David W. Hand

A kinetic model for H2O2/UV process in a completely mixed batch reactor

Abstract A dynamic kinetic model for the advanced oxidation process (AOP) using hydrogen peroxide and ultraviolet irradiation (H 2 O 2 /UV) in a completely mixed batch reactor (CMBR) is developed. The model includes the known elementary chemical and photochemical reactions, and literature reported photochemical parameters and chemical reaction rate constants are used in this model to predict organic contaminant destruction. Unlike most other kinetic models of H 2 O 2 /UV oxidation process, the model does not assume that the net formation rate of free radical species is zero (pseudo-steady state assumption). In addition, the model considers the solution pH decrease during the process as mineral acids and carbon dioxide are formed. The model is tested by predicting the destruction of a probe compound, 1,2-dibromo-3-chloropropane (DBCP) in distilled water with the addition of inorganic carbon. The new model developed in this work gives better predictions of the destruction of the target organic compound than the model based on the pseudo-steady state assumption. The model provides a comprehensive understanding of the impact of design and operational variables on process performance. Accordingly the ability of the model to select optimum process variables, such as hydrogen peroxide dosage, is illustrated.

Prediction of multicomponent adsorption equilibria using ideal adsorbed solution theory

Test de cette theorie pour la prevision des interactions entre les composes suivants: chloroforme, bromoforme, trichloroethylene, tetrachloroethylene, 1-2 dibromoethane et chlorodibromomethane

Fixed-bed photocatalysts for solar decontamination of water.

A solar decontamination process for water was developed using TiOt photocatalysts supported on silica-based material. The supported catalysts were systematically optimized with respect to catalyst type, catalyst dosage, silica-based support material, particle size, catalyst/ support bonding, and calcination temperature. The optimized supported catalysts outperformed an optimized slurry catalyst under identical operational conditions and had a reaction rate four times that of the slurry catalyst. Trichloroethylene (TCE) as a model compound was alsoused to investigate the impact of solar irradiance, influent concentration, pH value, and hydraulic loading

Prediction of multicomponent adsorption equilibria in background mixtures of unknown composition

Abstract In the past, most predictive mathematical modeling work has focused on mixtures of known composition. Unfortunately, drinking water and wastewater contain many competing organic solutes and most of them may never be identified. Accordingly, a technique has been developed to predict the adsorption equilibria of known organic solutes onto granular activated carbon (GAC) in mixtures of unknown composition. Ideal adsorbed solution theory (IAST) was used to describe the competitive interactions between adsorbates. Theoretical components (TCs) were used in IAST calculations to account for the competitive effects of the unknown mixture. The TC isotherm parameters and concentrations were determined by conducting a multicomponent isotherm of a tracer component which is added to the unknown mixture or singled out of the unknown mixture. Once the TC parameters were determined, the identical parameters were used to predict the competitive interactions between any known component and the unknown mixture. This procedure was verified experimentally for two activated carbons, three synthetic mixtures and a contaminated groundwater. The organic solutes were halogenated one and two carbon aliphatics which are common groundwater contaminants.

Removal of dissolved organic carbon using granular activated carbon

Abstract Granular activated carbon (GAC) is used to reduce disinfection by-products by removing dissolved organic carbon (DOC). The optimum empty bed contact time (EBCT) for a single adsorber was determined and the influence of parallel bed operation on GAC usage rate was examined using both pilot-plant data and mass transfer models. To describe the GAC performance using mass transfer models, the DOC was broken down into fictitious components, and individual fictive component equilibrium and mass transfer parameters were determined using bench scale laboratory studies. The complexities of model parameter determination are described and DOC removal in GAC pilot plants are compared to model predictions using parameters that were determined from bench scale scale tests.

Adsorption and Regeneration on Activated Carbon Fiber Cloth for Volatile Organic Compounds at Indoor Concentration Levels

Abstract There are increasing concerns about indoor volatile organic compounds (VOCs) regarding their health effects and frequent occurrence. Adsorption using granular activated carbon (GAC) is a safe methodology for removing VOCs from indoor air. Although GAC has been widely used to remove VOCs from indoor air, the use of activated carbon fiber cloth (ACFC) is a promising substitute to the conventional activated carbon because of its regenerative properties; hence, this paper provides promising results for the application of ACFC as a regenerative adsorbent for the removal of VOCs from indoor air. The impacts of operating variables on the adsorption/regeneration performance of the ACFC were assessed. A single-layer ACFC exhibited remarkable adsorption and regenerative properties using 100 parts per billion by volume (ppbv) toluene as the indoor contaminant. The use of Joule heating regeneration technique showed that the ACFC was rapid and efficient in removing the low initial loading of toluene. Even after continuous adsorption/regeneration cycles the ACFC showed very good performance. After over 300 heating and cooling cycles the ACFC showed excellent durability and adsorption capacity

User-oriented batch reactor solutions to the homogeneous surface diffusion model for different activated carbon dosages.

This paper presents a simplified approach and user-oriented solutions to the homogeneous surface diffusion model (HSDM) equations for determining the surface diffusivity using a batch reactor system. Once the surface diffusivity is known, this model could also be used to estimate the performance of activated carbon (AC) applications as a function of contact time. In addition, fixed-bed performance can be predicted using the user-oriented solutions to the HSDM for fixed beds. The step-by-step procedure for determining surface diffusion coefficients of an activated carbon adsorber, which was initially developed by Hand, Crittenden and Thacker in 1983 for a carbon dose where C(equilibrium)/C(0)=0.5, is modified to allow calculations for different carbon dosages. This modification provides solutions to the HSDM equations for different activated carbon dosages. The solutions to the HSDM framework are provided as simplified algebraic equations suitable for quick and easy estimations of D(S). The excel spread sheet is provided in the supplemental information and a detailed example is discussed.

Removal and Destruction of Organic Contaminants in Water Using Adsorption, Steam Regeneration, and Photocatalytic Oxidation: A Pilot-Scale Study

The overall objective of this pilot-scale study is to investigate the technical feasibility of the removal and destruction of organic contaminants in water using adsorption and photocatalytic oxidation. The process consists of two consecutive operational steps: (1) removal of organic contaminants using fixed-bed adsorption; and (2) regeneration of spent adsorbent using photocatalysis or steam, followed by decontamination of steam condensate using photocatalysis. The pilot-scale study was conducted to evaluate these options at a water treatment plant in Wausau (Wisconsin) for treatment of groundwater contaminated with tetrachloroethene (PCE), trichloroethene (TCE), cis-dichloroethene (cis-DCE), toluene, ethylbenzene (EB), and xylenes. The adsorbents used were F-400 GAC and Ambersorb 563. In the first treatment strategy, the adsorbents were impregnated with photocatalyst and used for the removal of aqueous organics. The spent adsorbents were then exposed to ultraviolet light to achieve photocatalytic regeneration. Regeneration of adsorbents using photocatalysis was observed to be not effective, probably because the impregnated photocatalyst was fouled by background organic matter present in the groundwater matrix. In the second treatment strategy, the spent adsorbents were regenerated using steam, followed by cleanup of steam condensate using photocatalysis. Four cycles of adsorption and three cycles of steam regeneration were performed. Ambersorb 563 adsorbent was successfully regenerated using saturated steam at 160 °C within 20 hours. The steam condensate was treated using fixed-bed photo-catalysis using 1% Pt-TiO2 photocatalyst supported on silica gel. After 35 minutes of empty bed contact time, more than 95% removal of TCE, cis-DCE, toluene, EB, and xylenes was achieved, and more than 75% removal of PCE was observed. In the case of activated carbon adsorbent, steam regeneration was not effective, and a significant loss in adsorbent capacity was observed.

Destruction of Organic Compounds in Water Using Supported Photocatalysts

Photocatalytic destruction of organic compounds in water is investigated using tanning lamps and fixed-bed photoreactors. Platinized titanium dioxide (Pt-TiO{sub 2}) supported on silica gel is used as a photocatalyst. Complete mineralization of influent concentrations of 4.98 mg/L tetrachloroethylene and 2.35 mg/L p-dichlorobenzene requires a reactor residence time less than 1.3 minutes. While for influent concentrations of 3.58 mg/L 2-chlorobiphenyl, 2.50 mg/L methyl ethyl ketone and 0.49 mg/L carbon tetrachloride, complete mineralization requires reactor residence times of 1.6, 10.5, and 16.8 minutes, respectively. A reactor model is developed using Langmuir-Hinshelwood kinetics and the model parameters are determined using a reference compound, trichloroethylene. Based on the results of experiments with trichloroethylene, the model predicts the mineralization of the aforementioned compounds from ultraviolet (UV) irradiance, influent concentration, hydroxyl radical rate constants, and the known physical properties of the compounds. The model is also able to predict organic destruction using solar insolation (which has a different spectral distribution from the tanning lamps) based on the UV absorption characteristics of titanium dioxide.

Investigation of the Treatability of the Primary Indoor Volatile Organic Compounds on Activated Carbon Fiber Cloths at Typical Indoor Concentrations

Abstract Volatile organic compounds (VOCs) are a major concern for indoor air pollution because of the impacts on human health. In recent years, interest has increased in the development and design of activated carbon filters for removing VOCs from indoor air. Although extensive information is available on sources, concentrations, and types of indoor VOCs, there is little or no information on the performance of indoor air adsorption systems for removing low concentrations of primary VOCs. Filter designs need to consider various factors such as empty bed contact time, humidity effects, competitive adsorption, and feed concentration variations, whereas adsorption capacities of the indoor VOCs at the indoor concentration levels are important parameters for filter design. A preliminary assessment of the feasibility of using adsorption filters to remove low concentrations of primary VOCs can be performed. This work relates the information (including VOC classes in indoor air, the typical indoor concentrations, and the adsorption isotherms) with the design of a particular adsorbent/adsorbates system. As groundwork for filter design and development, this study selects the primary VOCs in indoor air of residences, schools, and offices in different geographical areas (North America, Europe, and Asia) on the basis of occurrence, concentrations, and health effects. Activated carbon fiber cloths (ACFCs) are chosen as the adsorbents of interest. It is demonstrated that the isotherm of a VOC (e.g., toluene on the ACFC) at typical indoor concentrations—parts per billion by volume (ppbv) level—is different than the isotherm at parts per million by volume (ppmv) levels reported in the publications. The isotherms at the typical indoor concentrations for the selected primary VOCs are estimated using the Dubinin–Radushkevitch equation. The maximum specific throughput for an indoor VOC removal system to remove benzene is calculated as a worst-case scenario. It is shown that VOC adsorption capacity is an important indicator of a filter’s lifetime and needs to be studied at the appropriate concentration range. Future work requires better understanding of the realistic VOC concentrations and isotherms in indoor environments to efficiently utilize adsorbents.