The in-situ treatment of solid wastes might be regarded as cost-effective and minimum environmental fingerprint solution, particularly with reference to contaminated soils, offering several benefits ...compared to ex-situ methods. In this short communication it is described the study of a lab-scale coaxial dielectric barrier discharge (DBD) plasma reactor simulating the in-situ soil remediation conditions for the first time. In this conceptual design, the contaminated medium is handled as a part of the electrical discharge, while the plasma discharges are produced directly within the contaminated porous medium under treatment, thus scattering reactive species directly in the air contained inside its interconnected pores. The in-situ cold plasma setup was used to remediate bauxite samples highly contaminated by oil sludge contaminants. A very high TOC removal (∼70%) was achieved after 30 min of plasma treatment time with the corresponding energy consumption being 0.53 kWh kg−1. Carbon balance analysis of the exhaust gases revealed that 61% of the removed pollutant was converted to CO2, 19% was decomposed to CO, and 20% was emitted as VOCs. The scale-up of the presented in-situ cold plasma approach could lead to a promising alternative for the fast, cost-effective, and green in-situ remediation of granular porous, heavily contaminated with hydrocarbons contaminated sites.
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•A promising cold plasma approach for decontaminating in-situ polluted sites.•The contaminated medium is part of the electrical discharge.•Generation of plasma species directly in the air contained inside the sample pores.•High pollutant mineralization within a short period of plasma treatment.•Achievement of low energy consumption (∼0.53 kWh kg-1) with the in-situ plasma method.
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Banana (BP), cucumber (CP) and potato peels (PP) were used as biosorbents for the removal of both cationic (Methylene blue) and anionic (Orange G) dyes from wastewater. The ...biosorbents were characterized by ATR-FTIR, N2 Sorption, SEM, and XRD attempting to shed light on the adsorption mechanisms. The ATR-FTIR spectroscopy played a key-role for the chemical characterization of the different biosorbents in order to investigate their composition and in parallel for clarifying the nature of the adsorbent/dye interactions. The effect of pH, biosorbent dose, contact time and dye concentration were investigated. The ranking of adsorption capacity for CMB = 10–80 mg/L was BP > PP > CP whereas for CMB = 80–300 mg/L was BP > CP > PP. Regarding OG, the ranking was CP > PP > BP over the whole concentration range (10–300 mg/L). The biosorption of MB on BP and PP followed the Langmuir isotherm whereas biosorption on CP followed the Freundlich isotherm for low MB concentration values and the Langmuir isotherm for high MB concentrations. The biosorption of OG on BP, PP and CP was better described by the Langmuir isotherm. The maximum monolayer adsorption capacities for MB were found to be 211.9, 107.2 and 179.9 mg/g for BP, PP and CP (pH = 6) respectively, whereas the corresponding ones for OG were found to be 20.9, 23.6 and 40.5 mg/g (pH = 2). Adsorption kinetic models revealed that chemisorption was the dominant biosorption mechanism.
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•NAPL degradation by DBD plasma depends on air flow rate and applied voltage.•NAPL oxidation products in soil are independent of air flow rate and applied voltage.•NOx and O3 are the ...main gaseous plasma active molecules.•NOx concentration increases with air flow rate and applied voltage.•NAPL is completely oxidized to COx at low air flow rate, minimizing VOCs’ release.
A new metallic plane-to-grid dielectric barrier discharge (DBD) reactor was designed for the efficient remediation of polluted soils at atmospheric pressure. A synthetic NAPL composed of equal mass fractions of n-C10, n-C12 and n-C16 was mixed with soil at a high initial NAPL concentration equal to 100g/kg-soil. The NAPL was removed after a few minutes of plasma treatment, depending on NAPL composition, air flow rate and applied voltage. At 28kV peak-to-peak, the NAPL was completely removed from soil very fast (1–3min) for a flow rate ranging from 1.0 to 4.0Lmin−1. At a constant flow rate (i.e. 2.0Lmin−1) the NAPL removal efficiency was 99%, 61.4% and 18.8% for applied voltage 28, 25 and 22kV, respectively, after 2min of plasma treatment. NOx and O3 were detected as the main gaseous plasma active molecules, with the NOx concentration being an increasing function of the applied voltage and air flow rate. The intermediates of the NAPL oxidation in soil were identified as ketones and alcohols regardless of the experimental conditions (i.e. air flow rate and applied voltage). The temperature in the vicinity of the soil found to be varied in the range 285–340°C stimulating the evaporation of NAPL. The total carbon content of initial NAPL detected in exhaust gas in the form of COx increased from 25.5% to 99% when the air flow rate decreased from 4.0 to 0.15Lmin−1, minimizing the release of VOCs and environmental fingerprint. Except of the pollutant remediation efficiency and electric energy consumption, the process sustainability associated with the composition of exhaust gases should be taken into account when designing DBD plasma reactors and determining the optimal operational window.
•Soil remediation by DBD plasma resulted in the fast and complete removal of NAPL.•The plasma species were identified and gas temperature was determined.•High-throughput organic profiling analysis by ...GC–MS to identify the intermediates.•Ketones and alcohols were identified as intermediate products of alkane oxidation.•The energy consumed by DBD plasma is low and almost independent of soil thickness.
A plane-to-grid dielectric barrier discharge (DBD) reactor operating with air at atmospheric pressure was used to investigate the removal of non-aqueous phase liquids (NAPLs) from soil layers. A mixture of n-C10, n-C12 and n-C16 was used as a model NAPL that polluted the soil at a very high initial concentration (100,000mg/kg-soil). The effect of treatment time, energy consumption, and soil thickness on the NAPL removal efficiency was investigated, the plasma active species were identified, and the macroscopic gas temperature was determined. The NAPL remediation efficiency found to be as high as 99.9% after 60–120s of plasma treatment, depending on soil thickness. The energy density required to remediate completely the NAPL was about 600J/g-soil and was practically independent of the soil thickness, indicating that the DBD-based plasma has the potential to become a highly cost-effective technology for the remediation of NAPL-contaminated soils. N2+, N2∗, NOx and O3 were identified as plasma-induced reactive species, a maximum gas temperature close to 300°C was recorded, and the total carbon detected in exhaust gases, in the form of CO and CO2, was ca 40% of that contained in the NAPL removed from the soil. The main mechanisms of NAPL removal by plasma found to be the evaporation of organic compounds coupled with their oxidation in liquid and gas phase. Using ATR-FTIR in combination with high-throughput organic profiling analysis by GC–MS, ketones and alcohols were identified as the main intermediate products of alkanes oxidation in soil matrix.
To develop “smart fluids” for enhanced oil recovery from reservoir rocks, comb-type amphiphilic copolymers were synthesized through free radical polymerization (FRP) of: (i) the hydrophilic, anionic ...monomer 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) that offer a hydrophilic character to the final copolymers; (ii) the weakly acidic hydrophilic monomer acrylic acid (AA); (iii) the hydrophobic monomer dodecyl methacrylate (DMA). The polymers were characterized by Proton Nuclear Magnetic Resonance (1H NMR), Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR), fluorescence probing, Dynamic Light Scattering (DLS) and electrophoresis. Stable polymer solutions were prepared without and with the presence of salts (NaCl, CaCl2, MgSO4). The dynamic air/water surface and oil/water interfacial tensions were measured by the pendant drop method, and their steady-state values were estimated with fitting to asymptotic relations predicting the long-time behavior. Moreover, the wettability of water/air and water/oil to glass or poly(methyl methacrylate) (PMMA) surface was quantified by measuring the contact angles. Oil-in-water Pickering emulsions were prepared by mixing n-dodecane with polymer solutions and their stability was evaluated macroscopically with optical inspection, and microscopically by measuring the oil drop size distribution and shear viscosity. Polymer solutions and Pickering emulsions were tested as agents for the displacement of the residual n-dodecane from a glass-etched pore network. The long-lasting retention of polymer solution in the pore network makes the solid surface more hydrophilic, facilitating the fission of oil ganglia into smaller ones which are mobilized easier, resulting in a final EOR efficiency between 10% and 18%. When using an emulsion as displacing fluid, the viscosity ratio and capillary number increase by orders of magnitude, the viscous forces prevail against the capillary ones, and the growth pattern becomes a frontal drive leading to a high EOR efficiency of ∼94%.
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•Functional amphiphilic terpolymers were successfully synthesized and characterized.•Oil-in-water Pickering emulsions were stabilized by the amphiphilic copolymers.•Emulsions were stabilized under the adverse conditions of high salt concentration.•EOR efficiencies of 10% - 18% were achieved with copolymer solutions.•An EOR efficiency of ∼94% was achieved with a polymer-based emulsion.
The water
k
rw and oil
k
ro relative permeability curves of a glass-etched planar pore network are estimated with history matching from transient displacement experiments performed at varying values ...of the capillary number,
Ca, for two fluid systems: one of intermediate and one of strong wettability. The transient
k
rw
,
k
ro
are compared to corresponding ones measured with the steady-state method on the same porous medium Avraam DG, Payatakes AC. Flow regimes and relative permeabilities during steady-state two-phase flow in porous media. J Fluid Mech 1995;293:207–36; Avraam DG, Payatakes AC. Generalized relative permeability coefficients during steady-state two-phase flow in porous media and correlation with the flow mechanisms. Transport Porous Med 1995;20:135–68; Avraam DG, Payatakes AC. Flow mechanisms, relative permeabilities, and coupling effects in steady-state two-phase flow through porous media. The case of strong wettability. Ind Eng Chem Res 1999;38:778–86., and potential differences from them are interpreted in the light of the differences between the transient growth pattern, and the steady-state two-phase flow regime. For intermediate wettability, the transient
k
ro and
k
rw exceed the corresponding steady-state functions at low
Ca values and have the tendency to become smaller than the steady-state ones at high
Ca values. For strong wettability, the transient
k
ro and
k
rw are increasing functions of
Ca, the transient
k
ro is higher than the steady-state one, whereas the transient
k
rw decreases substantially and becomes lower than the steady-state one at low
Ca values. The dynamic capillary pressure estimated from transient experiments is a decreasing function of
Ca in agreement with previous theoretical and experimental studies.
Oil drilling cuttings produced during oil exploration and extraction contain a high percentage of crude oil, ranging from 5% to 20% weight ratio (w/w) on a dry basis, and must be managed and treated ...properly before their release to the environment. In this study, non-thermal plasma (NTP) was investigated as an advanced oxidation process for the efficient, sustainable and cost-effective treatment of oil drilling cuttings. To this end, a plane-to-grid dielectric barrier discharge (DBD) reactor operating at atmospheric pressure was tested under different plasma conditions. The effect of treatment time, DBD power and air flow rate on the total organic carbon (TOC) removal efficiency was assessed and the energy efficiency of the process was determined. Within 10 min of plasma treatment, a very high TOC and total petroleum hydrocarbons (TPH) removal (∼90% and ∼99%, respectively) was achieved, while polycyclic aromatic hydrocarbons (PAHs) were degraded by ∼50% within 2 min of treatment. Depending on the experimental conditions, the energy efficiency of the process varied from 5 to 35 mg/kJ. From GC-MS analysis, several byproducts of the oxidation of oil drilling cuttings were identified, while the analysis of exhaust gases revealed that ∼85.1% of the removed organics from oil drilling cuttings was transformed to CO2 and CO. This study provides critical information on the effectiveness of the NTP process for the treatment of heavily contaminated solid wastes and can be considered as the critical step for its application for the treatment of solid wastes from the oil industry.
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An energy-autonomous and portable pilot unit was designed and manufactured. The unit was placed on a wheeled support consisting of a photovoltaic panel, four (4) metallic photo-reactors, each ...equipped with 6 W UV-A lamps, two (2) peristaltic pumps of 5 W, and an external recirculation tank. The annular space of reactors was packed with ZnO-coated Duranit spheres. The pilot unit was assessed with regard to the degradation capacity of phenol solution and effluents collected from wastewater treatment plant (WWTP). Measurements of the UV-light intensity were combined with the 2-flux radiation model to determine the radial profile of UV-radiant flux across the annular photoreactor. The experimentally measured transient responses of phenol concentration, total organic, and inorganic carbon were fitted with one-dimensional (1D) numerical models to estimate the apparent 1st order kinetic constant of photo-degradation processes. On average, the energy demand of the unit was counterbalanced by the electric power generated by the photovoltaic panel. The repeated use of the same photocatalysts in all experiments confirmed the long-term energy efficiency of the unit. The apparent kinetic constants of phenol, intermediates species, and total organic carbon (TOC) degradation were found to be governed by the corresponding mass-transfer coefficients of relevant species from the bulk liquid to the active catalyst surface. At early times, the total inorganic carbonates (TIC) concentration increases, and at late times the fast mass-transfer of dissolved CO2 to gas phase compensates for the production of inorganic carbon. Preliminary tests showed that the photocatalytic unit is capable of reducing the COD and TOC of WWTP effluents and occasionally, the concentration of nitrates and ammonia may also decrease.
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•An energy-autonomous and portable photocatalytic unit was manufactured and tested.•The energy efficiency of unit was stable after several cycles of operation.•A model capable of predicting the transient responses of TOC and TIC was developed.•The apparent kinetic constants were affected by the external mass-transfer rate.•COD & TOC of effluent of wastewater treatment plant were reduced by more than 50%.
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•Mortars present a refinement of pores as a function of curing time and CNT content.•Refinement is due to CNTs dispersion and deflocculating of cement by dispersants.•Small amounts of ...CNTs (up to 0.4 wt%) are beneficial for the transport properties.•Dispersive agents’ role is crucial in controlling transport of nanomodified mortars.
The current study investigates the dependence of transport properties of carbon nanotube (CNT)-modified mortars on tube content, type of dispersive agent and microstructure. CNT addition was found to result in up to 50% reduction of sorptivity, due to the refinement of pores in the mortars. No relation was found between water absorption at equilibrium, chloride diffusion and gas permeability coefficient with CNT content, dispersive agent type and microstructural parameters. The behavior was linked with the presence of high amount of dispersive agents which, not only control the level of compaction, but also chemically interact with water or methanol altering transport.
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•Estimation of species concentration in a DBD plasma discharge reactor.•Ozone contribution to overall degradation rate estimated to 22.2%.•Pollutant degradation rate is strongly ...affected by permeability.•Moisture presence affects the reactor efficiency.•Extraction of the overall pollutant removal rate from experimental data.
A Dielectric Barrier Discharge (DBD) plasma multiscale simulator has been developed, addressing key mechanisms of soil remediation with characteristic time scales ranging from nanoseconds to minutes in a hierarchical approach. The simulated microscopic DBD plasma processes were linked to the macroscopic remediation modeling through the local species concentrations. A complex, 100 species-based reaction set was implemented in the plasma simulator for the calculation of the concentrations of highly reactive species produced in pertinent operational conditions. These species concentrations were extracted from the microscopic plasma process in the nanoseconds time scale, and introduced as source terms for the solution of the macroscopic problem. In addition, an effective mobility term was introduced to capture the structure effect of the soil medium on the plasma process. The momentum, mass, and energy transport phenomena were modeled and used to predict the degradation rate of atrazine pollutant as a function of specific key reactive molecules, namely, O3 and OH radicals. The activity of these species was examined under different working scenarios, providing valuable information for the remediation process. A wide range of flow rate scenarios were examined, showing that the air velocity influences the remediation process significantly. Another case study involved the application of several sandy soil materials with varying porosity and permeability values, and assessed their impact on the degradation rate. This model analysis was accompanied with experimental data, which were used as reference and validation points for the numerical investigation. Improved operational conditions for the DBD reactor were suggested for the case of atrazine degradation.
