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Abstract The aim of this study is to evaluate the role of PZC and wettability of the catalysts in heterogeneous catalytic ozonation process. For that purpose, 18 solid materials examined as potential catalysts for heterogeneous catalytic... more
Abstract The aim of this study is to evaluate the role of PZC and wettability of the catalysts in heterogeneous catalytic ozonation process. For that purpose, 18 solid materials examined as potential catalysts for heterogeneous catalytic ozonation, regarding the degradation of small amounts (4 μΜ) of p-chlorobenzoic acid (p-CBA - typical micropollutant) at pH 7. The examined catalysts belong to three main categories, i.e., metal oxides/hydroxides, minerals, and carbons. Alumina 507, SiO2, Bayoxide, zeolite, calcite and dolomite were found to be the optimum catalysts with p-CBA removal rates higher than 99.4% after the 3rd min of the process. The obtained results indicate the importance of surface charge and the wettability degree of the catalysts. It was found that the affinity between ozone and the catalyst surface and the subsequent production of hydroxyl radicals (•OH) depends on these parameters. More specifically catalysts of high wettability and neutrally to slightly positive surface charged led to enhanced p-CBA degradation. The strongly negative or positive surface charged materials that present low wettability were found to decrease the •OH production. Although, in the gas phase ozone presents better affinity with the non-polar/hydrophobic surfaces, when it is dissolved in water and participates in aqueous phase oxidation reactions, the contact with the catalysts’ surface is enhanced by the higher wettability of the solids, promoting the production of •OH. In addition to the activation of ozone on the catalysts’ surface, it was shown that their efficiency is enhanced by the initial p-CBA adsorption on the surface of applied catalysts.
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The increasing need for remediation of contaminated sites has led to the development of new technologies that emphasize on the biological detoxification and destruction of the (organic) contaminants. Bioremediation is among these... more
The increasing need for remediation of contaminated sites has led to the development of new technologies that emphasize on the biological detoxification and destruction of the (organic) contaminants. Bioremediation is among these technologies that destroy or render harmless various contaminants, using the biological activity of certain microorganisms. Needless to say that as bioremediation actually relies on the microbial growth and activity, its effectiveness is highly dependent on the applied environmental parameters that influence the microbial growth and the degradation rate. Bioremediation technologies can be classified into two general categories: ex situ and in situ. The ex situ techniques are those that require the physical removal of the contaminated material and its transportation to another area for further treatment, for example, by bioreactors, land farming, and composting. The in situ technologies are those that involve treatment of contaminated material in place, for example, by bioventing and biostimulation. Overall, bioremediation is considered as a very promising technology with great potential when dealing with certain types of contaminated sites. So far, it has been used at an increasing number of sites worldwide, including Europe, with varying success. The application of bioremediation and phytoremediation offers significant benefits to environmental pollution abatement and, more importantly, to human health; however, the risk of adverse health effects may be present due to the variability of contaminants and their possible biotransformation toward not-controlled metabolites. Therefore, specific control procedures should also take place.
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In tanning procedures, the main and most widely currently used reagent for skin/hide treatment is the trivalent chromium salt (usually the sulfate one). However, the low yield of the reactions, taking place in the respective chromium... more
In tanning procedures, the main and most widely currently used reagent for skin/hide treatment is the trivalent chromium salt (usually the sulfate one). However, the low yield of the reactions, taking place in the respective chromium bath, commonly results in a significant proportion of this metal, passing unused into the corresponding wastes (mostly wastewater, but also to some extension in the solid waste). These wastes are considered as hazardous, and their sustainable management is recommended/enforced by international and national legislative organizations. An attractive approach to address this issue is the application of circular economy principles, where the Cr(III) content of wastewaters can be appropriately recovered and then reused again into the tanning process, as raw material. The chromium-rich tannery wastes, in which Cr(III) recovery has been examined, are mainly the tanning liquor and the resulting sludge from the physicochemical/biological treatment of wastewater stream. Regarding the tanning liquor, the treatment technique that shows the highest efficiency and also applied in the field is precipitation. This method requires the addition of an appropriate alkaline media in order to increase the solution’s pH and to precipitate Cr(OH)3; subsequently, this precipitate can be re-dissolved in sulfuric acid, before feeding it back to the tanning bath. On the other hand, the most effective technology for chromium recovery from the tannery sludge is the selective, mainly acidic dissolution of chromium by applying simple hydrometallurgical principles, followed by precipitation and eventually re-dissolution, before reuse.
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Abstract In recent years, research in the field of Membrane Bio-Reactor (MBR) technology is turning toward the bigger use of ceramic membranes for the separation of biomass during municipal or industrial wastewater treatment. Apart from... more
Abstract In recent years, research in the field of Membrane Bio-Reactor (MBR) technology is turning toward the bigger use of ceramic membranes for the separation of biomass during municipal or industrial wastewater treatment. Apart from their higher stability against chemical cleaning, their capability to operate in higher than usual temperatures, and showing better resistance to mechanical forces, ceramic membranes may also present lower fouling propensity than the respective polymeric ones. However, the application of ceramic MBR is not yet widespread, since membrane fouling still remains the major drawback of this technology in general; also, there are certain challenges that need to be specifically addressed in the future research to improve the respective efficiency of these systems. Most of them include the optimization of investment cost by introducing new fabrication and coating technologies and the improvement of selectivity, water permeability, and packing densities, in relation to the increased fragility issues of ceramic materials.
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Nowadays the problem of industrial wastes handling and disposal is increasing continuously, as more strict environmental considerations have to be taken into account. In this paper, selected experimental results are presented from our... more
Nowadays the problem of industrial wastes handling and disposal is increasing continuously, as more strict environmental considerations have to be taken into account. In this paper, selected experimental results are presented from our current research in toxic metals removal (e.g. Cu, Pb, As), related to the applications of mineral particles as by-products (red mud, pyrite, dolomite, etc.) for the induced removal of toxic metals from aqueous solutions. These by-products, existing in finely divided form and considered rather as solid industrial wastes, have been used as a cheap solid adsorbent or substrate. Appropriate methods for the subsequent solid/liquid separation were examined, among them flotation. Different parameters were tested and high removals of toxic metals were achieved. In this way, a useful application may be realized for the waste mineral particles.
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... Ion flotation using a common cationic surfactant (dodecylamine) as collector was used for the quantitative recovery of molybdenum from dilute aqueous solutions. When arsenic co-existed with molybdenum in the solution, both arsenic and... more
... Ion flotation using a common cationic surfactant (dodecylamine) as collector was used for the quantitative recovery of molybdenum from dilute aqueous solutions. When arsenic co-existed with molybdenum in the solution, both arsenic and molybdenum were recovered. ...
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Several mineral particles were shown to act as sorbents for metal ions. Among them, goethite, an abundant iron mineral, was found to present the specific advantage of being able to remove both cations and oxyanions, such as arsenic. The... more
Several mineral particles were shown to act as sorbents for metal ions. Among them, goethite, an abundant iron mineral, was found to present the specific advantage of being able to remove both cations and oxyanions, such as arsenic. The modelling of the sorption process, using the diffuse double layer model, was attempted in this paper. A good agreement with experimental results was found; therefore, it proved to be a useful tool for such sorption applications. A brief review of this scientific area is critically presented.
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The synthesis of iron oxyhydroxides and hydroxides is reported in this work, by the use of a novel, simple and low-cost method. The preparation involves the hydrolysis of aqueous solutions of ferric salts followed by membrane purification... more
The synthesis of iron oxyhydroxides and hydroxides is reported in this work, by the use of a novel, simple and low-cost method. The preparation involves the hydrolysis of aqueous solutions of ferric salts followed by membrane purification and freeze drying of the products. Three different iron precursors have been tested and combined to three different volatile precipitating agents. The obtained products were akaganeite, goethite and iron(III) hydroxide. Irrespective of the starting materials used, all three products, although different in chemical nature, presented some very interesting and unique features; they consisted of nanoparticles with mean sizes ranging from 1 to 10 nm and they had very high surface areas and pore sizes in the meso- and micropore regions. The produced materials were examined by powder X-ray diffraction for crystalline phase identification, TEM and XRD for particle size estimation and nitrogen sorption for surface area, pore volume and pore size distribution measurement.
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This study evaluates the possibility of using magnetite as an adsorbent for the removal of Cr(VI) in a bed column setup under continuous flow conditions. For this purpose, granular magnetite was synthesized on a large scale and tested in... more
This study evaluates the possibility of using magnetite as an adsorbent for the removal of Cr(VI) in a bed column setup under continuous flow conditions. For this purpose, granular magnetite was synthesized on a large scale and tested in both batch and rapid small-scale column experiments using reliable conditions of drinking water treatment. Column tests, which were designed to scale-down larger adsorption systems in terms of size, time and water flow, indicate a higher removal capacity compared to that observed during batch experiments with magnetite powder, reaching 9.2 mg/g at pH 6.4 before residual Cr(VI) exceeds 10 μg/L. The main parameters of this process, including pH, contact time and granular size, were also examined under similar column tests suggesting the improvement of the overall effectiveness and operation time at lower water pH, higher empty bed contact times and larger particle dimensions.
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Abstract The removal of nickel ions from aqueous solutions, using fly ash, a cheap industrial by‐product, was investigated. Its addition to the solution raised the pH, effectively removing the totality of the nickel ions. The removal may... more
Abstract The removal of nickel ions from aqueous solutions, using fly ash, a cheap industrial by‐product, was investigated. Its addition to the solution raised the pH, effectively removing the totality of the nickel ions. The removal may be attributed, depending upon the ...
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Combined sewer overflows (denoted hereafter as CSOs) occur when flows exceed the hydraulic capacity of either the wastewater treatment plant (denoted as WWTP) or the collection system that transports the combined flow of storm water and... more
Combined sewer overflows (denoted hereafter as CSOs) occur when flows exceed the hydraulic capacity of either the wastewater treatment plant (denoted as WWTP) or the collection system that transports the combined flow of storm water and sanitary sewage to the WWTP. The principal components of a combined sewer system include (1) the contributing drainage area (catchment) and wastewater sources, (2) the combined sewer pipe network and interceptor(s), (3) the regulator and diversion structures, and (4) the CSO outlets. When an overflow occurs, the excess flows tend to be discharged into the neighboring receiving body of surface water. CSOs typically discharge a variable mixture of raw sewage, industrial/commercial wastewater, polluted runoff, and scoured materials that build up in the collection system during dry weather. These discharges contain a variety of pollutants that may adversely impact the receiving waterbody, including pathogenic microorganisms, viruses, cysts, and chemical and floatable materials. Keywords: combined sewer overflow (CSO); treatment; retention basins; swirl; vortex; screening; floatables control; dissolved air flotation; filtration; disinfection; chlorine; ozone; UV radiation; peracetic acid; electron beam irradiation; constructed wetlands
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Abstract The addition of alumina (Al2O3), chromite concentrate (CC) and ore (CO) and maghemite (Fe2O3) in the magnesite minerals enrichment wastes investigated, aiming to upgrade the refractory properties of products after thermal... more
Abstract The addition of alumina (Al2O3), chromite concentrate (CC) and ore (CO) and maghemite (Fe2O3) in the magnesite minerals enrichment wastes investigated, aiming to upgrade the refractory properties of products after thermal treatment at 1300° C. Firing shrinkage, water absorption, apparent porosity and bulk density, considered as the main relevant parameters of importance, determined accordingly for the products, and optical microscopy micrographs appropriately received, whereas the mineralogical characterization implemented by X-Ray Diffraction (XRD) measurements. The chemical analysis of microstructure also performed by using the point analysis feature of SEM-EDS and the main mineral phases at the surface of products determined, aiming to the better explanation of relevant mechanisms/transformations. Alumina is not suitable as additive for upgrading the refractory properties, due to the presence of high percentage glassy phase on the surface of respective product, higher apparent porosity levels and lower bulk density values, which attribute to the formation of spinel and proto-enstatite. The addition of maghemite showed better results, due to the increase of bulk density and better surface sintering of powdered raw materials. However, the best results were found by the addition of chromite additives (CC and CO), as the firing shrinkage levels showed a decreasing trend, with the highest reduction noticed with chromite ore, due to highest MgO content. The MgO content, maximizes the formation of forsterite at the examined firing temperature 1300 °C, resulting to the improvement of refractory properties. The aim of this research is to convert the mining wastes/by-products, produced during the magnesite ore enrichment processes, into a potentially commercial refractory product with added value, contributing to circular economy and zero waste mining production.
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Dilute aqueous solutions, generated or used by mineral industry, generally contain several metal species; the latter are known to be non-biode-gradable substances. For this reason, various processes suitable for metal ions removal from... more
Dilute aqueous solutions, generated or used by mineral industry, generally contain several metal species; the latter are known to be non-biode-gradable substances. For this reason, various processes suitable for metal ions removal from water and effluents will be briefly reviewed, among them the conventional ones such as precipitation, sorption and ion exchange. Nevertheless, attention will be mainly paid to the application of innovative processes, particularly aiming for metals recovery. In today’s world of water shortage, water reuse in the mineral processing plants is also of great importance. Stress will be given to the necessary solid-liquid separation technique applied downstream, following the metals removal. The important aspect of applying industrial by-products (i.e. mineral fines, etc.) as efficient sorbents, including the biosorbents, will be discussed. Finally, the chemistry of pyrite flotation will be reported.
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Fluoride is present in several groundwaters due to natural or anthropogenic origins. Although it is necessary for physiological human functions (in small amounts, i.e., 0.5–1.2 mg/L), it could be very harmful when it exceeds the maximum... more
Fluoride is present in several groundwaters due to natural or anthropogenic origins. Although it is necessary for physiological human functions (in small amounts, i.e., 0.5–1.2 mg/L), it could be very harmful when it exceeds the maximum permissible concentration limit of 1.5 mg/L (according to WHO). Among the numerous technologies for removing fluoride from waters, metal–organic framework (MOF) materials are considered to be promising adsorbents due to their advantages of high porosity, high specific surface area, diverse functions and easy modification. In this study, the synthesis of MOFs and the progress of their application to the removal of fluoride from contaminated water, as published in the recent literature mainly over the past five years, are reviewed. The adsorption mechanism(s) and its main characteristics, such as effect of initial fluoride concentration, adsorbent dosage, solution pH, contact time, adsorption capacity, thermodynamic and regeneration studies, etc., for ...
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Abstract The demand for more chemically and thermally stable membranes in water and wastewater treatment is growing rapidly over the past few years. As a result, ceramic membranes are increasingly applied, due to their inherent advantages... more
Abstract The demand for more chemically and thermally stable membranes in water and wastewater treatment is growing rapidly over the past few years. As a result, ceramic membranes are increasingly applied, due to their inherent advantages over conventional polymeric membranes, such as good chemical stability, favorable mechanical strength, high surface hydrophilicity (if desirable), good antimicrobial ability, and high separation efficiency. The Ceramic Membrane Bio-Reactor is a state-of-the-art technology, which employs ceramic membranes in aerobic or anaerobic bioreactors for industrial or municipal wastewater treatment. Coupling ceramic membranes into anaerobic MBRs (AnMBRs) is more common, as it offers greater potentials, thanks to their generally higher resistance toward the presence of corrosive chemicals and of harsh chemical environments, as well as to relatively higher temperatures, than those usually encountered in convenient aerobic Membrane Bio-Reactor systems. So far, several research studies have shown the successful implementation of ceramic membranes in AnMBR systems in terms of removal efficiency and fouling mitigation. The main challenges for the future include the optimization of manufacturing cost (still relatively higher than the convenient polymeric membranes) and of the respective surface properties, pore sizes, etc., as well as the specific operational conditions (especially in terms of energy consumption).
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Dead end membrane operation maximizes O3 dissolution.
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This study presents for the first time the synthesis and characterization of GO (graphene oxide), PFSiC (polyferric silicate chloride), and hybrid GO-PFSiC derivatives, aiming to enhance synergistically the performance of coagulation,... more
This study presents for the first time the synthesis and characterization of GO (graphene oxide), PFSiC (polyferric silicate chloride), and hybrid GO-PFSiC derivatives, aiming to enhance synergistically the performance of coagulation, when applied for the treatment of water. The structure and the morphology of composite GO-PFSiC coagulants were studied in detail by the application of FTIR, XRD, and SEM characterization techniques. Furthermore, the proposed coagulants were applied for the treatment of simulated turbid surface water. The effects of the reagent’s dosage, pH value, and experimental/operational conditions on the coagulation efficiency, applied mainly for the removal of turbidity, were examined. The results, obtained from the FTIR and XRD measurements, showed the presence of a bond between the PFSiC and the GO surface, indicating that the PFSiC particles are distributed uniformly on the surface of graphene, which was also confirmed by the SEM images. Especially, the compo...
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ABSTRACT Novel adsorbents consisting of ZnFe2O4/Zn5(OH)6(CO3)2 (hydrozincite) nanocomposite materials were studied for efficient As(V) removal from water. Nanocomposites were synthesized by the co-precipitation of Zn and Fe salts in... more
ABSTRACT Novel adsorbents consisting of ZnFe2O4/Zn5(OH)6(CO3)2 (hydrozincite) nanocomposite materials were studied for efficient As(V) removal from water. Nanocomposites were synthesized by the co-precipitation of Zn and Fe salts in alkaline conditions. Depending on the Zn/Fe molar ratio, a variety of materials was produced with different ZnFe2O4/Zn5(OH)6(CO3)2 contents. The adsorbent’s efficiency for As(V) removal was enhanced proportionally to the percentage of Zn5(OH)6(CO3)2 content. The nanocomposite with 74 ± 7 wt% of Zn5(OH)6(CO3)2 provided a capacity of 18.4 μg As(V)/mg for residual concentration of 10 μg/L (pH 7) which is over twice that of an iron oxy-hydroxide prepared under similar conditions.
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In this study, the implementation of an iron oxy-hydroxide (FeOOH) as a surface catalyst for Cr(VI) reduction by inorganic sulfur reductants (ISRs) was investigated. Batch Cr(VI) removal tests, performed to evaluate and compare the... more
In this study, the implementation of an iron oxy-hydroxide (FeOOH) as a surface catalyst for Cr(VI) reduction by inorganic sulfur reductants (ISRs) was investigated. Batch Cr(VI) removal tests, performed to evaluate and compare the efficiency of ISRs in the presence of FeOOH, qualified Na2S2O4 as the optimum for drinking water treatment. Application of Na2S2O4 in continuous flow rapid small scale column tests, using a FeOOH adsorbent at pH 7 ± 0.1 and artificial (resembling natural) water matrix, verified the high potential for Cr(VI) removal at sub-ppb level. Indeed, a 15 mg S/L Na2S2O4 dose diminished an initial Cr(VI) concentration of 100 μg/L below the method's detection limit of 1.4 μg/L at least for 105 bed volumes. X-ray absorption fine structure spectroscopy revealed that Cr(VI) forms outer sphere complexes, while Cr(III) is involved in 2E, 2C and 1 V geometries with the surface Fe-oxyhydroxyl groups. It can, therefore, be concluded that FeOOH attracts Cr(VI) to its surf...
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Abstract The removal of toxic materials is becoming ever more critical due to diminishing water resources, increasing wastewater disposal costs, and stricter discharge regulations that have lowered permissible contaminant levels in waste... more
Abstract The removal of toxic materials is becoming ever more critical due to diminishing water resources, increasing wastewater disposal costs, and stricter discharge regulations that have lowered permissible contaminant levels in waste streams. The present work presents an overview of various techniques (such as chemical precipitation, electrochemical treatment, coagulation—flocculation, flotation, membrane filtration, adsorption and ion exchange, catalytic oxidation, phytoremediation, and biodegradation processes) for the removal of toxic materials from water and wastewater, including their advantages, limitations, and applications. Secure management methods of wastes containing toxic materials, including waste minimization, recycling, degradation, vitrification, and stabilization, are also summarized and annotated. The chapter is completed with case studies for potential application of toxic materials removal techniques in water and wastewater treatment.
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A tannery sludge, produced from physico-chemical treatment of tannery wastewaters, was incinerated without any pre-treatment process under oxic and anoxic conditions, by controlling the abundance of oxygen. Incineration in oxic conditions... more
A tannery sludge, produced from physico-chemical treatment of tannery wastewaters, was incinerated without any pre-treatment process under oxic and anoxic conditions, by controlling the abundance of oxygen. Incineration in oxic conditions was performed at the temperature range from 300°C to 1200°C for duration of 2h, while in anoxic conditions at the temperature range from 400°C to 600°C and varying durations. Incineration under oxic conditions at 500°C resulted in almost total oxidation of Cr(III) to Cr(VI), with CaCrO4 to be the crystalline phase containing Cr(VI). At higher temperatures a part of Cr(VI) was reduced, mainly due to the formation of MgCr2O4. At 1200°C approximately 30% of Cr(VI) was reduced to Cr(III). Incineration under anoxic conditions substantially reduced the extent of oxidation of Cr(III) to Cr(VI). Increase of temperature and duration of incineration lead to increase of Cr(VI) content, while no chromium containing crystalline phase was detected.