Initial Contaminant Concentration Research Articles

A novel potato peels waste β-cyclodextrin biocomposite for the efficient uptake of diuron and glyphosate herbicides.

A novel biocomposite (FPPW-β-CD) was prepared by a simple and sustainable method involving fine potato peel waste, β-cyclodextrin (β-CD), and green citric acid through the crosslinking reaction. The polymer was characterized using SEM, FTIR, XRD, TGA, and DSC analyses. The adsorbent performance was evaluated about the glyphosate and diuron adsorption from the aqueous solution. Pesticide removal was investigated regarding the influence of solution pH, temperature, and initial concentration of contaminants. Also, it highlights the main interactions involved in the adsorption phenomenon based on the pH effect and characteristics of adsorbent and adsorbate molecules. The maximum adsorption capacity values according to the Sips model were higher than 2000µgg-1. The pseudo-second-order and general-order models described the kinetic data well. Thermodynamic parameters indicated that pesticide removal was spontaneous and favorable. The magnitude of enthalpy variation values (27.37kJmol-1 and - 100.79kJmol-1) revealed that the glyphosate and diuron adsorption occurred through the physisorption and chemisorption, respectively. The novel biocomposite is a promising green adsorbent for the uptake of micropollutant pesticides in aqueous solutions at concentrations of µg L-1.

Simultaneous removal of malachite green and lead from water by consortium dry-biomasses of Bacillus licheniformis AG3 and Bacillus cereus M116

Synthetic textile dye malachite green (MG) and heavy metals present in industrial wastewater are hazardous to the ecosystem. Bioremediation of dyes and heavy metals using dry-biomasses has advantages over chemical methods. This study screened an acclimatized, heavy metal-resistant, and dye-degrading Gram positive Bacillus licheniformis AG3 strain from the textile wastewater near Kolkata, West Bengal. The EDXRF analysis of this colored wastewater effluent showed 36.33 mg/L lead, significantly higher than the WHO recommendation. Previously, Bag et al. showed bioremediation of synthetic dyes using dry-biomass of Bacillus cereus M116 from an aqueous solution (Bag et al. Arch Microbiol 203(7):3811–3823, 2021). Here, a consortium of dry-biomasses of B.licheniformis AG3 and B. cereus M116 strains (1:1 w/w ratio) was prepared for the simultaneous removal of lead and MG from wastewater. Statistical optimization determines that the pH, initial concentration of contaminants, and dry-biomass concentrations are critical for bioremediation under batch procedures. Further, optimization using the response surface methodology showed that 0.01% consortium dry-biomasses eliminated a maximum of 99.35% MG and 96.01% lead (II) within 6 h. SEM–EDS and FTIR confirmed a strong surface biosorption. Furthermore, a fixed-bed biofilter column of the consortium dry-biomasses was prepared, which was able to remove 98.1% MG and 98.5% lead at the 0.5–1 mL/min flow rate. Together, this study developed a biofilter with a consortium dry biomasses of B. licheniformis AG3 and B. cereus M116 for the simultaneous removal of MG and lead from wastewater.

Strong Magnetic p-n Heterojunction Fe3O4-FeWO4 for Photo-Fenton Degradation of Tetracycline Hydrochloride

With the abuse of antibiotics, its pollution poses an increasing threat to the environment and human health. Effective degradation of organic pollutants in water bodies is urgent. Compared to traditional treatment methods, advanced oxidation processes that have developed rapidly in recent years are more environmentally friendly, efficient and applicable to a wider range of organic compounds. FeWO4 was used in this study as the iron-based semiconductor material to modify and optimize the material design. Fe3O4/FeWO4 composites were prepared by a two-step hydrothermal method. The crystal structure, surface morphology, electrochemical properties and separability of the composite semiconductor were analyzed by XRD, XPS, UV-vis, SEM, EDS and Mott-Schottky. The results showed that, when the initial contaminant concentration was 30 mg/L, the initial solution pH was 4, the dosage of the catalyst was 25 mg and the dosage of hydrogen peroxide was 30 μL, the degradation efficiency of tetracycline hydrochloride (TCH) could reach 91% within 60 min, which was significantly improved compared to the performance of the single semiconductors Fe3O4 and FeWO4. In addition, the catalyst prepared in this experiment can be easily recovered by magnetic separation technology in practical application, which will not affect the turbidity of water while reducing the cost of catalyst separation and recovery.

Monocomponent Biosorption of Copper Ions (II) onto Nanocrystalline Cellulose from Coconut Husk Fibers

Introduction: Nanocrystalline cellulose (NCC) is one of the most suitable cellulose derivatives for the treatment of wastewater. Various agricultural wastes have been used for the extraction of NCC. Coconut wastes have been widely studied as potential adsorbents for the removal of pollutants, including dyes and heavy metals. Methods: In this work, nanocrystalline cellulose (NCC) was successfully isolated from coconut husk fibers through alkaline pretreatment accompanied by sulfuric acid hydrolysis. Then, the ability of NCC to adsorb Cu2+ from aqueous solution in batch studies was investigated. Results: Results indicated that the optimal hydrolysis parameters were achieved at 50° C for 45 min with 64% sulfuric acid to extract NCC as rod-like particles with diameters between 4-10 nm. The potential of NCC as a biosorbent to remove copper ions (Cu2+) from aqueous solution was investigated in terms of batch mode and maximum adsorption capacity (qm) of 79.491 mg/g of Cu2+. The adsorption efficiency of Cu2+ions increased with an increase in the adsorbent dosage, decreased with an increase in the initial concentration of contaminant, and increased with the contact time. Under optimal conditions, adsorption kinetic followed a pseudo-second-order kinetic model and the adsorption isotherm fitted most closely with the Langmuir model. Conclusion: According to a literature review, NCC from coconut husk fibers has not been used for the adsorption of heavy metals, mainly copper ions. This study shows that NCC from coconut husk fibers can be used as a low-cost and environmentally friendly adsorbent for the removal of Cu2+ from aqueous solutions.

Biotransformation of Chlorpyrifos Shewanella oneidensis MR-1 in the Presence of Goethite: Experimental Optimization and Degradation Products.

In this study, the degradation system of Shewanella oneidensis MR-1 and goethite was constructed with chlorpyrifos as the target contaminant. The effects of initial pH, contaminant concentration, and temperature on the removal rate of chlorpyrifos during the degradation process were investigated. The experimental conditions were optimized by response surface methodology with a Box-Behnken design (BBD). The results show that the removal rate of chlorpyrifos is 75.71% at pH = 6.86, an initial concentration of 19.18 mg·L-1, and a temperature of 30.71 °C. LC-MS/MS analyses showed that the degradation products were C4H11O3PS, C7H7Cl3NO4P, C9H11Cl2NO3PS, C7H7Cl3NO3PS, C9H11Cl3NO4P, C4H11O2PS, and C5H2Cl3NO. Presumably, the degradation pathways involved are: enzymatic degradation, hydrolysis, dealkylation, desulfur hydrolysis, and dechlorination. The findings of this study demonstrate the efficacy of the goethite/S. oneidensis MR-1 complex system in the removal of chlorpyrifos from water. Consequently, this research contributes to the establishment of a theoretical framework for the microbial remediation of organophosphorus pesticides in aqueous environments.

Low cost MXene synthesis for regenerative adsorption of benzene, toluene, ethylbenzene and xylene (BTEX)

MXenes, a group of emerging 2D metal carbides with unique properties and expanding potential applications, have attracted researchers’ interests. However, high synthesis costs and safety concerns have imposed limitations on their research and development. Here, we report a low-cost and safer synthesis method for a titanium-MXene, which we then test for its efficacy as an adsorbent for organics contamination in water. For the synthesis, we examine how different carbon forms (graphite and activated charcoal (AC)) impact the MXene properties and application. Instead of expensive and high-risk pure titanium as a precursor, cheap and easy-to-handle titanium oxide was used, while achieving lower-temperature synthesis through the molten-salt shielded synthesis approach. The resulting 3D MAX phases were separately etched into 2D-MXenes and characterized extensively. The synthesised MXenes were tested as adsorbents in adsorption experiments under various conditions. The data obtained were fitted to isotherm and kinetic models to understand the adsorption mechanisms. Although the AC-based MXene exhibited a much larger BET surface area compared to the graphite-based MXene (24 m2/g vs 2 m2/g respectively), other characterization results indicated that both materials had remarkably similar morphological and functional properties. Additionally, both MXenes effectively removed at least 80 % of the initial contaminant concentration. However, AC-based MXene is cheaper to produce and demonstrated superior regenerative capabilities over three cycles of regeneration and reuse. Also, its reuse potential is less affected by oxidation during the regeneration process. This study concludes that MXenes can be synthesized at a lower cost and highlights the crucial role of the carbon form used in synthesis for the MXene subsequent application. Specifically, AC-based MXenes show great potential for clean water recovery applications and could be a good candidate for analytical chemistry purposes.

Is redox zonation an appropriate method for determining the stage of natural remediation in deep contaminated groundwater?

Groundwater contamination resulting from petroleum development poses a significant threat to drinking water sources, especially in developing countries. In situ natural remediation methods, including microbiological processes, have gained popularity for the reduction of groundwater contaminants. However, assessing the stage of remediation in deep contaminated groundwater is challenging and costly due to the complexity of diverse geological conditions and unknown initial concentrations of contaminants. This research proposes that redox zonation may be a more convenient and comprehensive indicator than the concentration of contaminants for determining the stage of natural remediation in deep groundwater. The combination of sequencing microbial composition using the high-throughput 16S rRNA gene and function predicted by FAPROTAX is a useful approach to determining the redox conditions of different contaminated groundwater. The sulfate-reducing environment, represented by Desulfobacteraceae, Peptococcaceae, Desulfovibrionaceae, and Desulfohalobiaceae could be used as characteristic early stages of remediation for produced water contamination in wells with high concentrations of SO42−, benzene, and salinity. The nitrate-reducing environment, enriched with microorganisms related to denitrification, sulfur-oxidizing, and methanophilic microorganisms could be indicative of the mid stages of in situ bioremediation. The oxygen reduction environment, enriched with oligotrophic and pathogenic Sphingomonadaceae, Caulobacteraceae, Syntrophaceae, Legionellales, Moraxellaceae, and Coxiellaceae, could be indicative of the late stages of remediation. This comprehensive approach could provide valuable insights into the process of natural remediation and facilitate improved environmental management in areas of deep contaminated groundwater.

True Order Determination of Sonochemical Degradation Kinetics of Organic Contaminants in Water Using the Half-lives Method

In the literature, the modeling of the sonolytic decomposition kinetics of organic contaminants in water has been carried out using the pseudo-first and pseudo-second order equations. The results obtained with this method are totally biased because it requires the assumption of the order of the degradation reaction, which is a real limitation, and the sonochemical oxidation mechanism is a very complex phenomenon that cannot be described by such simple models. In this paper, for the first time, the true order of the sonochemical degradation kinetics of organic pollutants in aqueous solutions at various initial substrate concentrations was determined using the half-lives method combined with the general rate law model, i.e., the pseudo-nth order equation. Linear and nonlinear regression techniques were used to determine the order of the sonolytic destruction reaction. The half-life technique for the general rate law model can adequately describe the experimental results of the sono-destruction of the investigated pollutants. For rhodamine B and naphthol blue black, the sono-destruction mechanism for both contaminants does not change as the initial contaminant concentration varies over the range examined, while for 4-isopropylphenol and furosemide, the sono-destruction mechanism changes as the initial substrate concentration varies. A fractional order of the sonolytic destruction reaction was determined for all the pollutants tested. These fractional orders of sono-destruction reactions indicate the complex nature and behavior of the reactions, often involving multiple steps or mechanisms. They also reveal a more complex interaction between pollutant concentration and sonolytic destruction rate. In a word, the method developed in this paper should be used to determine the real order of the sono-oxidation reaction of nonvolatile organic pollutants in aqueous phase.

Prediction models for effective PVD-enhanced in-situ flushing remediation of multi-layered soils

The re-utilization of original industrial sites poses a significant challenge in the remediation of contaminated soils, driven by the transformation of urban industrial spaces. In this study, a prediction model is proposed to address this challenge by focusing on the in-situ flushing remediation of multi-layered soils enhanced with PVDs. The analytical model is versatile for various scenarios where the boundaries have different diffusion capacities by introducing imperfect diffusion boundaries. It incorporates the effects of the sandy silt layer and the decay characteristics of initial contaminant concentrations with depth on remediation efficiency of multi-layered contaminated soils. To validate the model, the solutions derived from the matrix analysis were compared with experimental data and numerical simulation results from COMSOL Multiphysics. Parametric analysis reveals that the model effectively captures different boundary conditions ranging from fully non-diffusive to completely diffusive by utilizing the imperfect diffusion capacity coefficient within the range of 0 to 50. Furthermore, the remediation of the upper and lower silty clay layers of the sandy silt layer was different but both decreased in efficiency as the thickness of the sandy silt layer increased. Notably, the concentration of the contaminant exhibits more pronounced variations with increasing radial dispersivity compared to vertical dispersivity.

Modelling Well Location Between River and Second Contaminant Source in Riverbank Filtration Systems

Extracting water from pumping well near to river in riverbank filtration systems leads to the natural treatment for surface water. To increase the system efficiency, the well should be located at a distance from the river in which the well can produce high percentage of river water that satisfies the requirements of water quality. In case the well is located between river and a contaminant source, its location should be relocated to a suitable place between the two sources. In this article, an analytical solution is produced to specify the suitable distance of pumping well and polluted river in a riverbank filtration systems if there is a contaminant source to the present well. The analytical solution is obtained by using Green’s function. This approach is chosen because of its simplicity for solving multidimensional problems, and its flexibility to deal with arbitrary initial and boundary conditions. The model is compared with numerical one obtained by using MODFLOW software. The results indicate that the location obtained from proposed model is suitable for use to determine the well location. Additionally, the results show that increasing either the pumping rate or initial contaminant concentration leads to an increment to the distance between river well.

Advanced oxidation/reduction processes (AO/RPs) for wastewater treatment, current challenges, and future perspectives: a review.

Advanced oxidation/reduction processes (AO/RPs) are considered as effective water treatment technologies and thus could be used to solve the problem of water pollution. These technologies of wastewater treatment involve the production of highly reactive species such as •OH, H•, e-aq, SO4•-, and SO3•-. These radicals can attack the targeted contaminants present in aqueous media and result in their destruction. The efficiency of AO/RPs is highly affected by various operational parameters such as initial concentration of contaminant, solution pH, catalyst amount, intensity of light source, nature of oxidant and reductant used, and the presence of various ionic species in aquatic media. Among AO/RPs, the solar light-based AO/RPs are most widely used nowadays for contaminant removal from aqueous media because of their high environmental friendliness and cost effectiveness. By using these techniques, almost all types of pollutants can be easily removed from aquatic media within short intervals of time, and hence, the problem of water pollution can be solved effectively. This review focuses on various AO/RPs used for wastewater treatment. The effects of different operational parameters that affect the efficiency of these processes toward contaminant removal have been discussed. Besides, challenges and future recommendations are also briefly provided for the researchers in order to improve the efficiency of these processes.

Central composite design approach for concurrent desulfurization and denitrogenation of model liquid fuel over Mo‐AAC

AbstractThe primary objective of this work was to investigate the simultaneous removal of refractory sulfur (dibenzothiophene, DBT) and nitrogen compounds (indole, IND) from model gasoline. This research aimed to develop an efficient adsorption process to mitigate the emission of sulfur oxide and nitrogen oxides, which pose direct threats to human health and the environment. Additionally, the study focused on addressing technical challenges encountered in the refinery process, particularly the poisoning of catalysts due to the presence of these compounds. To achieve the study's goals, granular activated carbon (GAC) was subjected to acid treatment for modification. Molybdenum species were then incorporated into the acid‐treated GAC using the wet impregnation technique. The composition and distribution of elements on the surface of the modified GAC (Mo‐AAC) were analyzed via X‐ray photoelectron spectroscopy (XPS). Various characterization techniques were employed to confirm the uniform dispersion of molybdenum species on the GAC surface. The specific surface area of the adsorbent was increased from 257 m2/g to 316 m2/g following the acid treatment and molybdenum modification. The study explored the impact of several key parameters on the removal of DBT and IND using central composite design (CCD). A regression model was derived using CCD through hybrid central composite design, and its adequacy was verified with the means of tests such as analysis of variance (ANOVA), a lack of fit test, and residuals distribution consideration. Experimental results match well with the results obtained by CCD model, justifying the accuracy of models. The results showed that all four parameters have a significant impact on removal of DBT and IND. Increasing temperature and the adsorbent dose positively affected the removal of both DBT and IND, indicating that higher temperatures and greater adsorbent dosages improved removal efficiency. On the other hand, the concentration of DBT and IND had a negative impact, signifying that higher initial contaminant concentrations hindered removal efficiency. The study determined the optimum initial contaminant concentrations for DBT and IND, temperature, and adsorbent dose to be 186 mg/L, 50 mg/L, 25.5°C, and 32 g/L, respectively. These conditions yielded the highest removal efficiency. The research demonstrated that Mo‐AAC has the capability to effectively reduce the sulfur and nitrogen content of model gasoline, making it a promising solution for addressing environmental and refinery challenges associated with these compounds.

Testing and Evaluation Performance of Borosilicate Glasses for Ammonia, Nitrate, and Total Nitrogen Removal from Industrial Wastewater

Several studies were conducted utilizing various adsorbents in an effort to remove NH3+, NO3, and total nitrogen (TN) by adsorption process. In this study, Borosilicate glass is used as an adsorbent material. The effectiveness of the adsorbent in removing NH3+, NO3, and TN was examined, that in relation to the effect of solution characteristics. Three different types of glass intermediate oxides (Al2O3, SnO, and Bi2O3) were used to synthesize three different samples of borosilicate glass (adsorbents), that to study their effect on the adsorption efficiency of borosilicate glass. Aluminum oxide Al2O3 was used to synthesize adsorbent (I), tin oxide SnO was used to synthesize adsorbent (J), and bismuth oxide Bi2O3 was used to synthesize adsorbent (K). Adsorbents (I, J, and K) achieved a clear improvement in the performance of the adsorption process. Despite the convergence of competencies, adsorbents J and K were superior to adsorbent I. With adsorbent K and an initial concentration of contaminants 28 mg NH3+/ L, 28 mg NO3/ L, and 60 mg TN / L, the removal efficiency of NH3+, NO3, and TN was 49.5%, 55%, and 40%, respectively. The removal efficiency increased with initial concentration of contaminants increasing, which became around 79% NH3+, 93% NO3, and 88% TN for adsorbent K. The best efficiency of ammonia removal achieved with pH value 8.9, it was 64.1%, 75.3%, and 77.1% for adsorbents I, J, and K, respectively. The highest efficiency of nitrate removal was in acidic case, reaching 90.1%, 95.2%, and 93.8% for adsorbents I, J, and K, respectively, at pH value 4.1. Adsorption data were fitted with Langmuir and Freundlich isotherm models to demonstrate the adsorption behavior of NH3+, NO3, and TN onto adsorbents (I, J, and K). It was found that the data were well fitted to both models. Overall, the findings demonstrated that borosilicate glass has the potential to be an effective adsorbent for the removal of ammonia, nitrate, and total nitrogen from industrial effluent.

Application of the general rate law model to the sonolytic degradation of nonvolatile organic pollutants in aqueous media

The pseudo-first and pseudo-second order equations have been the most commonly used models to characterize the sonolytic disappearance kinetics of nonvolatile pollutants in aqueous media. In this work, the general rate law model, i.e., pseudo-nth order kinetics equation, was applied for the first time to the sono-decomposition of different nonvolatile organic pollutants, naphthol blue black (NBB), furosemide (FSM), 4-isopropylphenol (4-IPP), and rhodamine B (RhB), in water. It was shown that the general rate law for a chemical reaction would apply to the kinetics of sonochemical decomposition. It is not feasible to set the order of ultrasonic pollutant degradation kinetics to pseudo-first or pseudo-second, as is typically used in numerous studies. The sonochemical oxidation reaction has a fractional order, the order is often non-integer, which frequently indicates a complex sonolytic decomposition reaction mechanism. The degradation mechanism of NBB and RhB does not change with the initial substrate concentration. They are ultrasonically degraded by hydroxyl radicals both in the bulk liquid solution and at the liquid/bubble interfacial layer. The destruction mechanism of FSM and 4-IPP changes as the initial contaminant concentration changes. At low initial substrate concentrations, these pollutants are oxidized mainly by reaction with hydroxyl radicals in the bulk liquid solution and at the interfacial shell of the cavitation bubbles. At high initial substrate concentrations, FSM and 4-IPP are degraded by thermal destruction in the liquid/bubble interfacial layer and by •OH radicals both in the bulk liquid solution and at the liquid/bubble interfacial layer. Additionally, the pseudo-nth order model predicts very well the sonolytic degradation at various sonication frequencies and intensities. The general rate law expression should be used to assess the real kinetics order of the sonolytic destruction process without any predetermined assumptions or constraints.

Magnetic polyacrylonitrile-melamine nanoadsorbent (PAN-Mel@Fe3O4) for effective adsorption of Cd (II) and Pb (II) from aquatic area

A magnetic polyacrylonitrile-melamine nanoadsorbent (PAN-Mel@Fe3O4) has been developed as a polymer-based adsorbent in three steps involving the preparation of polyacrylonitrile (PAN), the modification of PAN with melamine, and the in-situ magnetization of the PAN-Mel nanocomposite. During the fabrication of PAN-Mel@Fe3O4 nanocomposite, various analyses were used to investigate its physicochemical properties. The PAN-Mel@Fe3O4 nanoadsorbent was investigated to be able to efficiently adsorb cadmium (Cd) and lead (Pb) from aqueous media. Several experimental conditions were employed for evaluating adsorption performance, involving pH of medium, adsorbent dosage, contact time, and initial contaminant concentration. Therefore, the Cd (II) and Pb (II) maximum adsorption capacity (Qmax) in the optimized conditions reached 454.54 and 416.66 mg/g, respectively. The experimental adsorption data for both studied heavy metals was fitted well by the Freundlich isotherm model and adsorption kinetics for both heavy metals descriptions satisfactorily by the pseudo-second-order model. The PAN-Mel@Fe3O4 adsorbs mainly Cd (II) and Pb (II) by electrostatic interaction due to a great number of the nitrogen-rich bidentate chelating ligands. Regarding the adsorption–desorption of the PAN-Mel@Fe3O4 nanoadsorbent, after recycling it four times, no significant decrease in its efficiency was observed and it could be used for the four time as well.

Removal efficiency of organic chloride from naphtha fraction using micro and nano-γ-Al2O3 sintered adsorbents

Abstract This research examines the removal efficiency of organic chloride (OC) compounds from the naphtha fraction of polluted crude oil (CO) using sintered micro and nano γ-Al2O3 at a consistent temperature of 30 °C. The adsorbents were characterized through BET, SEM-EDS, and XRD analyses. When utilizing micro-adsorbents to eliminate OC components from naphtha fraction samples containing initial contaminant concentrations of 105 and 8.5 mg/L, the maximum removal efficiency reached only 28 % and 56 %, respectively. In contrast, the use of nano-based adsorbents resulted in significantly higher adsorption percentages, exceeding 45 % and 96 % for the same two samples, respectively. Equilibrium investigations revealed that the Freundlich isotherm model yielded a superior match for the adsorption equilibrium data for the nano-adsorbents case, while the Langmuir model accurately characterized the data for the micro-adsorbents. Kinetic data analysis indicated that the adsorption kinetics for nano-adsorbents followed the pseudo-second-order model, while the micro-adsorbents obeyed the intra-particle diffusion mechanism. Overall, these findings suggest that sintered γ-Al2O3 nanoparticles (NPs) are more effective than microparticles (MPs) for the adsorptive removal of organic chlorides (OCs) from crude oil’s naphtha distillate.

Simultaneous removal of fluoride and phosphate from semiconductor wastewater via chemical precipitation of calcium fluoride and hydroxyapatite using byproduct of recycled aggregate

Semiconductor wastewater with high concentrations of fluoride and phosphate is an environmental issue that cannot be ignored. Moreover, the byproduct of recycled aggregates, concrete fines, cannot be reused in concrete manufacturing, which is a key issue to address for the sustainable development of the concrete industry. The objective of this study was to tackle the crucial environmental issues of these two industries by developing concrete fines as an alternative material to treat semiconductor wastewater. The chemical precipitation of calcium fluoride and hydroxyapatite in the presence of concrete fines was determined as the mechanism underpinning the removal of fluoride and phosphate in wastewater. Owing to the wide range of contaminant concentration and solution pH and the possibility of multi-stage treatment, the effects of the initial contaminant concentration (F: 100–1000 mg/L; P: 20–200 mg/L) and solution pH (pH: 2–7) on the removal reactions were determined. The highest F and P removal percentages were more than 99%, and the final F and P concentrations met the effluent standard (F: 15 mg/L, P: 1.3 mg/L). The removal reactions of F and P are generally in competition, and the removal of F has priority over the removal of P. The pseudo-second-order model can describe the kinetics of the removal reactions well. The formation of fluorapatite can reduce the F concentration below the concentration achievable by CaF2 precipitation alone. Furthermore, using the byproduct of recycled aggregates instead of conventional chemicals to treat semiconductor wastewater is promising in terms of reducing CO2 emissions, and prospective applications are discussed. This study can lead to the development of a sustainable and clean process for semiconductor wastewater treatment using byproducts from the concrete industry.

Zinc oxide – mesoporous silica nanocomposite: preparation, characterisation and application in water treatment for lead, cadmium and chromium removal

ABSTRACT Applications of nanomaterials in water and wastewater treatment and in environmental clean-up operations depend on the adsorption capacity of the materials for contaminants such as potentially toxic elements (PTEs). However, on their own nanoparticles can lose effectiveness as contaminant sorbents because of flocculation and aggregation. Embedding nanoparticles within a silica matrix offers one potential solution to the problem; hence, in this study, zinc oxide nanoparticles (ZnO-NP) were embedded in a mesoporous silica (MCM-41) matrix to create a composite material with potential for contaminants removal from water. The composite material (ZnO-mSiO2) and original ZnO-NP were characterised via UV-Vis, FTIR, XRD, TGA/DTA, BET, and SEM techniques, and were then evaluated for their capacities to remove cadmium (Cd), chromium (Cr) and lead (Pb) from water samples across varying conditions (pH, initial contaminant concentration, contact time and adsorbent mass: solution volume ratios). Langmuir and Freundlich adsorption isotherms were fit to the data to describe the adsorption observed. The ZnO-mSiO2 composite material proved highly effective at removing the PTEs (particularly Pb) across a wide range of conditions, with optimum removal rates achieved at pH 7 and above and 90 minutes contact time.

Recent Progress on Semiconductor Heterogeneous Photocatalysts in Clean Energy Production and Environmental Remediation

Semiconductor-based photocatalytic reactions are a practical class of advanced oxidation processes (AOPs) to address energy scarcity and environmental pollution. By utilizing solar energy as a clean, abundant, and renewable source, this process offers numerous advantages, including high efficiency, eco-friendliness, and low cost. In this review, we present several methods to construct various photocatalyst systems with excellent visible light absorption and efficient charge carrier separation ability through the optimization of materials design and reaction conditions. Then it introduces the fundamentals of photocatalysis in both clean energy generation and environmental remediation. In the other parts, we introduce various approaches to enhance photocatalytic activity by applying different strategies, including semiconductor structure modification (e.g., morphology regulation, co-catalysts decoration, doping, defect engineering, surface sensitization, heterojunction construction) and tuning and optimizing reaction conditions (such as photocatalyst concentration, initial contaminant concentration, pH, reaction temperature, light intensity, charge-carrier scavengers). Then, a comparative study on the photocatalytic performance of the various recently examined photocatalysts applied in both clean energy production and environmental remediation will be discussed. To realize these goals, different photocatalytic reactions including H2 production via water splitting, CO2 reduction to value-added products, dye, and drug photodegradation to lessen toxic chemicals, will be presented. Subsequently, we report dual-functional photocatalysis systems for simultaneous energy production and pollutant photodegradation for efficient reactions. Then, a brief discussion about the industrial and economical applications of photocatalysts is described. The report follows by introducing the application of artificial intelligence and machine learning in the design and selection of an innovative photocatalyst in energy and environmental issues. Finally, a summary and future research directions toward developing photocatalytic systems with significantly improved efficiency and stability will be provided.

Approximate analytical solution to the axisymmetric model for PVD-enhanced in-situ flushing of double-layered contaminated soils

The in-situ soil flushing technique which utilizes prefabricated vertical drains (PVDs) is an effective remediation method for sandy, silt, and low-permeability clayey soils. It offers several advantages, such as reducing the seepage path, achieving uniform flushing of contaminated areas, and shortening the construction time. This paper proposes an axisymmetric analytical model for PVD-enhanced in-situ flushing remediation of double-layered contaminated soils considering the decay of the initial contaminant concentration along the depth. The derived solutions are then verified against experimental results and existing analytical solutions. The accuracy of the simplified solution is found to improve as the number of stratifications increases by vertically dispersing the initial contaminant concentration, as compared to the numerical results obtained from COMSOL Multiphysics. The study also reveals that a decrease in the spacing between adjacent injection and extraction PVDs or an increase in the injection/extraction rate enhances the flushing efficiency. However, the effects of the two parameters on soil remediation are non-linear and linear, respectively. Furthermore, the difference in the geotechnical properties of the upper soil layers in a bi-layered contaminated soil leads to a variation in the contaminant concentration at any depth and this variation grows larger with time until the soil is completely remediated.