Heavy Metals Removal Using Activated Carbon, Silica and Silica Activated Carbon Composite

Reduction of tar, sulfur, chlorine and CO2 in syngas produced by gasification of refuse-derived fuel pellets

Effective waste management is an increasingly urgent global challenge, with gasification emerging as promising alternative to conventional disposal methods. However, the major challenge in thermochemical waste processing is the presence of contaminants in the product streams. Therefore, this study focuses on the experimental gasification of refuse-derived fuel (RDF) pellets, with the aim of characterizing the products, analyzing contaminant distribution, and purifying the syngas from multiple contaminants simultaneously. Gasification experiments were conducted in a two-stage batch reactor, and the produced syngas was purified using two continuous packed absorption columns. Yields of gaseous, liquid, and solid products were 52.5%, 23.5%, and 7.3%, respectively. Resulting char exhibited a lower heating value (LHV) of 18.24 MJ/kg and retained 76.8% of the sulfur and 35.8% of the chlorine from the RDF. Heavy metal concentrations in the char remained below environmental limits. Syngas achieved a maximum LHV of 11.9 MJ/Nm3. Its purification using aqueous solutions of NaOH and methyl-diethanolamine achieved removal efficiencies of 97.77% for H₂S and 43.06% for COS. Efficiency of HCl removal with NaOH solution ranged from 82.15% to 89.27%, also contributing to CO₂ removal. Tar content in the syngas was significantly reduced through catalytic treatment with Ni/activated carbon, achieving a maximum removal efficiency of 85.89%. Concentrations of key contaminants in syngas were reduced to 6.13 ppm for H2S, 41.58 ppm for COS, 19.37 mg/Nm3 for HCl, and 2.11 g/Nm3 for tar. These results demonstrate the feasibility of integrated gasification and multi-contaminant purification for producing cleaner syngas from RDF, advancing sustainable waste-to-energy solutions.

Green remediation of heavy metals from metal finishing sludge by stabilization/solidification with cement and activated carbon: immobilization and leaching mechanisms

Metal finishing sludges usually require proper disposal due to their high content of leachable harmful species such as heavy metals. This study proposed an efficient and green remediation approach for the S/S of hazardous metal finishing sludge by incorporation of activated carbon (AC) as a cement replacement. Mechanical strength and leaching properties of the treated sludge were investigated. Meanwhile, the immobilization mechanisms were discussed on the basis of X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive spectrometry (SEM-EDS). The effectiveness of the AC/cement binder in S/S was evaluated by comparing it to OPC alone. The experimental results showed that the addition of 10 wt.% of AC resulted in an improvement of the compressive and flexural strength at 28 days of curing by 13.5% and 10.2%, respectively. According to the TCLP test, the concentrations of heavy metals in the leachates of S/S specimens were within the corresponding regulations. From the pH-dependent leaching test, the release of the selected metals was strongly pH-dependent. AC replacement had a significant effect in the reduction of the metal's leachability except for Zn. MLT leaching test indicated that the immobilization rate of heavy metals exceeded 97% for both binders. Linear regression analysis revealed that the leaching mechanism of heavy metals was dominated by diffusion. However, traces of surface wash-off and solubility were also detected. The SEM-EDS method demonstrated that heavy metals were stabilized through adsorption onto activated carbon.

Efficient Removal of Mercury Ions Stabilized by Gold Solution Using Chitosan-Guar Gum Polymer Blend in Basic Media

The highly efficient removal of mercury metal ions at a higher pH (basic media) is barely reported in the literature. In this study, we developed a novel adsorbent by blending chitosan with guar gum, designed to effectively remove mercury ions from basic media by stabilizing them with a gold (Au3⁺) solution. The FTIR confirmed the compatibility of chitosan and guar gum through hydrogen bonding. The morphology of the blend exhibited an amorphous and porous structure. A mesoporous structure with a surface area, volume, and diameter of 11.843 (m2/g), 0.184 (cm2/g), and 17.072 nm, respectively, was confirmed by BET. The adsorption behavior was analyzed using isotherms and kinetics models, which best fitted with the pseudo-second-order kinetic model and Freundlich adsorption isotherm model, respectively. The adsorbent was shown to be an excellent candidate for the removal of mercury ions in water, with an adsorption efficiency of 92% at pH 12 in 60 min and a maximum adsorption capacity of 370.37 (mg/g).

Advances in structure designing and function tailoring strategy toward alginate-based hydrogels for efficient water remediation: A review

Alginate (mainly sodium alginate, SA), as a natural polysaccharide material, has been widely applied in water remediation due to its excellent biocompatibility, degradability, and high hydration properties. Alginate hydrogels exhibit high adsorption capacity, effectively removing heavy metal ions, dyes, antibiotics, phosphate ions, and other pollutants from wastewater. This review begins with a description of the chemical structure of sodium alginate and its physicochemical properties, followed by a detailed discussion of the preparation methods of alginate-based composite hydrogels, including physical and chemical crosslinking, emulsification, electrostatic complexation, self-assembly, ultrasound and microwave-assisted methods. Based on the different compositions of the composites, alginate-based composite hydrogels are classified into several types for the removal of specific pollutants. Moreover, the paper systematically summarizes the research progress of alginate-based composite hydrogels in adsorbing heavy metal ions, dyes, antibiotics, phosphate ions for application effects. Although alginate-based composite hydrogels demonstrate great potential in water remediation, challenges such as insufficient mechanical strength, poor regeneration ability, and low stability under extreme conditions still exist. Finally, the future development prospects of alginate composite hydrogels in the field of water remediation, as well as potential research directions to improve their adsorption performance, enhance their regeneration capacity, and improve their environmental friendliness are presented.

Sustainable Valorization of Rice Straw into Biochar and Carbon Dots Using a Novel One-Pot Approach for Dual Applications in Detection and Removal of Lead Ions

Lead (Pb) is a highly toxic heavy metal that causes significant health hazards and environmental damage. Thus, the detection and removal of Pb2+ ions in freshwater sources are imperative for safeguarding public health and the environment. Moreover, the transformation of single resources into multiple high-value products is vital for achieving sustainable development goals (SDGs). In this regard, the present work focused on the preparation of two efficient materials, i.e., biochar (R-BC) and carbon dots (R-CDs) from a single resource (rice straw), via a novel approach by using extraction and hydrothermal process. The various microscopic and spectroscopy techniques confirmed the formation of porous structure and spherical morphology of R-BC and R-CDs, respectively. FTIR analysis confirmed the presence of hydroxyl (-OH), carboxyl (-COO) and amine (N-H) groups on the R-CDs' surface. The obtained blue luminescent R-CDs were employed as chemosensors for the detection of Pb2+ ions. The sensor exhibited a strong linear correlation over a concentration range of 1 µM to 100 µM, with a limit of detection (LOD) of 0.11 µM. Furthermore, the BET analysis of R-BC indicated a surface area of 1.71 m2/g and a monolayer volume of 0.0081 cm3/g, supporting its adsorption potential for Pb2+. The R-BC showed excellent removal efficiency of 77.61%. The adsorption process followed the Langmuir isotherm model and second-order kinetics. Therefore, the dual use of rice straw-derived provides a cost-effective, environmentally friendly solution for Pb2+ detection and remediation to accomplish the SDGs.

Recent advances in heavy metals uptake by tailored silica-based adsorbents

In the last decade, numerous designed adsorbent materials like metal-organic frameworks (MOFs), covalent organic frameworks (COF), carbon nanotubes (CNTs), etc. have been developed and investigated for metal ions extraction applications in the contaminated aquatic environment. These materials are facing the problems associated with large-scale production, cost, stability, and reusable. Conventional adsorption like carbon and silica is still valuable and is in use for industrial applications. In the last decade, silica has gone through a lot of alteration and modification to enhance its efficiency for heavy metal adsorption. In this review, the tailoring of the silica properties by surface functionalization or developing new hybrid composites for the scavenging of the heavy have been summarized. Silica functionalization with various organic functional groups, composites like silica/polymers, silica/metal oxide, silica aerogels, etc., has been explored. Moreover, interpretations of the effective metal uptake mechanisms associated with metal ions adsorption onto silica adsorbents are also investigated. Overall, the review offers comprehensive insights into the interface between metal ions and silica-based materials.

Removal of Pb(II), Cr(III), Co(II), Cu(II) cations from aqueous solutions using tetraethylenepentamine-functionalized HY cubic zeolite: optimization, characterization, and mechanistic insights

This research utilized tetraethylenepentamine-functionalized HY cubic zeolite as an adsorbent to effectively remove heavy metals from aqueous solutions. The adsorbent was characterized using FT-IR, XRD, TGA, FE-SEM, and EDS-MAP techniques. The synthesis aimed to optimize and evaluate the removal efficiency of Pb(II), Cr(III), Co(II), and Cu(II) from aqueous solutions by investigating key parameters, including initial pH, concentration, adsorbent dosage, and contact time. The results indicate that the highest adsorption capacities for each metal follow the order: Pb(II) > Cr(III) > Co(II) > Cu(II), with respective percentages of 99.7%, 98.2%, 95.1%, and 92.4%. Analysis of the batch systems reveals that the equilibrium data for Pb(II), Cr(III), Co(II), and Cu(II) align well with the Langmuir and Freundlich isotherms also show a good fit, with correlation coefficients (R2) higher than 0.9335 and 0.9478, respectively. The maximum adsorption capacities (181.82, 175.44, 169.49, and 158.73 mg/g) reflect the nature of the adsorption process. Kinetic studies for Pb(II), Cr(III), Cu(II), and Cu(II) yielded correlation coefficients (R2) higher than 0.9971. These high R2 values suggest that the experimental data closely fit a pseudo-second-order model, indicating a two-step adsorption mechanism. Heavy metal removal is attributed to ion exchange and chemisorption within the zeolite pores, involving interactions with nitrogen lone pairs.

Bioinspired hierarchical and dual-morphology humic-acid/pectin/chitosan composite aerogels for efficient removal of pollutants from wastewater

How to solve the contradiction between the efficiency and adsorption rate of porous materials in adsorbing pollutants has always been one of the focus issues. In this study, the small landscape cypress trees structure like biomimetic of a hierarchical and dual morphology 3D porous HA-based aerogel was designed and synthesized to use humic acid (HA), pectin (PE) and chitosan (CTS) as raw materials, which it was formed by the disorderly overlapping of lamella composed of fiber networks in 3D space. Due to its special microstructure, it can be used like separation membrane, which allowing for rapid adsorption of pollutants in the water while the water flow passes through quick. In general, this work provides a new concept for owning fast adsorption rate and efficient adsorption of porous materials of preparation to use green method.

A Novel Approach for Nanosponge: Wool Waste as a Building Block for the Synthesis of Keratin-Based Nanosponge and Perspective Application in Wastewater Treatment

Wool waste is a huge environmental problem that needs to be addressed in order to avoid the continuous accumulation of biohazardous waste in landfills. In recent years, wool has proven to be an excellent source of keratin that can be used for various purposes. But never before has keratin from wool waste been used as a building block to synthesize a well-known class of biopolymers called nanosponges. Typically, nanosponges are produced by the reaction of cyclodextrins with an appropriate cross-linker to obtain an insoluble hyper-cross-linked polymer, which has applications in various fields. For this reason, a novel, affordable approach for the synthesis of a novel class of nanosponge using wool keratin as the building block has been presented. The keratin nanosponge was synthesized by reacting keratin with pyromellitic dianhydride as a cross-linking agent. The formation of a cross-linked polymer was successfully confirmed by CHNS-elemental analysis, TGA, DSC, FTIR-ATR, SEM, and water absorption capacity measurements. Surprisingly, the keratin-based nanosponge showed ∼50% uptake of heavy metals after only 24 h of contact time. The adsorption kinetics was also evaluated, indicating a pseudo-second-order model fit and the mechanism is predominantly the intraparticle diffusion process. The novel synthesized nanosponge proved to be a possible alternative for wastewater treatment.

Porous sodium alginate/cellulose nanofiber composite hydrogel microspheres for heavy metal removal in wastewater

High adsorption capacity, high adsorption rate and reusable adsorbents are urgent needed for removing heavy metals from wastewater. In this study, porous sodium alginate/cellulose nanofiber (SA/CNF) composite hydrogel microspheres were prepared by combining sodium alginate with cellulose nanofibers by microfluidics technology and adding polyethylene glycol (PEG) as pore making agent. The SA/CNF composite hydrogel microspheres could efficiently adsorb heavy metals (Pb2+, Cu2+ and Cd2+) in wastewater. The influencing factors of adsorption process, including pH, temperature, initial concentration, coexisting ions and aquatic environments, were systematically discussed. The adsorption process was more consistent with Langmuir isotherm model and pseudo-second-order model in batch system, indicating the adsorption process was mainly chemical adsorption. The adsorption capacity to Pb2+ obtained by Langmuir model was as high as 544.66 mg/g at 20 °C. Fixed-bed column adsorption experiments demonstrated the excellent performance of the as-prepared SA/CNF microspheres for treatment of the flowing wastewater in a column system. Overall, a highly practical adsorption process based on hydrogel adsorbents was developed for the removal of heavy metals from actual wastewater.

Recycling of Sewage Sludge: Synthesis and Application of Sludge-Based Activated Carbon in the Efficient Removal of Cadmium (II) and Lead (II) from Wastewater

The limited supply of drinking water has aroused people's curiosity in recent decades. Adsorption is a popular method for removing hazardous substances from wastewater, especially heavy metals, as it is cheap, highly efficient, and easy to use. In this work, a new sludge-based activated carbon adsorbent (thickened samples SBAC1 and un-thickened samples SBAC2) was developed to remove hazardous metals such as cadmium (Cd+2) and lead (Pb+2) from an aqueous solution. The chemical structure and surface morphology of the produced SBAC1 and SBAC2 were investigated using a range of analytical tools such as CHNS, BET, FT-IR, XRD, XRF, SEM, TEM, N2 adsorption/desorption isothermal, and zeta potential. BET surface areas were examined and SBAC2 was found to have a larger BET surface area (498.386 m2/g) than SBAC1 (336.339 m2/g). While the average pore size was 10-100 nm for SBAC1 and 45-50 nm for SBAC2. SBAC1 and SBAC2 eliminated approximately 99.99% of Cd+2 and Pb+2 out the water under all conditions tested. The results of the adsorption of Cd+2 and Pb+2 were in good agreement with the pseudo-second-order equation (R2 = 1.00). Under the experimental conditions, the Cd+2 and Pb+2 adsorption equilibrium data were effectively linked to the Langmuir and Freundlich equations for SBAC1 and SBAC2, respectively. The regeneration showed a high recyclability for the fabricated SBAC1 and SBAC2 during five consecutive reuse cycles. As a result, the produced SBAC1 and SBAC2 are attractive adsorbents for the elimination of heavy metals from various environmental and industrial wastewater samples.

N-doped nano-casted carbon monolith for Pb (II) removal and photocatalytic degradation of thiamethoxam from aqueous solution

Single rock-like N-doped carbon monolith (ND-PFCM) was successfully constructed via nanocasting method. Phenol formaldehyde resin was taken as carbon source and nitrogen was incorporated in monoliths through NaNH2 activation. The synthesized monoliths were used for the removal of Pb (II) from aqueous solution. Various characterization techniques, namely Brunauer-Emmett-Teller (BET), Raman spectroscopy, UV-visible diffuse reflectance spectra (DRS) UV-DRS, zeta potential, scanning electron microscopy (SEM), TEM (transmission electron microscopy), TGA (thermogravimetric analysis), and XPS (X-ray photoelectron spectroscopy), were utilized to characterize synthesized monolithic samples. The different parameters such as pH, adsorbent dosage, and time were enquired on the removal efficiency of monoliths toward Pb(II). ND-PFCM exhibited the highest adsorption capacity of 330.03 mg g-1 in 180 min at pH 6. This is attributed to the fact that the better texture properties and presence of nitrogen functional groups enhance the uptake of Pb (II) ions on the monolith surface. In the kinetic studies, pseudo-second-order model fitted best with the experimental data. Furthermore, the removal of thiamethoxam (TM) from aqueous solution was done by using different weight ratios of ND-PFCM under the visible light. The maximum removal efficiency of 97.35% with rate constant of 0.02085 min-1 was obtained in 160 min. Moreover, monoliths exhibited good reusability for five consecutive cycles. The findings suggest that the synthesized monoliths exhibit characteristics suitable and eco-friendly for sustainable use in water treatment applications.

Comprehensive review on toxic heavy metals in the aquatic system: sources, identification, treatment strategies, and health risk assessment

Heavy metal pollution in water sources has become a major worldwide environmental issue, posing a threat to aquatic ecosystems and human health. The pollution of the aquatic environment is increasing as a result of industrialization, climate change, and urban development. The sources of heavy metal pollution in water include mining waste, leachates from landfills, municipal and industrial wastewater, urban runoff, and natural events such as volcanism, weathering, and rock abrasion. Heavy metal ions are toxic and potentially carcinogenic. They can also buildup in biological systems and cause bioaccumulation even at low levels of exposure, heavy metals can cause harm to organs such as the nervous system, liver and lungs, kidneys and stomach, skin, and reproductive systems. There were various approaches tried to purify water and maintain water quality. The main purpose of this article was to investigate the occurrence and fate of the dangerous contaminants (Heavy metal and metalloids) found in domestic and industrial effluents. This effluent mixes with other water streams and is used for agricultural activities and other domestic activities further complicating the issue. It also discussed conventional and non-conventional treatment methods for heavy metals from aquatic environments. Conclusively, a pollution assessment of heavy metals and a human health risk assessment of heavy metals in water resources have been explained. In addition, there have been efforts to focus on heavy metal sequestration from industrial waste streams and to create a scientific framework for reducing heavy metal discharges into the aquatic environment.

Adsorption of arsenic and fluoride: Modeling of single and competitive adsorption systems

The elevated co-occurrence of arsenic and fluoride in surface and groundwater poses risks to human health in many parts of the world. Using single and competitive batch equilibrium adsorption studies, this research focuses on As(V) and F adsorption by activated carbon and its modeling. BET, XRD, FESEM, EDS, and FTIR analysis were used to discern the structural characteristics of activated carbon. The influence of dosage, pH, and contact time were also investigated in single and simultaneous adsorption systems. The maximum adsorption capacity of activated carbon for arsenic and fluoride were found to be 3.58 mg/g and 2.32 mg/g, respectively. Kinetics studies indicated that pseudo-second-order kinetic model fit better than pseudo-first-order, Elovich, and intraparticle diffusion kinetic models. The non-linear regression analysis of Langmuir, Freundlich, Toth, Redlich Petersons, and Modified Langmuir Freundlich models was used to determine single-component asorption model parameters. Additionally, the simultaneous adsorption was rigorously modeled and compared using the Extended Langmuir (EL), Extended Langmuir Freundlich (ELF), Modified Competitive Langmuir (MCL), and Jeppu Amrutha Manipal Multicomponent (JAMM) isotherm models, and competitive mechanisms were interpreted for the simultaneous adsorption system. Further, the model performances were evaluated by statistical error analysis using the normalized average percentage error (NAPE), root mean square errors (RMSE), and the correlation coefficient (R2). According to the modeling results, single equilibrium data fitted better with the Modified Langmuir Freundlich isotherm model, with a higher R2 of 0.99 and lower NAPE values of 3.8 % and 1.28 % for As(V) and F, than other models. For the binary adsorption, the Extended Langmuir Freundlich isotherm model demonstrated excellent fit with lowest errors. All the competitive isotherm models fit the As(V) and F simultaneous sorption systems reasonably well. Furthermore, the research unveiled a nuanced hierarchy of isotherm fitting, with ELF > EL > MCL > JAMM in varying arsenic at a constant fluoride concentration, and ELF > JAMM > EL > MCL in varying fluoride at a constant arsenic concentrations. In addition, competitive studies divulged crucial insights into selective adsorption, as As(V) exhibits a pronounced adsorption selectivity over F on activated carbon. In essence, As(V) showed a more pronounced antagonistic behavior over F, whereas F exhibited a much lesser competitive behavior in the adsorption of arsenic.

Equilibrium, Kinetic, and Diffusion Mechanism of lead(II) and cadmium(II) Adsorption onto Commercial Activated Carbons

The adsorption of Pb(II) and Cd(II) on three commercial microporous activated carbons was analysed. Adsorption kinetics and statistics were investigated, and the results were described with different models. The highest values of the correlation coefficient R2 were obtained for the pseudo-second-order kinetics model for all ions tested and all sorbents used. The adsorption process was found to be determined by both diffusion in the liquid layer and intraparticle diffusion. The adsorption equilibrium is very well described by Langmuir, Temkin, Thoth or Jovanovic isotherm models. Based on the values of n from the Freundlich isotherm and KL from the Langmuir isotherm, the adsorption of cadmium and lead ions was found to be favourable. The highest monolayer capacities were obtained during the adsorption of lead ions (162.19 mg/g) and for cadmium (126.34 mg/g) for activated carbon WG-12. This carbon is characterised by the highest amount of acid functional groups and the largest specific surface area. The adsorption efficiency of the tested ions from natural water is lower than that from a model solution made from deionised water. The lowest efficiencies are obtained when the process occurs from highly mineralised water.

Biotechnological applications of amyloid fibrils

Protein aggregates and amyloid fibrils have special qualities and are used in a variety of biotechnological applications. They are extensively employed in bioremediation, biomaterials, and biocatalysis. Because of their capacity to encapsulate and release pharmaceuticals and their sensitivity to certain molecules, respectively, they are also used in drug delivery and biosensor applications. They have also demonstrated potential in the domains of food and bioremediation. Additionally, amyloid peptides have drawn interest in biological applications, especially in the investigation of illnesses like Parkinson's and Alzheimer's. The unique characteristics of amyloid fibrils, namely their mechanical strength and β-sheet structure, make them adaptable to a wide range of biotechnological uses. Even with their promise, one important factor to keep in mind before widely using modified amyloid materials is their potential toxicity. Thus, current research aims to overcome safety concerns while maximizing their potential.

Pyrolysis of exhausted biochar sorbent: Fates of cadmium and generation of products

Biochar is a promising sorbent for Cd removal from water, while the disposal of the exhausted Cd-enriched biochar remains a challenge. In this study, pyrolysis was employed to treat the exhausted biochar under N2 and CO2 atmospheres at 600-900 °C, and the fate of Cd during pyrolysis and characteristics of high-valued products were determined. The results indicated that higher temperature and CO2 atmosphere favored the volatilization of Cd. Based on the toxicity characteristic leaching procedure (TCLP) results, the pyrolysis treatment under both atmospheres enhanced the stability of Cd, and the leached Cd concentration of regenerated biochar obtained at high temperatures (>800 °C) was lower than 1 mg/L. Compared with the pristine biochar, the regenerated biochar demonstrated higher carbon content and pH, whereas the contents of oxygen and hydrogen declined, and exhibited promising sorption properties (35.79 mg/g). The atmosphere played an important role in modifying biochar properties and syngas composition. The N2 atmosphere facilitated CH4 production, whereas the CO2 atmosphere increased the proportion of CO. These results implied that pyrolysis can be a valuable and environmental-friendly strategy for the treatment and reuse of exhausted biochar sorbent.

Metal sequestration by Microcystis extracellular polymers: a promising path to greener water treatment

The problem of heavy metal pollution in water bodies poses a significant threat to both the environment and human health, as these toxic substances can persist in aquatic ecosystems and accumulate in the food chain. This study investigates the promising potential of using Microcystis aeruginosa extracellular polymeric substances (EPS) as an environmentally friendly, highly efficient solution for capturing copper (Cu2+) and nickel (Ni2+) ions in water treatment, emphasizing their exceptional ability to promote green technology in heavy metal sequestration. We quantified saccharides, proteins, and amino acids in M. aeruginosa biomass and isolated EPS, highlighting their metal-chelating capabilities. Saccharide content was 36.5 mg g-1 in biomass and 21.4 mg g-1 in EPS, emphasizing their metal-binding ability. Proteins and amino acids were also prevalent, particularly in EPS. Scanning electron microscopy (SEM) revealed intricate 3D EPS structures, with pronounced porosity and branching configurations enhancing metal sorption. Elemental composition via energy dispersive X-ray analysis (EDAX) identified essential elements in both biomass and EPS. Fourier transform infrared (FTIR) spectroscopy unveiled molecular changes after metal treatment, indicating various binding mechanisms, including oxygen atom coordination, π-electron interactions, and electrostatic forces. Kinetic studies showed EPS expedited and enhanced Cu2+ and Ni2+ sorption compared to biomass. Thermodynamic analysis confirmed exothermic, spontaneous sorption. Equilibrium biosorption studies displayed strong binding and competitive interactions in binary metal systems. Importantly, EPS exhibited impressive maximum sorption capacities of 44.81 mg g-1 for Ni2+ and 37.06 mg g-1 for Cu2+. These findings underscore the potential of Microcystis EPS as a highly efficient sorbent for heavy metal removal in water treatment, with significant implications for environmental remediation and sustainable water purification.

End-of-life tyre conversion to energy: A review on pyrolysis and activated carbon production processes and their challenges

The number of end-of-life waste tyres has increased enormously worldwide, which is one of the non-biodegradable Municipal Solid Waste (MSW) piling up in an open space for a long time. Every year, various types of tyres are released in the environment from different vehicles, such as trucks, buses, cars, motorcycles, and bicycles, which negatively impact the environment. Nowadays, waste tyres are treated in several ways, whereas thermochemical conversion is one of them, including combustion, gasification, incineration, and pyrolysis. Many literatures revealed that pyrolysis is a more environmentally friendly process than others since it can convert waste tyres into crude oil, char, and syngas without emitting harmful gases. In this study, the pyrolysis of tyres and the chemical activation of tyres are reviewed in terms of their kinetic behaviour. According to the literature, the most influential factors of the pyrolysis process are reactors, temperature, heating rate, residence time, feedstock size and catalyst. As the main ingredient of the tyre is rubber, tyre pyrolysis starts from 300 °C and completely decomposed nearly 550 °C. It can be found from literature that Pyrolysed tyre can produce 30-65% oil, 25-45% char and 5-20 % gas. It is also explained how the properties of active carbon (AC) are affected by activating conditions, including activation temperature, agent, the ratio of reagent mixture and others. Generally, pyrolytic char has surface area between 20 and 80 m2/g, whereas tyre-derived activated carbon's (TDAC) surface area varied from 90 to 970 m2/g. For large surface area and porous structure, TDAC has large application in purification and energy storage sector. The individuality of this article is to depict the entire pathway of AC production from waste tyres. The findings of this literature review help to improve technologies for producing activated carbon from waste tyres pyrolysed char.

Well-designed protein amyloid nanofibrils composites as versatile and sustainable materials for aquatic environment remediation: A review

Amyloid nanofibrils (ANFs) are supramolecular polymers originally classified as pathological markers in various human degenerative diseases. However, in recent years, ANFs have garnered greater interest and are regarded as nature-based sustainable biomaterials in environmental science, material engineering, and nanotechnology. On a laboratory scale, ANFs can be produced from food proteins via protein unfolding, misfolding, and hydrolysis. Furthermore, ANFs have specific structural characteristics such as a high aspect ratio, good rigidity, chemical stability, and a controllable sequence. These properties make them a promising functional material in water decontamination research. As a result, the fabrication and application of ANFs and their composites in water purification have recently gained considerable attention. Despite the large amount of literature in this field, there is a lack of systematic review to assess the gap in using ANFs and their composites to remove contaminants from water. This review discusses significant advancements in design techniques as well as the physicochemical properties of ANFs-based composites. We also emphasize the current progress in using ANFs-based composites to remove inorganic, organic, and biological contaminants. The interaction mechanisms between ANFs-based composites and contaminants are also highlighted. Finally, we illustrate the challenges and opportunities associated with the future preparation and application of ANFs-based composites. We anticipate that this review will shed new light on the future design and use of ANFs-based composites.

Synthesis and characterization of cost-effective and high-efficiency biochar for the adsorption of Pb2+ from wastewater

This study aimed to investigate the adsorption mechanism of Pb2+ in wastewater using activated carbon derived from inexpensive materials, specifically avocado, bitter orange, and walnut leaves, through a single-step chemical activation process. The activated carbon was prepared using sulfuric acid as an activator, with a particle size of 1 mm. The pyrolysis reactor (slow-pyrolysis) operated at 600 °C for 90 min with a nitrogen flow rate of 5 L/min. Batch experiments were conducted under various conditions to determine the optimal dosage (1.5 g/L), equilibrium contact time (180 min), and pH (6.5). The study focused on employing cost-effective and highly efficient adsorbents, namely biochar produced from tree leaves, for the adsorption process. The results indicated that the pseudo-second-order kinetic model accurately described the adsorption process, while the Freundlich isotherm model best fit the experimental data. These findings suggest that tree leaves can serve as cost-effective and efficient adsorbents for a wide range of applications. Furthermore, multiple adsorption factors were evaluated in batch mode, including contact duration, pH, adsorbent dosage, concentration of the Pb2+ solution, and temperature. The maximum adsorption capacities for the activated carbon derived from avocado, bitter orange, and walnut leaves were found to be 60.46, 59.42, and 58.48 mg/g, respectively. Thus, this study highlights the effectiveness and economic feasibility of using pyrolysis-derived activated carbon from low-cost materials for the removal of Pb2+ from wastewater.

Thermodynamic and Kinetic Aspects of Gold Adsorption in Micrometric Activated Carbon and the Impact of Their Loss in Adsorption, Desorption, and Reactivation Plants

The production and loss of fine particles of activated carbon (AC) loaded with gold in the adsorption processes is a worldwide problem, mainly due to the behavior of increasing its adsorption capacity with respect to the decrease in particle size, which becomes relevant to determine the thermodynamic and kinetic activity of the gold adsorption and the economic impact of its loss, with the escape towards the later stages of the system of adsorption, desorption, and reactivation (ADR) plants of AC. Through the adsorption of gold in a synthetic medium with sodium cyanide concentration, using different particle sizes, AC weights, and adsorption times, data were generated for analysis by three different isotherm models, resulting in a better tendency for the Freundlich isotherm, from which thermodynamic parameters of ΔG equal to -2.022 kcal/mol, ΔH equal to -16.710 kcal/mol, and ΔS equal to -0.049 kcal/molK were obtained, which shows that it is a spontaneous, exothermic process with a lower degree of disorder. The kinetic analysis was performed with two different models, from which the pseudo-second-order model was used due to a better tendency and displayed a behavior that leaves open the interpretation of the increase in adsorption with respect to the decrease in the AC particle size but demonstrated the importance of recovering these particles in relation to their gold concentration and the economic impact from their poor recovery, which, for this case study, amounted to ~0.3 million dollars per year.

Water pollution control and revitalization using advanced technologies: Uncovering artificial intelligence options towards environmental health protection, sustainability and water security

In Ghana, illegal mining (galamsey) activities have polluted most of the river bodies. For example, water bodies in Ghana that are polluted amounts to 60% with most of them in deteriorating condition. However, to live a sustainable life, there is the need to follow rules of environmental management, where pollution control and advanced treatment technologies are imperative. The adoption of control strategies and advanced technologies in galamsey-affected-water basins in Ghana will help provide real-time revitalization for supply of quality water. The control strategies for water pollution management and advanced technologies would particularly help utility companies in ensuring that all Ghanaians continue to get potable, reliable, and sustainable water supplies for the current and future generations. The paper covers three key control strategies for water pollution management, vis-à-vis six major aspects of advanced technologies and the use of artificial intelligence (AI). AI based decision-making tools help optimize the use of various treatment technologies, such as adsorption, ion exchanges, electrokinetic processes, chemical precipitation, phytobial remediation, and membrane technology to effectively remove pollutants from affected water bodies. The paper also focuses on advantages and disadvantages of several advanced technologies, challenges on leveraging the technologies while identifying gaps, and possible technology roadmap. The review contributes to water quality issues in Ghana's Pra river basin by embracing AI and other cutting-edge technologies to address the current water pollution crisis and also ensure sustainable and secure water supply for future generations. This contribution is in line with the United Nations' Agenda 2030 Sustainable Development Goals' (SDGs) goal 6 (clean water and sanitation) and goal 3 (good health and well-being).

MXenes and MXene-based materials for removal of pharmaceutical compounds from wastewater: Critical review

The rapid increase in the global population and its ever-rising standards of living are imposing a huge burden on global resources. Apart from the rising energy needs, the demand for freshwater is correspondingly increasing. A population of around 3.8 billion people will face water scarcity by 2030, as per the reports of the World Water Council. This may be due to global climate change and the deficiency in the treatment of wastewater. Conventional wastewater treatment technologies fail to completely remove several emerging contaminants, especially those containing pharmaceutical compounds. Hence, leading to an increase in the concentration of harmful chemicals in the human food chain and the proliferation of several diseases. MXenes are transition metal carbide/nitride ceramics that primarily structure the leading 2D material group. MXenes act as novel nanomaterials for wastewater treatment due to their high surface area, excellent adsorption properties, and unique physicochemical properties, such as high electrical conductivity and hydrophilicity. MXenes are highly hydrophilic and covered with active functional groups (i.e., hydroxyl, oxygen, fluorine, etc.), which makes them efficient adsorbents for a wide range of species and promising candidates for environmental remediation and water treatment. This work concludes that the scaling up process of MXene-based materials for water treatment is currently of high cost. The up-to-date applications are still limited because MXenes are currently produced mainly in the laboratory with limited yield. It is recommended to direct research efforts towards lower synthesis cost procedures coupled with the use of more environmentally friendly materials to avoid secondary contamination.

Investigation of kinetic, isotherm and adsorption efficacy of thorium by orange peel immobilized on calcium alginate

In this research work the thorium uptake on immobilized protonated orange peel was studied in a batch system. The effects of effective parameters such as biosorbent dosage, initial metal ion concentration, and contact time on the biosorption of thorium were analyzed. The biosorption capacity of the immobilized orange peel for thorium at optimal conditions of initial pH 3.8, biosorbent dosage 8 g/L, and initial thorium concentration 170 mg/L was found to be 18.65 mg/g. According to the results of contact time, the biosorption process reached equilibrium after around 10 h of contact. Investigation of the kinetics showed that the biosorption of thorium onto immobilized orange peel follows the pseudo-second-order model. The Langmuir and Freundlich isotherms were used to model the experimental equilibrium data. The results showed better agreement by the Langmuir isotherm. The maximum absorption capacity of immobilized protonated orange peel for thorium adsorption was predicted by the Langmuir isotherm at 29.58 mg/g.

A Review on the Adsorption Isotherms and Design Calculations for the Optimization of Adsorbent Mass and Contact Time

Adsorption is a widely used chemical engineering unit operation for the separation and purification of fluid streams. Typical uses of adsorption include the removal of targeted pollutants like antibiotics, dyes, heavy metals, and other small to large molecules from aqueous solutions or wastewater. To date several adsorbents that vary in terms of their physicochemical properties and costs have been tested for their efficacy to remove these pollutants from wastewater. Irrespective of the type of adsorbent, nature of the pollutant, or experimental conditions, the overall cost of adsorption depends directly on the adsorption contact time and the cost of the adsorbent materials. Thus, it is essential to minimize the amount of adsorbent and the contact time required. We carefully reviewed the attempts made by several researchers to minimize these two parameters using theoretical adsorption kinetics and isotherms. We also clearly explained the theoretical methods and the calculation procedures involved during the optimization of the adsorbent mass and the contact time. To complement the theoretical calculation procedures, we also made a detailed review on the theoretical adsorption isotherms that are commonly used to model experimental equilibrium data that can be used to optimize the adsorbent mass.

Activated Carbon and Clay Pellets Coated with Hydroxyapatite for Heavy Metal Removal: Characterization, Adsorption, and Regeneration

In the present work, activated-carbon-containing pellets were preparedby direct chemical activation of sawdust, using clays as a binder. The obtained pellets (ACC) were coated with hydroxyapatite (HAp) nanoparticles (ACC-HAp) to improve adsorption towards Pb(II), Cu(II), Zn(II), and Ni(II). The pellets were characterized by scanning electron microscopy (SEM), by Fourier transform infrared spectroscopy (FTIR), and with a gas sorptometer. The effect of pH, contact time, and initial concentration on adsorption performance was investigated. Additionally, desorption studies were performed, and the regeneration influence on compressive strength and repeated Pb(II) adsorption was investigated. The results showed that, after coating ACC pellets with HAp nanoparticles, the adsorption capacity increased for all applied heavy metal ions. Pb(II) was adsorbed the most, and the best results were achieved at pH 6. The adsorption process followed the pseudo-second-order kinetic model. The adsorption isotherm of Pb(II) is better fitted to the Langmuir model, showing the maximum adsorption capacity of 56 and 47 mg/g by ACC-HAp and ACC pellets, respectively. The desorption efficiency of Pb(II)-loaded ACC-HAp pellets increased by lowering the pH of the acid, resulting in the dissolution of the HAp coating. The best desorption results were achieved with HCl at pH 1 and 1.5. Therefore, the regeneration procedure consisted of desorption, rinsing with distilled water, and re-coating with HAp nanoparticles. After the regeneration process, the Pb(II) adsorption was not affected. However, the desorption stage within the regeneration process decreased the compressive strength of the pellets.

Radiation fabrication of hybrid activated carbon and functionalized terpolymer hydrogel for sorption of Eu(III) and Sm(III) ions

In this work, a hybrid composite of activated carbon (AC) functionalized with terpolymer hydrogel of polyvinyl alcohol/polyacrylamide/polyacrylic acid (PVA/PAAm/PAA) was prepared by γ-irradiation and used efficiently for sorption of Eu(III) and Sm(III) ions from aquatic solutions. Sewage sludge from the wastewater treatment plant was used to prepare AC, then activated by zinc chloride (ZnCl2) and thermal treatment at 550 °C. The modification of AC by functionalized terpolymer has successfully occurred mainly to limit its precipitation and to increase its adsorption capacity which allowed capable interaction with the metal ions. Different advanced techniques were used to investigate the structure and properties of (PVA/PAAm/PAA)/AC composite before and after the sorption process. Using 20 kGy is sufficient to get gel fraction of 87.5% and equilibrium swelling was 39.1 g/g. The (PVA/PAm/PAA)/AC composite hydrogel showed a pHpzc at pH ∼3. FTIR and EDS confirmed the successful integration of the functional groups and constituent elements of AC into terpolymer hydrogel components. XRD results confirmed the typical diffraction peaks of AC in the composite and the calculated average crystallite size was 167.4 nm. The SEM morphology of AC appeared as grains distributed well into the composite. The effect of synthesized AC, PVA/PAAm/PAA and (PVA/PAAm/PAA)/AC sorbents were tested to uptake of Eu(III) and Sm(III) ions. The highest uptake was noticed for (PVA/PAAm/PAA)/AC composite and it was selected for studying the parameters affecting the sorption process such as pH, shaking time, initial concentration, and adsorbent dosage. Results of the experimental data showed that Langmuir isotherm and Pseudo-second-order kinetic models fit well the sorption process of both Eu(III) and Sm(III) ions with maximum sorption capacities of 173.24 and 160.41 mg/g and uptake percentage of 82.3% and 83.4%, respectively at the optimum conditions of pH 4, 180 min, 100 mg/L metal concentration and 0.01 g adsorbent mass. The thermodynamic parameters indicated endothermic and spontaneous nature of the sorption process. Additionally, the as-prepared composite afford high selectivity and uptake capacity for Eu(III) and Sm(III) ions at pH 4 even in the presence of competing cations; Cd(II), Co(II), Sr(II) and Cs(I). The (PVA/PAAm/PAA)/AC composite was used efficiently as a unique and selective adsorbent for the sorption of Eu(III) and Sm(III) ions.

A Carbonized Zeolite/Chitosan Composite as an Adsorbent for Copper (II) and Chromium (VI) Removal from Water

To address Cu(II) and Cr(VI) water pollution, a carbonized zeolite/chitosan (C-ZLCH) composite adsorbent was produced via pyrolysis at 500 °C for two hours. C-ZLCH was characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and zeta potential measurements. The batch experiments were performed by varying the initial pH, concentration, and contact time. The optimal pH values for Cu(II) and Cr(VI) were 8.1 and 9.6, respectively. The highest adsorption capacities for Cu(II) and Cr(VI) were 111.35 mg/g at 60 min and 104.75 mg/g at 90 min, respectively. The effects of chemicals such as sodium (Na⁺), glucose, ammonium (NH₄⁺), and acid red 88 (AR88) were also studied. Statistical analysis showed that sodium had no significant effect on Cu(II) removal, in contrast to Cr(VI) removal. However, there was a significant effect of the presence of glucose, ammonium, and AR88 on both Cu(II) and Cr(VI) removal. The adsorption isotherm and kinetic models were fitted using Langmuir and pseudo-second-order models for Cu(II) and Cr(VI), respectively.

Hybrid Inorganic Organic PSF/Hap Dual-Layer Hollow Fibre Membrane for the Treatment of Lead Contaminated Water

Lead (Pb) exposure can be harmful to public health, especially through drinking water. One of the promising treatment methods for lead contaminated water is the adsorption-filtration method. To ensure the cost-effectiveness of the process, naturally derived adsorbent shall be utilised. In this study, hydroxyapatite particles, Ca₁₀(PO₄)₆(OH)₂ (HAP) derived from waste cockle shell, were incorporated into the outer layer of polysulfone/HAP (PSf/HAP) dual-layer hollow fibre (DLHF) membrane to enhance the removal of lead from the water source due to its hydrophilic nature and excellent adsorption capacity. The PSf/HAP DLHF membranes at different HAP loadings in the outer layer (0, 10, 20, 30 and 40 wt%) were fabricated via the co-extrusion phase inversion technique. The performance of the DLHF membranes was evaluated in terms of pure water flux, permeability and adsorption capacity towards lead. The results indicated that the HAP was successfully incorporated into the outer layer of the membrane, as visibly confirmed by microscopic analysis. The trend was towards an increase in pure water flux, permeability and lead adsorption capacity as the HAP loading increased to the optimum loading of 30 wt%. The optimized DLHF membrane displayed a reduced water contact angle by 95%, indicating its improved surface hydrophilicity, which positively affects the pure water flux and permeability of the membrane. Furthermore, the DLHF membrane possessed the highest lead adsorption capacity, 141.2 mg/g. The development of a hybrid inorganic-organic DLHF membrane via the incorporation of the naturally derived HAP in the outer layer is a cost-effective approach to treat lead contaminated water.

Biosorption of zinc (II) from synthetic wastewater by using Inula Viscosa leaves as a low-cost biosorbent: Experimental and molecular modeling studies

The use of biosorption as a strategy for lowering the amount of pollution caused by heavy metals is particularly encouraging. In this investigation, a low-cost and efficient biosorbent, Inula Viscosa leaves were used to remove zinc ions (Zn²⁺) from synthetic wastewater. A Fourier transform infrared spectroscopy experiment, a scanning electron microscopy experiment, and an energy dispersive X-ray spectroscopy experiment were used to describe the support. Several different physicochemical factors, such as the beginning pH value, contact duration, initial zinc concentration, biosorbent dose, and temperature, were investigated in this study. When the Langmuir, Freundlich, Temkin, Toth, and Redlich-Peterson models were used to match the data from the Inula Viscosa leaves biosorption isotherms, it was found that the biosorption isotherms correspond most closely with the Langmuir isotherm. On the other hand, the kinetic biosorption process was investigated using pseudo-first-order, pseudo-second-order (PS2), and Elovich models. The PS2 model was the one that provided the most accurate description of the biosorption kinetics. The thermodynamics process shows the spontaneous and endothermic character of Zn²⁺ sorption on Inula Viscosa leaves, which also entails the participation of physical interactions. In addition, the atom-in-molecule analysis, density functional theory, and the conductor like screening model for real solvents, were used to investigate the relationship that exists between quantum calculations and experimental outcomes.

Sulfur-Doped Binary Layered Metal Oxides Incorporated on Pomegranate Peel-Derived Activated Carbon for Removal of Heavy Metal Ions

In this study, a novel biomass adsorbent based on activated carbon incorporated with sulfur-based binary metal oxides layered nanoparticles (SML-AC), including sulfur (S2), manganese (Mn), and tin (Sn) oxide synthesized via the solvothermal method. The newly synthesized SML-AC was studied using FTIR, FESEM, EDX, and BET to determine its functional groups, surface morphology, and elemental composition. Hence, the BET was performed with an appropriate specific surface area for raw AC (356 m2·g−1) and modified AC-SML (195 m2·g−1). To prepare water samples for ICP-OES analysis, the suggested nanocomposite was used as an efficient adsorbent to remove lead (Pb2+), cadmium (Cd2+), chromium (Cr3+), and vanadium (V5+) from oil-rich regions. As the chemical structure of metal ions is influenced by solution pH, this parameter was considered experimentally, and pH 4, dosage 50 mg, and time 120 min were found to be the best with high capacity for all adsorbates. At different experimental conditions, the AC-SML provided a satisfactory adsorption capacity of 37.03−90.09 mg·g−1 for Cd2+, Pb2+, Cr3+, and V5+ ions. The adsorption experiment was explored, and the method was fitted with the Langmuir model (R2 = 0.99) as compared to the Freundlich model (R2 = 0.91). The kinetic models and free energy (<0.45 KJ·mol−1) parameters demonstrated that the adsorption rate is limited with pseudo-second order (R2 = 0.99) under the physical adsorption mechanism, respectively. Finally, the study demonstrated that the AC-SML nanocomposite is recyclable at least five times in the continuous adsorption−desorption of metal ions.

Facile synthesis of rose-like composites of zeolites and layered double hydroxides: Growth mechanism and enhanced properties

Excellent performances of various materials often depend on high specific surface areas. Therefore, increase of specific surface areas is one of the most important means to improve the properties and performances of materials. Herein, we report a facile strategy to prepare novel composite materials of zeolites and hydrotalcite-like layered double hydroxides, with high specific surface areas. The composites with a rose-like morphology were synthesized hydrothermally by adding synthetic zeolites to the raw materials used for the formation of hydrotalcite. The resultant composites were shown to contain two distinct layered double hydroxides with different Mg/Al molar ratios. Nitrogen (N₂) adsorption-desorption measurements showed that the specific surface areas and the pore volumes of these composites increased by an order of magnitude in comparison with hydrotalcite. The new composites were shown to be capable of effectively removing Cr(VI), Cu(II) and methylene blue from aqueous environments and had better performances for the latter two contaminants than hydrotalcite. Moreover, this strategy potentially opens up the synthesis of new composite materials with tunable compositions and enhanced properties for environmental and other applications.

Effect of Exhausted Coffee Ground Particle Size on Metal Ion Adsorption Rates and Capacities

Spent coffee grounds (SCGs) are common waste products that can be used as low-cost adsorbents to remove contaminants from water. SCGs come in a range of particle sizes based on how they were ground to brew coffee. However, few studies have investigated how SCG particle size influences the adsorption rate and capacities of metal ions. In this study, SCGs were washed under alkaline conditions, creating exhausted coffee grounds (ECGs). ECGs were sieved into four particle size ranges (106-300, 300-500, 500-710, and 710-1000 μm). Monocomponent batch adsorption experiments were conducted with each size fraction using 0.3 mM Pb²⁺, Cu²⁺, Zn²⁺, and Ni²⁺ at pH 5.5 to examine the effect of particle size on the adsorption rates and capacities. The initial adsorption rates for all the four metal ions were 8-12 times higher for the smallest ECGs compared to the largest ECGs. Slower initial adsorption rates with increasing particle size were due to intraparticle diffusion of metal ions into the porous structure of ECGs. However, the equilibrium adsorption capacities for each metal ion and the surface acidic group concentrations were similar across the range of particle sizes studied, suggesting that grinding ECGs does not substantially change the number of adsorption sites. The equilibrium adsorption capacities for Cu²⁺ and Pb²⁺ were 0.18 and 0.17 mmol g^-1, respectively. Zn²⁺ and Ni²⁺ had lower adsorption capacities of 0.12 and 0.10 mmol g^-1, respectively. The time needed to reach equilibrium ranged from less than 2 h for Zn²⁺ and Ni²⁺ adsorption onto the smallest ECGs to several hours for Pb²⁺ or Cu²⁺ adsorption onto the largest ECGs. Future adsorption studies should consider the effect of ECG particle size on reported adsorption capacities, particularly for shorter experiments that have not yet reached equilibrium.

Novel adsorbents for the removal of toxic cadmium ions from polluted water

Cadmium is one of the most toxic heavy metal ions found in wastewaters and its remedial methods are globally investigated. Removal methods based on biomaterials as adsorbents are proving to be simple, effective and eco-friendly. In the present investigation, bio-adsorbents derived from Cochlospermum regium plant stems (CRSP) and its active carbon (CRAC) are observed to have good adsorption for toxic cadmium ions. Hence, extraction conditions are optimized for maximum Cd-extraction: 55.0% with 'CRSP' and 70.0% with 'CRAC', from Cd²⁺ solutions of concentration: 25.0 mg/L. The adsorption capacities are 6.9 mg/g with CRSP and 12.6 mg/g with 'CRAC'. When 'CRAC' is impregnated with nano-CeO₂ (CRAC.nCeO₂) and is used as adsorbent, the percentage of Cd-extraction is increased to 90.0% and adsorption capacity to 22.5 mg/g at the optimized extraction conditions. To overcome the agglomeration of nanoparticles, the 'CRAC.nCeO₂' is immobilized in Zr-alginate beads and thus obtained beads are investigated as adsorbent. With beads (CRAC.nCeO₂-Zr.alg), the percentage of Cd-adsorption is enhanced to 95.0% and adsorption capacity to 24.6 mg/g. The adsorbents are characterized by adopting XRD and FTIR techniques. The adsorption mechanism is assessed by evaluating thermodynamic parameters, isotherm and kinetic models. The thermodynamic parameters and FTIR spectral characteristics indicate the formation of 'surface complex' between Cd²⁺ and adsorbent's functional groups. The adsorption follows Freundlich isotherm and pseudo-second order model. Many co-ions have not effected the percentage of extraction and interestingly, the presence of some cations (Al³⁺ and Fe³⁺) have synergistically enhanced the Cd-extraction. Spent sorbents can be regenerated and reused with marginal loss of adsorption capacity. The adsorbents developed are successfully used to treat real Cd-polluted wastewater. The novelty of the present investigation is that the effective, eco-friendly, renewable and robust sorbents with high sorption capacities are developed for Cd-remediation of water.

Clay-Alginate Beads Loaded with Ionic Liquids: Potential Adsorbents for the Efficient Extraction of Oil from Produced Water

Produced water (PW) generated from the petroleum industry, during the extraction of oil and gas, has harmful impacts on human health and aquatic life, due to its complex nature. Therefore, it is necessary to treat it before discharging it into the environment in order to avoid serious environmental concerns. In this research, oil adsorption from PW was investigated using clay-alginate beads loaded with ionic liquids (ILs), as the adsorbent material. The effects of several process parameters, such as the initial concentration of oil, contact time, pH, and temperature on the removal efficiency of the beads, were analyzed and optimized. Different characterization methods, such as the Fourier transform infrared spectrophotometer (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and thermal gravimetric analysis (TGA), were used to investigate the surface morphology, the chemical bond structure and functional group, and the thermal stability of the ILs-based beads. The results revealed that the clay-alginate-ILs beads indicated a removal efficiency of 71.8% at the optimum conditions (600 ppm initial oil concentration, 70 min contact time, 10 pH, and at room temperature) with an adsorption capacity of 431 mg/g. The FTIR analysis confirmed the successful chemical bond interaction of the oil with the beads. The SEM analysis verified that the beads have a porous and rough surface, which is appropriate for the adsorption of oil onto the bead’s surface. The TGA analysis provides the thermal degradation profile for the clay-alginate-ILs. The beads used in the adsorption process were regenerated and used for up to four cycles.

Heavy Metal Pollution in Aquaculture: Sources, Impacts and Mitigation Techniques

Aquaculture is one of the fastest growing agro-industries as it presently accounts for nearly 50% of all fish for direct human consumption and 43% of total seafood supply. Fish provide about 20% average daily intake of animal protein for about 3.2 billion people globally. The treatment of aquaculture in recent years for the mitigation of heavy metals and other contaminants has been gaining traction due to the benefits of aquaculture to both man and the environment. This paper provides a review of the sources, impacts, and the various methods that have been deployed in recent years by various researchers for the treatment of heavy metal contaminated aquaculture. Related works of literature were obtained and compiled from academic search databases and were carefully analysed in this study. The dangers these metals pose to the sustainability of aquaculture were studied in this review. Studies indicate that some heavy metals, such as mercury, lead, and cadmium, due to their long-term persistence in the environment, allow them to accumulate in the food chain. Mitigation techniques such as adsorption, bio-sorption, and phytoremediation have been deployed for the treatment of heavy metal contaminated aquaculture. Some research gaps were also highlighted which could form the basis for future research, such as research centred on the effects of these metals on the embryonic development of aquaculture organisms and the alterations the metals caused in their stages of development.

A critical review on diverse technologies for advanced wastewater treatment during SARS-CoV-2 pandemic: What do we know?

Advanced wastewater treatment technologies are effective methods and currently attract growing attention, especially in arid and semi-arid areas, for reusing water, reducing water pollution, and explicitly declining, inactivating, or removing SARS-CoV-2. Overall, removing organic matter and micropollutants prior to wastewater reuse is critical, considering that water reclamation can help provide a crop irrigation system and domestic purified water. Advanced wastewater treatment processes are highly recommended for contaminants such as monovalent ions from an abiotic source and SARS-CoV-2 from an abiotic source. This work introduces the fundamental knowledge of various methods in advanced water treatment, including membranes, filtration, Ultraviolet (UV) irradiation, ozonation, chlorination, advanced oxidation processes, activated carbon (AC), and algae. Following that, an analysis of each process for organic matter removal and mitigation or prevention of SARS-CoV-2 contamination is discussed. Next, a comprehensive overview of recent advances and breakthroughs is provided for each technology. Finally, the advantages and disadvantages of each method are discussed.

Recycling of Waste Toner Powder as Adsorbent to Remove Aqueous Heavy Metals

The removal of Cd²⁺, Zn²⁺ and Ni²⁺ from metal solutions onto waste toner power (WTP) was investigated. The influence of parameters such as pH, contact time, initial metal concentration and adsorbent dosage was studied in batch adsorption experiments. Batch equilibrium experiments showed that the highest removal efficiency for Zn²⁺ and Cd²⁺ occurs at pH 7, while pH 5 is the most suitable for Ni²⁺ removal. The amount of metal removed (mg/g) improved when increasing the initial concentration, and sorption of heavy metals reached equilibrium in 24 h. Metals’ uptake increased with increasing adsorbent dosage. The adsorption isotherms of Zn²⁺, Cd²⁺ and Ni²⁺ onto WTP fit the Langmuir better than the Freundlich model with correlation coefficient R² values ranging from 0.998 to 0.968 and 0.989 to 0.881, respectively. The data showed that the maximum adsorption capacity of heavy metals, a_max, ranged from 2.42 to 1.61 mg/g, from 6.22 to 2.01 mg/g and from 3.49 to 2.56 mg/g for Ni²⁺, Zn²⁺ and Cd²⁺, respectively, with the three WTPs used in this study. This adsorbent can potentially be used to remove metal ions from wastewater.