ion competition are expected to affect the mobility and fate of Cr(VI). Sea level rise (SLR), and consequent seawater intrusion, is creating a new biogeochemical soil environment at coastal margins, potentially impacting Cr(VI) retention at contaminated sites. We employed in-situ ATR-FTIR spectroscopy and DFT calculations to investigate at the molecular level the adsorption of Cr(VI) on the hematite surface and its desorption by sulfate, as a function of pH and ionic strength. We further used a batch experiment to assess Cr(VI) desorption at varying artificial seawater (ASW) concentrations. IR results demonstrate the complexity of Cr(VI) adsorption, showing a combination of monodentate inner-sphere complexation at high pH and dichromate outer-sphere (∼75%) at low pH. The Cr(VI)-complexes exhibited desorption induced by increasing pH values (58% of desorption) and sulfate competition (∼40% desorption). ASW desorbed ∼20% more Cr(VI), even at just 1% concentration. Our findings provide insight into Cr(VI)-adsorption complexation that controls the retention and remobilization of Cr(VI) on Fe-oxide minerals. The results point to an elevated risk of Cr(VI) mobilization in contaminated soils affected by SLR.

Synthesis of PVP-capped trimetallic nanoparticles and their efficient catalytic degradation of organic dyes

The study proposes a simple and efficient way to synthesize a heterogeneous catalyst that can be used for the degradation of organic dyes. A simple and fast chemical process was employed to synthesize Au: Ni: Co tri-metal nanohybrid structures, which were used as a catalyst to eliminate toxic organic dye contamination from wastewater in textile industries. The catalyst's performance was tested by degrading individual dyes as well as mixtures of dyes such as methylene blue (MB), methyl orange (MO), methyl red (MR), and Rose Bengal (RB) at various time intervals. The experimental results show the catalytic high degradation efficiency of different dyes achieving 72-90% rates in 29 s. Moreover, the material displayed excellent recycling stability, maintaining its degradation efficiency over four consecutive runs without any degradation in performance. Overall, the findings of the study suggest that these materials possess efficient catalytic properties, opening avenues toward their use in clean energy alternatives, environmental remediation, and other biological applications.

Microbial fuel cell: A green eco-friendly agent for tannery wastewater treatment and simultaneous bioelectricity/power generation

This review paper emphasised on the origin of hexavalent chromium toxicity in tannery wastewater and its remediation using novel Microbial Fuel Cell (MFC) technology, including electroactive bacteria, which are known as exoelectrogens, to simultaneously treat wastewater and its action in the production of bioenergy and the mechanism of Cr⁶⁺ reduction. Also, there are various parameters like electrode, pH, mode of operation, time of operation, and type of exchange membrane used for promising results shown in enhancing MFC production and remediation of Cr⁶⁺. Destructive anthropological activities, such as leather making and electroplating industries are key sources of hexavalent chromium contamination in aquatic repositories. When Cr⁶⁺ enters the food chain and enters the human body, it has the potential to cause cancer. MFC is a green innovation that generates energy economically through the reduction of toxic Cr⁶⁺ to less toxic Cr³⁺. The organic substrates utilized at the anode of MFC act as electrons (e^-) donors. This review also highlighted the utilization of cheap substrates to make MFCs more economically suitable and the energy production at minimum cost.

Template Method for Synthesizing Hierarchically Porous MIL-101(Cr) for Efficient Removal of Large Molecular Dye

As one of the most important prototypical chromium-based MOFs, MIL-101(Cr) is well-studied and widely employed in various scientific fields. However, due to its small capture window sizes and curved internal apertures, its application in large molecular removal is quite limited, and given its high stability and high synthetic temperature (>200 °C), it is difficult to achieve hierarchically porous MIL-101(Cr). In our study, hierarchically porous MIL-101(Cr) involving a high macro-/meso-/micropores ratio was designed and synthesized using acetic acid as an additive and silicon dioxide (SiO2) nanoparticles as a template. The optimal hierarchically porous MIL-101(Cr) (A-4) possessed a high specific surface area (2693 m2 g−1) and an abundant macro-/mesoporous structure with the addition of SiO2 of 200 mg. Compared with the control sample (A-0) with a less macro-/mesoporous structure, A-4 showed good adsorption properties for both coomassie brilliant blue R-250 (CBB, 82.1 mg g−1) and methylene blue (MB, 34.3 mg g−1) dyes, which were 1.36 times and 9.37 times higher than those of A-0. Moreover, A-4 also had good recyclability, and the removal rate of CBB was still higher than 85% after five cycles of adsorption.

Co3O4 Nanopetals Grown on the Porous CuO Network for the Photocatalytic Degradation

Designing a novel photocatalytic composite for the efficient degradation of organic dyes remains a serious challenge. Herein, the multi-layered Co₃O₄@NP-CuO photocatalyst with unique features, i.e., the self-supporting, hierarchical porous network as well as the construction of heterojunction between Co₃O₄ and CuO, are synthesized by dealloying-electrodeposition and subsequent thermal treatment techniques. It is found that the interwoven ultrathin Co₃O₄ nanopetals evenly grow on the nanoporous CuO network (Co₃O₄@NP-CuO). The three-dimensional (3D) hierarchical porous structure for the catalyst provides more surface area to act as active sites and facilitates the absorption of visible light in the photodegradation reaction. Compared with the commercial CuO and Co₃O₄ powders, the newly designed Co₃O₄@NP-CuO composite exhibits superior photodegradation performance for RhB. The enhanced performance is mainly due to the construction of heterojunction of Co₃O₄/CuO, greatly promoting the efficient carrier separation for photocatalysis. Furthermore, the possible photocatalytic mechanism is analyzed in detail. This work provides a promising strategy for the fabrication of a new controllable heterojunction to improve photocatalytic activity.

Nanofused Hierarchically Porous MIL-101(Cr) for Enhanced Methyl Orange Removal and Improved Catalytic Activity

Hierarchically porous MIL-101(Cr) (H-MIL-101(Cr)) with meso/macro-pores was directly prepared via nanofusion progress by using butyric acid as a modulating agent. In the methyl orange (MO) adsorption experiments, H-MIL-101(Cr) showed a high adsorption capability of 369.8 mg g⁻¹, which was 1.52-fold greater than that of pristine MIL-101(Cr) (P-MIL-101(Cr)). While in the oxidation reaction of indene and 1-dodecene tests, H-MIL-101(Cr) presented much higher catalytic efficiency, with turnover frequency (TOF) values of 0.7242 mmol g⁻¹ min⁻¹ and 0.1492 mmol g⁻¹ min⁻¹, respectively, which were 28% and 34% greater than that in the case of P-MIL-101(Cr). Thus, compared with P-MIL-101(Cr), H-MIL-101(Cr) exhibited better removal efficiency and higher levels of activity in the oxidation reactions of indene and 1-dodecene. The unique structure of H-MIL-101(Cr) also contributed to its superior performance in these processes.

Self-driven directional dehydration enabled eco-friendly manufacture of chrome-free leather

Manufacture of eco-friendly chrome-free leather is of great significance for realizing sustainable development of leather industry. Conventional tanning theory believes that it is impossible to convert raw hide to leather without the utilization of cross-linking agent (e.g., chrome salts) among collagen fibers in raw hide. Here, we developed a brand-new leather manufacture strategy that relied on the composite dehydration media enabled self-driven directional dehydration mechanism to accomplish chrome-free leather manufacture for the first time, rather than followed the classic cross-linking mechanism that has been obeyed for more than one century in leather industry. We demonstrated that the essence of leather making is to regulate the water content in raw hide rather than to form cross-linkage among collagen fibers. The composite dehydration media comprised of anhydrous ethanol and molecular sieves (3A activated zeolite powder) successfully guaranteed continuous self-driven directional dehydration of raw hide by establishing stable water concentration gradient between raw hide and ethanol, which significantly increased the dispersity of collagen fibers in raw hide (with the water content reduced from 56.07% to 5.20%), thus obtaining chrome-free leather that is more ecological than chrome-tanned leather due to the elimination of any tanning agent. The as-prepared chrome-free leather exhibited outstanding tear force (174.86 N), tensile strength (24.56 N mm−2), elongation at break (53.28%) and dry-thermal stability, superior to chrome-tanned leather. Notably, the used composite dehydration media was recyclable for chrome-free leather manufacture, therefore facilitating an environmentally benign leather manufacture process. Our investigations are expected to open up a new conceptual leather making strategy that is applicable for realizing substantial manufacture of eco-friendly leather.

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Vegetable wastes as a bio-additive for low-salt preservation of raw goat skin: An attempt to reduce salinity in leather manufacture

Preservation or curing of hides/skins is performed as the primary step of leather processing to conserve them from putrefaction. Normally preservation is carried out using common salt (NaCl), which is discharged in the soak liquor contributing to ~ 70%, of total dissolved solids (TDS) load of entire leather manufacturing. In an attempt to reduce the TDS and chlorides, phyto-based preservation using garlic peel (Allium sativum) and white onion peel (Allium cepa) was carried out. Different concentrations of salt in combination with garlic peel and white onion peel were applied on freshly flayed goat skins based on its green weight and compared to control (40% salt). Sensory evaluation of the preserved skin was done by assessing different parameters like hair slip, putrefaction and odour. Estimation of hydroxyproline (HP) release, moisture content and microbial load were carried out at regular intervals. Skins that remained in good condition for 14 days were further processed into leather and properties were examined which were found comparable to the conventionally cured skins. Hence, this cleaner curing technique helps in reducing the TDS and chlorides in the effluent, thus controlling the pollution caused by tanneries through sustainable leather processing.

Tannery wastewater treatment: conventional and promising processes, an updated 20-year review

Mismanagement of various wastes especially waste water produced by tanning processes has caused serious environmental problems and ultimately impaired human health. Constant efforts have been making to alleviate the pollution of tannery wastewater (TWW), yet terminal treatment still takes dominance. In this review, research on TWW treatment from 2000 to 2021 was summarized, and main methods such as coagulation and flocculation, adsorption, biological treatment, membrane filtration, advanced oxidation process were briefly discussed. More detailed introduction was given to the method of electrochemical treatment since it has excellent performance such as environmental friendliness and high efficiency, hence attracting more and more research attention in recent years. In view of the harsh physi-chemical conditions of TWW, integrated or combined treatment methods are accordingly recommended with better performance and multi-function, however comprehensive studies on optimization of methods combination and cost-effectiveness are needed. The certain issues that the residue Cr in treatment sludge and high salinity in effluent still remain were put forward in this work and potential solutions were provided. Moreover, this review proposed the perspective that realizing multi-function, recycling, and intensification should be the developing direction for future TWW treatment. This review is expected to provide a general guide for researchers who aspire to ameliorate TWW pollution problems and understand various methods utilized in this field.

Graphical abstract

Application of random forest for modeling batch and continuous fixed-bed removal of crystal violet from aqueous solutions using Gypsophila aretioides stem-based biosorbent

In this work, the Gypsophila aretioides (GYP-A) stem is used as a biosorbent to remove crystal violet (CV) by the static and dynamic systems from aqueous solutions; the biosorbent is interesting in green chemistry and, on the other hand, cheaper than activated carbon and does not have the limitation of industrialization. The effects of different operating parameters such as pH(3-9), biosorbent dosage(0.4-1.8 mg/L), and initial concentration of CV(100-250 mg/L) and time for the batch method and the bed height, inlet CV concentration(75-250 mg/L), and flow rate(3-8) on the breakthrough curves for the continuous method is investigated. The result of CV adsorption onto GYP-A using the batch method indicates that the model fits Freundlich > Temkin > Langmuir > R-D, and R² equal 0.9953, 0.9847, 0.9161, 0.7909 were obtained for isotherm model, respectively. A pseudo-second-order model (R² = 0.9995-0.9997) is recommended to describe the adsorption kinetics. The Thomas and Yoon-Nelson models were analyzed to study the adsorption kinetics. The random forest model shows an excellent ability to predict the parameters involved in the CV adsorption process with appropriate accuracy and useable for large data, robust against noise; it can be very effective in selecting important variables.

Enhanced Degradation of Rhodamine B by Metallic Organic Frameworks Based on NH2-MIL-125(Ti) under Visible Light

Samples of the bimetallic-based NH2-MIL-125(Ti) at a ratio of Mn+/Ti4+ is 0.15 (Mn+: Ni2+, Co2+ and Fe3+) were first synthesized using the solvothermal method. Their fundamental properties were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectra, scanning electron microscopy (SEM), N2 adsorption-desorption measurements, and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The as-acquired materials were used as high-efficiency heterogeneous photocatalysts to remove Rhodamine B (RhB) dye under visible light. The results verified that 82.4% of the RhB (3 × 10-5 M) was degraded within 120 min by 15% Fe/Ti-MOFs. Furthermore, in the purpose of degrading Rhodamine B (RhB), the rate constant for the 15% Fe/Ti-MOFs was found to be 2.6 times as fast as that of NH2-MIL-125(Ti). Moreover, the 15% Fe/Ti-MOFs photocatalysts remained stable after three consecutive cycles. The trapping test demonstrated that the major active species in the degradation of the RhB process were hydroxyl radicals (HO∙) and holes (h+).

Photocatalytic Activity of Nanocoatings Based on Mixed Oxide V-TiO2 Nanoparticles with Controlled Composition and Size

V-TiO2 photocatalyst with 0 ≤ V ≤ 20 mol% was prepared via the sol–gel method based on mixed oxide titanium–vanadium nanoparticles with size and composition control. The mixed oxide vanadium–titanium oxo-alkoxy nanonoparticles were generated in a chemical micromixing reactor, coated on glass beads via liquid colloid deposition method and underwent to an appropriate thermal treatment forming crystallized nanocoatings. X-ray diffraction, Raman, thermogravimetric and differential thermal analyses confirmed anatase crystalline structure at vanadium content ≤ 10 mol%, with the cell parameters identical to those of pure TiO2. At a higher vanadium content of ~20 mol%, the material segregation began and orthorhombic phase of V2O5 appeared. The crystallization onset temperature of V-TiO2 smoothly changed with an increase in vanadium content. The best photocatalytic performance towards methylene blue decomposition in aqueous solutions under UVA and visible light illuminations was observed in V-TiO2 nanocoatings with, respectively, 2 mol% and 10 mol% vanadium.

Tanning Wastewater Treatment by Ultrafiltration: Process Efficiency and Fouling Behavior

Ultrafiltration is a promising, environment-friendly alternative to the current physicochemical-based tannery wastewater treatment. In this work, ultrafiltration was employed to treat the tanning wastewater as an upstream process of the Zero Liquid Discharge (ZLD) system in the leather industry. The filtration efficiency and fouling behaviors were analyzed to assess the impact of membrane material and operating conditions (shear rate on the membrane surface and transmembrane pressure). The models of resistance-in-series, fouling propensity, and pore blocking were used to provide a comprehensive analysis of such a process. The results show that the process efficiency is strongly dependent on the operating conditions, while the membranes of either PES or PVDF showed similar filtration performance and fouling behavior. Reversible resistance was the main obstacle for such process. Cake formation was the main pore blocking mechanism during such process, which was independent on the operating conditions and membrane materials. The increase in shear rate significantly increased the steady-state permeation flux, thus, the filtration efficiency was improved, which resulted from both the reduction in reversible resistance and the slow-down of fouling layer accumulate rate. This is the first time that the fouling behaviors of tanning wastewater ultrafiltration were comprehensively evaluated, thus providing crucial guidance for further scientific investigation and industrial application.

Photocatalytic Porous Silica-Based Granular Media for Organic Pollutant Degradation in Industrial Waste-Streams

Photocatalytic treatment of organic contaminants in industrial wastewaters has gained interest due to their potential for effective degradation. However, photocatalytic slurry reactors are hindered by solution turbidity, dissolved salt content, and absorbance of light. Research presented here introduces the development and application of a novel, photocatalytic, porous silica-based granular media (SGM). SGM retains the cross-linked structure developed during synthesis through a combination of foaming agent addition and activation temperature. The resultant media has a high porosity of 88%, with a specific surface area of ~150 m2/gram. Photocatalytic capabilities are further enhanced as the resultant structure fixes the photocatalyst within the translucent matrix. SGM is capable of photocatalysis combined with diffusion of nucleophiles, electrophiles, and salts from pore space. The photocatalytic efficiencies of SGM at various silica contents were quantified in batch reactors using methylene blue destruction over time and cycles. Methylene blue concentrations of 10 mg/L were effectively degraded (>90%) within 40 min. This effectiveness was retained over multiple cycles and various methylene blue concentrations. SGM is a passive and cost-effective granular treatment system technology which can translate to other organic contaminants and industrial processes.

TiO2 Photocatalyzed Degradation of the Azo Dye Disperse Red 1 in Aqueous Micellar Environments†

The photoinduced degradation of the azo dye Disperse Red 1 was studied in a microheterogeneous system comprising titanium oxide (TiO₂ ) and sodium dodecyl sulfate, exposed to UV light. Degussa P25, Anatase and TiO₂ synthesized in acidic conditions were supported on raschig rings. The TiO₂ photocatalyzed degradation is enhanced in the vicinity of the surfactant critical micelle value. Further increase on the surfactant concentration leads to a loss in photodegradation performance up to values equivalent to that observed without surfactant. Surfactant influence can be explained by two different phenomena taking place. The increasing concentration of surfactant leads to an increase in micellar concentration, inducing the incorporation of the dye to the hydrophobic moiety of the micelles, rendering the hydroxyl radical unable to interact with the dye. Similarly, the increased concentration of micelles at the photocatalyst/water interface might lead to a decrease in the number of active sites on the TiO₂ surface able to either generate reactive species and/or interact with de dye molecules. Additives such as H₂ O₂ , NaCl, Na₂ SO_4, and Na₂ CO₃ are able to override the influence of the surfactant both positively and negatively, being the final outcome of the influence highly dependent on the crystalline form of the TiO₂ photocatalyst.

Modified Nano-TiO2 Based Composites for Environmental Photocatalytic Applications

TiO2 probably plays the most important role in photocatalysis due to its excellent chemical and physical properties. However, the band gap of TiO2 corresponds to the Ultraviolet (UV) region, which is inactive under visible irradiation. At present, TiO2 has become activated in the visible light region by metal and nonmetal doping and the fabrication of composites. Recently, nano-TiO2 has attracted much attention due to its characteristics of larger specific surface area and more exposed surface active sites. nano-TiO2 has been obtained in many morphologies such as ultrathin nanosheets, nanotubes, and hollow nanospheres. This work focuses on the application of nano-TiO2 in efficient environmental photocatalysis such as hydrogen production, dye degradation, CO2 degradation, and nitrogen fixation, and discusses the methods to improve the activity of nano-TiO2 in the future.

Recovery, physicochemical and functional characteristics of proteins from different meat processing wastewater streams

Recovery, physicochemical and functional characteristics of proteins recovered from different meat processing wastewater streams were revealed in the present study. Wastewaters from surimi processing (SPW) and slaughterhouses, namely fish (FSW), cattle (CSW), poultry (PSW), and goat (GSW), exhibited protein, fat, ash, moisture, and microbial load in the range of 1.28-7.04%, 0.86-2.34%, 0.02-0.80%, 89.81-97.44%, and 5.33-5.81 CFU/mL, respectively. Among the wastewaters, SPW presented slightly higher protein (7.04%), fat (2.34%), and ash (0.80%) contents (P < 0.05). Furthermore, proteins recovered from SPW (SPWP) and FSW (FSWP), CSW (CSWP), PSW (PSWP), and GSW (GSWP) presented yield, protein, fat, ash, and moisture content in the range of 55.54-76.81%, 65.86-78.22%, 7.26-11.45%, 4.58-11.75%, and 5.67-14.79%. All protein samples displayed higher essential amino acid (EAA) content with leucine (8.47-14.52 g/100 g) as a predominant amino acid. GSWP and SPWP scored the highest and lowest EAA contents, respectively. SPWP displayed myofibrillar proteins as dominant proteins, while slaughterhouses' wastewater proteins showed blood proteins as major proteins. β-Sheet is the major secondary structure presented by all protein samples. SPWP showed the highest lightness value as compared to other protein counterparts (P < 0.05). All protein samples from slaughterhouse wastewaters had the lowest protein solubility at pH 4.5. However, SPWP presented minimum solubility at pH 5.5. Among all protein samples, SPWP presented slightly higher water holding capacity and foaming property (P < 0.05), whereas FSWP displayed slightly higher emulsion property (P < 0.05). Overall, all meat processing wastewater streams served as good sources of high-quality proteins, which could be used as protein ingredients in animal feed formulation.

Assessing chromium pollution and natural stabilization processes in agricultural soils by bulk and micro X-ray analyses

A combined approach based on multiple X-ray analytical techniques and conventional methods was adopted to investigate the distribution and speciation of Cr in a polluted agricultural soil, from the bulk-scale down to the (sub)micro-level. Soil samples were collected from two different points, together with a control sample taken from a nearby unpolluted site. The bulk characterization revealed that the polluted soils contained much higher concentrations of organic matter (OM) and potentially toxic elements (PTE) than the control. Chromium was the most abundant PTE (up to 5160 g kg^-1), and was present only as Cr(III), as its oxidation to Cr(VI) was hindered by the high OM content. According to sequential extractions, Cr was mainly associated to the soil oxidisable fraction (74%) and to the residual fraction (25%). The amount of Cr potentially bioavailable for plant uptake (DTPA-extractable) was negligible. Characterization of soil thin sections by micro X-ray fluorescence (μXRF) and field emission scanning electron microscopy coupled with microanalysis (FEGSEM-EDX) showed that Cr was mainly distributed in aggregates ranging from tens micrometres to few millimetres in size. These aggregates were coated with an aluminosilicate layer and contained, in the inner part, Cr, Ca, Zn, P, S and Fe. Hyperspectral elaboration of μXRF data revealed that polluted soils were characterised by an exogenous organic-rich fraction containing Cr (not present in the control), and an endogenous aluminosilicate fraction (present also in the control), coating the Cr-containing aggregates. Analyses by high-resolution micro X-ray computed tomography (μCT) revealed a different morphology of the soil aggregates in polluted soils compared with the control. The finding of microscopic leather residues, combined with the results of bulk- and micro-characterizations, suggested that Cr pollution was likely ascribable to soil amendment with tannery waste-derived matrices. However, over the years, a natural process of Cr stabilization occurred in the soil thus reducing the environmental risks.

Treatment technologies for pharmaceutical effluents-A scientometric study

Treatment of highly polluted pharmaceutical effluents is a major challenge all over the world for technical and economic considerations. In this study, scientometric study is performed on the application of various methods for the treatment of pharmaceutical effluents to explore further developments. In this regard, a total of 1964 documents were retrieved from the Web of Science (WoS) database using a set of relevant keywords to cover all published documents. The extracted documents were subjected to scientometric study including the contributed authors, publications, citations received, contributing countries and institutions as well as the subject categories. From the data retrieved, the status of scientific knowledge on the subject history and current trends were identified and scientific gaps were critically discussed. Publications in this area started to appear since the sixties and were considerably promoted around the beginning of 2000s. Scientific publications of years 1960-2018 followed sigmoidal trend. It was found that leading countries are China and the United States in terms of scientific output on treatment technologies for pharmaceutical effluents. Among the active journals published, "Water Research" has received the most citations. A detailed discussion on the science and developments in this field is provided including the potential applications of scientometry.

Surfactant specific ionic strength effects on membrane fouling during produced water treatment

Membrane filtration is a technique that can be successfully applied to remove oil from stable oil-in-water emulsions. This is especially interesting for the re-use of produced water (PW), a water stream stemming from the petrochemical industry, which contains dispersed oil, surface-active components and often has a high ionic strength. Due to the complexity of this emulsion, membrane fouling by produced water is more severe and less understood than membrane fouling by more simple oil-in-water emulsions. In this work, we study the relation between surfactant type and the effect of the ionic strength on membrane filtration of an artificial produced water emulsion. As surfactants, we use anionic sodium dodecyl sulphate (SDS), cationic hexadecyltrimethylammonium bromide (CTAB), nonionic Triton ^TMX-100 (TX) and zwitterionic N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS), at various ionic strengths (1, 10, 100 mM NaCl). Filtration experiments on a regenerated cellulose ultrafiltration (UF) membrane showed a pronounced effect of the ionic strength for the charged surfactants SDS and CTAB, although the nature of the effect was quite different. For anionic SDS, an increasing ionic strength leads to less droplet-droplet repulsion, allowing a denser cake layer to form, resulting in a much more pronounced flux decline. CTAB, on the other hand leads to a lower interfacial tension than observed for SDS, and thus more deformable oil droplets. At high ionic strength, increased surfactant adsorption leads to such a low oil-water surface tension that the oil droplets can permeate through the much smaller membrane pores. For the nonionic surfactant TX, no clear effect of the ionic strength was observed, but the flux decline is very high compared to the other surfactants. For the zwitterionic surfactant DDAPS, the flux decline was found to be very low and even decreased with increasing ionic strength, suggesting that membrane fouling decreases with increasing ionic strength. Especially promising is that at lower surfactant concentration (0.1 CMC) and high ionic strength no flux decline was observed, while a high oil retention (85%) was obtained. From our results, it becomes clear that the type of the surfactant used is crucial for a successful application of membrane filtration for PW treatment, especially at high ionic strengths. In addition, they point out that the application of zwitterionic surfactants can be highly beneficial for PW treatment with membranes.

Detoxification Assays of Tunisian Tannery Wastewater under Nonsterile Conditions Using the Filamentous Fungus Aspergillus niger

The ability of Aspergillus niger strain to reduce organic and mineral pollution as well as the toxicity of two tannery wastewaters, the unhairing effluent (UE) and the final effluent (FE), taken from a local Tunisian tannery and under nonsterile conditions, was studied. Raw effluents show alkaline pH ≥11; thus experiments were carried out at initial pH values and at pH adjusted to 6. Characterization of effluents also revealed high salt levels (EC > 17 mS/cm) and high organic matter content (25 g/L for the UE and 7.2 g/L for the FE) but a low biodegradability since BOD₅ did not exceed 2.5 and 1.25 g/L for the UE and the FE, respectively. The results of the biological treatment showed that A. niger was able not only to grow at high pH and salinity values, but also to reduce organic and mineral pollutant load. After treatment, the COD reduction for the UE reached 90% and 70% at pH=6 and at initial pH (12.13), respectively. For the FE, the decrease of COD values reached 75% at pH=6 and 64% at initial pH (11.64). Monitoring of mineral pollution levels showed a reduction in chromium (Cr) concentrations reaching 70% for the FE. This was reflected by an increase of the biomass of A. niger from 9.25 g/L (control) to 9.84 g/L for the FE. To confirm the efficiency of the biological treatment using A. niger, phytotoxicity (tomato seeds) and microtoxicity (Escherichia coli and Bacillus subtilis) tests were carried out. Results of this monitoring showed an important decrease in the toxicity levels for both effluents.

A dansyl-appended N-heterocycle for Cu2+ and S2- recognition via a displacement mode

A novel l-proline based heterocycle 3 of C₂ symmetry has been designed and synthesized for cation and anion recognition in aqueous solution. Ligand 3 shows a strong affinity to Cu²⁺ ion, and their interaction induces a remarkable fluorescence quenching in DMSO:H₂O=9:1 (HEPES buffer, 0.01M, pH7.4) among various metal ions. Both the in-situ generated and isolated 3-Cu²⁺ complex exhibit specific fluorescence recovery upon addition of S^2-, even in the presence of S₂O₃^2-, L-histidine, and thiol-containing amino acids. For this dual functional switch, a combination of ¹H NMR titration, ESI mass and FT-IR spectra suggest that its sensing behavior is via a displacement mode. Sequential "on-off-on" fluorescence bio-imaging of the heterocycle 3 to Cu²⁺ and S^2- was carried out in HeLa cells.

A new ZIF molecular-sieving membrane for high-efficiency dye removal

A new and robust ZIF membrane was prepared and demonstrated excellent dye removal capacity due to its unique pore structure.

Exploring the Reusability of Synthetically Contaminated Wastewater Containing Crystal Violet Dye using Tectona grandis Sawdust as a Very Low-Cost Adsorbent

Present investigation explores the possible reusability of synthetically contaminated wastewater containing crystal violet (CV) organic dye using Tectona grandis sawdust (TGSD) waste as a very low-cost adsorbent. The adsorbent was characterized by proximate, SEM/EDX, FTIR, and XRD analyses. Batch adsorption studies were carried under changing conditions of contact time, the initial concentration of CV, pH, TGSD dose, TGSD particle size, and temperature. The experimental data were tested using Langmuir, Freundlich and Temkin isotherm models, and the data were best followed by Langmuir one. The kinetic results were examined in the light of different models and pseudo-second-order was obtained to be best obeyed. The values of ΔH° (28.642 kJ/mol), ΔG° (-10.776 to -7.080 kJ/mol) and ΔS° (121.8 J/K/mol) in the temperature range of 293-323 K suggested the overall process to be spontaneous, endothermic and associated with an increase in randomness. On the basis of experimental results and their analyses, it has been established that TGSD is one of the most effective adsorbents among those obtained from the domestic, agricultural and industrial wastes. Thus this adsorbent can be effectively utilized to make the impure wastewater reusable.

Investigation of electrodialysis anti-fouling configuration for desalting and treating tannery unhairing wastewater: Feasibility of by-products recovery and water recycling

The desalination and treatment of tannery unhairing wastewater by electrodialysis (ED) is investigated in this research in order to separate, concentrate, recover and reuse low molecular weight charged species (S^2-, HS^-, OH^-, Cl^-, Ca²⁺, Na⁺ and amino acids), and to separate proteins and recycle treated water. Therefore, a novel electrodialysis membrane configuration was proposed. This was based on a double anti-fouling membrane. The ED anion exchange membrane (AEM), which is very sensitive to organic fouling, was protected by an ultra filtration membrane impermeable to the negatively charged proteins that could not reach the AEM surface. The experimental results were quite promising, and in spite of only one desalination compartment ED cell; the demineralization efficiency was 56 ± 1.25% (5.5-2.4 mS/cm), with a sensitive removal of sulphide, calcium and chloride. The organic matter (protein, peptides…) was isolated in the dilute compartment. The most important result was the total absence of membrane fouling. The experimental results remarkably proved the initial hypothesis, and suggested promising solutions for industrial pollution, where the membrane processes have never been successful.

Novel, one-step synthesis of zwitterionic polymer nanoparticles via distillation-precipitation polymerization and its application for dye removal membrane

In this work, poly(MBAAm-co-SBMA) zwitterionic polymer nanoparticles were synthesized in one-step via distillation-precipitation polymerization (DPP) and were characterized. [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) as monomer and N, N′-methylene bis(acrylamide) (MBAAm) as cross-linker are used for the synthesis of nanoparticles. As  far as our knowledge, this is the first such report on the synthesis of poly(MBAAm-co-SBMA) nanoparticles via DPP. The newly synthesized nanoparticles were further employed for the surface modification of polysulfone (PSF) hollow fiber membranes for dye removal. The modified hollow fiber membrane exhibited the improved permeability (56 L/ m² h bar) and dye removal (>98% of Reactive Black 5 and >80.7% of Reactive orange 16) with the high permeation of salts. Therefore, the as-prepared membrane can have potential application in textile and industrial wastewater treatment.

Poly(sodium methacrylate)/eggshell particles hydrogel composites as dye sorbent

Eggshell (ES) particles as an available and low-cost waste material were utilized to prepare novel hydrogel composites for dye adsorbing application. For this purpose, solution polymerization of sodium methacrylate was carried out in the presence of ES particles with various size ranges. Results showed that incorporation of ES particles resulted in heterogeneous pores and cavities in the structure of the poly(sodium methacrylate) (PNaMA) matrix. Hydrogel composites with lower content (20 wt%) and smaller size (<75 μm) of ES particles presented higher water absorption capacity. The equilibrium water absorption values in distilled water were higher than phosphate buffered saline medium. ES particles showed low methylene blue (MB) and crystal violet (CV) adsorption capacities due to electrostatic repulsion of the positively charged species on the surface of ES particles and dye molecules. In contrast, hydrogel composites depicted fast and considerable dye adsorbability. The combination of 60 wt% ES particles within PNaMA provided a cost-effective adsorbent with similar CV adsorption capacity compared with the unfilled matrix, while MB removal was slightly decreased. The dye adsorption by either ES particles or hydrogel composites followed the pseudo-second-order kinetics, indicating that chemical sorption is the rate-limiting step for both of them.

Determination of Spatial Chromium Contamination of the Environment around Industrial Zones

This study was conducted to determine the spatial levels of chromium contamination of water, agricultural soil, and vegetables in the leather tanning industrial areas using spectrophotometric methods. The results showed elevated accumulation of total Cr ranging from 10.85 ± 0.885 mg/L to 39.696 ± 0.326 mg/L, 16.225 ± 0.12 mg/Kg to 1581.667 ± 0.122 mg/Kg, and 1.0758 ± 0.05348 mg/Kg to 11.75 ± 0.206 mg/Kg in water, agricultural soil, and vegetable samples, respectively. The highest levels of chromium (VI) found from the speciation study were 2.23 ± 0.032 mg/Kg and 0.322 ± 0.07 mg/L in soil and water samples, respectively, which decreased with distance from the tannery. Among the vegetables, the highest load of Cr(VI) was detected in onion root (0.048 ± 0.065 mg/Kg) and the lowest (0.004 ± 0.007 mg/Kg) in fruit of green pepper. The detected levels of Cr in all of the suggested samples were above the WHO permissible limits. The variations of the levels Cr(III) and Cr(VI) contamination of the environment with distance from the tannery were statistically significant (p = 0.05). Similarly, significant difference in the levels of Cr among the tested vegetables was recorded. The levels increased with decreasing distance from the effluent channel.

A new integrated approach for dye removal from wastewater by polyoxometalates functionalized membranes

Membrane technique is a promising way for the removal of dyes from wastewater. A unique approach combining both the adsorptive and the catalytic membrane processes was proposed on the basis of a new functionalized membrane. The membrane integrating both the adsorptive and catalytic activities was developed by introducing polyoxometalates (POMs) as an ideal candidate for the membrane functionalization via a novel sol-gel method. A two-step protocol, adsorptive separation and catalytic degradation, was designed for dye removal, realizing an excellent dye rejection with easy and economic membrane regeneration through simply soaking the membrane in a limited volume of dilute oxidant solution. This approach is feasible and versatile owing to the flexible selection of distinct POMs and design of catalytic degradation routes as required. As a result, the current research provides insight into a new methodology of the membrane technique in dye removal applications.

A pillar[5]arene-containing cross-linked polymer: synthesis, characterization and adsorption of dihaloalkanes and n-alkylene dinitriles

A pillar[5]arene-containing cross-linked polymer was synthesized and utilized to adsorb dihaloalkanes and n-alkylene dinitriles.

Is biosorption suitable for decontamination of metal-bearing wastewaters? A critical review on the state-of-the-art of biosorption processes and future directions

For the past few decades, biosorption has been widely investigated for the removal of different contaminants in aqueous media. A number of biomasses of different genre have been identified to possess good biosorption capacity. Insights into biosorption mechanisms have been provided by various researchers in order to develop a fundamental scientific understanding of the biosorption process. However, biosorption has not been employed widely for its large-scale commercial applications. The key factors that affect the growth and evolution of biosorption as a practical technology for decontamination of wastewaters include, (1) lack of investigations on multi-component solutions and wastewaters with complex matrix effects, (2) incomplete understanding of physico-chemical characteristics of biomasses of different types, (3) lack of studies to improve the performance of biosorbents through surface functionalization, and (4) non-integration of biosorption in wastewater/water treatment plants. This critical review aims to identify and discuss the practical limitations of biosorption and provide future research directions to make biosorption a technologically viable process with emphasis on selection and modification of biomasses to suit desired treatment applications, identify appropriate operation modes for large-scale applications of biosorption, and perform techno-economic evaluation of overall biosorption processes.

Integration of ion-exchange and nanofiltration processes for recovering Cr(III) salts from synthetic tannery wastewater

This study aims to investigate the possibility of integrating both ion-exchange (IX) and nanofiltration (NF) processes for the recovery of Cr(III) salts from a synthetic solution prepared with concentrations of Cr(III), [Formula: see text] and Cl(-) in the range of industrial effluents of tanneries. Ion exchange should be used as a pre-treatment for uptaking Cl(-) ions from the effluent, and thereafter the treated solution is fed to an NF unit to recover chromium sulphate salt for reuse in the tanning bath. The strong anionic resin Diaion PA316 was selected for evaluating chloride-sulphate ion-exchange equilibrium, with respect to mass of resin, NaCl concentration, temperature and ratio [Formula: see text]. It was observed that the separation factor, [Formula: see text], depends on the total electrolyte concentration and the ratio [Formula: see text] plays a role as well. Moreover, it was determined that the resin prefers sulphate over chloride since [Formula: see text] is less than 1. The performance of the NF process is dependent on [Formula: see text] and the rejection of Cr(III) may decrease from 90% to 70% as the ratio increases from 0.5 to 2. Regarding the integration of both IX and NF, the feed solution after treatement with the resin was fed to NF where the ratio of [Formula: see text] led to the best operating conditions for this process (90% of Cr(III) rejection and up to 77% for [Formula: see text] ions). This strategy may be considered as a sustainable approach since it permits to obtain a solution enriched in Cr(III) salt for reuse in the tanning process, thus contributing to environmental protection.

Transition metal/metal oxide modified MCM-41 for pollutant degradation and hydrogen energy production: a review

Metal/metal oxide modified MCM-41 materials are suitable for various catalytic applications. The high surface area, mesoscopic pore size and tunable pore volume of the materials play a key role in enhancing the catalytic activity.

Preparation and characterization of chitosan/silver nanoparticle/copper nanoparticle/carbon nanotube multifunctional nano-composite for water treatment: heavy metals removal; kinetics, isotherms and competitive studies

A chitosan/Ag NP/Cu NP/CNT multifunctional composite has superior water treatment efficiency compared with bare chitosan and bi-composite systems.