Removal of Mn and As from drinking water by red mud and pyrolusite

A comprehensive investigation of the adsorption behaviour and mechanism of industrial waste sintering and bayer red muds for heavy metals

The issue of heavy metal pollution is a critical global concern that requires urgent solution. However, conventional heavy metal adsorbents are too costly to be applied in large-scale engineering. In this study, adsorption behavior and mechanism of sintering red mud (RM-A) and bayer red mud (RM-B) for heavy metals were investigated to address the disposal of red mud as industrial waste and remediation of heavy metal pollution. Batch adsorption experiments were conducted to explore the adsorption performances of RM-A and RM-B under various conditions. Characterization of RM-A and RM-B before and after adsorption by XRD, FTIR and SEM-EDX was applied to investigate the specific adsorption behavior and mechanism. Adsorption experiments of both RM-A and RM-B fitted pseudo-second-order kinetic model and Langmuir isotherm model, with estimated maximum adsorption capacity of 21.96 and 25.19 mg/g for Cd2+, 21.47 and 26.06 mg/g for Cu2+ and 55.47 and 59.65 mg/g for Pb2+, respectively. Precipitation transformation of calcite was the primary adsorption mechanism for RM-A, whereas ion exchange of cancrinite, surface coordination compounds of hematite and minor precipitation transformation of calcite accounted for the adsorption mechanism for RM-B. Overall, RM-A and RM-B exhibited best adsorption performance for Pb2+, with RM-B showing greater adsorption capacity attributed to its higher specific surface area. This study compared the adsorption properties of RM-A and RM-B for the first time and demonstrated that both red muds can be effectively applied to remove heavy metals, thereby contributing to the sustainable industrial waste management and resourceful reuse.

Understanding the role of manganese oxides in retaining harmful metals: Insights into oxidation and adsorption mechanisms at microstructure level

The increasing intensity of human activities has led to a critical environmental challenge: widespread metal pollution. Manganese (Mn) oxides have emerged as potentially natural scavengers that perform crucial functions in the biogeochemical cycling of metal elements. Prior reviews have focused on the synthesis, characterization, and adsorption kinetics of Mn oxides, along with the transformation pathways of specific layered Mn oxides. This review conducts a meticulous investigation of the molecular-level adsorption and oxidation mechanisms of Mn oxides on hazardous metals, including adsorption patterns, coordination, adsorption sites, and redox processes. We also provide a comprehensive discussion of both internal factors (surface area, crystallinity, octahedral vacancy content in Mn oxides, and reactant concentration) and external factors (pH, presence of doped or pre-adsorbed metal ions) affecting the adsorption/oxidation of metals by Mn oxides. Additionally, we identify existing gaps in understanding these mechanisms and suggest avenues for future research. Our goal is to enhance knowledge of Mn oxides' regulatory roles in metal element translocation and transformation at the microstructure level, offering a framework for developing effective metal adsorbents and pollution control strategies.

Nature-Based Solutions for Restoring an Agricultural Area Contaminated by an Oil Spill

A feasibility study is presented for a bioremediation intervention to restore agricultural activity in a field hit by a diesel oil spill from an oil pipeline. The analysis of the real contaminated soil was conducted following two approaches. The first concerned the assessment of the biodegradative capacity of the indigenous microbial community through laboratory-scale experimentation with different treatments (natural attenuation, landfarming, landfarming + bioaugmentation). The second consisted of testing the effectiveness of phytoremediation with three plant species: Zea mays (corn), Lupinus albus (lupine) and Medicago sativa (alfalfa). With the first approach, after 180 days, the different treatments led to biodegradation percentages between 83 and 96% for linear hydrocarbons and between 76 and 83% for branched ones. In case of contamination by petroleum products, the main action of plants is to favor the degradation of hydrocarbons in the soil by stimulating microbial activity thanks to root exudates. The results obtained in this experiment confirm that the presence of plants favors a decrease in the hydrocarbon content, resulting in an improved degradation of up to 18% compared with non-vegetated soils. The addition of plant growth-promoting bacteria (PGPB) isolated from the contaminated soil also promoted the growth of the tested plants. In particular, an increase in biomass of over 50% was found for lupine. Finally, the metagenomic analysis of the contaminated soil allowed for evaluating the evolution of the composition of the microbial communities during the experimentation, with a focus on hydrocarbon- oxidizing bacteria.

Covalent and Non-covalent Functionalized Nanomaterials for Environmental Restoration

Nanotechnology has emerged as an extraordinary and rapidly developing discipline of science. It has remolded the fate of the whole world by providing diverse horizons in different fields. Nanomaterials are appealing because of their incredibly small size and large surface area. Apart from the naturally occurring nanomaterials, synthetic nanomaterials are being prepared on large scales with different sizes and properties. Such nanomaterials are being utilized as an innovative and green approach in multiple fields. To expand the applications and enhance the properties of the nanomaterials, their functionalization and engineering are being performed on a massive scale. The functionalization helps to add to the existing useful properties of the nanomaterials, hence broadening the scope of their utilization. A large class of covalent and non-covalent functionalized nanomaterials (FNMs) including carbons, metal oxides, quantum dots, and composites of these materials with other organic or inorganic materials are being synthesized and used for environmental remediation applications including wastewater treatment. This review summarizes recent advances in the synthesis, reporting techniques, and applications of FNMs in adsorptive and photocatalytic removal of pollutants from wastewater. Future prospects are also examined, along with suggestions for attaining massive benefits in the areas of FNMs.

Immobilization of lead, copper, cadmium, nickel, and zinc in sediment by red mud: adsorption characteristics, mechanism, and effect of dosage on immobilization efficiency

The objective of this work was to determine the effect of dosage on the immobilization of lead (Pb), copper (Cu), cadmium (Cd), nickel (Ni), and zinc (Zn) in sediment by red mud (RM). To achieve this aim, the adsorption characteristics and mechanism of Pb, Cu, Cd, Ni, and Zn from aqueous solution on RM were studied at first, and then the influence of the RM dosage on the fractionation and leaching potential of Pb, Cu, Cd, Ni, and Zn in sediment was investigated. The results showed that RM possessed high adsorption capacities for Pb(II), Cu(II), Cd(II), Ni(II), and Zn(II) in aqueous solution. The maximum monolayer Pb(II), Cu(II), Cd(II), Ni(II), and Zn(II) adsorption capacities for RM derived from the Langmuir isotherm model were found to be 296, 39.2, 70.2, 46.0, and 50.7 mg/g, respectively. The addition of RM into sediment could effectively reduce the toxicity characteristic leaching procedure (TCLP)-leachable concentrations of Pb, Cu, Cd, Ni, and Zn in the sediment. The added RM could effectively immobilize the mobile (exchangeable, reducible, and oxidizable fractions) Pb in sediment by the conversion of the exchangeable and reducible fractions into the residual fraction, and it could effectively immobilize the mobile Cu, Cd, Ni, and Zn in sediment by the conversion of the exchangeable fraction into the residual fraction. The quantities of mobile Pb, Cu, Cd, and Ni immobilized by RM had a good linear relationship with the added RM. The above results suggest that RM is a promising amendment for the immobilization of mobile Pb, Cu, Cd, Ni, and Zn in sediment, and the linear relationship between the RM dosage and the quantities of immobilized Pb, Cu, Cd, and Ni by RM can be employed to determine the RM dosage required for the immobilization of mobile Pb, Cu, Cd, and Ni in sediment.

Surface treated Phoenix sylvestris for bioadsorption of oil from aqueous solution: Isotherms and kinetic studies

Biosorption is a versatile technique of removing the oil spill - one of the major toxicants that causes water pollution, which threatens the ecological balance of the aquatic ecosystem. The proposed research aims in developing a viable adsorbent from discarded agricultural waste, Phoenix sylvestris, which was surface altered, assessed and utilised as a biosorbent for the effective removal of diesel from aqueous solution in batch adsorption trials. Waste palm leaves, Phoenix sylvestris (RPS)was physically (PMPS) and chemically modified (CMPS) to adsorb diesel in the emulsion. The synthesised materials were characterised by FTIR, SEM, and EDS, confirming a well-defined microporous structure consisting of ionisable groups. The studies indicated optimised conditions of 10 g, 4.5 g and 2 g of RPS, PMPS and CMPS respectively at 303K for an optimised adsorption time of 60 min. Freundlich isotherm agreed well with experimental data, and the kinetic mechanism claimed better results with RPS, PMPS and CMPS for Pseudo first-order model. The adsorbents could be reused five times without much loss of efficiency. From the performed studies, it can be inferred that good adsorption capacities at optimised conditions followed the order of CMPS > PMPS > RPS. Thermodynamic analysis proved the feasibility of such biosorption with exothermic nature predicting spontaneous attraction of oil components to the surface of PMPS and CMPS. Moreover, the density of the CMPS layer rendered proven results for such biosorption displaying a hyperbolic dependency assuring its efficacy. Hence, it can be concluded that the prepared adsorbent from Phoenix sylvestris, an agricultural waste, possess good adsorptive properties.

A Novel Graphite-Based Sorbent for Oil Spill Cleanup

The performance of an innovative material based on expanded graphite, Grafysorber^® G+ (Directa Plus), has been tested through laboratory, tank, and confinement tests for oil removal in case of an oil spill and water treatment. In addition to the ability to retain oil, the possibility of reusing this material after regeneration via squeezing was also evaluated. As a comparison, the same experimental tests were conducted using polypropylene flakes (PP), the material currently most used to deal with spill accidents. Oils with different chemical and physical properties were used, namely kerosene, diesel, and crude oil. From the laboratory tests, the capacity of Grafysorber^® G+ to retain oil was found to be directly proportional to the viscosity of the latter, with adsorption values ranging from 76.8 g/g for diesel to 50.8 g/g for kerosene, confirming the potential of the innovative material compared to the PP. Cyclical use tests have confirmed certain reusability of the material, even if its adsorbent capacity decreases significantly after the first cycle and continues to decrease in subsequent cycles, but a less marked manner. Finally, some considerations based on the adsorption capacities were found to suggest that the adoption of the new material is also economically preferable, resulting in savings of 20 to 40% per kg of hydrocarbon treated.

Dealing with complex contamination: A novel approach with a combined bio-phytoremediation strategy and effective analytical techniques

Phytoremediation is a sustainable technology capable of efficiently removing low or moderate contamination. However, complex pollution conditions can drastically reduce efficiency, as plants can show themselves sensitive to organic contaminants, growing slowly and thus impairing metals' absorption. In cases where the action of indigenous bacteria degrading hydrocarbons and promoting plant growth is not sufficient, more sophisticated strategies are necessary. This investigation aims to evaluate the effectiveness of a train of technologies that sees advanced phytoremediation in combination with other biological approaches to remediate soil from a disused industrial area contaminated by N-containing compounds, alkyl aromatic hydrocarbons, copper, and nickel. In particular, a stepwise procedure was used with a pre-treatment (landfarming and bioaugmentation), significantly affecting the soil's fertility, increasing germinability up to 85%, and allowing the plants to extract the metals adequately. Furthermore, with EDTA as a mobilizing agent, nickel absorption has increased up to 36% in Helianthus annuus and up to 88% in Zea mays. For copper, an increase of up to 262% in Helianthus annuus and up to 202% in Zea Mays was obtained. Analysis through Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry highlighted the biodegradation of some of the N-containing compounds recording, after phytoremediation, a decrease of up to almost 90%. Metagenomic analysis of the soil showed a typical microbial population of oxidizing hydrocarbon strains with a prevalence of the Nocardiaceae family (43%). The results obtained appear to confirm the usefulness of the approach developed, and the employed cutting-edge analytical techniques allowed a top-notch characterization of the remediation scenario.

Efficient graphene-coated iron oxide (GCIO) nanoadsorbent for removal of lead and arsenic ions

ABSTRACTThe graphene-coated iron oxide (GCIO) was used for the removal of Pb²⁺ and As³⁺ ions from aqueous solution. For the characterization of GCIO, several techniques (FTIR, XRD, EDX, SEM, TEM, TGA, DSC and vibrating sample magnetometry) were used which indicated the interaction of Pb²⁺ and As³⁺ with adsorbent. In addition, the effects of adsorbate concentration, different composition of adsorbent, temperature, pH of the solution and contact time of adsorbate-adsorbent were studied. After analysis of these experiments, it was found that GCIO offered very fast removal of Pb²⁺ and As³⁺ with small amount of GCIO (0.09 g) in 100 mg/L adsorbate solution. The maximum removal of Pb²⁺ ions (up to 97.62%) was achieved when 100 mg/L standard solution of metal ion was treated with GCIO for 35 min at 45°C in weak acidic medium (5 pH). The adsorption of Pb²⁺ ions followed Freundlich model with high correlation coefficient 0.98 R². In case of As³⁺ ions, maximum removal of metal ion (up to 86.62%) was attained when 100 mg/L adsorbate solution is treated with GCIO for 25 min in slightly acidic medium (6 pH) at 25°C. The adsorption of As³⁺ ions followed D-R model with 0.98 R² value. The adsorption of both metal ions (Pb²⁺ and As³⁺) follows second-order kinetic model. The high percentage removal of metal ions with little quantity of GCIO confirmed that GCIO is an excellent, effective and economic adsorbent.

Experimental and Physico-Chemical Comparison of ZnO Nanoparticles’ Activity for Photocatalytic Applications in Wastewater Treatment

In this contribution, the photoactivity upon activation by simulated sunlight of zinc oxide (ZnO) obtained from two different synthetic pathways (Acetate and Nitrate) is investigated for water purification. Different reagents and processes were exploited to obtain ZnO nanoparticles. Products have been characterized by means of X-Ray Diffraction, Scanning Electron Microscopy along with Energy Dispersive Spectrometer, Dynamic Light Scattering, and Diffuse Reflectance Measurements, to highlight the different outcomes ascribable to each synthesis. A comparison of characteristics and performances was also carried out with respect to commercial ZnO. Nanoparticles of this semiconductor can be obtained as aggregates with different degrees of purity, porosity, and shape, and their physical-chemical properties have been addressed to the specific use in wastewater treatment, testing their effectiveness on the photocatalytic degradation of methylene blue (MB) as a model pollutant. Excluding the commercial sample, experimental results evidenced a better photocatalytic behavior for the ZnO Nitrate sample annealed at 500 °C, which was found to be pure and stable in water, suggesting that ZnO could be effectively exploited as a heterogeneous photocatalyst for the degradation of emerging pollutants in water, provided that thermal treatment is included in the synthetic process.

Research on High-Pressure Hydrochloric Acid Leaching of Scandium, Aluminum and Other Valuable Components from the Non-Magnetic Tailings Obtained from Red Mud after Iron Removal

Red mud is a hazardous waste of the alumina industry that contains high amounts of iron, aluminum, titanium and rare-earth elements (REEs). One of the promising methods for the extraction of iron from red mud is carbothermic reduction with the addition of sodium salts. This research focuses on the process of hydrochloric high-pressure acid leaching using 10 to 20% HCl of two samples of non-magnetic tailings obtained by 60 min carbothermic roasting of red mud at 1300 °C and the mixture of 84.6 wt.% of red mud and 15.4 wt.% Na2SO4 at 1150 °C, respectively, with subsequent magnetic separation of metallic iron. The influence of temperature, leaching duration, solid-to-liquid-ratio and acid concentration on the dissolution behavior of Al, Ti, Mg, Ca, Si, Fe, Na, La, Ce, Pr, Nd, Sc, Zr was studied. Based on the investigation of the obtained residues, a mechanism for passing valuable elements into the solution was proposed. It has shown that 90% Al, 91% Sc and above 80% of other REEs can be dissolved under optimal conditions; Ti can be extracted into the solution or the residue depending on the leaching temperature and acid concentration. Based on the research results, novel flowsheets for red mud treatment were developed.

Green development challenges within the environmental management framework

Green development of energy, water and environment systems is essential as these three systems represent the basic life needs of humankind. Therefore, environmental problems arising from each of these three systems need to be carefully addressed to preserve the energy, water and environment resources for future generations. This paper discusses some of the latest developments in three main areas of sustainability themes, namely energy, water and environment, that emerged from the 14th Sustainable Development of Energy, Water and Environment Systems (SDEWES) Conference held in 2019. As such, it acts as an editorial paper for the virtual special issue of the Journal of Environmental Management, dedicated to the SDEWES 2019 conference.

Removal of Zn(II), Mn(II) and Cu(II) by adsorption onto banana stalk biochar: adsorption process and mechanisms

Low-cost banana stalk (Musa nana Lour.) biochar was prepared using oxygen-limited pyrolysis (at 500 °C and used), to remove heavy metal ions (including Zn(II), Mn(II) and Cu(II)) from aqueous solution. Adsorption experiments showed that the initial solution pH affected the ability of the biochar to adsorb heavy metal ions in single- and polymetal systems. Compared to Mn(II) and Zn(II), the biochar exhibited highly selective Cu(II) adsorption. The adsorption kinetics of all three metal ions followed the pseudo-second-order kinetic equation. The isotherm data demonstrated the Langmuir model fit for Zn(II), Mn(II) and Cu(II). The results showed that the chemical adsorption of single molecules was the main heavy metal removal mechanism. The maximum adsorption capacities (mg·g^-1) were ranked as Cu(II) (134.88) > Mn(II) (109.10) > Zn(II) (108.10)) by the single-metal adsorption isotherms at 298 K. Moreover, characterization analysis was performed using Fourier transform infrared spectroscopy, the Brunauer-Emmett-Teller method, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results revealed that ion exchange was likely crucial in Mn(II) and Zn(II) removal, while C-O, O-H and C = O possibly were key to Cu(II) removal by complexing or other reactions.

An Accurate Inverse Model for the Detection of Leaks in Sealed Landfills

Leaks from landfills to underlying soil layers are one of the main problems that endanger the sustainability of waste disposal in landfills. Indeed, the possible failing of in-situ equipment can give rise to serious pollution consequences or costly inspection work in the landfill body. In this paper, we develop the time dependent mathematical relationship between the concentration of water at the surface of the landfill and the flux at the bottom of the landfill. This makes it possible to detect a leak using non-expensive measurements made at the surface of the landfill. The resulting model is obtained by analytically solving Richard’s equation with a piecewise linear boundary condition at the bottom. The unknown coefficients of the piecewise linear functions, which can be estimated using the measurements at the surface, provide the necessary information for detecting leaks. The algorithm has been numerically tested using simulated data of rain precipitation. The method proposed could be conveniently used to complement the usual monitoring techniques due to the limited costs of its implementation.

Environmental problems arising from the sustainable development of energy, water and environment system

Integration of energy, water and environment systems is essential in the multidisciplinary concept of sustainable development, as they represent the basic life needs of mankind. Therefore, problems arising from the sustainable development concept need to be carefully addressed to preserve the energy, water and environment resources for future generations. This article discusses some of the latest developments in three main areas of sustainability themes, namely energy, water and environment, that emerged from three Sustainable Development of Energy, Water and Environment Systems (SDEWES) conferences held in 2018. As such, it acts as an editorial paper for the virtual special issue of the Journal of Environmental Management, dedicated to the SDEWES2018 conferences.

Chromium(III) Removal from Wastewater by Chitosan Flakes

Chitosan is very effective in removing metal ions through their adsorption. A preliminary investigation of the adsorption of chromium(III) by chitosan was carried out by means of batch tests as a function of contact time, pH, ion competition, and initial chromium(III) concentration. The rate of adsorption was rather rapid (t1/2 < 18 min) and influenced by the presence of other metal ions. The obtained data were tested using the Langmuir and Freundlich isotherm models and, based on R2 values, the former appeared better applicable than the latter. Chitosan was found to have an excellent loading capacity for chromium(III), namely 138.0 mg Cr per g of chitosan at pH = 3.8, but metal ions adsorption was strongly influenced by the pH. About 76% of the recovered chromium was then removed simply by washing the used chitosan with 0.1 M EDTA (Ethylenediaminetetraacetic acid) solution. This study demonstrates that chitosan has the potential to become an effective and low-cost agent for wastewater treatment (e.g., tannery waste) and in situ environmental remediation.

Enhancing Cd(II) sorption by red mud with heat treatment: Performance and mechanisms of sorption

Red mud is a waste generated from the aluminum industry in large quantities. The potential of red mud as a sorbent for beneficial reuse has been the focus of research efforts. However, the limited sorption capacity of red mud has hindered its applications in the removal of environmental pollutants. In this study, the feasibility of heat treatment in improving the sorption of toxic Cd(II) by red mud was investigated in the temperature range of 200-900 °C. Heat treatment at 500 °C resulted in the highest sorption capacity (42.64 mg g^-1) and the fastest sorption rate. Further analyses revealed that heat treatment at 500 °C led to significant increases in specific surface area (32.77 m² g^-1), which likely contributed to the enhanced Cd(II) sorption performance. Notably, heat treatment at 500 °C nearly doubled Cd(II) sorption stability as compared with that of raw red mud, as demonstrated by leaching experiments with simulated rainwater. Sequential extraction and XPS analyses indicated that specific sorption was the predominant mechanism involved in Cd(II) removal by red mud heat-treated at 500 °C (RM500). The strength of specific sorption following heat treatment likely contributed to the increase in sorption stability due to the formation of inner-sphere complex (-OCdOH). Metal-metal ion exchange was identified as another sorption mechanism, which, however, likely had only a limited effect on Cd(II) sorption performance. As the final pH (6.57) of the sorption system was typically lower than the pH_PZC (about 10.6) of RM500, positive charges would develop on the red mud surface and impede the retention of Cd(II) cations, resulting in weak electrostatic attraction between Cd(II) cations and red mud. In summary, heat treatment at 500 °C considerably enhanced the capacity, rate and stability of Cd(II) sorption by red mud, suggesting red mud could be optimized by heat treatment as a more effective sorbent for Cd(II) removal. These findings represent the first mechanistic characterization of Cd(II) sorption by heat-treated red mud, providing much needed insights into the potential strategies to enhance the effectiveness of red mud in the sorptive removal of toxic heavy metals.

Arsenic accumulation in edible vegetables and health risk reduction by groundwater treatment using an adsorption process

The heavy metals transfer from the soil, where they accumulate, to the edible parts of the plants, and then, their entrance in the food chain can represent a source of concern for human health. Among heavy metals, arsenic is one of the most widespread in the soil of Lazio (central region of Italy), where the phytoavailable geogenic arsenic enters the food chain, with a dangerous exposition of the local population. In the first part of this work, plants of radish (Raphanus sativus L.) and lettuce (Lactuca sativa L.) were grown in protected culture in the experimental farm of CREA-AA, where they were daily treated with different concentrations of sodium arsenate dibasic heptahydrate in order to investigate differences in their arsenic accumulation capacities. In order to confirm the results achieved, in the second part of this study, the arsenic concentration was determined in commercial products obtained from contaminated areas of Lazio, and the potential exposition risk for human health through consumption of these widely consumed vegetables was estimated. The highest arsenic concentrations were found in the samples of lettuce. To evaluate the potential health risk from consumption of L. sativa and R. sativus, the estimated daily intake (EDI) for adults, adolescents, and elderly was calculated, finding that HRI (health risk index) index value for arsenic was low (< 1) in the case of chronic consumptions for all samples of radishes, and for the lettuces grown in the area of Viterbo. On the contrary, the lettuces obtained from Tuscania and Tarquinia presented very high concentrations of arsenic and a worrying HRI value. In order to reduce the risk of As toxicity in the people through consumption of the vegetables, the irrigation water should contain less than 0.1 mg As L-1. For this reason, the authors tested the application of red mud (RM) to remove As from groundwater before using it for the irrigation of radish and lettuce in greenhouse production.

High arsenic contamination and presence of other trace metals in drinking water of Kushtia district, Bangladesh

Drinking water with excessive concentration levels of arsenic (As) is a great threat to human health. A hydrochemical approach was employed in 50 drinking water samples (collected from Kushtia district, Bangladesh) to examine the occurrence of geogenic As and the presence of trace metals (TMs), as well as the factors controlling As release in aquifers. The results reveal that the drinking water of shallow aquifers is highly contaminated by As (6.05-590.7 μg/L); 82% of samples were found to exceed the WHO recommended limit (10 μg/L) for potable water, but the concentrations of Si, B, Mn, Sr, Se, Ba, Fe, Cd, Pb, F, U, Ni, Li, and Cr were within safe limits. The Ca-HCO₃-type drinking water was identified as having high contents of As, pH and HCO₃^-, a medium-high content EC, and low concentrations of NO₃^-, SO₄^2-, K⁺, and Cl^-. The significant correlation between As and NO₃^- indicates that NO₃^- might be attributed to the use of phosphate fertilizers and a factor responsible for enhancing As in aquifers. The study also reports that the occurrence of high As and the presence of TMs in drinking water may be a result of local anthropogenic activities, such as irrigation, intensive land use and the application of agrochemicals. The insignificant correlation between As and SO₄^2- demonstrated that As is released from SO₄^2- minerals under reducing conditions. An elevated pH value along with decoupling of As and HCO₃^- plays a vital role in mobilizing As to aquifer systems. Moreover, the positive relationship between As and Si indicated that As is transported in the biogeochemical environment. The reductive suspension of Mn(IV)-oxyhydroxides also accelerated the As mobilization process. Over exploitation of tube-well water and the competitive ion exchange process are also responsible for the release of As in aquifers.

Enhanced Oil Spill Remediation by Adsorption with Interlinked Multilayered Graphene

The performances of an innovative material based on graphene multilayers in a 3D structure similar to expanded graphite, Grafysorber^® G+ (Directa Plus), have been tested via in field applications on a real contaminated site. Several experimental tests were performed using Grafysorber^® inside adsorbent devices (booms and pillows) to treat waters polluted by oil. The experimental campaign was carried out with the aim of comparing the performances of Grafysorber^® with those of polypropylene (PP), which is the material used worldwide in case of water oil spill clean-up activities. The results achieved have confirmed a considerably higher selective adsorption capacity of Grafysorber^® compared to PP, and configure the new material as a promising alternative to standard materials in enhancing oil spill remediation by selective adsorption.

Enhancements in phytoremediation technology: Environmental assessment including different options of biomass disposal and comparison with a consolidated approach

Phytoremediation represents a solution for treating soils contaminated by heavy metals, provided that appropriate plant species are selected and the proper strategy chosen. When dealing with soil contaminated with arsenic and/or lead, which are non-essential elements for plants but also among the most toxic metals, this task is particularly difficult to achieve. In a previous contribution we showed that metals accumulation by Lupinus albus, Brassica juncea and Helianthus annuus can be improved by dosing suitable chemicals (i.e. phosphate and EDTA), leading to a quicker and cheaper intervention. This study discusses the assisted phytoremediation of a real site contaminated by several metals, presenting an environmental assessment realized by using the GaBi LCA software. The environmental sustainability of the reclamation technology was analyzed in terms of Global Warming Potential (GWP-100 years), considering different destinations for the harvested biomass, and comparing its ecological footprint with the outcomes of a conventional treatment of excavation and landfill disposal. The comparison clearly shows the great advantage of the phytoremediation, in terms of environmental impact, highlighting the importance of correctly handling the disposal of contaminated biomass produced. In fact, its incineration (aimed at reducing the volumes to be disposed of) could be more onerous than a direct landfilling, but re-qualify as a more sustainable choice if combined with energy recovery. The same applies to fast pyrolysis, which seems to be the most sustainable approach to date, at least in terms of technological maturity, although this requires technical-economic considerations on the quality and use of biofuels produced.