Conventional Remediation Techniques Research Articles

Recent advancements in encapsulation of poly aromatic hydrocarbons via macrocyclic host-guest chemistry

Polyaromatic hydrocarbons (PAHs) pose a significant threat to ecosystems and human health due to their widespread presence and persistence in the environment. Conventional remediation techniques often fall short in both efficiency and environmental impact. However, recent advancements in utilizing organic macrocyclic host molecules show considerable promise for effectively sequestering and eliminating PAHs across diverse media. These macrocyclic host molecules play a central role in host–guest chemistry and supramolecular chemistry. It offers distinct advantages by virtue of their precisely tailored cavities and customizable functionalities, greatly enhancing their selective recognition abilities towards guest PAHs. The pursuit of designing and synthesizing novel functional macrocycles has captivated the attention of researchers, driven by the quest to address various challenges in supramolecular research. Over decades of dedicated exploration in host–guest chemistry and supramolecular chemistry, an expansive array of macrocyclic host molecules, constructed from diverse building blocks, have emerged as pivotal tools for encapsulating PAHs. This review presents an overview of the recent progress in the design, synthesis, and application of purely organic macrocyclic molecules in the encapsulation of PAHs. It elucidates the underlying principles that govern their ability to recognise PAHs, such as host–guest interactions, shape complementarity, and π-π stacking interactions. Furthermore, the review discusses various experimental methodologies, such as spectroscopic analyses, chromatography, and computational modelling, employed to assess the efficiency of organic cage molecules in PAH trapping. Additionally, considerations regarding the scalability and environmental implications of organic cage-based PAH trapping systems are addressed. The insights gleaned from this research provide valuable guidance for the development of robust strategies to combat PAH pollution in diverse environmental contexts.

UPTAKE OF Co(II), Pb(II) AND Ni(II) IONS BY Annona senegalensis STEM BARK BIOCHAR FROM AQUEOUS SOLUTION: OPTIMIZATION, KINETIC AND THERMODYNAMIC STUDIES

The concern for heavy metal pollution in the environment is especially so since they are non-biodegradable. The use of agro materials in the removal of these heavy metal pollutants has been recognized as a low-cost alternative to the costly conventional remediation techniques. The equilibrium sorption of the chemically activated Anonna senegalensis stem bark was investigated. Using standard techniques, the physicochemical properties of activated carbon (MAASC) were ascertained. By using a simultaneous batch adsorption approach, the adsorption of Co2+, Pb2+, and Ni2+ onto MAASC was examined as a function of pH, solution temperature, initial metal ion concentration, agitation time, adsorbent dose, particle size, and carbonization temperature. The equilibrium sorption data generated were fitted into Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models as well as pseudo first-order, pseudo-second-order and intraparticle diffusion kinetic models. From the obtained results, it was discovered that the Langmuir isotherm provided the best match conformation of all the models, except for Pb2+, which was best for Freundlich with an R2 of 0.95. Physisorption was shown to be the mechanism by Dubinin-Radushkevich. For Co2+, Pb2+, and Ni2+, respectively, the pseudo second-order kinetic model had R2 values of 0.997, 0.999, and 0.999 that best matched the data. Both intraparticle diffusion and the boundary layer effect also contributed to regulating the rates of the adsorption process. The study's thermodynamic results showed that Ho for Co2+, Pb2+, and Ni2+ were 27.51, 19.70, and 13.37 KJ/mol, respectively. These values are all positive and suggest an endothermic reaction, supporting the physisorption mechanism.

Assisted phytoextraction as a nature-based solution for the sustainable remediation of metal(loid)-contaminated soils.

Soil contamination is a significant environmental issue that poses a threat to human health and the ecosystems. Conventional remediation techniques, such as excavation and landfilling, are often expensive, disruptive, and unsustainable. As a result, there has been growing interest in developing sustainable remediation strategies that are cost-effective, environmentally friendly, and socially acceptable. One such solution is phytoextraction: a nature-based approach that uses the abilities of hyperaccumulator plants to uptake and accumulate metals and metalloids (potentially toxic elements [PTE]) without signs of toxicity. Once harvested, plant biomass can be treated to reduce its volume and weight by combustion, thus obtaining bioenergy, and the ashes can be used for the recovery of metals or in the construction industry. However, phytoextraction has shown variable effectiveness due to soil conditions and plant species specificity, which has led researchers to develop additional approaches known as assisted phytoextraction to enhance its success. Assisted phytoextraction is a remediation strategy based on modifying certain plant traits or using different materials to increase metal uptake or bioavailability. This review article provides a practical and up-to-date overview of established strategies and the latest scientific advancements in assisted phytoextraction. Our focus is on improving plant performance and optimizing the uptake, tolerance, and accumulation of PTE, as well as the accessibility of these contaminants. While we highlight the advantages of using hyperaccumulator plants for assisted phytoextraction, we also address the challenges and limitations associated with this approach. Factors such as soil pH, nutrient availability, and the presence of other contaminants can affect its efficiency. Furthermore, the real-world challenges of implementing phytoextraction on a large scale are discussed and strategies to modify plant traits for successful phytoremediation are presented. By exploring established strategies and the latest scientific developments in assisted phytoextraction, this review provides valuable guidance for optimizing a sustainable, nature-based technology. Integr Environ Assess Manag 2024;00:1-20. © 2024 SETAC.

Controlled-Release Materials for Remediation of Trichloroethylene Contamination in Groundwater

Groundwater contamination by trichloroethylene (TCE) presents a pressing environmental challenge with far-reaching consequences. Traditional remediation methods have shown limitations in effectively addressing TCE contamination. This study reviews the limitations of conventional remediation techniques and investigates the application of oxidant-based controlled-release materials, including encapsulated, loaded, and gel-based potassium permanganate since the year 2000. Additionally, it examines reductant controlled-release materials and electron donor-release materials such as tetrabutyl orthosilicate (TBOS) and polyhydroxybutyrate (PHB). The findings suggest that controlled-release materials offer a promising avenue for enhancing TCE degradation and promoting groundwater restoration. This study concludes by highlighting the future research directions and the potential of controlled-release materials in addressing TCE contamination challenges.

A concise overview of perchlorate sources, contamination, and remediation techniques

Perchlorate has become one of the most significant contaminants in our environment. Perchlorate is responsible for difficulties relating to both human and environmental health. In contaminated areas, microorganisms that degrade perchlorate are now promising bioremediation techniques. Microorganisms based on chemical, physical, and other biological approaches are favored for economic and environmental reasons. These microbes were accountable for the breakdown of perchlorate in the environment. This state-of-the-art review explores the perchlorate is a nonvolatile anion that is non-reactive and kinetically stable due to the most oxidized form of the chlorine atom. However, several industrial applications of perchlorate contamination have become a global concern. Perchlorate has several undesirable effects on the ecosystem as it degrades the environmental quality along with numerous anthropogenic activities. Currently, perchlorate-reducing microbes have proven to be a promising approach toward bioremediation. It can be hypothesized that bioreactors using perchlorate-reducing microbes would facilitate water treatment’s efficacy and prevent several deadly diseases caused by perchlorate contamination. Additionally, this study delves into innovative and conventional remediation techniques used to mitigate perchlorate contamination. It covers a wide range of strategies, including biological treatments, ion exchange, chemical reduction, and phytoremediation, among others. Furthermore, it discusses each technique’s advantages, limitations, and feasibility, considering factors such as cost, scalability, and site-specific conditions.

NUMERICAL MODELING OF GROUND WATER TREATMENT THROUGH CERAMIC MEMBRANES

Recent advances in oil field water treatment have led to the conclusion that conventional remediation techniques are expensive, slow and ineffective in removing oil products from reservoir waters. The need to introduce methods that remove the disadvantages of conventional ones led to the appearance of modern depollution techniques, methods such as chemical, biological or thermal, etc. However, before starting a depollution process, a profitability study must be carried out and a compromise established between the cost of depollution and the depollution yield. The article presents the classic depollution methods but also a new, modern method (water treatment with ceramic filters) which, even if it has quite high investment costs, even proves its economic efficiency in addition to the qualitative one of protecting the environment.

Visible-light-induced self-propelled nanobots against nanoplastics

The accumulation of plastic debris in aquatic organisms has raised serious concerns about the potential health implications of their incorporation into the food chain. However, conventional water remediation techniques are incapable of effectively removing nanoplastics (NPs) smaller than 200 nm, which can have harmful effect on animal and human health. Herein, we demonstrate the “on-the-fly” capture of NPs through their enlargement (approximately 4,100 times) using self-propelled nanobots composed of a metal-organic framework. Under visible-light irradiation, the iron hexacyanoferrate (FeHCF) nanobot exhibits fuel-free motion by electrostatically adsorbing NPs. This strategy can contribute to reducing plastic pollution in the environment, which is a significant environmental challenge. Light-induced intervalence charge transfer in the FeHCF nanobot lattice induces bipolarity on the nanobot surface, leading to the binding of negatively charged NPs. The local electron density in the lattice then triggers self-propulsion, thereby inducing agglomeration of FeHCF@NP complexes to stabilize their metastable state. The FeHCF nanobot exhibits a maximum removal capacity of 3,060 mg∙g−1 and rate constant of 0.69 min−1, which are higher than those recorded for materials reported in the literature.

Beyond Cleansing: Ecosystem Services Related to Phytoremediation.

Phytotechnologies used for cleaning up urban and suburban polluted soils (i.e., brownfields) have shown some weakness in the excessive extent of the timeframe required for them to be effectively operating. This bottleneck is due to technical constraints, mainly related to both the nature of the pollutant itself (e.g., low bio-availability, high recalcitrance, etc.) and the plant (e.g., low pollution tolerance, low pollutant uptake rates, etc.). Despite the great efforts made in the last few decades to overcome these limitations, the technology is in many cases barely competitive compared with conventional remediation techniques. Here, we propose a new outlook on phytoremediation, where the main goal of decontaminating should be re-evaluated, considering additional ecosystem services (ESs) related to the establishment of a new vegetation cover on the site. The aim of this review is to raise awareness and stress the knowledge gap on the importance of ES associated with this technique, which can make phytoremediation a valuable tool to boost an actual green transition process in planning urban green spaces, thereby offering improved resilience to global climate change and a higher quality of life in cities. This review highlights that the reclamation of urban brownfields through phytoremediation may provide several regulating (i.e., urban hydrology, heat mitigation, noise reduction, biodiversity, and CO2 sequestration), provisional (i.e., bioenergy and added-value chemicals), and cultural (i.e., aesthetic, social cohesion, and health) ESs. Although future research should specifically be addressed to better support these findings, acknowledging ES is crucial for an exhaustive evaluation of phytoremediation as a sustainable and resilient technology.

Sorptive removal of phosphorus by flue gas desulfurization gypsum in batch and column systems

Phosphorus (P) over-loading is often a central topic due to its linkage to harmful algal blooms (HABs) and its importance in wastewater treatment that has fueled immediate remediation attempts to reduce P loading from point (e.g., wastewater) and nonpoint sources (e.g., fertilizers). Conventional remediation techniques (e.g., filtration) are often expensive, ineffective, and difficult to implement at large scales. The flue gas desulfurization (FGD) gypsum produced as an energy plant waste byproduct has recently been advocated as a physiochemical remediation strategy for P through sorptive removal. However, limited research is available on the practical applications of FGD gypsum for P removal from water. Herein, batch sorption experiments were performed to investigate the sorptive removal efficiency of P by FGD gypsum under environmentally relevant P concentrations (0.01–0.25 mM). In parallel, fixed-bed column experiments packed with FGD gypsum were performed using elevated P concentrations (0.1–1.0 mM) to understand the scalability of FGD gypsum for large-scale practical applications. During batch experiments, P sorption equilibrium was reached within 24 h that includes an initially fast step (via boundary layer diffusion), followed by a slow rate-determining step (via intraparticle diffusion). P sorption kinetics followed the pseudo second-order kinetics, indicating chemisorption. P sorption at equilibrium can be simulated by both the Freundlich and Langmuir sorption isotherms. The Langmuir sorption isotherm yielded a maximum sorption capacity (Qmax) of 36.1 mM kg−1. The fixed-bed column experimental results showed that sorption rate depends on the applied flow rate, irrespective of the tested P concentrations. Our findings can be extrapolated to evaluate the feasibility and scalability of FGD gypsum in removing P to counteract P runoff and mitigate HABs and P-loaded wastewater.

Review on Phytoremediation Potential of Floating Aquatic Plants for Heavy Metals: A Promising Approach

Water pollution due to heavy metals has become a serious environmental concern due to their hazardous properties. Since conventional water remediation techniques are generally ineffective and non-environmentally friendly, phytoremediation has gained increasing attention from worldwide researchers and scientists due to its cost-effectiveness and environmental friendliness. Hence, this review first discussed soil and water remediations. Phytoremediation can be divided into five techniques to remove heavy metals from the polluted environment, namely, phytostabilization (phytosequestration), phytodegradation (phytotransformation), phytofiltration (rhizofiltration), phytoextraction (phytoaccumulation), and phytovolatilization. Four common floating aquatic plants (accumulator plants), such as duckweed (Lemna minor), water lettuce (Pistia stratiotes), water hyacinth (Eichhornia crassipes), and watermoss (Salvinia) were discussed in detail due to their great capability in absorbing the metal ions by their roots and further translocating the metal ions to the aerial parts. Furthermore, the parameter studies, such as optimum pH and temperature of the water, exposure duration, initial metal concentration, water salinity, and the addition of chelating agents, were evaluated. The absorption kinetics of the plants was discussed in detail. In short, phytoremediation is a promising green and sustainable water remediation approach. However, further research is necessary to enhance its practicability and performance at large-scale implementation.

Nature-based Solutions to Restoration of Contaminated Soils and Enhance Biodiversity and Human Health

The soil environment and its biodiversity are the basis of human health, but currently, soil degradation on a large scale is causing soil pollution and threatening human development. In this context, the use of conventional soil remediation techniques will lead to waste of resources and secondary contamination of soil, in contrast to nature-based solutions that use natural processes to restore the original contaminated soil resources and improve sustainability, which is an appropriate and sustainable approach to address the problems associated with soil contamination. In this paper, we compiled the nature-based remediation measures for contaminated soils and proposed ecologically oriented measures based on plants, soil microorganisms, biochar and soil animals, and engineering-oriented measures based on artificial wetlands, non-intensive agricultural management and green natural nanomaterials, and focused on their mechanism of action and synergistic relationship, focusing on the effects of the two together on the soil remediation process and results. The focus is on the added benefits of nature-based solutions in the process and outcome of soil restoration to enhance biodiversity and human health.

Natural surfactant mediated bioremediation approaches for contaminated soil.

The treatment of environmental pollution by employing microorganisms is a promising technology, termed bioremediation, which has several advantages over the other established conventional remediation techniques. Consequently, there is an urgent inevitability to develop pragmatic techniques for bioremediation, accompanied by the potency of detoxifying soil environments completely. The bioremediation of contaminated soils has been shown to be an alternative that could be an economically viable way to restore polluted soil. The soil environments have long been extremely polluted by a number of contaminants, like agrochemicals, polyaromatic hydrocarbons, heavy metals, emerging pollutants, etc. In order to achieve a quick remediation overcoming several difficulties the utility of biosurfactants became an excellent advancement and that is why, nowadays, the biosurfactant mediated recovery of soil is a focus of interest to the researcher of the environmental science field specifically. This review provides an outline of the present scenario of soil bioremediation by employing a microbial biosurfactant. In addition to this, a brief account of the pollutants is highlighted along with how they contaminate the soil. Finally, we address the future outlook for bioremediation technologies that can be executed with a superior efficiency to restore a polluted area, even though its practical applicability has been cultivated tremendously over the few decades.

Microorganisms and their application in mining and allied industries

Mining activities cause significant damage to nature but it is inevitable. The nature of ore along mining method not only guide the volume of waste generation but also the nature of waste. Bioremediation is considered as an alternative and economically viable technique compared to conventional remediation techniques. It is found to be suitable alternative in treating mine wastes and recovery of toxic heavy metals. Out of all the waste generated during and after mining operation, Acid mine drainage/ acid rock drainage is the most dangerous one laden with heavy and toxic metals, remain untreated. Use of microorganisms not only help in detoxification but also facilitates extraction. Sulfate-reducing microorganisms have been applied for the treatment of acid mine waste Amongst all the known microorganisms, SRB plays a vital role in mine waste treatment, neutralizing acidity & reviving alkalinity. Due to simultaneous elimination of sulfate and metals, and the possibility to reuse, bioreactors with SRB represent a promising option for remediation of mine waste..Such a technique picked up its momentum due to its low cost, easy availability of ingredients, and eco-friendly nature. Considering the dependency of microorganisms on other factors for their survival, such a treatment system may/ may not be used alone. Therefore, it advisable to use the same along with other techniques depending upon site conditions, nature of deposit and availability of essential requisites. In this paper, attempts were made to highlight the potential thrust areas requiring applying this technique, limiting factors.

In Situ Remediation of Arsenic-Contaminated Groundwater by Injecting an Iron Oxide Nanoparticle-Based Adsorption Barrier

Arsenic contamination of groundwater occurs due to both geogenic and anthropogenic processes. Conventional arsenic remediation techniques require extraction of groundwater into pump-and-treat systems, which are expensive and require long operational times. Hence, there is a need for cost-effective remediation. In this study, we assessed and validated the in situ remediation of arsenic contamination in groundwater resources using permeable reactive barriers (PRBs) made of injectable, colloidal iron oxide nanoparticles in the laboratory and in field-scale pilot tests. Sand-packed, flow-through column studies were used in order to assess the sorption behavior of the iron oxide nanoparticles using field materials (sand, groundwater) in the laboratory. The breakthrough curves were analyzed using a reactive transport model considering linear and nonlinear adsorption isotherms and were fitted best with a chemical nonequilibrium consideration. The results were used to design a pilot-scale field test. The injected 28 m3 of nanoparticles (ca. 280 kg dry weight of iron oxide) were successfully delivered to the aquifer via an injection well. No mobile iron was detected downstream, confirming that a stable in situ barrier was formed that did not move with the groundwater flow. Arsenic concentrations in groundwater were reduced to the aimed 50% of the background value, despite the relatively short contact time between arsenic and the iron oxide in the barrier, due to the high flow velocity of 1.21 m/day. We compared the results of the laboratory and field tests and concluded that the single-parameter models based on retardation factor and/or adsorption capacity fail to predict the longevity of the barrier and the evolution of arsenic breakthrough with time, most likely because they do not consider the chemical nonequilibrium effects. Therefore, we propose that upscaling the laboratory findings to field design must be carried out with care and be coupled with detailed reactive transport models.

Low temperature–produced and VFA–coated biochar enhances phenanthrene adsorption and mitigates toxicity in marine sediments

Polycyclic aromatic hydrocarbons (PAHs) are widespread in marine environments, having negative implications on both ecological systems and human health. At the same time, research on highly–efficient and environmentally–friendly alternatives compared to conventional remediation techniques must be stepped up. In this work, for the first time, a novel modification procedure of willow–derived biochar based on volatile fatty acids (VFA) has been employed to enhance biochar structures aimed at avoiding phenanthrene (PHE) desorption. Batch adsorption–desorption experiments showed a PHE removal of 93% and a hysteresis index of 4.9 after 72 h with biochar pyrolyzed at 400 °C (BC400) and modified with VFAs (MBC400), respectively. A lower efficiency was obtained with higher temperature–produced biochars (i.e. 700 °C) due to lower surface area and functional group abundance compared to the biochars obtained at 400 °C. Physisorption and chemisorption mechanisms were mainly involved in a multilayer PHE adsorption onto the heterogeneous BC400 and MBC400 surfaces, as shown by pseudo–first– and –second–order kinetic (R2 = 0.988) and Freundlich isotherm (R2 = 0.951–0.995) models. A more complicated and advanced subsequent application of biochar in PHE–polluted marine sediments with a dosage of 0.1–5% (w/w) led to the reduction of pore water PHE up to 24% after 28 days. An ecotoxicological test showed a mitigated toxicity of the sediment remediated with BC400 and MBC400 towards Folsomia candida springtails due to a decrease in adult mortality and reproduction inhibition, which was directly correlated with the reduction of PHE bioavailability (rPHE–FC = 0.76).

Review on Microbial Degradation of Aromatic Hydrocarbons: Focus on Kinetics Modelling

Many anthropogenic activities produce huge quantities of chemical pollutants that find their ways into the natural environment. Those chemicals can either be of organic or inorganic sources, depending on their originating compounds. Over the years, there had been research findings regarding the application of microorganisms to provide solutions in the environment. This becomes imperative as salient issues in researches on microbial bioremediation will be understood. This review focused more on Kinetics modeling during biodegradation of aromatic hydrocarbons and their nature and effect on the environment coupled with the conventional remediation techniques. Kinetics modeling during bioremediation predicts microbial activities through their mechanism of actions towards the targeted contaminants. This gives better understanding of the rate of chemical degradation through different variable parameters. Modeling the cultivation of degrading organisms can highlight the inhibitory properties of the cells involved. Therefore, specific microbial growth rates can be modeled at various initial concentrations of the involving substrates. Such could be achieved using secondary models of Monod, Teissier, Aiba, Haldane, Yano and Luong. The models can reveal the substrate inhibitory effects to the reduction rate (as in the case of Monod) or inhibitory to the substrate rates like in the other models. Many studies were recently conducted on modeling microbial growth. Hence, utilization of those models are the best evidence that indicate when the substrates are toxic or inhibitory to the microbes. This provides better understanding on the future researches regarding the bioremediation effectiveness on scientific arguments.

Modified ion exchange jackfruit seeds resin for removal of selected trace heavy metal ions from aqueous solution

Water is essential for every life processes. However, its quality is deteriorating every day due to the recent industrial advancements. Anthropogenic processes such as industrialization, mining and agricultural activities have led to alarming discharge of heavy metal ions to the aquatic bodies. This possess a greater threat to human, animal and the entire ecosystem wellbeing. Accumulation of heavy metal ions in drinking water beyond permissible limits is detrimental to human health. Therefore, their removal is paramount. Conventional remediation techniques have been employed but have remained expensive and not universally appropriate. This has therefore spurred research interests in the use of adsorption techniques from locally available materials as an environmentally sustainable alternative. Jackfruit seeds are discarded as wastes of a Jackfruit and can be utilized as an ion exchange resin in heavy metal ions removal from wastewater. The present study involved application of previously prepared raw and modified Jackfruit seed resins to study thermodynamics of copper (II), lead (II) and cadmium (II) ions adsorption from synthetic water. FTIR results showed presence of functional groups in raw and modified resins as important sites for studying thermodynamics of adsorption of copper (II), lead (II) and cadmium (II) ions. Thermodynamic data showed that standard Gibb’s free energy () values for all metals were negative indicating that adsorption process was feasible and favourable. Standard enthalpy change (), standard entropy () and activation energy () were positive (> 40 kJ mol-1) and in the order lead (II) > copper (II) > cadmium (II). This confirmed adsorption of copper (II), lead (II) and cadmium (II) ions onto both raw and modified resins was predominated by chemical interactions between the metal ions and the resin active sites. This was confirmed by very low values of sticking probability (S*). The findings indicated that ion exchange Jackfruit seeds resin is promising for heavy metal ions removal from wastewater in an optimized temperature controlled system.

Environmental Footprint Assessment of a Cleanup at Hypothetical Contaminated Site

Contaminated site management is currently a critical problem area all over the world, which opens a wide discussion in the areas of policy, research and practice at national and international levels. Conventional site management and remediation techniques are often aimed at reducing the contaminant levels to an acceptable level in a short period of time at low cost. Owing to the fact that the conventional approach may not be sustainable as it overlooks many ancillary environmental effects, there is an immense need of “sustainable” or “green” approaches. Green approaches address environmental, social and economic impacts throughout the remediation process and are capable of conserving the natural resources and protecting air, water and soil quality through reduced emissions and other waste burdens. This paper presents a methodology to quantify the environmental footprint of a cleanup for a hypothetical contaminated site by using the US Environmental Protection Agency’s (EPA) Spreadsheet for Environmental Footprint Assessment (SEFA). The hypothetical contaminated site is selected from a metropolitan city of Pakistan and the environmental footprint of the cleanup is analyzed under three different scenarios: cleanup without any renewable energy sources at all, cleanup with a small share of renewable energy sources, and cleanup with a large share of renewable energy sources. It is concluded that integration of renewable energy sources into the remedial system design is a promising idea which can reduce CO2, NOx, SOx, PM and HAP emissions up to 68%.

Nutshells as Efficient Biosorbents to Remove Cadmium, Lead, and Mercury from Contaminated Solutions.

The release of potentially toxic elements into the environment, and their effects on aquatic ecosystems still present a real threat. To avoid such contamination, the use of biological sorbents as an alternative to conventional and expensive water remediation techniques has been proposed. The present study evaluated the potential of 0.5 g L−1 of peanut, hazelnut, pistachio, walnut, and almond shells to remove the requisite concentrations of cadmium (Cd), lead (Pb), and mercury (Hg) from contaminated water. Hazelnut shells were identified as the sorbent with the highest potential and were evaluated in mono- and multi-contaminated mineral water. The influence of sorbent-intrinsic and solution-intrinsic characteristics were assessed. Differences among sorbents were attributed to varying percentages of their main components: cellulose, hemicellulose, and lignin. Matrix complexity increase caused a decrease in Cd removal, presumably due to the diminution in electrostatic interaction, and complexation with anions such as Cl−. When simultaneously present in the solution, contaminants competed, with Pb showing higher affinity to the sorbent than Hg. High efficiencies (>90%) obtained for hazelnut shells for all elements in ultrapure water and for Pb and Hg in mineral water) reveals the high potential of this low-cost and abundant waste for use in the remediation of contaminated waters (circular economy).

Process optimization of silica encapsulation technique as a unique remediation technology for the treatment of crude oil contaminated soil

The effect of hydrocarbon pollution on soil quality is globally challenging. Addressing the menace of pollution on soil necessitates research into the development of viable remediation technique that is fast, effective, efficient and environmentally friendly; with cutting edge advantages over conventional remediation techniques. The technique was designed using a formulated silica encapsulating product and applied on soil contaminated by simulation with 10% crude oil. Soil was characterized for its physicochemical properties using standard methods, while its TPH content determined by molecular spectroscopy. Properties such as conductivity, pH and phosphorus levels were severely impacted by the hydrocarbon effect. Silica encapsulating product was formulated from sodium silicate and sodium dodecyl sulphate using proper optimization procedures. The encapsulating product (sodium silicate and SDS) were used in a ratio of 1:2. Optimum concentrations of 60,000 ppm sodium silicate solution, 120,000 ppm SDS, applied at optimum pH and temperature of 5 and 25 °C respectively were established from the process optimization of the experimental technique. The technique shows rapid response towards TPH removal, as 86.79% TPH reduction is achieved after seven days of treatment. The encapsulation process follows pseudo first order kinetics. Significant reduction in metals; Ni (0.61–0.036 mg/kg), V (0.82–0.11 mg/kg) and Cd (0.05–0.016 mg/kg) shows the efficacy of the technique, thereby providing a dual alternative for the remediation of hydrocarbons and heavy metals. The technique seems to be effective in restoring some lost soil properties as seen in pH, conductivity and total nitrogen after treatment. The environmental friendliness, cost effectiveness and merits associated with this technique gives it a unique advantage over other conventional methods; as such presents promising alternative route for remediation experts in addressing the challenges associated with hydrocarbon and metals pollution on soil. Silica encapsulation technique is therefore suitable for outright applications in real field challenges.