Removal of soluble microbial products and dyes using heavy metal wastes decorated on eggshell

Two decades of research trends in microbial-induced carbonate precipitation for heavy metal removal: a bibliometric review and literature review

Amidst the increasing significance of innovative solutions for bioremediation of heavy metal removal, this paper offers a thorough bibliometric analysis of microbial-induced carbonate precipitation (MICP) for heavy metal removal, as a promising technology to tackle this urgent environmental issue. This study focused on articles published from 1999 to 2022 in the Scopus database. It assesses trends, participation, and key players within the MICP for heavy metal sequestration. Among the 930 identified articles, 74 countries participated in the field, with China being the most productive. Varenyam Achal, the Chinese Academy of Sciences, and Chemosphere are leaders in the research landscape. Using VOSviewer and R-Studio, keyword hotspots like "MICP", "urease", and "heavy metals" underscore the interdisciplinary nature of MICP research and its focus on addressing a wide array of environmental and soil-related challenges. VOSviewer emphasises essential terms like "calcium carbonate crystal", while R-Studio highlights ongoing themes such as "soil" and "organic" aspects. These analyses further showcase the interdisciplinary nature of MICP research, addressing a wide range of environmental challenges and indicating evolving trends in the field. This review also discusses the literature concerning the potential of MICP to immobilise contaminants, the evolution of the research outcome in the last two decades, MICP treatment techniques for heavy metal removal, and critical challenges when scaling from laboratory to field. Readers will find this analysis beneficial in gaining valuable insights into the evolving field and providing a solid foundation for future research and practical implementation.

Fabrication and Characterization of Functional Biobased Membranes from Postconsumer Cotton Fabrics and Palm Waste for the Removal of Dyes

Textile industries currently face vast challenges for the active removal of colored wastewater. Indeed, sustainable, recyclable, and green approaches are still lacking to achieve this aim. Thus, the present study explored the utilization of highly functional, green, recyclable, fully bio-based, and cost-effective composite membranes from post-consumer cotton fabrics and palm waste for wastewater treatment purposes. Highly functional cellulose nanofibers (CNF) were produced from waste cotton fabrics and filter paper using an acid hydrolysis technique. The yield of nanofibers extracted from waste cotton fabrics and filter paper was 76.74 and 54.50%, respectively. The physical, chemical, and structural properties of nanofibers were studied using various advanced analytical techniques. The properties of isolated nanofibers were almost similar and comparable to those of commercial nanofibers. The surface charge densities were -94.0, -80.7, and -90.6 mV for the nanofibers of palm waste, cotton fibers, and filter paper, respectively. After membrane fabrication using vacuum and hot-pressing techniques, the characteristics of the membrane were analyzed. The results showed that the average pore size of the palm-waste membrane was 1.185 nm, while it was 1.875 nm for membrane from waste cotton fibers and filter paper. Congo red and methylene blue dyes were used as model solutions to understand the behavior of available functional groups and the surface ζ-potential of the membrane frameworks' interaction. The membrane made from palm waste had the highest dye removal efficiency, and it was 23% for Congo red and 44% for methylene blue. This study provides insights into the challenges associated with the use of postconsumer textile and agricultural waste, which can be potentially used in high-performance liquid filtration devices for a more sustainable society.

A recent update on green synthesized iron and iron oxide nanoparticles for environmental applications

Nanotechnology is considered the budding discipline in various fields of science and technology. In this review, the various synthesis methods of iron and iron oxide nanoparticles were summarised with more emphasis on green synthesis - a sustainable and eco-friendly method. The mechanism of green synthesis of these nanomaterials was reviewed in recent literature. The magnetic properties of these nanomaterials were briefed which makes them unique in the family of nanomaterials. An overview of various removal methods for the pollutants such as dye, heavy metals, and emerging contaminants using green synthesized iron and iron oxide nanoparticles is discussed. The mechanism of pollutant removal methods like Fenton-like degradation, photocatalytic degradation, and adsorption techniques was also detailed. The review is concluded with the challenges and possible future aspects of these nanomaterials for various environmental applications.

Laccase-assisted degradation of emerging recalcitrant compounds - A review

The main objective of this review is to provide up to date, brief, irrefutable, organized data on the conducted experiments on a range of emerging recalcitrant compounds such as Diclofenac (DCF), Chlorophenols (CPs), tetracycline (TCs), Triclosan (TCS), Bisphenol A (BPA) and Carbamazepine (CBZ). These compounds were selected from the categories of pharmaceutical contaminants (PCs), endocrine disruptors (EDs) and personal care products (PCPs) on the basis of their toxicity and concentration retained in the environment. In this context, detailed mechanism of laccase mediated degradation has been conversed that laccase assisted degradation occurs by one electron oxidation involving redox potential as underlying element of the process. Further, converging towards biotechnology, laccase immobilization increased removal efficiency, storage and reusability through various experimentally conducted studies. Laccase is being considered noteworthy as mediators facilitate laccase in oxidation of non-phenolic compounds and thereby increasing its substrate range which is being discussed in further in the review. The laccase assisted degradation mechanism of each compound has been elucidated but further studies to undercover proper degradation mechanisms needs to be performed.

Biosorption of heavy metals by microorganisms: Evaluation of different underlying mechanisms

Globally, ecotoxicologists, environmental biologists, biochemists, pathologists, and other experts are concerned about environmental contamination. Numerous pollutants, such as harmful heavy metals and emerging hazardous chemicals, are pervasive sources of water pollution. Water pollution and sustainable development have several eradication strategies proposed and used. Biosorption is a low-cost, easy-to-use, profitable, and efficient method of removing pollutants from water resources. Microorganisms are effective biosorbents, and their biosorption efficacy varies based on several aspects, such as ambient factors, sorbing materials, and metals to be removed. Microbial culture survival is also important. Biofilm agglomerates play an important function in metal uptake by extracellular polymeric molecules from water resources. This study investigates the occurrence of heavy metals, their removal by biosorption techniques, and the influence of variables such as those indicated above on biosorption performance. Ion exchange, complexation, precipitation, and physical adsorption are all components of biosorption. Between 20 and 35 °C is the optimal temperature range for biosorption efficiency from water resources. Utilizing living microorganisms that interact with the active functional groups found in the water contaminants might increase biosorption efficiency. This article discusses the negative impacts of microorganisms on living things and provides an outline of how they affect the elimination of heavy metals.

Studies of Protein Wastes Adsorption by Chitosan-Modified Nanofibers Decorated with Dye Wastes in Batch and Continuous Flow Processes: Potential Environmental Applications

In this study, reactive green 19 dye from wastewater was immobilized on the functionalized chitosan nanofiber membranes to treat soluble microbial proteins in biological wastewater. Polyacrylonitrile nanofiber membrane (PAN) was prepared by the electrospinning technique. After heat treatment, alkaline hydrolysis, and chemically grafted with chitosan to obtain modified chitosan nanofibers (P-COOH-CS), and finally immobilized with RG19 dye, dyed nanofibers were generated (P-COOH-CS-RG19). The synthesis of P-COOH-CS and P-COOH-CS-RG19 are novel materials for protein adsorption that are not deeply investigated currently, with each of the material functions based on their properties in significantly improving the adsorption efficiency. The nanofiber membrane shows good adsorption capacity and great recycling performance, while the application of chitosan and dye acts as the crosslinker in the nanofiber membrane and consists of various functional groups to enhance the adsorption of protein. The dyed nanofibers were applied for the batch adsorption of soluble protein (i.e., lysozyme), and the process parameters including chitosan’s molecular weight, coupling pH, chitosan concentration, dye pH, dye concentration, and lysozyme pH were studied. The results showed that the molecular weight of chitosan was 50 kDa, pH 5, concentration 0.5%, initial concentration of dye at 1 mg/mL dye and pH 12, lysozyme solution at 2 mg/mL at pH 8, and the maximum adsorption capacity was 1293.66 mg/g at a temperature of 318 K. Furthermore, thermodynamic, and kinetic studies suggested that the adsorption behavior of lysozyme followed the Langmuir adsorption isotherm model and the pseudo-second-order kinetic model. The optimal adsorption and desorption conditions based on batch experiments were directly applied to remove lysozyme in a continuous operation. This study demonstrated the potential of dyed nanofibers as an efficient adsorbent to remove approximately 100% of lysozyme from the simulated biological wastewater.

Rapid effectual entrapment of arsenic pollutant by Fe2O3 supported on bimodal meso-macroporous silica for cleaning up aquatic system

Arsenic (As) contamination in aqueous media is a major concern due to its adverse impacts on humans and the ecosystem more broadly because of its non-biodegradability. Consequently, an effective and selective sorbent is needed urgently to scavenge As pollutant. Herein, the adsorption behaviors of As(V) by Fe₂O₃ and Fe₂O₃ supported on different silica materials, consisting of unimodal mesoporous silica (Fe₂O₃/U-SiO₂) and dual meso-macroporous silica (Fe₂O₃/B-SiO₂), were compared to examine their structure-efficiency relationships in the elimination of As(V). Fe₂O₃/B-SiO₂ was much faster at As(V) removal and had an impressively higher uptake capability, reaching nearly 50% and 2.5 mg g^-1 within 5 min compared to bare Fe₂O₃ (6% and 0.3 mg g^-1) and Fe₂O₃/U-SiO₂ (11.9% and 0.59 mg g^-1). These better results were because of the highly dispersed Fe₂O₃ nanoparticles on the B-SiO₂ support that provided abundant reactive sites as well as a macropore structure facilitating As(V) diffusion into adsorptive sites. The maximum adsorptive capacity of Fe₂O₃/B-SiO₂ (4.7 mg As per 1 g adsorbent) was 1.3- and 1.7-fold greater than for Fe₂O₃/U-SiO₂ and Fe₂O₃, respectively. The outstanding performance and reusability of Fe₂O₃/B-SiO₂ with its ease of production, economical and environmentally friendly features made it even more attractive for As(V) remediation. The explored relationship between the structure of SiO₂-supported Fe₂O₃ sorbents and their performance in removing As(V) could be informative for the future design of highly efficient adsorbents for the decontamination of water.

Waste eggshell-supported CuO used as heterogeneous catalyst for reactive blue 19 degradation through peroxymonosulfate activation (CuO/eggshell catalysts activate PMS to degrade reactive blue 19)

Advanced oxidation processes play an important role in the removal of organic pollutants from wastewater, in which it is essential to develop an eco-friendly, effective, stable, and inexpensive catalyst. Herein, waste eggshell-supported copper oxide (CuO/eggshell) was synthesized via a facile method and employed as peroxymonosulfate (PMS) activator for the elimination of reactive blue 19 (RB19). CuO/eggshell exhibited high degradation efficiency of RB19 (approximately 100%) by activation of PMS under the optimum conditions of 20 mg/L RB19, 0.2 g/L CuO/eggshell, 0.36 mM PMS, and initial pH 7.12 within 20 min. In addition, the effects of catalyst dosage, PMS concentration, initial pH, inorganic ions, and humic acid on RB19 degradation were investigated. Scavenging experiments and electron paramagnetic resonance revealed that multiple reactive oxygen species, including sulfate radicals (SO₄^·-), hydroxyl radicals (^·OH), superoxide radicals (O₂^·-), and singlet oxygen (¹O₂), contributed to RB19 degradation, and ¹O₂ played a dominant role. Finally, a possible PMS activation mechanism was proposed. This study suggests that loading catalytically active components onto waste eggshell is eco-friendly and effective for enhancing the degradation of dyes from wastewater.

Sustainable and effective degradation of aniline by sodium percarbonate activated with UV in aqueous solution: Kinetics, mechanism and identification of reactive species

In recent decades, sodium percarbonate (SPC) has been widely applied as a solid replacement for H₂O₂ in advanced oxidation process (AOPs). In this study, ultraviolet (UV) light was utilized for SPC activation to investigate the aniline degradation performance. The effects of SPC dosages and UV irradiation on aniline degradation were elaborated. The removal efficiency was significantly improved by increasing either the SPC dosage or UV irradiation intensity. Moreover, scavenging experiments showed that •OH, CO₃^•-, and O₂^•- were the predominant reactive species for aniline degradation. Meanwhile, the variation in the amount of •OH in the UV/SPC system was monitored, which revealed the dominant role of •OH. As a result, the mechanism of aniline degradation by the UV/SPC system was demonstrated based on confirmed free radicals. Furthermore, aniline degradation by the UV/H₂O₂ and UV/H₂O₂/Na₂CO₃ system were compared with the UV/SPC system, and an enhancement by the addition of Fe(II) in the UV/SPC system was verified. Aniline degradation was not significantly affected by the initial pH or the presence of Cl^-, SO₄^2- while NO₃^-, HCO₃^- and humid acid (HA) suppressed the reaction. In general, the UV/SPC system is a novel, green, and promising technology for aniline removal from aqueous solutions.

Plant microbe based remediation approaches in dye removal: A review

Increased industrialization demand using synthetic dyes in the newspaper, cosmetics, textiles, food, and leather industries. As a consequence, harmful chemicals from dye industries are released into water reservoirs with numerous structural components of synthetic dyes, which are hazardous to the ecosystem, plants and humans. The discharge of synthetic dye into various aquatic environments has a detrimental effect on the balance and integrity of ecological systems. Moreover, numerous inorganic dyes exhibit tolerance to degradation and repair by natural and conventional processes. So, the present condition requires the development of efficient and effective waste management systems that do not exacerbate environmental stress or endanger other living forms. Numerous biological systems, including microbes and plants, have been studied for their ability to metabolize dyestuffs. To minimize environmental impact, bioremediation uses endophytic bacteria, which are plant beneficial bacteria that dwell within plants and may improve plant development in both normal and stressful environments. Moreover, Phytoremediation is suitable for treating dye contaminants produced from a wide range of sources. This review article proves a comprehensive evaluation of the most frequently utilized plant and microbes as dye removal technologies from dye-containing industrial effluents. Furthermore, this study examines current existing technologies and proposes a more efficient, cost-effective method for dye removal and decolorization on a big scale. This study also aims to focus on advanced degradation techniques combined with biological approaches, well regarded as extremely effective treatments for recalcitrant wastewater, with the greatest industrial potential.

Biochar-based nanocomposite from waste tea leaf for toxic dye removal: From facile fabrication to functional fitness

The present study utilized discarded tea leaf waste to produce 'Tea leaf biochar' (TLB) as the functional matrix for the fabrication of hybrid nanocomposite (nAg-TC), with colloidal deposition of silver nanoparticles (nAg) via modified chemical co-precipitation, for treatment of dye-laden wastewater. The chemical composition, physicochemical properties, and morphology of nAg-TC, and active surface functional groups involved in adsorption were identified using BET, FESEM-EDX, FTIR, TGA, XPS, and XRD. The nAg-TC matrix was found to be heterogeneous, mesoporous, thermostable, with rich in active surface functional groups (-OH, =NH, =CH, CC, CO, CN, and CC), and nAg as a dopant material. The dye adsorption results indicated the maximum removal efficiency (RhB = 95.89%, CR = 94.10%) at 300 K for rhodamine B (RhB) and Congo red (CR) concentrations of 25 mg L^-1 and 22.5 mg L^-1, respectively. The present investigation agreed with Freundlich isotherm (R²_CR:0.991; R²_RhB:0.993) and pseudo-second order kinetic (R²_CR:0.999; R²_RhB:0.999) model, indicating overall adsorption of RhB and CR through spontaneous and exothermic chemisorption on the heterogeneous surface of nAg-TC. The mechanism of RhB and CR adsorption was complex where nAg-TC, possessing the synergistic effects of TLB and nAg, showed surface complexation, electrostatic attraction, and H-bonding, leading to chemisorption. Study showed excellent reusability of spent nAg-TC, and commendable treatment efficiency for dye-laden real industrial effluents. The study exhibits substantial techno-economic feasibility of adsorbent and translates the principles of circular economy into synthesis of value-added products through sustainable management of biowaste and bioresource.

Adsorption behavior of fluoroquinolone(ciprofloxacin) using zinc oxide impregnated activated carbon prepared from jack fruit peel: Kinetics and isotherm studies

Ciprofloxacin is a pharmaceutical component used for treating various tract infections. This is considered as an emerging contaminant due to the release of unreacted components getting disposed into the water bodies. This component is effectively treated using renewable biomass, which is converted into a useful renewable low-cost adsorbent material. Discarded Jack Fruit Peel (JFP) is used as an activated carbon incorporated with zinc oxide nanocomposite. The prepared activated carbon in this experiment was characterized by determining their functional groups, morphological characters, and nature of the adsorbent material by analyzing the Fourier Transform InfraRed (FTIR), Field Emission Scanning Electron Microscopy (FESEM), and X-ray Diffraction (XRD) characterization. Further, the prepared composite's correlation coefficients and equilibrium sorption of the adsorption process were calculated using Ultra Violet (UV)-Visible Spectroscopy and analyzed with isotherm models (Langmuir model, Freundlich model, and Temkin model) and kinetic models (Pseudo-first-order kinetics, Pseudo-second-order kinetics, Intraparticle diffusion model, and Elovich model). Among the different models, the Zinc oxide impregnated activated carbon show Freundlich Isotherm and Pseudo Second order equation having a maximum correlation with experimental studies indicating double-layer adsorption, which suggests that the process is chemisorption. The operational parameters, including the effect of pH, dosage of activated carbon, and contact time of adsorption was calculated to identify the optimal condition for maximum adsorption.

Performance indicators for the optimal BTE of biodiesels with additives through engine testing by the Taguchi approach

Biodiesel commercialization is questionable due to poor brake thermal efficiency. Biodiesel utilization should be improved with the addition of fuel additives. Hydrogen peroxide is a potential fuel additive due to extra hydrogen and oxygen content, which improves the combustion process. In this experimental study, biodiesel has been produced from Jatropha oil employing catalyzed transesterification homogeneously to examine its influence on the performance and emissions at engine loads with 1500 rpm utilizing a four-stroke single-cylinder diesel engine. D60B40 (having 60% diesel and 40% biodiesel) and D60B30A10 (60% diesel, 30% biodiesel and 10% hydrogen peroxide (H2O2)), are the fuel mixtures in the current study. The addition of H2O2 reduces emissions and enhances the combustion process. This effect occurred due to the micro-explosion of the injected fuel particles (which increases in-cylinder pressure and heat release rate (HRR)). An increase of 20% in BTE and 25% reduction in BSFC for D60B30A10 was observed compared to D60B40. Significant reduction in emissions of HC up to 17.54%, smoke by 24.6% CO2 by 3.53%, and an increase in NOx was noticed when the engine is operated with D60B30A10. The HRR increased up to 18.6%, ID reduced by 10.82%, and in-cylinder pressure increased by 8.5%. Test runs can be minimized as per Taguchi's design of experiments. It is possible to provide the estimates for the full factorial design of experiments. Exhaust gas temperature standards are evaluated and examined for all fuel blends.

Nitrogen doped carbon spheres from Tamarindus indica shell decorated with vanadium pentoxide; photoelectrochemical water splitting, photochemical hydrogen evolution & degradation of Bisphenol A

At present energy and environmental remediation are of highest priority for the well defined sustainability. Multifunctional materials that solve both the issues are on high demand. In the present work, a simple method has been followed to extract carbon spheres fromTamarindus indica(commonly known astamarind fruit) shelland doped with nitrogen (N-CS). Vanadium pentoxide nanoflakes were decorated aroundN-CS and the resultant is labeled as V₂O₅/N-CS nanocomposite. The spectroscopic, microscopic, elemental mapping and x-ray photoelectron spectroscopic characterization confirm the nitrogen doping and formation of hybrid material. N-CS, V₂O₅, and V₂O₅/N-CS nanocompositehave been evaluated for their efficiency to evolve hydrogen and for degradation of Bisphenol A (BPA) under visible light. In addition, electrocatalytic hydrogen evolution in presence of light has also been evaluated. The DRS spectrum proves the decrease in the bandgap of V₂O₅ upon its decoration around N-CS material. In a photochemical experiment, the V₂O₅/N-CS nanocomposite evolved 18,600 μmolg^-1 of H_2.Electrochemical hydrogen evolution has also been evaluated in presence of light and obtained the onset potential of -60mV with 52 mV dec^-1 Tafel slope value. Scavenger studies indicate superoxide radicals and hydroxyl radicals are the active species responsible for the degradation of BPA. BPA degradation pathway has been predicted with the support of LC-MS results of the intermediates. All these results indicate the synthesized nanocomposite could be an efficient, stable multifunctional material for photocatalytic applications.

Sunlight-promoted photodegradation of Congo red by cadmium-sulfide decorated graphene aerogel

Herein, a simpler-viable methodology for the surface decoration of pear fruit derived graphene aerogel (GA) via cadmium sulfide (CdS) has been presented. GA can be easily synthesized from bio-mass, which provide an economic advantage. Surface decoration via CdS imparts photocatalytic activities in functionalized graphene aerogels (f-GA). CdS-f-GA is being explored here as a photocatalyst for the degradation of a toxic azo dye named Congo red in the presence of sunlight. The rate and mechanism associated with photodegradation were analyzed by performing kinetics and radical trap-based quenching experiments. Nuclear magnetic resonance and fourier transform infrared spectroscopy analyses of the control and photodegraded products were performed to ensure the degradation of the organic framework of Congo red. Additionally, the real-life applicability of CdS-f-GA was also analyzed by degrading the dye in different types of industrial samples (via the method of external spiking), which can advance its practical relevance.

Impact of ZnO and Fe3O4 magnetic nanoscale on the methyl violet 2B removal efficiency of the activated carbon oak wood

In the current study, activated carbon oak wood (ACOW600) and modified activated carbon using ZnO (ACOW600/ZnO) and Fe₃O₄ (ACOW600/ZnO/Fe₃O₄) nanoparticles were used to remove methyl violet 2B dye (MV2B) from aqueous solutions. ACOW was synthesized at different temperatures (300-700 °C), and then the maximum MV2B removal efficiency (92.76 %) was achieved using ACOW synthesized at 600 °C. The morphology and characteristics of ACOW600, ACOW600/ZnO, and ACOW600/ZnO/Fe₃O₄ were studied using surface analyzes. According to the results, the adsorbents indicated a high ability to absorb MV2B from liquid solution, and their kinetic behavior follows a pseudo-second-order kinetic. In addition, the equilibrium study revealed that the MV2B uptake by the ACOW600/ZnO/Fe₃O₄ magnetic nanocomposite followed the Freundlich model. In contrast, the Langmuir model described the MV2B adsorption process using ACOW600 and ACOW600/ZnO. The maximum adsorption capacity (q_m) of MV2B using ACOW600, ACOW600/ZnO, and ACOW600/ZnO/Fe₃O₄ was determined 26.16 mg g^-1, 37.05 mg g^-1, and 48.59 mg g^-1, respectively, indicating that modification of ACOW600 led to improve its performance in removing MV2B. The enthalpy (ΔH), entropy (ΔG), and Gibbs free energy (ΔS) parameters revealed that the decontamination of MV2B using the studied adsorbents was exothermic and spontaneous. Also, random interactions of MV2B molecules and adsorbent surfaces were reduced during the adsorption process. Textile wastewater was significantly treated by ACOW600, ACOW600/ZnO, and ACOW600/ZnO/Fe₃O₄ adsorbents. The recycling of the adsorbents was demonstrated that the investigated adsorbents could be re-utilized many times in the MV2B removal process.

A new magnetic adsorbent of eggshell-zeolitic imidazolate framework for highly efficient removal of norfloxacin

Many effluents contain various antibiotics commonly, where the simultaneous removal of them is a big challenge. In this study, the magnetic biocomposite (eggshell-zeolitic imidazolate framework) was designed and synthesized by green and facile method. Zeolitic imidazolate framework-8 (ZIF-8) particles were stabilized on the surface of magnetic eggshell (Fe₃O₄-ES), generating a new Fe₃O₄-ES/ZIF-8 adsorbent, which was also fully characterized using FTIR, XRD, SEM and BET techniques. Thereafter, norfloxacin (NOR) adsorption processes were investigated through different influencing factors (dosage, concentration, pH and temperature). The Langmuir adsorption isotherm could confirm a maximum removal efficiency of 80.13% for NOR. Kinetic studies illustrated that the pseudo-first-order model was in line with the experimental data of the simultaneous removal of NOR. Moreover, the magnetic nature of the adsorbent caused an easy separation from the aqueous solution.

Effects of sheep bone biochar on soil quality, maize growth, and fractionation and phytoavailability of Cd and Zn in a mining-contaminated soil

Biochar prepared from various feedstock materials has been utilized in recent years as a potential stabilizing agent for heavy metals in smelter-contaminated soils. However, the effectiveness of animal bone-derived biochar and its potential for the stabilization of contaminants remains unclear. In the present study, sheep bone-derived biochar (SB) was prepared at low (500 °C; SBL) and high temperatures (800 °C; SBH) and amended a smelter-contaminated soil at 2, 5, and 10% (w/w). The effects of SB on soil properties, bioavailable Zn and Cd and their geochemical fractions, bacterial community composition and activity, and the response of plant attributes (pigments and antioxidant activity) were assessed. Results showed that the SBH added at 10% (SBH₁₀) increased soil organic carbon, total nitrogen, and phosphorus, and also increased the oxidizable and residual Zn and Cd fractions at the expense of the bioavailable fractions. The SBH₁₀ lowered the Zn and Cd contents in maize roots (by 57 and 60%) and shoot (by 42 and 61%), respectively, compared to unamended control. Additionally, SBH₁₀ enhanced urease (98%) and phosphates (107%) activities, but reduced dehydrogenase (58%) and β-glucosidase (30%) activities. Regarding the effect of the pyrolysis temperature, SBH enhanced the activity of Acidobacteria, Bacteroidetes, Firmicutes, Nitrospirae, Verrucomicrobia, Chlorobi, and Microgenomates, but reduced Actinobacteria and Parcubacteria in comparison to SBL. However, only the SBL₁₀ reduced the Proteobacteria community (by 9%). In conclusion, SB immobilized Zn and Cd in smelter-affected soils, enhanced the bacterial abundance and microbial function (urease, phosphates), and improved plant growth. However, validation of the results, obtained from the pot experiment, under field conditions is suggested.

Marble Waste Sludges as Effective Nanomaterials for Cu (II) Adsorption in Aqueous Media

This study evaluated the waste generated by a Spanish marble-producing company as adsorbent for the removal of copper (Cu [II]) from aqueous media. Six marble waste sludge samples were studied, and the following operational parameters were analyzed in discontinuous regime, including pollutant concentration, pH, temperature, nature of aqueous medium, and ionic strength. The applicability of the adsorbent material was assessed with experiments in both continuous and discontinuous regimes under close-to-real-life conditions. A pseudo-second order model yielded a better fit to the kinetic data. Application of the intraparticle diffusion model revealed two well-differentiated adsorption stages, in which the external material transfer is negligible and intraparticle diffusion is the controlling stage. The equilibrium study was better fitted to a Freundlich-type isotherm, predicting elevated maximum adsorption values (22.7 mg g⁻¹) at a relatively low initial Cu (II) concentration (25 ppm), yielding a highly favorable chemisorption process (n >> 1). X-ray fluorescence study identified calcite (CaCO₃) as the main component of marble waste sludges. According to X-ray diffraction analysis, Cu (II) ion adsorption occurred by intercalation of the metallic cation between CaCO₃ layers and by the formation of surface complexes such as CaCO₃ and Cu₂(CO₃)(OH)₂. Cu (II) was more effectively removed at medium pH, lower temperature, and lower ionic strength of the aqueous medium. The salinity and dissolved organic matter in surface, ground-, and waste-waters negatively affected the Cu (II) removal process in both continuous and discontinuous regimes by competing for active adsorption sites. These findings demonstrate the applicability and effectiveness of marble-derived waste sludges as low-cost and readily available adsorbents for the treatment of waters polluted by Cu (II) under close-to-real-life conditions.

Removal of protein wastes by cylinder-shaped NaY zeolite adsorbents decorated with heavy metal wastes

Cylinder-shaped NaY zeolite was used as an adsorbent for eradicating both heavy metal ions (Cu²⁺, Zn²⁺, Ni²⁺, and Co²⁺) and proteins from the waste streams. As a pseudo-metal ion affinity adsorbent, NaY zeolite was used in the capture of heavy metal ions in the first stage. The amount (molar basis) of metal ions adsorbed onto NaY zeolite decreased in the order of Cu²⁺ > Zn²⁺ > Co²⁺ > Ni²⁺. Bovine serum albumin (BSA) was utilized as a model of proteins used in the waste adsorption process by NaY zeolite. The adsorption capacities of NaY zeolite and Cu/NaY zeolite for BSA were 14.90 mg BSA/g zeolite and 84.61 mg BSA/g zeolite, respectively. Moreover, Cu/NaY zeolite was highly stable in the solutions made of 2 M NaCl, 500 mM imidazole or 125 mM EDTA solutions. These conditions indicated that the minimal probability of secondary contamination caused by metal ions and soluble proteins in the waste stream. This study demonstrates the potential of Cu/NaY zeolite complex as an efficient pseudo-metal chelate adsorbent that could remove metal ions and water-soluble proteins from wastewater concurrently.

Comparative Study of CoFe2O4 Nanoparticles and CoFe2O4-Chitosan Composite for Congo Red and Methyl Orange Removal by Adsorption

(1) Background: A comparative research study to remove Congo Red (CR) and Methyl Orange (MO) from single and binary solutions by adsorption onto cobalt ferrite (CoFe2O4) and cobalt ferrite-chitosan composite (CoFe2O4-Chit) prepared by a simple coprecipitation method has been performed. (2) Methods: Structural, textural, morphology, and magnetic properties of the obtained magnetic materials were examined by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, N2 adsorption-desorption analysis, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and magnetic measurements. The optimal operating conditions of the CR and MO removal processes were established in batch experiments. The mathematical models used to describe the processes at equilibrium were Freundlich and Langmuir adsorption isotherms. (3) Results: Cobalt ferrite-chitosan composite has a lower specific surface area (SBET) and consequently a lower adsorption capacity than cobalt ferrite. CoFe2O4 and CoFe2O4-Chit particles exhibited a superparamagnetic behavior which enabled their efficient magnetic separation after the adsorption process. The research indicates that CR and MO adsorption onto prepared magnetic materials takes place as monolayer onto a homogeneous surface. According to Langmuir isotherm model that best fits the experimental data, the maximum CR/MO adsorption capacity is 162.68/94.46 mg/g for CoFe2O4 and 15.60/66.18 mg/g for CoFe2O4-Chit in single solutions. The results of the kinetics study revealed that in single-component solutions, both pseudo-first-order and pseudo-second-order kinetics models represent well the adsorption process of CR/MO on both magnetic adsorbents. In binary solutions, adsorption of CR/MO on CoFe2O4 better follows the pseudo-second-order kinetics model, while the kinetic of CR/MO adsorption on CoFe2O4-Chit is similar to that of the dyes in single-component solutions. Acetone and ethanol were successfully used as desorbing agents. (4) Conclusions: Our study revealed that CoFe2O4 and CoFe2O4-Chit particles are good candidates for dye-contaminated wastewater remediation.