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The removal of groundwater contamination is a complex process due to the hydro-geochemical characteristics of the specific site, related maintenance and the possible presence of several types of pollutants, both organic and inorganic. In recent decades, there has been an increasing drive towards more sustainable treatment for contaminated groundwater as opposed to “intensive” treatments, i.e. with high requirements for onsite infrastructure, energy and resource use. In this study, a new remediation technology is proposed, combining the use of advanced drainage systems with adsorption processes, termed “In-situ reactive DRAINage system for groundwater TREATment” (In-DRAIN-TREAT). By taking advantage of the groundwater natural gradient, In-DRAIN-TREAT collects the contaminated groundwater via a drainage system and treats the polluted water directly into an active cell located downstream, avoiding external energy inputs. Preliminary results indicate the applicability and high efficiency of In-DRAIN-TREAT when compared with a permeable reactive barrier (PRB). In-DRAIN-TREAT is applied to remediate a theoretical aquifer with low permeability, contaminated by a 13 m wide hexavalent chromium (CrVI) plume. This is achieved in less than a year, via a drain DN500, 32 m long, a 30 m3 treatment cell filled with activated carbon and no energy consumption. A comparison with permeable barriers also shows a preliminary 63% volume reduction, with a related 10% decrease of remediation costs.

In this paper, the activity of a cobalt/molybdenum (Co/Mo) commercial catalyst for the Water Gas Shift Reaction for hydrogen production was investigated in a three fixed-bed reactor pilot plant using a tar-rich synthesis gas from a full-scale biomass gasification plant as feed-stream. A parametric variation study was carried out to assess CO conversion (X CO ) and selectivity for the water gas shift reaction as a function of the operating temperature (T) in the range 300–450 °C. The effects of four dry gas hourly space velocities (GHSV), Case A-Case D, two steam to dry synthesis gas ratios (H 2 O/SG), 56% v/v and 67% v/v, and a H 2 S concentration in the range 100–220 ppm v,db were investigated: the highest CO conversion (∼95%) was observed in the base case (Case A GHSV) at 67% v/v H 2 O/SG, and 450 °C, the lower the operating temperature the lower the CO concentration, the lower the gas hourly space velocity the higher the CO conversion and the higher the H 2 O/SG the higher the CO conversion. The effect of H 2 S variation on CO conversion was also studied, keeping the operating temperature constant (≈365 °C) and using the Case D GHSV: CO conversion increased as the H 2 S concentration increased and X CO ≈ 40%. Selectivity was not influenced by the parameters investigated. Finally, the effect of the catalyst on tar removal was studied and a CO conversion close to 85% was found.

In the last decades the interest in the biomass gasification process has increased due to the growing attention to the use of sustainable energy. Biomass is a renewable energy source and represents a valid alternative to fossil fuels. Gasification is the thermochemical conversion of an organic material into a valuable gaseous product, called syngas, and a solid product, called char. The biomass gasification represents an efficient process for the production of power and heat and the production of hydrogen and second-generation biofuels. This paper deals with the state of the art biomass gasification technologies, evaluating advantages and disadvantages, the potential use of the syngas and the application of the biomass gasification. Syngas cleaning though fundamental to evaluate any gasification technology is not included in this paper since; in the authors' opinion, a dedicated review is necessary. © 2015 Science Press and Dalian Institute of Chemical Physics.

In this work, the results of equilibrium and dynamic adsorption tests of hexavalent chromium, Cr (VI), on activated carbon are presented. Adsorption isotherms were determined at different levels of pH and temperature. Dynamic tests were carried out in terms of breakthrough curves of lab-scale fixed bed column at different pH, inlet concentration and flow rate. Both the adsorption isotherms and the breakthrough curves showed non-linear and unconventional trends. The experimental results revealed that chromium speciation played a key role in the adsorption process, also for the occurrence of Cr(VI)-to-Cr(III) reduction reactions. Equilibrium tests were interpreted in light of a multi-component Langmuir model supported by ion speciation analysis. For the interpretation of the adsorption dynamic tests, a mass transfer model was proposed.Dynamic tests at pH 11 were well described considering the external mass transfer as the rate controlling step. Differently, for dynamic tests at pH 6 the same model provided a satisfying description of the experimental breakthrough curves only until a sorbent coverage around 1.6mgg-1. Above this level, a marked reduction of the breakthrough curve slope was observed in response to a transition to an inter-particle adsorption mechanism. © 2014 Elsevier B.V.

This paper presents an experimental study of the ultrasonic degradation of organic pollutants in terms of the effect of ultrasonic frequency (40–380–850–1000 kHz). The removal efficiency of two endocrine disrupting compounds [17β-estradiol (E2) and 17α-ethinylestradiol (EE2)] is investigated using laboratory scale ultrasonic baths at low power intensities. Higher ultrasonic frequencies were found to be more effective for pollutant degradation with 850 kHz the best: 9.0 × 10−1 mg/kW h for E2 and 6.8 × 10−1 mg/kW h for EE2 at initial concentrations of 1 ppm. Additionally, the removal of p-nitrophenol was investigated under the same conditions, as a dosimetry reaction for estimating the hydroxyl radical production, key component in organic pollutant removal. In order to describe the overall phenomena occurring inside the reactor and to predict the apparent hydroxyl radical production, a simulation algorithm is proposed. It incorporates the solution of ODE systems that embodies bubble dynamics, heat and mass transfer through the bubble wall and chemical reactions in the gas–vapor phase for an initial bubble nuclei population. The experimental degradation measures of p-nitrophenol over the range of frequencies studied were found to be comparable with the model results of hydroxyl radicals produced during the sonication treatment.

In this paper, a Permeable Reactive Barrier (PRB) made with activated carbon, namely a Permeable Adsorptive Barrier (PAB), is put forward as an effective technique for the remediation of aquifers simultaneously contaminated by some chlorinated organic compounds. A design procedure, based on a computer code and including different routines, is presented as a tool to accurately describe mass transport within the aquifer and adsorption/desorption phenomena occurring inside the barrier. The remediation of a contaminated aquifer near a solid waste landfill in the district of Napoli (Italy), where Tetrachloroethylene (PCE) and Trichloroethylene (TCE) are simultaneously present, is considered as a case study. A complete hydrological and geotechnical site characterization, as well as a number of dedicated adsorption laboratory tests for the determination of activated carbon PCE/TCE adsorption capacity in binary systems, are carried out to support the barrier design. By means of a series of numerical simulations it is possible to determine the optimal barrier location, orientation and dimensions. PABs appear to be an effective remediation tool for the in-situ treatment of an aquifer contaminated by PCE and TCE simultaneously, as the concentration of both compounds flowing out of the barrier is everywhere lower than the regulatory limits on groundwater quality.

The introduction of cyanide with a backflow attack into a water system was studied. The recent development of techniques for water network sectorization, aimed to improve the management of water systems, represents also an efficient way to protect networks from intentional contamination. The possibility of closing gate valves by a remote control system to create an i-DMA (isolated District Meter Area) can reduce the risk of contamination and thus the extent of damage of a terroristic attack. The study proposes a novel technique for designing i-DMAs compatible with hydraulic performance and optimized for water network protection.

In this work, an experimental study aimed at the assessment of the factors affecting the adsorption of trichloroethylene (TCE) from water solutions onto activated carbons is presented. The influence of sorbent properties, such as B.E.T. surface area, micropore volume, chemical composition and acid/basic surface functional groups on TCE adsorption capacity is experimentally assessed by testing a set of 12 sorbents. Moreover, the effect of the presence of other species in solution, such as sodium acetate and tetrachloroethylene (PCE), is studied through parametric TCE adsorption isotherms realization. The experimental results show that the TCE adsorption capacity is promoted by a high B.E.T. surface area, micropore volume and C content and it is significantly affected by the presence of a non-ionic compound of similar structure (PCE), however it does not depend on the presence of an organic salt (sodium acetate). These results confirm that neither TCE-carbon ionic interaction nor sorbent ionization phenomena are involved in the TCE adsorption, since its mechanism is based on dispersion forces (London-Van Der Walls interaction). A thorough analysis of the experimental data set suggests that, in consideration of the TCE adsorption mechanism, the maximization of basal plane extent (as the B.E.T. surface area) and its effective fraction (as the C content) is a valid criterion to select or synthesize a new suitable sorbent for TCE adsorption from waters. (C) 2009 Elsevier B.V. All rights reserved.

This work studies the reliability of an activated carbon permeable reactive barrier in removing cadmium from a contaminated shallow aquifer. Laboratory tests have been performed to characterize the equilibrium and kinetic adsorption properties of the activated carbon in cadmium-containing aqueous solutions. A 2D numerical model has been used to describe pollutant transport within a groundwater and the pollutant adsorption on the permeable adsorbing barrier (PRB). In particular, it has been considered the case of a permeable adsorbing barrier (PAB) used to protect a river from a Cd(II) contaminated groundwater. Numerical results show that the PAB can achieve a long-term efficiency by preventing river pollution for several months.

In this work the adsorption of pentavalent arsenic on a granular activated carbon (GAC) has been experimentally studied. The effects of arsenic concentration, pH, temperature and salinity on equilibrium adsorption capacity have been investigated. Experimental results show that the adsorption capacity is the highest at neutral pH conditions, low salinity levels and high temperatures. A model for the description of the arsenic adsorption mechanism is reported. This is based on the multicomponent Langmuir adsorption theory applied to the ionic species in solution. The model points out that the adsorption capacity is proportional to the concentration of arsenic anions in solution and decreases by increasing the concentration of competitive ions such as hydroxides and chlorides, allowing a correct interpretation of the pH and salinity effects on the adsorption capacity. Finally, one of the main goals of the proposed model is to preserve the exothermicity of the adsorption phenomena despite the observed trend of experimental results: the increase of adsorption capacity with temperature appears to be related to a higher arsenic dissociation. © 2007 Elsevier Ltd. All rights reserved.

Adsorption isotherms of chromium ions in aqueous solution have been experimentally measured on a granular activated carbon (GAC) and on a char of South African coal (CSAC). Experimental results show that the adsorption capacity for the GAC strongly depends on solution pH and salinity, with maximum values around 7mg/g at neutral pH and low salinity levels. On the contrary, the CSAC shows a smaller adsorption capacity, near 0.3mg/g, which slightly decreases by increasing pH and salinity levels. Chromium adsorption mainly depends on the availability of chromium ions in solution and on the occurrence of redox reactions between the surface groups and the Cr(VI) which lead to the formation of Cr(III). The reduction of Cr(VI) and the following sorption of Cr(III) cations appears as the leading mechanism for chromium uptake on the CSAC. A similar behaviour can be observed for the GAC at pH below 3. On the contrary, at pH>7, the multicomponent competitive adsorption of Cr(VI), OH(-) and Cl(-) has to be considered.

In this work the attention was focused on the adsorption and desorption of elemental mercuric on HGR activated carbon produced by Calgon-Carbon Corp. The study was performed in an apparatus at laboratory scale in which Hg 0 vapors in a nitrogen gas stream, at a given temperature and mercury concentration, flowed through a fixed bed of adsorbent material. The experiments showed that the adsorption phenomena are faster than the desorption phenomena. SEM micrographs of the fresh carbon and of the carbon after adsorption or desorption had occurred have shown that mercury is adsorbed on the surface on particular sites where high sulfur concentration exists.

A study on the oxidation of calcium sulfite catalyzed by Mn(2+) is presented in this paper. A laboratory-scale well-mixed thermostated reactor was used, with continuous feeding of both gas and liquid phase. The gas phase was a mixture of oxygen and nitrogen, with O(2) partial pressure varying from 5.1 to 40.5 kPa. The liquid phase was obtained by mixing inside the reactor two separate aqueous solutions, one obtained by dissolving Ca(OH)(2) into a SO(2) solution, and the other one containing manganous sulfate. The temperature was kept constant in all the experiments at 45 degrees C. The results show that increasing catalyst concentration, the transition takes place from slow kinetic to slow diffusional and eventually to fast reaction regime. (C) 1999 Elsevier Science Ltd. All rights reserved.

In the present work attention was focused on a wet flue gas desulfurization process using limestone suspensions, which is the most common method used to reduce SO 2 emissions from power plant exhaust gases. The SO 2 absorption rate was measured varying both the SO 2 concentration in the gas phase and the limestone concentration in the suspension. The experiments were performed by bubbling mixtures of sulfur dioxide and nitrogen in the continuous limestone aqueous suspension. The absorption phenomenon was studied by making use of the film theory to describe the liquid-side mass transfer. It was assumed that the liquid-phase diffusional resistance is concentrated in a layer the thickness of which depends on fluid dynamics, but which is independent of the nature of the reactions taking place. The equations considered by the model describe conditions of thermodynamic equilibrium as well as material and electrical balances. Furthermore, they take into account the effect of the gradient of the electric potential of diffusion on the diffusive transport of ions and molecules in the film surrounding the gas-liquid interface. The SO 2 absorption rate and the limestone dissolution rate experimentally determined were used to integrate the model equations, yielding the value of the film thickness, and allowing the determination of the concentration profiles of the different species in the liquid film and of the enhancement factor for chemical absorption. Consistency between model and experimental results, on the basis of the hypothesis of the model, was found.

An experimental investigation has been carried out on velocities and amplitudes of pressure disturbances in fluidized beds made of 100–200 μm glass ballotini. Disturbances were originated by gas jetting in a 0.35 m i.d. fluidized bed. A fluidization tube 0.10 m i.d. has also been used. Different types of disturbances have been induced in the bed contained in this tube: injection of a freely rising bubble and of a captive bubble; injection of a bubble chain; and compression of the bed free surface. The dynamic wave character of the disturbances has been shown. Velocities and amplitudes of waves moving through the beds have been measured. In particular, wave velocities have been compared with theoretical results obtained by the application of “pseudo-homogeneous” and “separated phase flow” models.