Poly- and perfluoroalkyl substances (PFAS) are a wide group of environmentally persistent organic compounds of industrial origin, which are of great concern due to their harmful impact on human ...health and ecosystems. Amongst long-chain PFAS, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are the most detected in the aquatic environment, even though their use has been limited by recent regulations. Recently, more attention has been posed on the short-chain compounds, due to their use as an alternative to long-chain ones, and to their high mobility in the water bodies. Therefore, short-chain PFAS have been increasingly detected in the environmental compartments. The main process investigated and implemented for PFAS removal is adsorption. However, to date, most adsorption studies have focused on synthetic water.
The main objective of this article is to provide a critical review of the recent peer-reviewed studies on the removal of long- and short-chain PFAS by adsorption. Specific objectives are to review 1) the performance of different adsorbents for both long- and short-chain PFAS, 2) the effect of organic matter, and 3) the adsorbent regeneration techniques. Strong anion-exchange resins seem to better remove both long- and short-chain PFAS. However, the adsorption capacity of short-chain PFAS is lower than that observed for long-chain PFAS. Therefore, short-chain PFAS removal is more challenging. Furthermore, the effect of organic matter on PFAS adsorption in water or wastewater under real environmental conditions is overlooked. In most studies high PFAS levels have been often investigated without organic matter presence. The rapid breakthrough of PFAS is also a limiting factor and the regeneration of PFAS exhausted adsorbents is very challenging and needs more research.
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•Most PFAS adsorption studies were carried out under unrealistic conditions.•Organic matter often improves long-chain PFAS adsorption by aggregates formation.•Co-existing OM reduces the short-chain PFAS adsorption efficiency.•Short-chain PFAS are better removed by anion-exchange mechanism.•Regeneration of PFAS-saturated adsorbents often needs harmful organic solvents.
Five soil size aggregate fractions, corresponding to coarse (500–840
μm), medium (200–350
μm), fine (75–200
μm) sand, silt (10–75 μm) and clay (<4 μm), were artificially contaminated with diesel, and ...thermally treated using a laboratory scale apparatus to investigate the effect of soil texture on contaminant adsorption and removal. Ex situ thermal process was simulated using helium as the carrier gas at a flow rate of 1.5
L
min
−1, different temperatures (100–300
°C) and different treatment times (5–30
min). The amount of contaminant adsorbed on the soil and the residual amount after thermal treatment was determined by gas chromatography. Results showed that adsorption phenomena and desorption efficiency were affected by the soil texture and that temperature and time of treatment were key factors in remedial process. A temperature of 175
°C is sufficient to remedy diesel polluted sandy and silty soils, whereas a higher temperature (250
°C) is needed for clays. Thermal desorption of diesel polluted soil was shown to be governed by first-order kinetics. Results are of practical interest and may be used in scaling-up and designing desorption systems for preliminary cost and optimal condition assessment.
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•Microwave irradiation was used to remediate PAH and nitro-PAH contaminated soils.•Contaminant removal kinetics were assessed as a function of different operating ...conditions.•Contaminant polarity influences soil final temperature and contaminant removal.•Microwave treatment is very effective in removing PAH/nitro-PAH from soils.
The main goal of this study was the application of a bench-scale microwave (MW) heating treatment of soils contaminated with polycyclic aromatic hydrocarbon (PAHs) and nitro-PAHs (N-PAHs), investigating the effects of various operating conditions on contaminant removal kinetics. For simulated MW treatment, a fine sandy soil was artificially contaminated with PAHs or N-PAHs and irradiated for a period of 5–60min, applying powers in the range of 250–1000W. Kinetic models were fitted with contaminant residual concentrations in order to calculate the desorption parameters useful for studying the removal process. Results suggest that contaminant properties, especially polarity, significantly influence the maximum temperature reachable during the heating processes and the contaminant removal kinetics. The total PAH removal was achievable only for biphenyl (Bph) or fluorene (Flu), whereas residual concentrations were reduced to less than 2mgkg−1 for anthracene (Ant) or phenanthrene (Phe). N-PAH concentrations lower than 0.05ngkg−1 were observed for all the compounds investigated. Overall, different mechanisms, namely, thermal desorption, molecular bond breaking, selective heating and contaminant stripping took place during PAH or N-PAH removal. The kinetic parameters are useful for studying the removal process and for predicting the response of the remediation activities, as well as for guiding the design and the scale-up of microwave treatment systems. PAH/N-PAH removal mechanism results could also provide basic information and be helpful in order to improve the development of novel MW based-remediation technologies for soils contaminated with PAHs and their derivatives.
In this study, the remediation of diesel-polluted soils was investigated by simulating an ex situ microwave (MW) heating treatment under different conditions, including soil moisture, operating power ...and heating duration. Based on experimental data, a technical, energy and economic assessment for the optimization of full-scale remediation activities was carried out. Main results show that the operating power applied significantly influences the contaminant removal kinetics and the moisture content in soil has a major effect on the final temperature reachable during MW heating. The first-order kinetic model showed an excellent correlation (r
2
> 0.976) with the experimental data for residual concentration at all operating powers and for all soil moistures tested. Excellent contaminant removal values up to 94.8% were observed for wet soils at power higher than 600 W for heating duration longer than 30 min. The use of MW heating with respect to a conventional ex situ thermal desorption treatment could significantly decrease the energy consumption needed for the removal of hydrocarbon contaminants from soils. Therefore, the MW treatment could represent a suitable cost-effective alternative to the conventional thermal treatment for the remediation of hydrocarbon-polluted soil.
In this work, the Hg removal potentiality of an electrokinetic (EK) decontamination treatment enhanced by a biodegradable complexing agent (MGDA) also in combination with a biodegradable surfactant ...(Tween® 80) was investigated to decontaminate heavily contaminated marine sediments. The main results revealed that the nature of sediments and their interactions with different enhancing agents significantly influenced the remediation processes. A general increase of pH values along the sediment specimen was observed due to the strong buffering capacity of the carbonates, which are the main constituent minerals. This, in combination with the high organic matter and sulphide sediment content, resulted in very poor contaminant mobilization without any appropriate conditioning agents. The use of EDTA as a processing fluid resulted in a modest increase in Hg removal of ∼15%, whereas a further improvement in the Hg removal rate (∼39%) was achieved by replacing EDTA with MGDA as the anodic solution in response to its ability to form stable negative complexes with mercury, which can be moved towards the anode. A significantly higher Hg-removal of ∼71% was obtained by the simultaneous use of MGDA and Tween® 80 due to their synergic action in remedial processes and, especially, due to the improved selective action of the non-ionic surfactant adopted in favour of organo-Hg-complex removal. Compared with other Hg-removal technologies, the investigated enhanced-EK treatment allows the achievement of remediation targets, which can hardly met by one-stage processes. The data can be useful for predicting the remediation activity responses, as well as for guiding the design and scaling-up of EK treatment of Hg-contaminated sediments. In addition, the knowledge of the investigated Hg-removal mechanism can provide basic information, which is helpful for improving the development of further novel enhanced-EK technologies.
This review highlights that microwave (MW) heating can be largely considered advantageous for environmental applications. MW has been largely proposed for the processing of sludge or radioactive and ...toxic wastes including hospital waste, tyres and industrial scores. Researchers demonstrated that MW heating is an eco-friendly technology for waste detoxification because of higher sustainability and effectiveness as complete detoxification process if compared with established techniques such as incineration or conventional pyrolysis. Experimental data demonstrated that MW heating could be also considered as a preferable choice compared with conventional chemical-physical or heating techniques in treating contaminated soils when soils present natural or enhanced high dielectric features. Analogously, for sediment decontamination processes, only conventional thermal treatments can be similarly effective as MW heating, but requiring high temperatures and costs. Undoubtedly, MW-absorber and irradiated matrix heavily affect the MW effectiveness and energy requirements. In general, the main advantages of MW are very rapid process, selective and environmentally sustainable. This depends on the principle of dielectric heating that allows the activation of effective removal mechanisms, namely selective heating and contaminant stripping by water distillation. However, despite the demonstrated possibility of combining eco-friendly with very high removals, the growth of industrial MW applications is still limited due to the lack of several information, which, at the moment represents difficult challenges. In fact, literature mainly relies on lab-scale experiments, and extending the obtained achievements to full-scale still faces to many problems. This still makes MW rarely applied to real practises. Material characterisation, scaling-up, pilot, modelling, design and demonstration studies are strongly desired to bridge the gap between existing literature and full-scale applications, and moving to industrial/production scale. Then, despite a change of approach being observed especially in the last three years, interdisciplinary future research is strictly required in order to exploit the full potential of MW-techniques.
•This review investigates microwave (MW) heating for environmental applications.•We investigate MW heating as waste detoxification technique.•We investigate MW heating for contaminated soil/sediment remediation.•We investigate MW heating for treating contaminated water and wastewater.•MW heating is very rapid, selective and environmentally sustainable process.
In this study, a hydrocarbon-contaminated marine sediment was treated applying ex-situ thermal desorption (ESTD) at bench-scale. Temperatures up to 280 °C and heating times (t) in the 5–30 min range ...were investigated. Results revealed that temperatures in the range 200–280 °C led to Total Petrol Hydrocarbon (TPH)-removal efficiency (RE) from 75 to 85% (t = 10 min). The maximum RE of 89% was obtained at 200 °C for 30 min. However, a shorter remediation time of 5 min (or lower temperatures of 160 and 180 °C with longer times) is needed to reach the TPH standard limit.
Data also demonstrated the selectivity of the treatment in TPH fraction removal. The modelling of the TPH removal kinetics and desorption isotherm jointly with activation energy calculation (>30 kJ mol−1) indicated that ESTD process is quite unfavorable for marine sediments. This is due to the fact that ESTD is regulated by chemisorption processes and occurred in two distinct TPH removal phases: evaporation and boiling vaporization. This depends on the strong affinity of the TPH with the fine sediment particles, as well as on the high initial water, salinity, organic matter and sulfides content. However, the comparison between alternative processes has shown that ESTD is the most feasible treatment process for TPH-contaminated marine sediment remediation. Obtained results also add relevant information that can be used as a basis for future scaling-up investigations of ESTD for hydrocarbon-contaminated marine sediments.
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•Thermal desorption was carried out on contaminated marine sediment for TPH removal.•Temperatures in the range of 160–280 °C were investigated at the bench-scale.•The maximum TPH-removal of 89% was obtained at 200 °C for 30 min.•TD allows the rapid achievement of the TPH regulatory limits.•The comparison with other processes revealed ESTD as the most feasible treatment.
Aquifer contamination with diesel fuel is a worldwide environmental problem, and related available remediation technologies may not be adequately efficient, especially for the simultaneous treatment ...of both solid and water phases. In this paper, a lab-scale 2.45 GHz microwave (MW) treatment of an artificially diesel-contaminated aquifer was applied to investigate the effects of operating power (160, 350 and 500 W) and time on temperature profiles and contaminant removal from both solid and water phases. Results suggest that in diesel-contaminated aquifer MW remediation, power significantly influences the final reachable temperature and, consequently, contaminant removal kinetics. A maximum temperature of about 120 °C was reached at 500 W. Observed temperature values depended on the simultaneous irradiation of both aquifer grains and groundwater. In this case, solid phase heating is limited by the maximum temperature that interstitial water can reach before evaporation. A minimal residual diesel concentration of about 100 mg kg−1 or 100 mg L−1 was achieved by applying a power of 500 W for a time of 60 min for the solid or water phase, respectively. Measured residual TPH fractions showed that MW heating resulted in preferential effects of the removal of different TPH molecular weight fractions and that the evaporation-stripping phenomena plays a major role in final contaminant removal processes. The power low kinetic equation shows an excellent fit (r2 > 0.993) with the solid phase residual concentration observed for all the powers investigated. A maximum diesel removal of 88 or 80% was observed for the MW treatment of the solid or water phase, respectively, highlighting the possibility to successfully and simultaneously remediate both the aquifer phases. Consequently, MW, compared to other biological or chemical-physical treatments, appears to be a better choice for the fast remediation of diesel-contaminated aquifers.
•We investigate microwave energy remediation of diesel polluted-aquifers.•We assess the influence of power and time on solid and water phase removal kinetics.•The nonlinear exponential decay fits well the solid phase residual concentration.•Temperatures and removal depend on the simultaneous irradiation of both phases.•MW treatment is very rapid and effective in remediating diesel-polluted aquifers.
The present study evaluates the concept of permeable reactive barrier (PRB) coupled with microwaves (MWs) as in situ-regenerating technology with focus on Cs-contaminated water. Experimental and ...modelling results data from batch and column tests were carried out, evaluating several chemical-physical and environmental parameters.
Main results showed a very rapid increase in GAC temperature during MW irradiation up to ∼680 °C. This highlights the GAC strong ability to transform MW power into heat due to GAC excellent dielectric properties (ε′ = 13.8). Physical characterization revealed that GAC pore volume and specific surface area change with the number of regeneration cycles. GAC regeneration efficiency variation reflects this behaviour with a maximum value of ∼112% (5th cycle). The final GAC weight loss of ∼7% further demonstrates GAC life span preservation during MW irradiation.
Results from column tests confirms that GAC can be regenerated by MW also in dynamic condition, due to sublimation/vaporization and vapour stripping Cs removal mechanisms and that the regeneration effectiveness is time-dependent. The breakthrough curve shape confirms significant benefits from MW irradiation. Overall, obtained finding demonstrated the feasibility of the proposed concept, also providing essential data to guide its scaling-up application.
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•A new pedrmeable reactive barrier system coupled with microwaves (MW-PRB) is shown.•MW-PRB feasibility is assessed on Cs-contaminated groundwater in laboratory tests.•Activated carbon dielectric properties enhance the efficiency of MW regeneration.•Results revealed the preservation of activated carbon life span during MW irradiation.
The present study tests the potentiality of a novel microwave based regenerating permeable reactive barrier (MW-PRB) system as combined treatment for Cs-contaminated groundwater. Granular activated ...carbon (GAC) was selected as adsorptive materials in batch and column MW-regeneration experiments. Experimental and modeling data were elaborated for technical and economic considerations in order to assess the MW-PRB feasibility jointly with essential information regarding its real field applicability. Batch experiments investigated the effects of 10 adsorption-MW regeneration cycles under different MW irradiation conditions (applied electric field = 200–460 V m−1; irradiation times = 1–15 min) by assessing GAC variation properties in term of regeneration yield (δ), specific area and weight loss (WL) variation. Column tests were carried using a dedicated setup essentially including a column filled with GAC implanted in a MW oven cavity (MW electric field of 385 V m−1, irradiation times 5–15 min). Lab-scale results shown the ability of MW in Cs removal from GAC as demonstrated by regeneration yield (δ = 79–110%) and WL (6.78% for 10 cycles) values. This was confirmed in dynamic conditions by data from MW-column tests highlighting the highest Cs removal of ~80% when the maximum regeneration time was applied. Residual Cs concentration in breakthrough curves fitted well with the proposed Yoon and Nelson model (R2 = ~0.97). Results from techno-economic analysis revealed the MW-PRB viability and its advantages also in comparison with conventional PRB systems, demonstrating the concept of combined MW-PRB treatment. Saved cost obtained demonstrated in fact the potential cost effectiveness of MW-PRB system and, consequently, the implementation of novel approach is encouraged. Calculated PRB longevity vs groundwater velocity curves are useful in order to predict long-term PRB performance and the response of the remediation activities, as well as for guiding the design and the scaling-up of MW-PRB treatment.
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•A novel permeable reactive barrier coupled with microwave (MW-PRB) is evaluated.•MW-PRB is assessed for the treatment of simulated Cs-impacted groundwater.•MW regeneration of granular activated carbon is investigated at laboratory scale.•Techno-economic analysis of MW-PRB system was compared with conventional PRB.•Saved costs encourage the implementation of proposed MW-PRB system.
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