Laboratory studies on the remediation of mercury contaminated soils

Mercury, in contrast to other toxic metals, cycles between the atmosphere, land, and water. During this cycle, it undergoes a series of complex chemical and physical transformations. Because of these transformations, it is found in the environment not only as simple inorganic and organic compounds, but also as complex compounds. As a result, it is difficult to remediate mercury contaminated materials. Laboratory studies were conducted with a mercury contaminated complex waste from an industrial site to evaluate the ability of extractants such as H₂O₂, H₂SO₄ and Na₂S₂O₃ to decontaminate the waste. Up to 87 percent of the total mercury present in the waste was extracted. Mercury was recovered as insoluble mercury sulfide by adding Na₂S solution to the combined filtrates from the H₂O₂ + H₂SO₄ and Na₂S₂O₃ treatment steps. The technique described in this article is capable of recovering mercury in a usable form and can be used as a pretreatment to remediate mercury contaminated waste before laud disposal.     

Sodium Persulfate Oxidation for the Remediation of Chlorinated Solvents (USEPA Superfund Innovative Technology Evaluation Program)

This study has been conducted at the University of Connecticut (UCONN) in connection with the USEPA Superfund Innovative Technology Evaluation (SITE) program to evaluate a chemical oxidation technology (sodium persulfate) developed at UCONN. A protocol to assess the efficacy of oxidation technologies has been used. This protocol, which consists of obtaining data from a treatability study, tested two in-situ chemical oxidation technologies that can be used on soil and groundwater at a site in Vernon, Connecticut. Based on the treatability report results and additional field data collected at the site, the design for the field implementation of the chemical oxidation remediation was completed. The results indicate that both sodium persulfate and potassium permanganate were able to effectively degrade the target VOCs (i.e., PCE, TCE and cis-DCE) in groundwater and soil-groundwater matrices. In the sodium persulfate tests (120 hrs), the extent of destruction of target VOCs was 74% for PCE, 86% for TCE and 84% for cis-DCE by Na₂S₂O₈ alone and 68% for PCE, 76% for TCE, and 69% for cis-DCE by Fe(II)-catalyzed Na₂S₂O₈. The results demonstrate the sodium persulfate's ability to degrade PCE, TCE and cis-DCE. It is expected that given sufficient dose and treatment time, a higher destruction rate of the dissolved phase contamination can be achieved. The data also indicates that the catalytic effect of the iron chelate on persulfate chemistry was much less pronounced in the soil-groundwater matrix. This indicates an interaction between the iron chelate solution and the soil, which may have resulted in a lower availability of the chelated iron for catalysis. The study showed that the remediation of the VOCs-contaminated soil and groundwater by in-situ chemical oxidation using sodium persulfate is feasible at the Roosevelt Mills site. As a result, the USEPA SITE program will evaluate this technology at this site.     

Chemical Crosslink Degradable PVA Aqueous Solution by Potassium Persulphate

The aim of this paper is to study the influence of the K₂S₂O₈ content on the properties of poly (vinyl alcohol, (PVA). Firstly, PVA was dissolved in distilled water by heating by heating at 70 °C and then K₂S₂O₈ was added in PVA solution under stirrer. The viscosity of PVA solution in the presence of K₂S₂O₈ was analyzed by Brookfield Viscometers. The effects of K₂S₂O₈ contents, PVA solution, temperature and reaction time on the viscosity of PVA solution were investigated. This was confirmed by Brookfield Viscometers. It is clear that the viscosity of PVA solution in the presence of K₂S₂O₈ increased as function of reaction time and PVA content in solution. Rate of modified PVA was proportional to K₂S₂O₈ contents and temperature and its activation energy was 16 kJ/mol. The structure of PVA in the presence of K₂S₂O₈ changed from original PVA confirmed by ATR-FTIR and solid state NMR. In addition, the thermal properties of PVA containing K₂S₂O₈ were also studied by TGA.     

Photochemical Degradation of Aqueous Polyvinyl Alcohol in a Continuous UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> Process: Experimental and Statistical Analysis

Polyvinyl alcohol (PVA), being a dominant contributor of total organic carbon (TOC) in textile wastewater, is not easily degradable by conventional methods of wastewater treatment. This study investigates the degradation of aqueous PVA in a continuous UV/H₂O₂ photoreactor since the feeding strategy of hydrogen peroxide proves to have considerable effects on the process performance. Response surface methodology involving the Box–Behnken method is adopted for the experimental design to study the effects of operating parameters on the process performance. Experimental analysis shows that the TOC removal varies from 16.11 to 42.70 % along with a reduction of the PVA molecular weights from 56.7 to 95.3 %. The TOC removal is significantly lower than the molecular weight reduction due to the generation of the intermediate products during oxidation. Operating the UV/H₂O₂ process in a continuous mode facilitates the degradation of highly concentrated polymeric solutions using a relatively small hydrogen peroxide concentration in the feed with a small residence time ranges from 6.13 to 18.4 min.     

Resurrection of the iron and phosphorus resource in steel-making slag

 This research focused on the treatment of steel-making slags to recycle and recover iron and phosphorus. The carbothermal reduction behavior of both synthesized and factory steel-making slag in microwave irradiation was investigated. The slags were mixed with graphite powder and heated to a temperature higher than 1873 K to precipitate a lump of Fe–C alloy with a diameter of 2–8 mm. The larger the carbon equivalent (C_eq, defined in the text), the higher the fractional reduction of iron and phosphorus. An increase in the SiO₂ content of slag led to a considerable improvement in the reduction for both iron and phosphorus because of the improvement in the fluidity of the slags and an increase in the activity coefficient of P₂O₅ in the slags. The extraction behavior of phosphorus from Fe–P–C_satd alloy was also investigated at 1473 K by carbonate flux treatment. For all the experiments with a processing time longer than 10 min, the phosphorus in the fluxes could be concentrated to more than 9% (w/w) showing that it could be used as a phosphorus resource. Compared with K₂CO₃ flux treatment, that using Na₂CO₃ was more effective for the extraction of phosphorus, and this was attributed to the lower evaporation of Na₂CO₃. Finally, a recycling scheme for steel-making slag is proposed. Received: March 16, 2001 / Accepted: November 12, 2001     

The use of waste basic oxygen furnace slag and hydrogen peroxide to degrade 4-chlorophenol

A new treatment method is developed to degrade 4-chlorophenol (4-cp) and its oxidation intermediates. The experimental results of this research demonstrate that 4-cp and its oxidation intermediates can be decomposed completely by basic oxygen furnace slag (BOF slag) with hydrogen peroxide (H₂O₂) in an acid solution. The factors that effect the treatment efficiency were studied including initial concentration of 4-cp, pH of the solution, concentration of H₂O₂ and amount of BOF slag. The BOF slags are final waste materials in the steel making process. The major components of BOF slag are CaO, SiO₂, Fe₂O₃, FeO, MgO and MnO. As the BOF slag in an acid solution, FeO and Fe₂O₃ can be dissociated to produce ferrous ion and ferric ion. Ferrous ion reacts with hydrogen peroxide to form “Fenton's reagent” which can produce hydroxyl radicals (OH^.). Hydroxyl radical possession of high oxidation ability can oxidize organic chemicals effectively. Results show that 100 mg/l of 4-cp is decomposed completely within 30 min by 438.7 g/l BOF slag with 8.2 mM hydrogen peroxide in pH=2.8±0.2 solution. The COD value of the solution is reduced from 290 to 90 mg/l. The factors studied which affect the 4-cp decomposition efficiency were the hydrogen peroxide concentration, BOF slag concentration, pH of the solution and initial concentration of 4-cp. Because large amounts of Fe₂O₃ and FeO are present in the BOF slag, the BOF slag not only has a high treatment efficiency, but also can be used repeatedly.     

Chemical Oxidation Performance in High Temperature,Saline Groundwater Impacted With Hydrocarbons

A series of laboratory microcosm experiments and a field pilot test were performed to evaluate the potential for in situ chemical oxidation (ISCO) of aromatic hydrocarbons and methyl tertiary butyl ether (MTBE), a common oxygenate additive in gasoline, in saline, high temperature (more than 30 °C) groundwater. Groundwater samples from a site in Saudi Arabia were amended in the laboratory portion of the study with the chemical oxidants, sodium persulfate (Na₂S₂O₈) and sodium percarbonate (Na₂(CO₃)₂), to evaluate the changes in select hydrocarbon and MTBE concentrations with time. Almost complete degradation of the aromatic hydrocarbons, naphthalene and trimethylbenzenes (TMBs), was found in the groundwater sample amended with persulfate, whereas the percarbonate‐amended sample showed little to no degradation of the target hydrocarbon compounds in the laboratory. Isotopic analyses of the persulfate‐amended samples suggested that C‐isotope fractionation for xylenes occurred after approximately 30 percent reduction in concentration with a decline of about 1 percent in the δ¹³C values of xylenes. Based on the laboratory results, pilot‐scale testing at the Saudi Arabian field site was carried out to evaluate the effectiveness of chemical oxidation using nonactivated persulfate on a high temperature, saline petroleum hydrocarbon plume. Approximately 1,750 kg of Na₂S₂O₈ was delivered to the subsurface using a series of injection wells over three injection events. Results obtained from the pilot test indicated that all the target compounds decreased with removal percentages varying between 86 percent for naphthalene and more than 99 percent for the MTBE and TMBs. The benzene, toluene, ethylbenzene, and xylene compounds decreased to 98 percent on average. Examination of the microbial population upgradient and downgradient of the ISCO reactive zone suggested that a bacteria population was present following the ISCO injections with sulfate‐reducing bacteria (SRB) being the dominant bacteria present. Measurements of inorganic parameters during injection and postinjection indicated that the pH of the groundwater remained neutral following injections, whereas the oxidation–reduction potential remained anaerobic throughout the injection zone with time. Nitrate concentrations decreased within the injection zone, suggesting that the nitrate may have been consumed by denitrification reactions, whereas sulfate concentrations increased as expected within the reactive zone, suggesting that the persulfate produced sulfate. Overall, the injection of the oxidant persulfate was shown to be an effective approach to treat dissolved aromatic and associated hydrocarbons within the groundwater. In addition, the generation of sulfate as a byproduct was an added benefit, as the sulfate could be utilized by SRBs present within the subsurface to further biodegrade any remaining hydrocarbons. ©2015 Wiley Periodicals, Inc.     

Ammonium removal from landfill leachate by chemical precipitation

The landfill leachate in Hong Kong usually contains quite high NH₄⁺–N concentration, which is well known to inhibit nitrification in biological treatment processes. A common pre-treatment for reducing high strength of ammonium (NH₄⁺–N) is by an air-stripping process. However, there are some operational problems such as carbonate scaling in the process of stripping. For this reason, some technical alternatives for NH₄⁺–N removal from leachate need to be studied. In this study, a bench-scale experiment was initiated to investigate the feasibility of selectively precipitating NH₄⁺–N in the leachate collected from a local landfill in Hong Kong as magnesium ammonium phosphate (MAP). In the experiment, three combinations of chemicals, MgCl₂·6H₂O+Na₂HPO₄·12H₂O, MgO+85% H₃PO₄, and Ca(H₂PO₄)₂·H₂O+MgSO₄·7H₂O, were used with the different stoichiometric ratios to generate the MAP precipitate effectively. The results indicated that NH₄⁺–N contained in the leachate could be quickly reduced from 5618 to 112 mg/l within 15 min, when MgCl₂·6H₂O and Na₂HPO₄·12H₂O were applied with a Mg²⁺:NH₄⁺:PO₄³⁻ mol ratio of 1:1:1. The pH range of the minimum MAP solubility was discovered to be between 8.5 and 9.0. Attention should be given to the high salinity formed in the treated leachate by using MgCl₂·6H₂O and Na₂HPO₄·12H₂O, which may affect microbial activity in the following biological treatment processes. The other two combinations of chemicals [MgO+85% H₃PO₄ and Ca(H₂PO₄)2·H₂O+MgSO₄·7H₂O] could minimise salinity after precipitation, but they were less efficient for NH₄⁺–N removal, compared with MgCl₂·6H₂O and Na₂HPO₄·12H₂O. COD had no significant reduction during this precipitation. It was found that the sludge of MAP generated was easily settled within 10 min to reach its solids content up to 27%. The other characteristics including capillary suction time (CST) and dry density (DD) of the MAP sludge were also tested. The experimental results indicate that the settled sludge is quite solid and can be directly dumped at a landfill site even without any further dewatering treatment.     

Groundwater treatment and aquatic toxicity reduction at a chemical production site

Contaminated groundwater at a chemical antioxidant and phenolic resin chemical production site was subjected to treatability studies to develop design criteria for surface water discharge. Raw groundwater required pretreatment for total suspended solids (TSS) and color removal prior to treatment by ultraviolet light/hydrogen peroxide (UV/H₂O₂). Because of high capital and operating costs for UV/H₂O₂, biological treatment was evaluated as an alternate. Respirometric analyses showed that completely mixed activated sludge could be applied as a treatment technology to the groundwater. Biotreatment resulted in an approximately 70 percent reduction in soluble chemical oxygen demand (SCOD). Residual SCOD was recalcitrant to further biodegradation. The treated effluent was tested for aquatic toxicity using fathead minnows (Pimephales promelas) and Ceriodaphnia dubia and was found to be toxic. Toxicity reduction of biotreatment effluent was evaluated in bench-scale experiments using activated carbon adsorption, filtration, and UV/H₂O₂. Subsequent toxicity testing showed that filtration alone could reduce the bioeffluent toxicity and that residual SCOD was not the primary source of toxicity.     

Evidence for biodegradation and volatilisation of dissolved petroleum hydrocarbons during in situ air sparging in large laboratory columns

Laboratory column experiments run for up to 13 days compared air sparging of groundwater contaminated by dissolved petroleum hydrocarbons in sterile and non-sterile aquifer sediments as well as uncontaminated sediments and groundwater. Loss of dissolved BTEX compounds in the contaminated columns was very rapid, occurring through volatilisation. The majority of the dissolved total organic carbon (TOC) persisted for much longer periods however. A direct comparison between losses from sterile and non-sterile columns suggested a negligible contribution of biodegradation to the removal of TOC. This was difficult to confirm through examination of O₂ utilisation because oxidation of a small amount of reduced sulphur in the aquifer materials was the dominant sink for O₂. Despite this, it was possible to conclude that less than 22% of the removal of TOC was through biodegradation during the first three days of air sparging.     

Recovery of uranium phosphate by a stepwise thermal treatment of uranium-bearing spent TBP

A stepwise thermal treatment process for the recovery of uranium phosphate from uranium-dissolved spent TBP was demonstrated. The pathway of the reactions involved in the thermal decomposition and oxidation processes of uranium-bearing spent TBP was established based on the results of thermogravimetric analyses. Relatively low-temperature pyrolysis is required to avoid the condensation of corrosive phosphoric acid via vaporization. Low-temperature pyrolysis residue was analyzed and found to be composed of pyrocarbon, phosphorus oxide (P₂O₅) and two types of uranium phosphate (UP₂O₇ and UP₄O₁₂). Uranium pyrophosphate (UP₂O₇) was recovered from the burning out of pyrocarbon in the pyrolysis residue after the dissolution removal of phosphorus oxide in water. A substantial recovery of uranium by the proposed stepwise thermal treatment method was successfully demonstrated by a treatment of pyrolysis residue from a bench-scale low-temperature pyrolysis process.     

Evaluation of gold and silver leaching from printed circuit board of cellphones

Electronic waste has been increasing proportionally with the technology. So, nowadays, it is necessary to consider the useful life, recycling, and final disposal of these equipment. Metals, such as Au, Ag, Cu, Sn and Ni can be found in the printed circuit boards (PCB). According to this, the aims of this work is to characterize the PCBs of mobile phones with aqua regia; obtaining “reference” values of leaching, to gold and silver, with cyanide and nitric acid, respectively; and study the process of leaching of these metals in alternative leaching with sodium thiosulfate and ammonium thiosulfate. The metals were characterized by digesting the sample with aqua regia for 1 and 2 h at 60 °C and 80 °C. The leaching of Au with a commercial reagent (cyanide) and the Ag with HNO₃were made. The leaching of Au and Ag with alternative reagents: Na₂S₂O_3, and (NH₄)₂S₂O₃ in 0.1 M concentration with the addition of CuSO₄, NH₄OH, and H₂O₂, was also studied. The results show that the digestion with aqua regia was efficient to characterize the metals present in the PCBs of mobile phones. However, the best method to solubilize silver was by digesting the sample with nitric acid. The leaching process using sodium thiosulfate was more efficient when an additional concentration of 0.015 and 0.030 M of the CuSO₄ was added.     

New Methods for the Preparation Nanosized Metal Coordination Polymers

Transition-metal coordination polymers [M(ndc)(bpy)·(H₂O)m]·xH₂O (where M = Co(II), Ni(II), Cu(II) and Zn(II), ndc = 1,4-naphthalenedicarboxylate, bpy = 4,4′-bipyridine; m = 0 or 1; x = 1 or 2) were prepared by reacting the ligands and metal ions at room temperature with the aid of microwave irradiation and sonication methods. The structure of the coordination polymers was assigned based on elemental analysis, FT-IR and electronic spectral studies, thermal analysis, scanning electron microscope and X-ray powder diffraction. Thermogravimetric analysis was also used to follow up the possible thermal decomposition steps and to calculate the thermodynamic parameters of the nano-sized metal complexes. The kinetic parameters were calculated making use of the Coats–Redfern and Horowitz–Metzger equations. All obtained results of the different technics used in our study stated the ability to synthesis the metal coordination polymers of our interest using both microwave irradiation and sonication methods.     

Mathematical model analysis of Fenton oxidation of landfill leachate

The treatment of concentrated landfill leachate rejected from reverse osmosis (RO) with Fenton process was studied, and the system model was developed through the examination of reaction kinetics. The leachate is typically non-biodegradable with low BOD₅/COD ratio 0.01. The oxidation reactions of Fenton process was found to be a two-stage process, where a fast initial reaction (H₂O₂/Fe²⁺) was followed by a much slower one (H₂O₂/Fe³⁺). A simple and more accurate mathematics model based on COD and TOC removals has been derived successfully to describe the two-stage reaction kinetics. The two corresponding parameters involved in this model have been identified as the initial reaction rate and the maximum oxidation removal efficiency, respectively. It was found to be very useful for evaluating the performance of Fenton system and/or for process design using the two parameters under different experimental conditions.     

Treatment of municipal landfill leachate by catalytic wet air oxidation: Assessment of the role of operating parameters by factorial design

The wet air oxidation (WAO) of municipal landfill leachate catalyzed by cupric ions and promoted by hydrogen peroxide was investigated. The effect of operating conditions such as WAO treatment time (15-30 min), temperature (160-200 °C), Cu²⁺ concentration (250-750 mg L⁻¹) and H₂O₂ concentration (0-1500 mg L⁻¹) on chemical oxygen demand (COD) removal was investigated by factorial design considering a two-stage, sequential process comprising the heating-up of the reactor and the actual WAO. The leachate, at an initial COD of 4920 mg L⁻¹, was acidified to pH 3 leading to 31% COD decrease presumably due to the coagulation/precipitation of colloidal and other organic matter. During the 45 min long heating-up period of the WAO reactor under an inert atmosphere, COD removal values up to 35% (based on the initial COD value) were recorded as a result of the catalytic decomposition of H₂O₂ to reactive hydroxyl radicals. WAO at 2.5 MPa oxygen partial pressure advanced treatment further; for example, 22 min of oxidation at 200 °C, 250 mg L⁻¹ Cu²⁺ and 0-1500 mg L⁻¹ H₂O₂ resulted in an overall (i.e. including acidification and heating-up) COD reduction of 78%. Amongst the operating variables in question, temperature had the strongest influence on both the heating-up and WAO stages, while H₂O₂ concentration strongly affected the former and reaction time the latter. Nonetheless, the effects of temperature and H₂O₂ concentration were found to depend on the concentration levels of catalyst as suggested by the significance of their 3rd order interaction term.     

Decomposition of dichloromethane and in situ alkali absorption of resulting halogenated products by a packed-bed non-thermal plasma reactor

For an effective decomposition and removal of organic halogenated compounds, a packed-bed non-thermal plasma reactor with in situ absorption of the resulting halogenated products by alkaline sorbent incorporated was proposed. In the plasma reactor, α-Al₂O₃ particles of 1 and 3 mm (mean particle diameter) were packed as solid dielectric medium to enhance the plasma power density in the reactor. Further, alkaline sorbent of Ca(OH)₂ was doped onto the surface of α-Al₂O₃ particles, in order to remove halogenated products by in situ absorption with Ca(OH)₂. A high-voltage and high-frequency pulsed power of −15 to 15 kV and 1 kHz was applied to the wire electrode of the plasma reactor by means of a DC power source. In the present study, as the sample of an organic halogenated compound that is most popularly used, we selected dichloromethane (CH₂Cl₂), and 500 ppm of the initial concentration of CH₂Cl₂ was fed into the reactor accompanied by air at a fixed flow rate of 500 × 10⁻⁶ m³ min⁻¹ at room temperature. As a result, it was recognized that the amount of CH₂Cl₂ decomposed by non-thermal plasma in an α-Al₂O₃ particle bed increased with an increase in plasma input power. The ratio of decomposition of CH₂Cl₂ was almost 100% at 13 kV of electric power and 1 kHz frequency, and CO₂, CH₃Cl, COCl₂, HCl, and Cl₂ were observed as the major reaction products. On the other hand, when CH₂Cl₂ was introduced into the plasma reactor where α-Al₂O₃ particles doped with Ca(OH)₂ were packed, the ratio of decomposition of CH₂Cl₂ became higher, compared to the case that α-Al₂O₃ particles were not doped with Ca(OH)₂. Moreover, there were no halogenated by-product gases detected in the outlet gas from the reactor. As the solid reaction products, CaClOH and Ca(ClO)₂·4H₂O were detected on Ca(OH)₂ by X-ray diffraction. From these findings, it was recognized that CH₂Cl₂ was decomposed more effectively without producing unwanted harmful halogenated by-products in the proposed non-thermal plasma reactor where α-Al₂O₃ particles doped with Ca(OH)₂ sorbent were packed.     

Reductive decomposition of waste gypsum with SiO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> additives

From the point of view of a sustainable and environment-friendly society based on the recycling of material resources, it is preferable to utilize waste gypsum as a substitute for lime, which is currently produced by the calcination of limestone. In the present work, the reductive decomposition of CaSO₄ was investigated under an atmosphere of CO: 2 vol%, CO₂: 30 vol%, with N₂ as a carrier gas without and with the addition of SiO₂, Al₂O₃, or Fe₂O₃. It was found that the decomposition temperature of CaSO₄ was significantly reduced from 1673 K to 1223 K when only 5 wt% Fe₂O₃ was added to CaSO₄. In the case of the addition of SiO₂ or Al₂O₃ to CaSO₄, the decomposition temperature was reduced from 1673 K to 1623 K. This was due to the formation of composite oxides (calcium ferrite, calcium silicate, or calcium aluminate) during the reaction of CaSO₄ with the additives at a lower temperature. In addition, the formation of unfavorable product CaS was inhibited in the presence of 5 wt% Fe₂O₃, and this inhibition effect further increased as the addition of Fe₂O₃ was increased. In contrast, no significant effect on the inhibition of CaS formation was observed on the addition of SiO₂ or Al₂O₃.     

Recovery of rare earth elements from waste fluorescent phosphors: Na2O2 molten salt decomposition

In this paper, an efficient recovery of rare earth elements from waste fluorescent phosphors has been reported and the novel process of alkali fusion and acid leaching has been proposed. The experimental results have shown that the key for efficient recycling is the complete dissolution of waste fluorescent phosphors. The Na₂O₂-to-waste mass ratio, calcination temperature and reactive time play considerable roles in rare earth elements extraction during the alkali fusion process. The optimal conditions in terms of temperature, time and Na₂O₂-to-waste mass ratio are 650 °C, 15 min and 2:1, respectively, under which more than 99.5 % rare earth elements are extracted. The possible reaction mechanism of alkali fusion has been proposed.     

Indoor Air Quality Assessment of Elementary Schools in Curitiba, Brazil

The promotion of good indoor air quality in schools is of particular public concern for two main reasons: (1) school-age children spend at least 30% of their time inside classrooms and (2) indoor air quality in urban areas is substantially influenced by the outdoor pollutants, exposing tenants to potentially toxic substances. Two schools in Curitiba, Brazil, were selected to characterize the gaseous compounds indoor and outdoor of the classrooms. The concentrations of benzene, toluene, ethylbenzene, and the isomers xylenes (BTEX); NO₂; SO₂; O₃; acetic acid (HAc); and formic acid (HFor) were assessed using passive diffusion tubes. BTEX were analyzed by gas chromatography–ion trap mass spectrometry and other collected gasses by ion chromatography. The concentration of NO₂ varied between 9.5 and 23?µg m^?3, whereas SO₂ showed an interval from 0.1 to 4.8?µg m^?3. Within the schools, BTEX concentrations were predominant. Formic and acetic acids inside the classrooms revealed intermediate concentrations of 1.5?µg m^?3 and 1.2?µg m^?3, respectively.     

Simple removal of dioxins by injecting combustion gas into water

A simple, low-cost method for suppression of dioxins/furans (hereinafter referred to as dioxins) is required because many middle- and, especially, small-scale incinerators have fallen into disuse or have been dismantled because of the high running and system costs of measures for the suppression of dioxins. Therefore, the purpose of the present study was to develop a simple removal method for dioxins from combustion gas and to evaluate the basic removal rate of dioxins. The removal method for suspended matter in a gas mixture (cold model) and dioxins in exhaust gases (hot model) has been investigated by means of gas injection into water, the mechanism of which is that the suspended matter in the gas gathers at the gas–liquid interface. In the cold model, the removal ratio of fine particles (R_P) by gas injection into water was reproduced well by the following equation: R_P (%) = 100 × {1−exp(−0.8 · S_S · t_C)}, where S_S (cm²/cm³) is the specific surface area of bubbles and t_C (s) is the residence time of bubbles in water. The removal ratio of fine particles increased as the product S_s · t_C increased. In a hot model using the exhaust gas from combustion experiments of polyvinyl chloride, the removal ratio of dioxins (R_D) by injecting the exhaust gas into water was estimated by the following equation: R_D (%) = 100 × {1−exp(−0.8 · S_S · t_C · C_D0 ^0.07)}, where C_D0 [ng/cm³ (at standard temperature and pressure)] is the dioxins concentration in the exhaust gas before injection into water. R_D depends greatly on the specific surface area of bubbles and the residence time of the bubbles in water, and only weakly on the dioxins concentration in the exhaust gas. Injection of the exhaust gas into water has been shown to be effective and was evaluated as a simple method for the removal of dioxins from exhaust gas.