Comparison of two methods for the determination of total organic halogen (TOX) in receiving waters

Two methods for the determination of total organic halogen (TOX), orginating from bleaching of pulp, in receiving waters have been compared. One of the methods (AC/MC) is based on adsorption of the halogenated matter onto an activated carbon sorbent. The halogen is determined by a microcoulometric technique after combustion of the carbon. The other method (XAD/PT) uses an XAD resin as sorbent and the determination of the halogen is carried out by potentiometric titration after a schöniger combustion of the resin eluate.Both methods showed good performance for samples consisting of spent bleach liquors diluted with distilled, fresh and brackish water. The repeatability was very good with a relative standard deviation less than a few per cent. The detection limit of the AC/MC method is about 0.1 μmol/1 and for the XAD/PT method about ten times higher. The AC/MC method gave in most cases 10–20% higher TOX concentrations compared to the XAD/PT method.     

Removal of acutely hazardous pharmaceuticals from water using multi-template imprinted polymer adsorbent

Molecularly imprinted polymer adsorbent has been prepared to remove a group of recalcitrant and acutely hazardous (p-type) chemicals from water and wastewaters. The polymer adsorbent exhibited twofold higher adsorption capacity than the commercially used polystyrene divinylbenzene resin (XAD) and powdered activated carbon adsorbents. Higher adsorption capacity of the polymer adsorbent was explained on the basis of high specific surface area formed during molecular imprinting process. Freundlich isotherms drawn showed that the adsorption of p-type chemicals onto polymer adsorbent was kinetically faster than the other reference adsorbents. Matrix effect on adsorption of p-type chemicals was minimal, and also polymer adsorbent was amenable to regeneration by washing with water/methanol (3:1, v/v) solution. The polymer adsorbent was unaltered in its adsorption capacity up to 10 cycles of adsorption and desorption, which will be more desirable in cost reduction of treatment compared with single-time-use activated carbon.     

弱碱性树脂吸附-解吸苦味酸

考察了水中苦味酸在弱碱性离子交换树脂D301R上的吸附与解吸。研究了吸附热力学、动力学特性及吸附机理。结果表明,树脂在pH=2.7～10.2时,吸附能力最好。等温平衡吸附遵循Freundlich模型。吸附过程为吸热、熵增的自发过程。吸附动力学符合Lagergren准二级速率方程,颗粒内扩散为吸附速率的主要控制步骤,吸附速率常数为7.23×10-5～1.20×10-4g/(mg.min),吸附活化能为19.4 kJ/mol。树脂上吸附的苦味酸可用HNO3+丙酮混合液定量洗脱,洗脱率达99%。静态吸附和脱附的比较结果证实了吸附过程中存在不可逆化学吸附。树脂对苦味酸的吸附主要是通过静电吸附、酸碱络合吸附、氢键吸附等协同作用来完成的。     

Enhanced Desorption of Atmospheric Samples from Activated Carbon

It has been previously shown that the desorption of either a chemisorbed or a physically adsorbed gas can be enhanced by the subsequent introduction of a foreign gas. Under conditions in which desorption recovery of butane from activated, carbon was 50 to 65%, subsequent adsorption of CCl₄ enhanced the recovery of butane to 100%. Recovery of CCl₂F₂, originally 79%, was enhanced to 99% by the same method. The method of enhanced desorption was applied to the recovery of samples from activated carbons exposed to atmospheres in Chicago, New Orleans, Philadelphia, Washington, D. C, and Cincinnati. Three different types of carbons, characterized by different distributions of pore diameters, were used simultaneously in the Cincinnati sampling. In general, the enhanced desorption technique was advantageous in providing analytical information on adsorbed samples recovered from carbon media. The enhancement effect is especially marked with hydrocarbon material. The effects of these structural attributes of the carbon media are evaluated by detailed consideration of infrared absorptions.     

VOC composition of current motor vehicle fuels and vapors, and collinearity analyses for receptor modeling

The formulation of motor vehicle fuels can alter the magnitude and composition of evaporative and exhaust emissions occurring throughout the fuel cycle. Information regarding the volatile organic compound (VOC) composition of motor fuels other than gasoline is scarce, especially for bioethanol and biodiesel blends. This study examines the liquid and vapor (headspace) composition of four contemporary and commercially available fuels: gasoline (<10% ethanol), E85 (85% ethanol and 15% gasoline), ultra-low sulfur diesel (ULSD), and B20 (20% soy-biodiesel and 80% ULSD). The composition of gasoline and E85 in both neat fuel and headspace vapor was dominated by aromatics and n-heptane. Despite its low gasoline content, E85 vapor contained higher concentrations of several VOCs than those in gasoline vapor, likely due to adjustments in its formulation. Temperature changes produced greater changes in the partial pressures of 17 VOCs in E85 than in gasoline, and large shifts in the VOC composition. B20 and ULSD were dominated by C₉ to C₁₆n-alkanes and low levels of the aromatics, and the two fuels had similar headspace vapor composition and concentrations. While the headspace composition predicted using vapor-liquid equilibrium theory was closely correlated to measurements, E85 vapor concentrations were underpredicted. Based on variance decomposition analyses, gasoline and diesel fuels and their vapors VOC were distinct, but B20 and ULSD fuels and vapors were highly collinear. These results can be used to estimate fuel related emissions and exposures, particularly in receptor models that apportion emission sources, and the collinearity analysis suggests that gasoline- and diesel-related emissions can be distinguished.     

活性炭吸附和脱附-等离子体氧化净化有机废气的研究

根据滑动弧放电等离子体适于降解高浓度有机物废气的特性,结合活性炭吸附法,提出了吸附器的吸附浓缩和热脱附-等离子体氧化净化有机废气的方法。在活性炭吸附过程中,最初2 h内甲苯净化率达到100%,随着时间的增加净化率下降;在热脱附滑动弧放电等离子体净化过程中,甲苯降解效率最高为97.3%。将滑动弧放电等离子体反应器出口气相产物收集进行FT-IR检测,发现放电后有CO2、CO、H2O和NO2产生,并分析了甲苯的降解机理。     

Adsorption of elemental mercury vapors from synthetic exhaust combustion gas onto HGR carbon

An activated carbon commercially available named HGR, produced by Calgon-Carbon Group, was used to adsorbe metallic mercury. The work is part of a wider research activity by the same group focused on the removal of metallic and divalent mercury from combustion flue gas. With respect to previously published papers, this one is aimed at studying in depth thermodynamic equilibria of metallic mercury adsorption onto a commercial activated carbon. The innovativeness lies in the wider operative conditions explored (temperature and mercury concentrations) and in the evaluation of kinetic and thermodynamic data for a commercially available adsorbing material. In detail, experimental runs were carried out on a laboratory-scale plant, in which Hg° vapors were supplied in a nitrogen gas stream at different temperature and mercury concentration. The gas phase was flowed through a fixed bed of adsorbent material. Adsorbate loading curves for different Hg° concentrations together with adsorption isotherms were achieved as a function of temperature (120, 150, 200°C) and Hg° concentrations (1.0?7.0 mg/m³). Experimental runs demonstrated satisfying results of the adsorption process, while Langmuir parameters were evaluated with gas–solid equilibrium data. Especially, they confirmed that adsorption capacity is a favored process in case of lower temperature and they showed that the adsorption heat was –20 kJ/mol. Furthermore, a numerical integration of differential equations that model the adsorption process was proposed. Scanning electron microscopy (SEM) investigation was an useful tool to investigate about fresh and saturated carbon areas. The comparison between them allowed identification of surface sites where mercury is adsorbed; these spots correspond to carbon areas where sulfur concentration is greater.

Implications: Mercury compounds can cause severe harm to human health and to the ecosystem. There are a lot of sources that emit mercury species to the atmosphere; the main ones are exhaust gases from coal combustion and municipal solid waste incineration. Furthermore, certain CO₂ capture processes, particularly oxyfuel combustion in a pulverized fuel coal-fired power station, produce a raw CO₂ product containing several contaminants, mainly water vapor, oxygen, and nitrogen but also mercury, that have to be almost completely removed; otherwise these would represent a strong drawback to the success of the process.     

Accuracy Assessment of EPA Protocol Gases Purchased In 1991

ABSTRACT

Fixed-roof tanks are used extensively at manufacturing, waste management, and other facilities to store or process liquids containing volatile organic compounds. Federal and state air standards require the control of organic air emissions from many of these tanks. A common practice used for some fixed-roof tanks that are required to use controls is to vent the tank through an activated carbon canister. When organic vapors are adsorbed on activated carbon, heat is released. Under certain conditions, the temperature of the carbon bed can increase to a level at which the carbon or organic vapors spontaneously ignite, starting a fire in the carbon bed. Bed fires in carbon canisters are not uncommon and can present a significant safety hazard at facilities if proper safety measures are not implemented. This article discusses how carbon adsorber bed fires occur and presents general guidance on safety measures for carbon canisters installed on fixed-roof tanks to reduce the likelihood of a carbon bed fire and to minimize the impact in the event of a fire.     

Adsorption of organic vapors on polar surfaces- Recent advances

This paper summarizes recent research on the adsorption of organic vapors on surfaces. Since the low gas phase concentration range is typical for environmental situations, this review is restricted to these adsorption coefficients. Two environmental parameters have a strong influence on the adsorption of organic vapors on polar surfaces:temperature andrelative humidity (which is the most suitable parameter for describing the influence of ambient moisture). An exponential relationship was found for the adsorption coefficientversus relative humidity and the reciprocal temperature, respectively. Comparing the heats of adsorption, two different groups of substances emerged: polar chemicals exhibited heats of sorption which were higher than their corresponding heats of condensation due to their ability to form hydrogen bonds, while for the nonpolar compounds the opposite was true. Sorption takes place on the surface of an adsorbed water film when the relative humidity exceeds the value which is necessary to form a monomolecular layer of water on the surface of the adsorbent (≥ 30 % relative humidity). Therefore, at temperature below 0 °C, a change in the adsorption behavior might be expected due to a change of properties of the adsorbed water film. However, no alterations were observed at temperatures from -12 °C to + 4 °C (adsorption on quartz sand). The results were comparable to those at much higher temperatures (50 – 80 °C). A statistical approach for the prediction of the adsorption coefficients from physico-chemical parameters of the substances (vapor pressure, polarizability, and electron-donating capability) was developed and good agreement was found with experimental results and independent data from the literature. Finally, two special cases, the adsorption on bulk water and ice, are discussed.     

Microwave Regeneration of Activated Carbon Used for Removal of Solvents from Vented Air

ABSTRACT

A microwave regeneration of activated carbon used to remove organic solvents from vented air has been investigated. Methyl ethyl ketone (MEK), acetone, and tetrachloroethylene (TCE) vapors were removed from vented air through adsorption onto granular activated carbon. The saturated carbon was then regenerated in a microwave field, where the solvent was quickly desorbed and recovered from the inner pores of the carbon granules. The microwave-induced regeneration restored the original adsorption capacity and surface area of the activated carbon.     

Adsorption/desorption of linear alkylbenzenesulfonate (LAS) and azoproteins by/from activated sludge flocs

Our study investigated the adsorption/desorption by/from activated sludge flocs, dispersed in river water or in diluted wastewater, of organic compounds (C(11)-LAS, azoalbumin and azocasein) at concentrations relevant to environmental conditions. Activated sludge flocs, used as a model of biological aggregates, are characterized by a very heterogeneous matrix able to sorb the three organic compounds tested at 4 degrees C. The adsorbed amount of C(11)-LAS by activated sludge flocs was higher than that of azocasein or azoalbumin, as shown by the Freundlich parameters (K(ads)=8.6+/-1.7, 1.6+/-0.3 and 0.3+/-0.1 micromol(1-1/n)g(-1)l(1/n) for C(11)-LAS, azocasein and azoalbumin, respectively; n=3 sludges). C(11)-LAS sorption from activated sludge appeared to be partially reversible in river water, while a marked hysteresis phenomenon was observed for azocasein and azoalbumin, implying a low degree of reversibility in their exchange between activated sludge and river water. It has also been displayed that the conductivity variation of bulk water (comprised between 214 and 838 microS cm(-1)) exerted no dramatic effect on the C(11)-LAS desorption from activated sludge flocs, while a little effect of it on azocasein desorption was observed. Thus, biological aggregates as activated sludge flocs can serve as an intermediate carrier for C(11)-LAS, while it represents a sink for proteins.     

Carbon bed fires and the use of carbon canisters for air emissions control on fixed-roof tanks

Fixed-roof tanks are used extensively at manufacturing, waste management, and other facilities to store or process liquids containing volatile organic compounds. Federal and state air standards require the control of organic air emissions from many of these tanks. A common practice used for some fixed-roof tanks that are required to use controls is to vent the tank through an activated carbon canister. When organic vapors are adsorbed on activated carbon, heat is released. Under certain conditions, the temperature of the carbon bed can increase to a level at which the carbon or organic vapors spontaneously ignite, starting a fire in the carbon bed. Bed fires in carbon canisters are not uncommon and can present a significant safety hazard at facilities if proper safety measures are not implemented. This article discusses how carbon adsorber bed fires occur and presents general guidance on safety measures for carbon canisters installed on fixed-roof tanks to reduce the likelihood of a carbon bed fire and to minimize the impact in the event of a fire.     

Influence of soil properties on heavy metal sequestration by biochar amendment: 2. Copper desorption isotherms

Contaminant desorption constrains the long-term effectiveness of remediation technologies, and is strongly influenced by dynamic non-equilibrium states of environmental and biological media. Information is currently lacking in the influence of biochar and activated carbon amendments on desorption of heavy metal contaminants from soil components. In this study, copper sorption-desorption isotherms were obtained for clay-rich, alkaline San Joaquin soil with significant heavy metal sorption capacity, and eroded, acidic Norfolk sandy loam soil having low capacity to retain copper. Acidic pecan shell-derived activated carbon and basic broiler litter biochar were employed in desorption experiments designed to address both leaching by rainfall and toxicity characteristics. For desorption in synthetic rain water, broiler litter biochar amendment diminished sorption-desorption hysteresis. In acetate buffer (pH 4.9), significant copper leaching was observed, unless acidic activated carbon (pH_pzc = 3.07) was present. Trends observed in soluble phosphorus and zinc concentrations for sorption and desorption equilibria suggested acid dissolution of particulate phases that can result in a concurrent release of copper and other sorbed elements. In contrast, sulfur and potassium became depleted as a result of supernatant replacements only when amended carbon (broiler litter biochar) or soil (San Joaquin) contained appreciable amounts. A positive correlation was observed between the equilibrium aluminum concentration and initial copper concentration in soils amended with acidic activated carbon but not basic biochar, suggesting the importance of cation exchange mechanism, while dissolution of aluminum oxides cannot be ruled out.     

Adsorption of Automotive Paint Solvents On Activated Carbon: I. Equilibrium Adsorption of Single Vapors

A bench scale system to measure adsorption of organic vapors on activated carbon is described in this report. The system was used to measure the equilibrium adsorption isotherms of n-heptane, n-butanol, and methyl isobutyl ketone at a concentration range of 50 to 900 ppm on a Columbia JXC activated carbon and the adsorption capacity of eleven additional solvents at a concentration of 365 ppm. It is found that the Polyani–Dubinin correlation describes the results well. Using n-heptane as a reference solvent, the mean error in the prediction of equilibrium adsorption capacity is 1.9% and the maximum error 7.2%.     

Microwave regeneration of activated carbon used for removal of solvents from vented air

A microwave regeneration of activated carbon used to remove organic solvents from vented air has been investigated. Methyl ethyl ketone (MEK), acetone, and tetrachloroethylene (TCE) vapors were removed from vented air through adsorption onto granular activated carbon. The saturated carbon was then regenerated in a microwave field, where the solvent was quickly desorbed and recovered from the inner pores of the carbon granules. The microwave-induced regeneration restored the original adsorption capacity and surface area of the activated carbon.     

微波再生载苯酚活性炭过程中再生产物分析

研究了载氮气和无载气2种条件下,微波再生载苯酚活性炭过程中再生产物的成分和苯酚随再生过程的去向分布。结果表明,无载气时,微波功率越高,再生反应器内温度越高,吸附质的高温裂解反应越彻底,再生产物以挥发性气体为主,有机质种类很少;而当微波功率较低或载氮气再生时,反应器内温度相对较低,苯酚难以被彻底分解,再生产物中含多种复杂的链状或环状有机物。此外,载氮气时,经气提、挥发而去除的苯酚量约占总吸附量的一半,再生炭上无苯酚残留,活性炭吸附性能可完全恢复乃至优化;无载气时,经挥发而去除的苯酚量只有19.9%,其余大量苯酚则在微波作用下裂解或缩合为其他物质随尾气而去除,且再生炭上仍有少量苯酚未被解吸出来。因此,前者活性炭再生的效果优于后者。     

Removal of organic contaminants in bioretention medium amended with activated carbon from sewage sludge

Bioretention, also known as rain garden, allows stormwater to soak into the ground through a soil-based medium, leading to removal of particulate and dissolved pollutants and reduced peak flows. Although soil organic matter (SOM) is efficient at sorbing many pollutants, amending the bioretention medium with highly effective adsorbents has been proposed to optimize pollutant removal and extend bioretention lifetime. The aim of this research was to investigate whether soil amended with activated carbon produced from sewage sludge increases the efficiency to remove hydrophobic organic compounds frequently detected in stormwater, compared to non-amended soil. Three lab-scale columns (520 cm³) were packed with soil (bulk density 1.22 g/cm³); activated carbon (0.5% w/w) was added to two of the columns. During 28 days, synthetic stormwater—ultrapure water spiked with seven hydrophobic organic pollutants and dissolved organic matter in the form of humic acids—was passed through the column beds using upward flow (45 mm/h). Pollutant concentrations in effluent water (collected every 12 h) and polluted soils, as well as desorbed amounts of pollutants from soils were determined using GC-MS. Compared to SOM, the activated carbon exhibited a significantly higher adsorption capacity for tested pollutants. The amended soil was most efficient for removing moderately hydrophobic compounds (log K _ow 4.0–4.4): as little as 0.5% (w/w), carbon addition may extend bioretention medium lifetime by approximately 10–20 years before saturation of these pollutants occurs. The column tests also indicated that released SOM sorb onto activated carbon, which may lead to early saturation of sorption sites on the carbon surface. The desorption test revealed that the pollutants are generally strongly sorbed to the soil particles, indicating low bioavailability and limited biodegradation.

     

Kinetics of phenanthrene desorption from activated carbons to water

We determined the kinetics of phenanthrene desorption from three activated carbons to water using Tenax beads as an infinite sink for organic compounds in water. Desorption kinetic data very well fitted a biphasic kinetic model based on the presence of two different adsorption sites, viz. low-energy sites and high-energy sites. Rate constants for desorption to water from these two types of sites in the three activated carbons did not reveal a relation with activated carbon grain size. These rate constants were comparable to those for desorption of various organic compounds from hard carbon in various sediments.     

Fate and mobility of pharmaceuticals in solid matrices

The sorption and mobility of six pharmaceuticals were investigated in two soil types with different organic carbon and clay content, and in bacterial biomass (aerobic and anaerobic). The pharmaceuticals examined were carbamazepine, propranolol, diclofenac sodium, clofibric acid, sulfamethoxazole and ofloxacin. The sorption experiments were performed according to the OECD test Guideline 106. The distribution coefficients determined by this batch equilibrium method varied with the pharmaceutical tested and the solid matrix type. Ofloxacin was particularly strongly adsorbed (except of the case of using anaerobic biomass for the solid matrix) while clofibric acid was found to be weakly adsorbed. The fate of pharmaceuticals in soil was also assessed using lysimeters. Important parameters that were studied were: the pharmaceutical loading rate and the hydraulic loading rate for adsorption and the rate and duration of a "rain" event for desorption. Major differences in the mobility of the six pharmaceuticals were observed and correlated with the adsorption/desorption properties of the compounds.     

Adsorption of phenolic compounds from aqueous solutions by a water-compatible hypercrosslinked polymeric adsorbent

A water-compatible hypercrosslinked polymeric adsorbent (NJ-8) for adsorbing and removing phenolic compounds from their aqueous solutions was prepared. This product can be used directly without a wetting process. Its adsorption property toward four phenolic compounds, phenol, p-cresol, p-chlorophenol, and p-nitrophenol was tested using the commercial Amberlite XAD-4 as a reference. The capacities of equilibrium adsorption for all four phenolic compounds on the NJ-8 from their aqueous solutions are around two times as high as that of Amberlite XAD4 within the temperature range 283-323 K, which may contribute to their micropore structure and the partial polarity on the network. Freundlich isotherm equations, as well as relative adsorption capacities and isosteric adsorption enthalpies for the four phenolic compounds, indicate that the adsorption of phenolic compounds on the NJ-8 resin is a physical adsorption process. Mini-column adsorption studies for phenol on Amberlite XAD4 and NJ-8 resins show that the breakthrough adsorption capacities are 0.54 and 0.99 mmol/ml, and the total capacities are 0.62 and 1.37 mmol/ml, while no extra acetone was needed to remove the adsorbed phenol from NJ-8 as from Amberlite XAD4.