Treatment of heavy metals containing wastewater using biodegradable adsorbents: A review of mechanism and future trends

Melatonin-mediated adaptation of spinach (Spinacia oleracea L.) in acidic soil

Soil acidity is a widespread and critical factor contributing to soil degradation. Melatonin (MT) as a protective biostimulant, plays a crucial role in plant growth under harsh environments. However, the role of MT in plant adaptation to acidic soil remains elusive. Hence, here we tested the effects of exogenous MT on the adaptation of spinach (Spinacia oleracea L.) crop to acidic soil (pH 4.0). Initially, a series of MT concentrations (0, 25, 50, 100, and 200 μM) were tested to evaluate the seed germination and growth attributes of spinach under low pH levels. Among the doses, 100 μM MT showed better results in terms of germination percentage and biomass accumulation, which was then selected for further experiments. Results showed that exogenous MT significantly increased plant adaptation to acidic soil as evidenced by increased photosynthesis rate and biomass accumulation with enhanced total antioxidant capacity, DPPH free radical scavenging, phenol, flavonoid, and glutathione contents compared with soil acidity treatment alone. Moreover, MT alleviated oxidative stress indices such as electrolyte leakage and malondialdehyde in acid-stressed plants, suggesting an effective strategy of adaptation. Furthermore, MT-treated plants exhibited higher macro and micronutrient accumulation along with higher vitamin B complex, vitamin C, and protein content, leading to an increased nutritional quality and yield compared to control. Therefore, the study concludes that the application of MT at 100 μM could be a sustainable alternative approach to adapt spinach farming in acidic soil.

A facile and green one-step synthesis of Ag/reduced graphene oxide and its application in catalysts and SERS

Herein, we present a facile one-step approach for synthesizing Ag/reduced graphene oxide (Ag-rGO) through synchronous reduction and in situ coagulation of graphene oxide (GO) and silver nitrate (AgNO3) under a nitrogen atmosphere. In this process, GO serves as the carrier and template, AgNO3 as the precursor, and rutin functions both as the reducing and stabilizing agent. The Ag-rGO nanocomposite is synthesized using an eco-friendly method, where spherical silver nanoparticles are randomly dispersed on the surface of reduced graphene oxide (rGO). This nanocomposite exhibits excellent catalytic activity for degrading methylene blue (MB) and demonstrates good surface-enhanced Raman scattering (SERS) activity as a SERS substrate. It was found that 3 mg Ag-rGO attained a decolorization rate of 96% within merely 9 minutes, with a corresponding reaction rate constant (k) of 0.362 min-1. SERS detection of R6G also exhibited good performance in terms of detection limits in the order of 10-7 M, an enhancement factor of 3.03 × 105, and high reproducibility (the maximum intensity deviation < 7.01%). The excellent performance can be attributed to the decreased size of Ag on the nanocomposite and the larger specific surface area achieved through the in situ synchronous reduction and coagulation method. Additionally, the in situ enrichment effect and superior electron transfer efficiency further enhance the catalytic performance of the nanocomposite, and the synergistic effect of chemical enhancement and electromagnetic enhancement contribute to the good Raman enhancement effect. The effects of reaction parameters such as time and varying reactant ratios on the catalytic and SERS activities of the nanocomposite were also investigated. These findings indicate the potential ability of the Ag-rGO for practical environmental monitoring and treatment applications.

Heavy metals and microplastics derived from laboratory effluents enhance toxicological risks to the ecosystems of canals in Bangladesh

The occurrence of chemical effluents in different water bodies is an emerging concern. However, the effect of laboratory effluents on the canal ecosystem in Bangladesh is largely unknown. In this study, we collected 10 components of the canal ecosystem including sediments, water, fish, crabs, snails, phytoplanktons, and weeds specifically from canals that directly receive laboratory effluents. We examined the occurrence of both the essential (Fe, Mn, Cu, and Zn) and toxic (Pb, Cd, Cr, Co, Ni, and As) metals as well as microplastics (MPs). Results explored that laboratory effluents strongly interact with the components of the canal ecosystem and enhance the abundance of toxic metals in the canal hydrosystem. Furthermore, diverse types of MPs including fibers, fragments, and microbeads were observed in all components of the canal ecosystem. Remarkably, our results unveiled that the co-occurrence of pollutants was more severe in benthic organisms like snails or crabs might be due to their omnivorous food habits. The cumulative pollutant accumulation was much higher in all components of the canal ecosystem indicating a greater ecological risk. Although the potential risk index (RI) or hazardous index (HI) from fish ingestion was found within acceptable limits, the biomagnification of pollutants due to repeated ingestions may have strong ecotoxicological impacts even at very low concentrations.

Membrane process and adsorption on pine nut shell for removal of dye from synthetic wastewater

Purification methods such as membrane technology and adsorption have been studied for the purification of textile effluents. This article aimed to evaluate the membrane separation process and adsorption on pine nut shell, separately and sequentially, for reactive dye blue 5G removal from a synthetic effluent. The membrane separation process was carried out in a front filtration module using polymeric membranes. The maximum dye retention was 35.9% using a regenerated cellulose membrane, with agitation and a pressure of 0.5 bar. The permeate flux was fully restored after cleaning the membrane. In the adsorption using pine nut shell, the best results were at pH 2, 50°C, and 50 ppm, with 85% dye removal. The Freundlich isotherm showed the best fit to the data, as did the pseudo-second-order kinetic model. The thermodynamic parameters indicated that the adsorption is of the physical type, with the process being endothermic and spontaneous. In the combined process, the permeate from the membrane separation process was subjected to adsorption on pine nut shell, achieving a removal rate of 98.7 for the initial concentration of 50 ppm. Therefore, this work shows the potential of pine nut shell as an adsorbent, not only to purify textile effluents but also to add value to a waste product, indicating that the combination of membrane technology and adsorption on pine nut shell could be an alternative for the treatment of textile effluents containing the reactive dye 5G blue.

Application of Electrospun Nanofiber-Based Electrochemical Sensors in Food Safety

Food safety significantly impacts public health and social welfare. Recently, issues such as heavy metal ions, drug residues, food additives, and microbial contamination in food have become increasingly prominent. Electrochemical sensing technology, known for its low cost, simplicity, rapid response, high sensitivity, and excellent selectivity, has been crucial in food safety detection. Electrospun nanofibers, with their high specific surface area, superior mechanical properties, and design flexibility, offer new insights and technical platforms for developing electrochemical sensors. This study introduces the fundamental principles, classifications, and detection mechanisms of electrochemical sensors, along with the principles and classifications of electrospinning technology. The applications of electrospun nanofiber-based electrochemical sensors in food safety detection over the past five years are detailed, and the limitations and future research prospects are discussed. Continuous innovation and optimization are expected to make electrospun nanofiber-based electrochemical sensors a key technology in rapid food safety detection, providing valuable references for expanding their application and advancing food safety detection methods.

Removal of Heavy Metals by Pseudomonas sp. - Model Fitting and Interpretation

Industrial and urban modernization processes generate significant amounts of heavy metal wastewater, which brings great harm to human production and health. The biotechnology developed in recent years has gained increasing attention in the field of wastewater treatment due to its repeatable regeneration and lack of secondary pollutants. Pseudomonas, being among the several bacterial biosorbents, possesses notable benefits in the removal of heavy metals. These advantages encompass its extensive adsorption capacity, broad adaptability, capacity for biotransformation, potential for genetic engineering transformation, cost-effectiveness, and environmentally sustainable nature. The process of bacterial adsorption is a complex phenomenon involving several physical and chemical processes, including adsorption, ion exchange, and surface and contact phenomena. A comprehensive investigation of parameters is necessary in order to develop a mathematical model that effectively measures metal ion recovery and process performance. The aim of this study was to explore the latest advancements in high-tolerance Pseudomonas isolated from natural environments and evaluate its potential as a biological adsorbent. The study investigated the adsorption process of this bacterium, examining key factors such as strain type, contact time, initial metal concentration, and pH that influenced its effectiveness. By utilizing dynamic mathematical models, the research summarized the biosorption process, including adsorption kinetics, equilibrium, and thermodynamics. The findings indicated that Pseudomonas can effectively purify water contaminated with heavy metals and future research will aim to enhance its adsorption performance and expand its application scope for broader environmental purification purposes.

Fabrication of nitrogen-doped carbon dots biomass composite hydrogel for adsorption of Cu (II) in wastewater or soil and DFT simulation for adsorption mechanism

With the increase of Cu (II) content, its bioaccumulation becomes a potential pollution to the environment. It is necessary to design an economical and efficient material to remove Cu (II) without causing other environmental hazards. A novel material of alginate composite bead (ALG@NCDs) was synthesized by embedding N-doped carbon dots into pure alginate bead for the adsorption of Cu (II) from wastewater and contaminated soil. The initial concentration, the amount of adsorbent, temperature, adsorption time, and pH value were optimized for the adsorption of Cu (II). According to the Langmuir isothermal adsorption model, the maximum adsorption amount of the material to Cu (II) was 152.44 mg/g. The results of selective adsorption showed that ALG@NCDs had higher affinity to Cu (II) than to Pb (II), Co (II), Ni (II), and Zn (II). After five adsorption-desorption experiment, adsorption capacity of the ALG@NCDs was kept 89% of the initial adsorption capacity. Its Cu (II) adsorption mechanism was studied by density functional theory calculations. In addition, the material could effectively adsorb Cu (II) and release the phytonutrient Ca (II) simultaneously when applied to actual wastewater and soil. The fabricated ALG@NCDs would be a promising material for the adsorption of Cu (II) from wastewater or soil.

Investigation of adsorption potential of waste jewelry meerschaum powder for Cu(II) and cationic dye

The presence of heavy metals and pollutant dyes can have detrimental effects on aquatic ecosystems and compromise aquatic aesthetics. This study investigates the use of unprocessed waste gem meerschaum powder as a new adsorbent in the removal of both Cu(II) and methylene blue (MB) from aqueous solutions to reduce water pollution. The structure of the waste powder was characterized by FT-IR, XRD, SEM and BET methods. Optimization of Cu(II) and MB dye removal was carried out using design of experiment technique. Under optimum conditions, remarkable removal efficiencies of 95.5% (± 3.7) for Cu(II) and 97.8% (± 0.4) for MB were achieved. The removal of Cu(II) followed the Freundlich isotherm model, while the removal of MB dye adhered to the Langmuir isotherm model. Both adsorption processes obeyed the pseudo-second-order kinetic model and occurred spontaneously. This innovative approach offers a promising solution to water pollution by highlighting the importance of sustainable and cost-effective waste use.

Synthesis of zeolite from industrial wastes: a review on characterization and heavy metal and dye removal

Increasing world population, urbanization, and industrialization have led to an increase in demand in production and consumption, resulting in an increase in industrial solid wastes and pollutant levels in water. These two main consequences have become global problems. The high Si and Al content of solid wastes suggests that they can be used as raw materials for the synthesis of zeolites. In this context, when the literature studies conducted to obtain synthetic zeolites are evaluated, it is seen that hydrothermal synthesis method is generally used. In order to improve the performance of the hydrothermal synthesis method in terms of energy cost, synthesis time, and even product quality, additional methods such as alkaline fusion, ultrasonic effect, and microwave support have been developed. The zeolites synthesized by different techniques exhibit superior properties such as high surface area and well-defined pore sizes, thermal stability, high cation exchange capacity, high regeneration ability, and catalytic activity. Due to these specific properties, zeolites are recognized as one of the most effective methods for the removal of pollutants. The toxic properties of heavy metals and dyes in water and their carcinogenic effects in long-term exposure pose a serious risk to living organisms. Therefore, they should be treated at specified levels before discharge to the environment. In this review study, processes including different methods developed for the production of zeolites from industrial solid wastes were evaluated. Studies using synthetic zeolites for the removal of high levels of health and environmental risks such as heavy metals and dyes are reviewed. In addition, EPMA, SEM, EDX, FTIR, BET, AFM, and 29Si and 27Al NMR techniques, which are characterization methods of synthetic zeolites, are presented and the cation exchange capacity, thermodynamics of adsorption, effect of temperature, and pH are investigated. It is expected that energy consumption can be reduced by large-scale applications of alternative techniques developed for zeolite synthesis and their introduction into the industry. It is envisaged that zeolites synthesized by utilizing wastes will be effective in obtaining a green technology. The use of synthesized zeolites in a wide variety of applications, especially in environmental problems, holds great promise.

Synthesis and characterization of iron oxide nanoparticles from Lawsonia inermis and its effect on the biodegradation of crude oil hydrocarbon

Crude oil hydrocarbons are considered major environmental pollutants and pose a significant threat to the environment and humans due to having severe carcinogenic and mutagenic effects. Bioremediation is one of the practical and promising technology that can be applied to treat the hydrocarbon-polluted environment. In this present study, rhamnolipid biosurfactant (BS) produced by Pseudomonas aeruginosa PP4 and green synthesized iron nanoparticles (G-FeNPs) from Lawsonia inermis was used to evaluate the biodegradation efficiency (BE) of crude oil. The surface analysis of G-FeNPs was carried out by using FESEM and HRTEM to confirm the size and shape. Further, the average size of the G-FeNPs was observed around 10 nm by HRTEM analysis. The XRD and Raman spectra strongly confirm the presence of iron nanoparticles with their respective peaks. The BE (%) of mixed degradation system-V (PP4+BS+G-FeNPs) was obtained about 82%. FTIR spectrum confirms the presence of major functional constituents (C=O, -CH3, C-O, and OH) in the residual oil content. Overall, this study illustrates that integrated nano-based bioremediation could be an efficient approach for hydrocarbon-polluted environments. This study is the first attempt to evaluate the G-FeNPs with rhamnolipid biosurfactant on the biodegradation of crude oil.

Adsorption of Cu(II) and Ni(II) from Aqueous Solutions Using Synthesized Alkali-Activated Foamed Zeolite Adsorbent: Isotherm, Kinetic, and Regeneration Study

Water pollution, particularly from heavy metals, poses a significant threat to global health, necessitating efficient and environmentally friendly removal methods. This study introduces novel zeolite-based adsorbents, specifically alkali-activated foamed zeolite (AAFZ), for the effective adsorption of Cu(II) and Ni(II) ions from aqueous solutions. The adsorbents' capabilities were comprehensively characterized through kinetic and isotherm analyses. Alkaline activation induced changes in chemical composition and crystalline structure, as observed via XRF and XRD analyses. AAFZ exhibited a significantly larger pore volume (1.29 times), higher Si/Al ratio (1.15 times), and lower crystallinity compared to ZZ50, thus demonstrating substantially higher adsorption capacity for Cu(II) and Ni(II) compared to ZZ50. The maximum monolayer adsorption capacities of ZZ50 and AAFZ for Cu(II) were determined to be 69.28 mg/g and 99.54 mg/g, respectively. In the case of Ni(II), the maximum monolayer adsorption capacities for ZZ50 and AAFZ were observed at 48.53 mg/g and 88.99 mg/g, respectively. For both adsorbents, the optimum pH for adsorption of Cu(II) and Ni(II) was found to be 5 and 6, respectively. Equilibrium was reached around 120 min, and the pseudo-second-order kinetics accurately depicted the chemisorption process. The Langmuir isotherm model effectively described monolayer adsorption for both adsorbents. Furthermore, the regeneration experiment demonstrated that AAFZ could be regenerated for a minimum of two cycles using hydrochloric acid (HCl). These findings highlight the potential of the developed adsorbents as promising tools for effective and practical adsorption applications.

Perspectives of nanomaterials in microbial remediation of heavy metals and their environmental consequences: A review

Nanomaterials (NMs) have diverse applications in various sectors, such as decontaminating heavy metals from drinking water, wastewater, and soil. Their degradation efficiency can be enhanced through the application of microbes. As microbial strain releases enzymes, which leads to the degradation of HMs. Therefore, nanotechnology and microbial-assisted remediation-based methods help us develop a remediation process with practical utility, speed, and less environmental toxicity. This review focuses on the success achieved for the bioremediation of heavy metals by nanoparticles and microbial strains and in their integrated approach. Still, the use of NMs and heavy metals (HMs) can negatively affect the health of living organisms. This review describes various aspects of the bioremediation of heavy materials using microbial nanotechnology. Their safe and specific use supported by bio-based technology paves the way for their better remediation. We discuss the utility of nanomaterials for removing heavy metals from wastewater, toxicity studies and issues to the environment with their practical implications. Nanomaterial assisted heavy metal degradation coupled with microbial technology and disposal issues are described along with detection methods. Environmental impact of nanomaterials is also discussed based on the recent work conducted by the researchers. Therefore, this review opens new avenues for future research with an impact on the environment and toxicity issues. Also, applying new biotechnological tools will help us develop better heavy metal degradation routes.

Aminopoly(carboxylic acid)-Functionalized PolyHIPE Beads toward Eliminating Trace Heavy Metal Ions from Water

Many advanced materials are designed for the removal of heavy metal ions from water. However, materials for eliminating trace heavy metal ions from wastewater to meet drinking water standards remain a major challenge. Herein, epoxy group-functionalized open-cellular beads are synthesized by UV polymerization of a water-in-oil-in-water system. The epoxy groups are further transformed into diethylenetriaminepentaacetic acid (DTPA) with hexamethylene diamine as a bridging agent. The resulting material (DTPA@polyHIPE beads) can eliminate trace Cu(II), Cr(III), Pb(II), Fe(III), or Cd(II) from water. When 0.15 g of DTPA@polyHIPE beads are used to adsorb metal ions of 20 mg in 100 mL of water, the residue concentrations of Cu(II), Cr(III), Pb(II), Fe(III), and Cd(II) are reduced to 0.08, 0.06, 0.02, 0.09, and 0.07 mg/L, respectively. The adsorption efficiencies of the beads for these ions are all higher than 99.55%. The adsorbent is durable and exhibits good recyclability by retaining an adsorption capacity of ≥91% after 5 cycles. The negative values of ΔG in the adsorption process indicate that the adsorption is feasible and spontaneous. The chemical adsorption follows the Freundlich adsorption model, indicating a multilayer heterogeneous adsorption. The DTPA@polyHIPE beads have a great potential application in dealing with trace heavy metal ion polluted water.

Efficient and Selective Removal of Heavy Metals and Dyes from Aqueous Solutions Using Guipi Residue-Based Hydrogel

The presence of organic dyes and heavy metal ions in water sources poses a significant threat to human health and the ecosystem. In this study, hydrogel adsorbents for water pollution remediation were synthesized using Guipi residue (GP), a cellulose material from Chinese herbal medicine, and chitosan (CTS) through radical polymerization with acrylamide (AM) and acrylic acid (AA). The characteristics of the hydrogels were analyzed from a physicochemical perspective, and their ability to adsorb was tested using model pollutants such as Pb2+, Cd2+, Rhodamine B (RhB), and methyl orange (MO). The outcomes revealed that GP/CTS/AA-co-AM, which has improved mechanical attributes, effectively eliminated these pollutants. At a pH of 4.0, a contact duration of 120 min, and an initial concentration of 600 mg/L for Pb2+ and 500 mg/L for Cd2+, the highest adsorption capabilities were 314.6 mg/g for Pb2+ and 289.1 mg/g for Cd2+. Regarding the dyes, the GP/CTS/AA-co-AM hydrogel displayed adsorption capacities of 106.4 mg/g for RhB and 94.8 mg/g for MO, maintaining a stable adsorption capacity at different pHs. Compared with other competitive pollutants, GP/CTS/AA-co-AM demonstrated a higher absorption capability, mainly targeted toward Pb2+. The adsorption processes for the pollutants conformed to pseudo-second-order kinetics models and adhered to the Langmuir models. Even after undergoing five consecutive adsorption and desorption cycles, the adsorption capacities for heavy metals and dyes remained above 70% and 80%. In summary, this study effectively suggested the potential of the innovative GP/CTS/AA-co-AM hydrogel as a practical and feasible approach for eliminating heavy metals and dyes from water solutions.

Comparison of Adsorption Performance of Biochar Derived from Urban Biowaste Materials for Removal of Heavy Metals

This study investigated the adsorption performance of biochar produced from different types of urban biowaste material viz., sugarcane bagasse (SB), brinjal stem (BS), and citrus peel (CP) for removal of heavy metal ions (Pb, Cu, Cr, and Cd) from aqueous solution. The effects of biowaste material, dosage of biochar, solution pH, and initial concentration of heavy metal ions and isotherm models were performed to understand the possible adsorption mechanisms. The results showed that the biochar derived from BS and SB removes Cu (99.94%), Cr (99.57%), and Cd (99.77%) whereas biochar derived from CP removes Pb (99.59%) and Cu (99.90%) more efficiently from the aqueous solution. Biochar derived from BS showed maximum adsorption capacity for Cu (246.31 mg g-1), Pb (183.15 mg g-1), and Cr (71.89 mg g-1) while the biochar derived from CP showed highest for Cd (15.46 mg g-1). Moreover, biochar derived from BS and SB has more polar functional groups and less hydrophobicity than the biochar derived from CP. This study reveals that solution pH and biochar doses play a major role in removal of heavy metal ions from aqueous solution. The results of Langmuir model fitted well for Pb and Cu while the Freundlich model for Cr and Cd. Our study concludes that the biochar derived from different biowaste materials adsorbs heavy metal ions majorly through surface complexation and precipitation processes. The results of this study will be very useful in selecting the effective urban biowaste material for making biochar for heavy metal removal from the aqueous environment.

Aerobic granular sludge for complex heavy metal-containing wastewater treatment: characterization, performance, and mechanisms analysis

Complex heavy metal (HM)-containing wastewater discharges pose substantial risks to global water ecosystems and human health. Aerobic granular sludge (AGS) has attracted increased attention as an efficient and low-cost adsorbent in HM-containing wastewater treatment. Therefore, this study systematically evaluates the effect of Cu(II), Ni(II), and Cr(III) addition on the characteristics, performance and mechanism of AGS in complex HM-containing wastewater treatment process by means of fourier transform infrared spectroscopy, inductively coupled plasma spectrocopcy, confocal laser scanning microscopy, extracellular polymeric substances (EPS) fractions detection and scanning electron microscope-energy dispersive X-ray. The results showed that AGS efficiently eliminated Cu(II), Ni(II), and Cr(III) by the orchestrated mechanisms of ion exchange, three-layer EPS adsorption [soluble microbial products EPS (SMP-EPS), loosely bound EPS (LB-EPS), tightly bound EPS (TB-EPS)], and inner-sphere adsorption; notably, almost 100% of Ni(II) was removed. Three-layer EPS adsorption was the dominant mechanism through which the HM were removed, followed by ion exchange and inner-sphere adsorption. SMP-EPS and TB-EPS were identified as the key EPS fractions for adsorbing Cr(III) and Cu(II), respectively, while Ni(II) was adsorbed evenly on SMP-EPS, TB-EPS, and LB-EPS. Moreover, the rates at which the complex HM penetrated into the granule interior and their affinity for EPS followed the order Cu(II) > Ni(II) > Cr(III). Ultimately, addition of complex HM stimulated microorganisms to excrete massive phosphodiesterases (PDEs), leading to a pronounced decrease in cyclic diguanylate (c-di-GMP) levels, which subsequently suppressed EPS secretion due to the direct linkage between c-di-GMP and EPS. This study unveils the adaptability and removal mechanism of AGS in the treatment of complex HM-containing wastewater, which is expected to provide novel insights for addressing the challenges posed by intricate real wastewater scenarios.

Simulation study of a practical approach to enhance cadmium removal via biological treatment by controlling the concentration of MLSS

The fate of cadmium at the Muharram Aisha wastewater treatment plant in Karbala governorate, Iraq was studied using the TOXCHEM model. Cadmium, a known carcinogen, and is considered one of the most dangerous heavy metals and high concentrations, greater than permissible limits, were found in the treated wastewater. The plant operates using an activated sludge system and this was modeled via TOXCHEM with a sensitivity analysis carried out on the extended aeration system. Prior to analysis, the model was calibrated and validated for cadmium, with the adjustments leading to a mean square error (RMSE) and correlation coefficient (R) of 0.0001 and 0.81, respectively. The mass balance of cadmium in the Muharram Aisha treatment plant was found to be 4832.44 g/day (37.1726%) in the treated wastewater and 8164.52 g/day (62.804%) in the sludge, which indicated that the mix liquor suspended solid (MLSS) was the most sensitive factor. The sensitivity to cadmium was analyzed via MLSS in the extended aeration system and the results o indicated that the higher the MLSS concentration (mg/L), the greater the removal of cadmium in the treated wastewater. It was found that increasing the MLSS through a biological treatment method reduced the concentration of cadmium without the need for additional of any (potentially harmful) chemical treatments. The plant was subsequently operated for a period of 5 months with the MLSS increased from 1500 to 4500 mg/L, and this reduced the concentration of cadmium in the wastewater from 0.36 to 0.01 mg/L as a consequence. This research demonstrates how the novel application of TOXCHEM can be a useful tool in the reduction of heavy metal contamination in the environment.

Modeling Cu removal from aqueous solution using sawdust based on response surface methodology

Copper (Cu), as one of the heavy metals widely used in industrial and agricultural activities, has a fundamental role in the pollution of water resources. Therefore, removing Cu from the aqueous solutions is considered an important challenge in the purification of water resources. Thus, in this study, sawdust with a diameter of 260-600 μm was used to remove Cu from the aqueous solutions. At first, sawdust was washed using distilled water and dried at laboratory temperature. Cu absorption experiments in closed conditions were performed based on the central composite design (CCD) model and with a range of initial Cu concentrations equal to 1-25 mgl-1. The amount of changes for other variables, including pH, time, and amount of sawdust, was equal to 2-10, 5-185 (min), and 5-25 (gl-1), respectively. After the completion of each test, the remaining Cu concentration in the solution was measured using atomic absorption, and the percentage of Cu removed was determined from the difference between the initial and final concentrations. The results showed that the CCD model has a favorable ability to predict Cu removal from the aqueous solutions (R2=0.90 and RSME=3.34%). Based on the Pareto analysis, contact time, the amount of sawdust, pH, and the Cu concentration had the most significant effect on removing Cu from the solution. Contact time, amount of sawdust, and pH were directly related, and the amount of dissolved Cu was proportional to the removal of Cu from the solution. Therefore, sawdust is desirable as a natural adsorbent, and the removal efficiency of Cu from solutions with low Cu concentration is very high (94%). In this regard, it is advised to use sawdust in the process of targeting Cu and heavy metals due to its low cost and availability.

Reversing the damage: ecological restoration of polluted water bodies affected by pollutants due to anthropogenic activities

Aquatic ecosystems provide a large number of cultural, regulating, and supporting services to humans and play a pivotal role in sustaining freshwater-dependent ecosystems. However, an increase in human population coupled with economic growth in the last few decades has severely affected their functioning and ecological health. This has led to an increase in concentrations of pollutants originating from anthropogenic activities such as heavy metals, plastics, semi-volatile organic compounds, and endocrine disruptors. These pollutants provoke deleterious impacts on aquatic biodiversity and affect the water quality and functioning. In this paper, we discuss the sources and impacts of such pollutants as well as restoration techniques for reducing their impact on aquatic ecosystems. Several physical and chemical ecological restoration techniques, such as dredging, sediment capping, water diversion, adsorption, aeration, and flushing, can be employed to improve the water quality of water bodies. Additionally, biological techniques such as phytoremediation, phycoremediation, the use of biomembranes, and the construction of ecological floating beds can be employed to increase the population of aquatic organisms and improve the overall ecological health of aquatic ecosystems. Restoration techniques can effectively reduce the concentrations of suspended solids and dissolved phosphorus and increase the levels of dissolved oxygen. The restoration techniques for improving the ecological health of water bodies should not be limited to simply improving the water quality but should also focus on improving the biological processes and ecosystem functioning since it is essential to mitigate the adverse effects of pollutants and restore the vital ecosystem services provided by water bodies for future generations.

Fabrication of carboxylic functionalized poly(methacrylic acid 2-(tert-butylamino)ethyl ester)-coated mesoporous silica nanoparticles and their application for removing ionic dyes from polluted water

The removal of dyes from wastewater that are released during industrial processes has become a significant concern in the environmental science in recent years. To tackle this issue, researchers are exploring the use of nanomaterials for designing new adsorbents. Another promising approach is to grow polymer brushes with high density functional groups via surface-initiated atom transfer radical polymerization (SI-ATRP), which can significantly enhance their ability to absorb dyes. The presence of carboxylic acid groups on the adsorbent material significantly contributes to its efficacy in dye removal by enhancing adsorption capacity, enabling selective adsorption, pH-dependent behavior, chelation, or complexation, and providing stability for repeated usage. In this work, a nanomaterial of carboxylic functionalized poly (methacrylic acid 2-(tert-butylamino)ethyl ester)-coated mesoporous silica nanoparticles (MSNPs-PMATBAE-COOH) was synthesized by the growth of PTBAEMA via surface-initiated atom-transfer radical polymerization, then reacted with succinic anhydride reaction. The chemical structure of MSNPs-PMATBAE-COOH was confirmed using multiple methods, including FT-IR and DLS, and the core-brush morphology was observed clearly using TEM. MSNPs-PMATBAE-COOH were subsequently employed to adsorb hazardous dyes efficiently. The anionic polymer brushes enabled the adsorption of methylene blue (MB) and tetraethylrhodamine (TER) at optimum pH value of 3. The results also indicated that MSNPs-PMATBAE-COOH possessed significant adsorption capacity (263.4 and 212.9 mg g-1 for MB and TER, respectively) and fast adsorption rate (within 15 min), which can be explained by the abundance of adsorptive polymer brushes and the small size of the nanoparticles. Overall, the findings indicate that MSNPs-PMATBAE-COOH is a highly effective adsorbent material for eliminating dye pollutants from wastewater.

Current Status of Biotechnological Approaches to Enhance the Phytoremediation of Heavy Metals in India-A Review

Rising waste construction, agricultural actions, and manufacturing sewages all contribute to heavy metal accumulation in water resources. Humans consume heavy metals-contaminated substances to make sustenance, which equally ends up in the food circle. Cleaning of these vital properties, along with the prevention of new pollution, has long been required to evade negative strength consequences. Most wastewater treatment techniques are widely acknowledged to be costly and out of the grasp of governments and small pollution mitigation businesses. Utilizing hyper-accumulator plants that are extremely resilient to heavy metals in the environment/soil, phytoremediation is a practical and promising method for eliminating heavy metals from contaminated environments. This method extracts, degrades, or detoxifies harmful metals using green plants. The three phytoremediation techniques of phytostabilization, phytoextraction, and phytovolatilization have been used extensively for soil remediation. Regarding their ability to be used on a wide scale, conventional phytoremediation methods have significant limitations. Hence, biotechnological attempts to change plants for heavy metal phytoremediation methods are extensively investigated in order to increase plant effectiveness and possible use of improved phytoremediation approaches in the country of India. This review focuses on the advances and significance of phytoremediation accompanied by the removal of various harmful heavy metal contaminants. Similarly, sources, heavy metals status in India, impacts on nature and human health, and variables influencing the phytoremediation of heavy metals have all been covered.

Bioremediation of Azo Dye Brown 703 by Pseudomonas aeruginosa: An Effective Treatment Technique for Dye-Polluted Wastewater

Dye-polluted wastewater poses a serious threat to humans’, animals’ and plants’ health, and to avoid these health risks in the future, the treatment of wastewater containing dyes is necessary before its release to environment. Herein, a biological approach is used; the textile azo dye brown 703 is degraded utilizing Pseudomonas aeruginosa. The bacterial strain was isolated from textile wastewater dumping sites in Mingora, Swat. The optimization for bacterial degradation was carried out on the nutrient broth medium, which was then subjected to a variety of environmental physicochemical conditions and nutritional source supplementation before being tested. Under micro-aerophilic circumstances, the maximum decolorization and degradation of dye occurred at a 20 ppm dye concentration within 3 days of incubation at a neutral pH and 38 °C. The decrease in the intensity of the absorbance peak in the UV–Vis spectrum was used to measure the extent of decolorization. Initially, 15 bacterial strains were isolated from the textile effluent. Out of these strains, Pseudomonas aeruginosa was found to be the most potent degrading bacteria, with a degradation extent of around 71.36% at optimum conditions. The appearance and disappearance of some new peaks in the FT-IR analysis after the degradation of brown 703 showed that the dye was degraded by Pseudomonas aeruginosa. The GC–MS analysis performed helped in identifying the degraded compounds of azo dye that were utilized in illustrating the under-study process of brown 703 degradation. The biodegradation brought about by Pseudomonas aeruginosa can be employed successfully in the future as an eco-friendly approach with far reaching results.

The ability of twisted nanographene for removal of Pb2+, Hg2+ and Cd2+ ions from wastewater: Computational study

CONTEXT

Heavy metal ion removal from wastewater has become a global concern due to its extensive negative effects on human health and the environment. The density functional theory is employed to investigate the possibility of removing Pb2+, Hg2+, and Cd2+ ions from wastewater using nano-graphene. Researchers have shown that NG can efficiently remove heavy metals from media. Additionally, it was shown that the adsorption of Pb2+, Hg2+, and Cd2+ ions might reduce the large pristine NG (HOMO-LUMO) gap.

METHODS

HSE06 may accurately represent NG electrical characteristics. The DFT-D3 method was also used to account for Van der Waals interactions in the present study. The results demonstrated that charge transfer and binding energy remained greater in cation-NG systems with greater electron transfer rates. Pb2+, Hg2+, and Cd2+ adsorption results indicated that Egap was significantly reduced by 68%, 15%, and 21%, respectively. The Pb2+@NG complex exhibited the strongest oscillator strength. This may be explained by the enormous occupation number difference between the 2px orbital of the C atoms and the 6 s orbital of the Pb2+ cations. The greater Ebin value of Pb2+@NG is consistent with the increased predicted redshifts (199 nm). DFT (hybrid functional HSE06) studies that rely on time showed that the relevant complexes have "ligand-to-metal charge transfer" excitations. In general, it was found that Pb2+@NG had the greatest k value, binding energy, redshifts, and charge transfer rate among the complexes. The theoretical insights of this study may influence experimental efforts to identify NG-based compounds that are effective and efficient at removing pollutants from wastewater.

Adsorption of heavy metals on natural zeolites: A review

Water pollution has jeopardized human health, and a safe supply of drinking water has been recognized as a worldwide issue. The increase in the accumulation of heavy metals in water from different sources has led to the search for efficient and environmentally friendly treatment methods and materials for their removal. Natural zeolites are promising materials for removing heavy metals from different sources contaminating the water. It is important to know the structure, chemistry, and performance of the removal of heavy metals from water, of the natural zeolites to design water treatment processes. This review focuses on critical analyses of the application of distinct natural zeolites for the adsorption of heavy metals from water, specifically, arsenic (As(III), As(V)), cadmium (Cd(II)), chromium (Cr(III), Cr(VI)), lead (Pb(II)), mercury(Hg(II)) and nickel (Ni(II)). The reported results of heavy-metal removal by natural zeolites are summarized, and the chemical modification of natural zeolites by acid/base/salt reagent, surfactants, and metallic reagents has been analyzed, compared, and described. Furthermore, the adsorption/desorption capacity, systems, operating parameters, isotherms, and kinetics for natural zeolites were described and compared. According to the analysis, clinoptilolite is the most applied natural zeolite to remove heavy metals. It is effective in removing As, Cd, Cr, Pb, Hg, and Ni. Additionally, an interesting fact is a variation between the natural zeolites from different geological origins regarding the sorption properties and capacities for heavy metals suggesting that natural zeolites from different regions of the world are unique.

Ability of Cupriavidus necator H16 to resist, bioremove, and accumulate some hazardous metal ions in water

Bacterial biomasses are suitable and inexpensive biosorbents for the removal of metal ions. The Gram-negative betaproteobacterium Cupriavidus necator H16 is found in soil and freshwater environments. In this study, C. necator H16 was used to remove chromium (Cr), arsenic (As), aluminum (Al), and cadmium (Cd) ions from water. Minimum inhibition concentration (MIC) values of C. necator to Cr, As, Al, and Cd were found as 76, 69, 341, and 275 mg/L, respectively. The highest rates of Cr, As, Al, and Cd bioremoval were 45, 60, 54, and 78%, respectively. pH levels between 6.0 and 8.0 and an average temperature of 30 °C were optimum for the most efficient bioremoval. Scanning electron microscopy (SEM) images of Cd-treated cells showed that the morphology of the cells was significantly impaired compared to the control. Shifts in the Fourier transform infrared spectroscopy analysis (FTIR) spectra of the Cd-treated cell walls also confirmed the presence of active groups. As a result, it can be said that C. necator H16 has a moderate bioremoval efficiency for Cr, As, and Al and a high bioremoval efficiency for Cd.

Insights into the Applications of Natural Fibers to Metal Separation from Aqueous Solutions

There is a wide range of renewable materials with attractive prospects for the development of green technologies for the removal and recovery of metals from aqueous streams. A special category among them are natural fibers of biological origin, which combine remarkable biosorption properties with the adaptability of useful forms for cleanup and recycling purposes. To support the efficient exploitation of these advantages, this article reviews the current state of research on the potential and real applications of natural cellulosic and protein fibers as biosorbents for the sequestration of metals from aqueous solutions. The discussion on the scientific literature reports is made in sections that consider the classification and characterization of natural fibers and the analysis of performances of lignocellulosic biofibers and wool, silk, and human hair waste fibers to the metal uptake from diluted aqueous solutions. Finally, future research directions are recommended. Compared to other reviews, this work debates, systematizes, and correlates the available data on the metal biosorption on plant and protein biofibers, under non-competitive and competitive conditions, from synthetic, simulated, and real solutions, providing a deep insight into the biosorbents based on both types of eco-friendly fibers.

Microbial biosorbent for remediation of dyes and heavy metals pollution: A green strategy for sustainable environment

Toxic wastes like heavy metals and dyes are released into the environment as a direct result of industrialization and technological progress. The biosorption of contaminants utilizes a variety of biomaterials. Biosorbents can adsorb toxic pollutants on their surface through various mechanisms like complexation, precipitation, etc. The quantity of sorption sites that are accessible on the surface of the biosorbent affects its effectiveness. Biosorption’s low cost, high efficiency, lack of nutrient requirements, and ability to regenerate the biosorbent are its main advantages over other treatment methods. Optimization of environmental conditions like temperature, pH, nutrient availability, and other factors is a prerequisite to achieving optimal biosorbent performance. Recent strategies include nanomaterials, genetic engineering, and biofilm-based remediation for various types of pollutants. The removal of hazardous dyes and heavy metals from wastewater using biosorbents is a strategy that is both efficient and sustainable. This review provides a perspective on the existing literature and brings it up-to-date by including the latest research and findings in the field.

Recent Application Prospects of Chitosan Based Composites for the Metal Contaminants Wastewater Treatment

Heavy metals, known for their toxic nature and ability to accumulate and magnify in the food chain, are a major environmental concern. The use of environmentally friendly adsorbents, such as chitosan (CS)—a biodegradable cationic polysaccharide, has gained attention for removing heavy metals from water. This review discusses the physicochemical properties of CS and its composites and nanocomposites and their potential application in wastewater treatment.

Nutrient removal from biogas slurry and biogas upgrading by microalgae-fungi-bacteria co-cultivation under different carbon nanotubes concentration

In this study, Chlorella vulgaris, Ganoderma lucidum, and endophytic bacteria were co-cultivated with the stimulation of strigolactone analogs GR24 to prepare pellets. During the purification of biogas slurry and biogas, multi-walled carbon nanotubes (MWCNTs) were introduced to enhance the removal efficiencies of nutrients and CO₂. The results showed that both GR24 and MWCNTs affected the purification of biogas slurry and biogas. The maximum chemical oxygen demand, total nitrogen, total phosphorus, and CO₂ removal efficiencies of the Chlorella vulgaris-Ganoderma lucidum-endophytic bacterial symbionts were 82.57 ± 7.96% (P < 0.05), 82.14 ± 7.87% (P < 0.05), 84.27 ± 7.96% (P < 0.05), and 63.93 ± 6.22% (P < 0.05), respectively, with the induction of 10^-9 M GR24 and 1 mg L^-1 MWCNTs. Moreover, the growth and photosynthetic performance of the symbionts were consistent with the removal effects. The Chlorella vulgaris-Ganoderma lucidum-endophytic bacterial symbionts obtained high growth rates and enzyme activity with the maximum growth rate of 0.365 ± 0.03 d^-1, mean daily productivity of 0.182 ± 0.016 g L^-1 d^-1, and carbonic anhydrase activity of 31.07 ± 2.75 units, respectively. These results indicated that an appropriate concentration of GR24 and MWCNTs could promote the growth of symbionts, reinforce the purification effects of biogas slurry and biogas, and provide a new idea for the simultaneous purification of wastewater and biogas.

Strategies for microbial bioremediation of environmental pollutants from industrial wastewater: A sustainable approach

Heavy metals are hazardous and bring about critical exposure risks to humans and animals, even at low concentrations. An assortment of approaches has been attempted to remove the water contaminants and keep up with water quality, for that microbial bioremediation is a promising way to mitigate these pollutants from the contaminated water. The flexibility of microorganisms to eliminate a toxic pollutant creates bioremediation an innovation that can be applied in various water and soil conditions. This review insight into the sources, occurrence of toxic heavy metals, and their hazardous human exposure risk. In this review, significant attention to microbial bioremediation for pollutant mitigation from various ecological lattices has been addressed. Mechanism of microbial bioremediation in the aspect of factors affecting, the role of microbes and interaction between the microbes and pollutants are the focal topics of this review. In addition, emerging strategies and technologies developed in the field of genetically engineered micro-organism and micro-organism-aided nanotechnology has shown up as powerful bioremediation tool with critical possibilities to eliminate water pollutants.

Sodium Alginate/β-Cyclodextrin Reinforced Carbon Nanotubes Hydrogel as Alternative Adsorbent for Nickel(II) Metal Ion Removal

Water pollution issues, particularly those caused by heavy metal ions, have been significantly growing. This paper combined biopolymers such as sodium alginate (SA) and β-cyclodextrin (β-CD) to improve adsorption performance with the help of calcium ion as the cross-linked agent. Moreover, the addition of carbon nanotubes (CNTs) into the hybrid hydrogel matrix was examined. The adsorption of nickel(II) was thoroughly compared between pristine sodium alginate/β-cyclodextrin (SA-β-CD) and sodium alginate/β-cyclodextrin immobilized carbon nanotubes (SA-β-CD/CNTs) hydrogel. Both hydrogels were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectral analysis, field emission scanning electron microscopy (FESEM), electron dispersive spectroscopy (EDX), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) surface area analysis. The results showed SA-β-CD/CNTs hydrogel exhibits excellent thermal stability, high specific surface area and large porosity compared with SA-β-CD hydrogel. Batch experiments were performed to study the effect of several adsorptive variables such as initial concentration, pH, contact time and temperature. The adsorption performance of the prepared SA-β-CD/CNTs hydrogel was comprehensively reported with maximum percentage removal of up to 79.86% for SA-β-CD/CNTs and 69.54% for SA-β-CD. The optimum adsorption conditions were reported when the concentration of Ni(II) solution was maintained at 100 ppm, pH 5, 303 K, and contacted for 120 min with a 1000 mg dosage. The Freundlich isotherm and pseudo-second order kinetic model are the best fits to describe the adsorption behavior. A thermodynamic study was also performed. The probable interaction mechanisms that enable the successful binding of Ni(II) on hydrogels, including electrostatic attraction, ion exchange, surface complexation, coordination binding and host-guest interaction between the cationic sites of Ni(II) on both SA-β-CD and SA-β-CD/CNTs hydrogel during the adsorption process, were discussed. The regeneration study also revealed the high efficiency of SA-β-CD/CNTs hydrogel on four successive cycles compared with SA-β-CD hydrogel. Therefore, this work signifies SA-β-CD/CNTs hydrogel has great potential to remove Ni(II) from an aqueous environment compared with SA-β-CD hydrogel.

ZnAl-SO4 Layered Double Hydroxide and Allophane for Cr(VI), Cu(II) and Fe(III) Adsorption in Wastewater: Structure Comparison and Synergistic Effects

Owing to their structure, layered double hydroxides (LDHs) and allophane are nowadays considered as promising materials for application in different fields. The goal of this work is to compare the efficacy of allophane and ZnAl-SO₄ LDH to remove, by adsorption, some cationic and anionic pollutants from industrial wastewater. Both compounds were synthesized via the co-precipitation route (direct method) followed by hydrothermal treatment, obtaining nanoscopic crystallites with a partially disordered turbostratic (ZnAl-SO₄ LDH) or amorphous (allophane) structure. The characterization of the obtained compounds was performed by means of powder x-ray diffraction (PXRD), thermal gravimetry analysis (TGA), field emission scanning electron microscopy analysis (FESEM), and Fourier-transform infrared spectroscopy (FT-IR). The sorbents were tested using wastewater produced by a real metalworking plant and containing ionic species such as Cu(II), Fe(III) and Cr(VI), whose concentration was measured by means of inductively coupled plasma-optical emission spectrometry (ICP-OES). This investigation represents an alternative procedure with respect to standard protocols based on customarily made and artificially lab-produced wastewaters. Both sorbents and their combination proved to be efficient in Cr(VI) removal, irrespective of the presence of cations like Cu(II) and Fe(III). A synergistic effect was detected for Cu(II) adsorption in a mixed allophane/LDH sorbent, leading to a Cu(II) removal rate of 89.5%.

Fabrication of Novel Agrowaste (Banana and Potato Peels)-Based Biochar/TiO2 Nanocomposite for Adsorption of Cr(VI), Statistical Optimization via RSM Approach

In this research work, a simple, efficient, and eco-friendly procedure for the biosorption of Cr(VI) ions was studied. A detailed comparative study was performed to check the adsorption efficiency of agrowaste (banana and potato peels)-based adsorbents. Firstly, mixed biosorbent was washed, dried and ground into powder, secondly, biosorbent was pyrolyzed into biochar and thirdly TiO2 nanocomposite (TiO2 NC) biosorbent was made by sonicating using prepared biochar and TiO2 NPs. Titanium dioxide nanoparticles (TiO2 NPs) were synthesized by a green method using Psidium guajava leaf extract. The synthesized adsorbents were characterized by SEM, EDX FT-IR, XRD and UV-visible analysis. The effect of four different factors, i.e., pH of the synthetic metallic solution, time, concentration and adsorbent dosage was studied. The optimum conditions were time (120 min), pH (3), concentration (10 ppm) and adsorbent dosage (1.0 g). The kinetic modeling showed that the adsorption of Cr(VI) ion follows a pseudo second-order mechanism and the Langmuir isotherm model was found to fit better for this study. Response surface methodology (RSM)-based optimized parameters provided optimal parameter sets that better represent the adsorption rate models. The uptake capacity of Cr(VI) from aqueous solution was found to be biomass (76.49 mg/L) ˂ biochar (86.51 mg/L) ˂ TiO2 NC (92.89 mg/L). It can be suggested that the produced TiO2 NC could possibly be an efficient biosorbent for the removal of Cr(IV).