Journal of Environmental Engineering

This paper was presented in part by V. L. Snoeyink as the Simon W. Freese Lecture at the 2002 Canadian Society of Civil Engineers/Environmental and Water Resources Institute of ASCE Environmental Engineering Conference in Niagara Falls, Ontario, Canada, July 22, 2002. The interactions of corroded iron pipe surfaces with water are of importance because they can lead to serious water quality degradation and material deterioration. A conceptual model has been developed in this paper to describe the formation and growth of iron scales, and their reactions that lead to colored water problems. Most corrosion scales have characteristic structural features, such as a loosely held top surface layer, a shell-like layer(s), and a porous core. According to this model corrosion scales are expected to grow from inside the scale via the corrosion reaction, i.e., the conversion of iron metal to ferrous ion. The average oxidation state of iron increases with distance from the pipe wall. The scale structure and scale reactions permit the ferrous iron to be released to the bulk water, where it undergoes conversion to particulate ferric iron, which is the cause of colored water. Scale structure and composition play important roles in the reactions of iron scales that lead to iron release, and water quality control to decrease the porosity of the scale is an important means of reducing iron release. It is anticipated that the conceptual model presented here will be used as a basis for changing water quality to minimize colored water formation, and as a guide for further research.

Urban rainfall-runoff mobilizes and transports significant loads of metal species. Promulgation of National Pollutant Discharge Elimination System Phase II regulations has spurred development of Unit Operations and Processes (UOPs) Best Management Practices (BMPs) for control of metal species. Recent UOP designs provide both adsorption and filtration using engineered media such as manganese oxide coated polymeric media (MOPM). Divalent metal species adsorption onto a manganese oxide coated polymeric medium was evaluated through batch adsorption experiments using a flowthrough batch reactor. Freundlich isotherms were utilized to fit the experiment data. For the media examined, MOPM, adsorption is pH dependent and results indicate a favorable solute pH range of >6 for metal species adsorption. The relative adsorption affinity of MOPM for four divalent metal species typically found in storm water is $\mathrm{Pb}\left(\mathrm{II}\right)>\mathrm{Cu}\left(\mathrm{II}\right)>\mathrm{Cd}\left(\mathrm{II}\right)>\mathrm{Zn}\left(\mathrm{II}\right)\text{.}$ Adsorption rates were rapid for this flowthrough batch system with over 50% removal in the first 30 min and over 90% removal within 5 h at a surface loading rate of 500 mL/cm² min. The pH drift patterns, due to surface complexation, during each experiment, coincided with the metal species removal rate curve. Study results indicated that the inclusion of a thin manganese coating can significantly increase media adsorption capacity. MOPM has a comparable adsorption capacity for the divalent metal species compared to other commercial and research media.

Divalent metal species adsorption onto a manganese oxide coated polymeric medium (MOPM) was evaluated through batch adsorption experiments using a flow-through batch reactor. In this paper, Part II, the batch equilibrium and kinetic data examined in Part I are modeled using a triple layer surface complexation model and a potential driving second order kinetic model. Surface complexation modeling using FITEQL-TLM generated intrinsic surface acidity constants for the MOPM of $\log K{ }_{\mathrm{a1}}^{\mathrm{int}}=3.196$ and $\log K{ }_{\mathrm{a2}}^{\mathrm{int}}=-5.802\text{.}$ The intrinsic surface reaction constants for Pb(II), Cu(II), and Zn(II) were $\log K{ }_{\mathrm{Pb}}^{\mathrm{int}}=-1.91\text{,}$ $\log K{ }_{\mathrm{Cu}}^{\mathrm{int}}=-2.53\text{,}$ and $\log K{ }_{\mathrm{Zn}}^{\mathrm{int}}=-4.45\text{,}$ respectively. A potential driving second order kinetic model was developed to predict sorption of the divalent metal ions onto the MOPM. The general adsorption kinetics for MOPM can be described as a fast reaction occurring within 30 min and a slower reaction continuing from 5 to 15 h. Kinetic results can be interpreted using assumptions of the potential driving second order model that the dominant control forces are the chemical potential of the MOPM activated surface sites and chemical potential of sorbate in the solution.

A significant amount of pollutants in urban stormwater runoff is transported as sediment-bound contaminants. It is important to have a clear understanding of the amount of pollutants attached to the different sediment sizes so that treatment facilities can be designed to effectively target the removal of the most polluted sediment sizes. This paper presents results from a study carried out to determine nutrient loads associated with different particle size ranges for dry surface pollutants and stormwater samples collected from an urban road surface. The results indicate that although more that half of the surface pollutant is coarser than 300 μm (microns), less than 15% of the total phosphorus (TP) and total nitrogen (TN) are attached to particle sizes greater than 300 μm. The pollutant loads in the different particle size ranges from different stormwater samples show a larger variability for TN than for TP. The dissolved component for TN ranges between 20 and 50% compared to 20–30% for TP. Practically all the particulate TP and TN in stormwater samples are attached to sediments between 11 and 150 μm. This suggests that to effectively remove TP and TN, pollutant treatment facilities must be able to remove particulates down to 11 μm.

Thermophilic aerobically digested (TAD) sludge supernatant has been found to be a potential carbon alternative for biological nutrient removal (BNR) enhancement in wastewater treatment plants. Carbonaceous substrates, other than the volatile fatty acids (VFAs) in TAD supernatant, were also found to be utilizable in BNR enhancement; however, these carbon compounds could not be detected by conventional chemical analyses (e.g., gas chromatography). A headspace carbon dioxide $\left({\mathrm{CO}}_2\right)$ monitoring method was tested in this study to estimate the overall available carbon source, or the VFAs accumulated in a microaerated TAD operation. This on-line method uses real activated sludge and TAD supernatant samples to determine the available carbon equivalent in real time. In comparison to the gas chromatography (GC) analyses of the TAD supernatant samples, the headspace ${\mathrm{CO}}_2$ monitoring method resulted in “overestimation” of VFA concentrations, in both the phosphorus release and denitrification reactions. Operating results suggested that the ${\mathrm{CO}}_2$ monitoring approach was capable of revealing the overall VFA equivalent that could be available for the main BNR reactions.

The kinetics and mechanisms associated with the ozonation of 2,6-, 3,4-, and 3,5-dichlorophenols (DCPs) in aqueous solutions were studied. It was found that 2 moles of ozone are required for the initial degradation of 1 mole of DCP. The overall reaction between ozone and a DCP was found to be second order (first order per reactant). The overall reaction rate constants of all three DCPs increased with pH because of increased dissociation of the dichlorophenol molecules to dichlorophenoxide ions. Due to its high dissociation constant, 2,6-DCP is most reactive of the three with ozone with the overall reaction rate constants varying from $1.31\times {10}^5$ to $3.36\times {10}^5{M}^{-1} s^{-1}$ within the pH range of 2.0–4.0. Various chlorobenzenediols, chlorocyclohexadienediones, ketones, esters, and carboxylic acids were identified as intermediate and final ozonation products using gas chromatography/mass spectrometry analysis. The initial electrophilic addition of ozone at the ortho and para positions of the molecular and ionic forms is proposed as the likely mechanism for DCP ozonation.

A characterization study on synthetic wastewaters containing various commercially available ink-jet inks was conducted. Analysis of this resulted in the identification of seven high-risk noncompliance parameters, namely, chemical oxygen demand (COD), biochemical oxygen demand at 5 days $\left({\mathrm{BOD}}_5\right)\text{,}$ total dissolved solids (TDS), phenols, copper, iron, and sulphate concentrations. Of these, COD reduction was found to be the most stringent treatment criterion based on the industry-accepted standard Fenton’s oxidation reaction for treatment. TDS and COD were also proposed as critical parameters for the initial assessment of the quality of untreated ink effluents. To provide for rapid and robust indications of the TDS and COD of the untreated ink effluents, a correlation for TDS as a function of conductivity and turbidity was obtained. Furthermore, a deterministic approach based on Beer’s law of absorbance additivity was developed for determining COD of mixtures of ink effluents using absorbance measurements at 210, 436, 525, and 620 nm. These were validated successfully against experimental data. Based on an in-depth analysis of the compositions of ink effluents, a list of simple and rapid on-site water quality parameters was proposed for monitoring the quality of the treated ink wastewater. This consisted of measurements of UV-absorbance at 210 nm, conductivity, pH, turbidity, and color. Based on the discharge limits imposed by a particular country, one can then develop a range of values for these quality parameters in order to meet the discharge regulations of that country. The Singapore context was used as a case study to illustrate this approach. In addition, it was found that the copper content in the cyan ink effluents was substantially reduced by more than 96% along with the standard Fenton’s reaction. Through the course of investigating the Fenton’s oxidation reaction, it was found that measurements of oxidation-reduction potential and/or temperature are suitable indicators of the progress of the reaction.

Photocatalytic oxidation (PCO) is an advanced oxidation process that has recently been shown to be effective in the treatment of recalcitrant metal complexes, such as Cu(II)-ethylenediaminetetraacetic acid (EDTA). The PCO of Cu(II)-EDTA was studied to determine copper recovery and the reusability of the titanium dioxide $\left({\mathrm{TiO}}_2\right)$ photocatalyst. Aqueous solutions of Cu(II)-EDTA $\left({10}^{-4} M\right)$ were treated using illuminated ${\mathrm{TiO}}_2\text{.}$ After PCO treatment, ${\mathrm{TiO}}_2$ was filtered and extracted with $H_2{\mathrm{SO}}_4$ (0.1, 0.5, 1 N) to remove adsorbed copper. The recovered ${\mathrm{TiO}}_2$ catalyst was then reused in subsequent experiments. The recovered copper was concentrated in the extraction solution by a factor of 14.7 over that of the initial copper concentration. An additional experiment was performed using the same ${\mathrm{TiO}}_2$ without copper removal for eight consecutive PCO treatments. In both experiments, the initial rate of photocatalysis did not change significantly with reuse and was similar to that obtained from virgin ${\mathrm{TiO}}_2$ (5.6 μM/min). It is suggested that Cu(II)-EDTA could be effectively treated using an integrated cyclic procedure of PCO, catalyst recovery, and acid extraction for Cu recovery.

A kinetic model based on the mass balance principle with equilibrium partitioning of gaseous ozone into pore water was developed to delineate the reactions of ozone in variably saturated porous media contaminated with phenanthrene. Dimensionless fraction factors were used in the kinetic model to account for the reactions of ozone with soil organic matter (SOM), metal oxide (MO), and phenanthrene as a function of water saturation. The enhanced removal of phenanthrene resulting from heterogeneous catalytic reactions between ozone and soil organic matter and metal oxide was incorporated as lumped parameters in the reaction rate coefficients of gaseous and dissolved ozone with phenanthrene. Laboratory experiments employing 5 cm long mini column reactor systems were conducted to estimate the reaction constants for three porous medium types (glass beads, baked field soil, and field soil) at various water-saturation levels. Water saturation and SOM were found to significantly affect the decomposition of gaseous ozone in both uncontaminated and contaminated porous media. It was found that water saturation over 75% completely eliminates gas-to-solid interfacial ozone reactions with SOM and MO. The kinetic model, with the reaction parameters estimated in this study, predicted reasonably well the experimental data obtained from both the mini column reactor and 20 cm long columns packed with field soil, suggesting that the kinetic model would be suitable for describing the fate and reactions of ozone in variably saturated porous media for soil types and experimental conditions similar to those tested in this study.

Previous electrokinetic remediation studies involving the geochemical characterization of heavy metals in high acid buffering soils, such as glacial till soil, revealed significant hexavalent chromium migration towards the anode. The migration of cationic contaminants, such as nickel and cadmium, towards the cathode was insignificant due to their precipitation under the high pH conditions that result when the soil has a high acid buffering capacity. Therefore the present laboratory study was undertaken to investigate the performance of different electrolyte (or purging) solutions, which were introduced to either dissolve the metal precipitates and/or form soluble metal complexes. Tests were conducted on a glacial till soil that was spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1,000, 500, and 250 mg/kg, respectively, under the application of a 1.0 VDC/cm voltage gradient. The electrolyte solutions tested were $0.1M$ EDTA (ethylenediaminetetraacetic acid), $1.0M$ acetic acid, $1.0M$ citric acid, $0.1M$ $\mathrm{NaCl}/0.1M$ EDTA, and $0.05M$ sulfuric $\mathrm{acid}/0.5M$ sulfuric acid. The results showed that 46–82% of the Cr(VI) was removed from the soil, depending on the purging solution used. The highest removal of Ni(II) and Cd(II) was 48 and 26%, respectively, and this removal was achieved using $1.0M$ acetic acid. Although cationic contaminant removal was low, the use of $0.1M$ NaCl as an anode purging solution and $0.1M$ EDTA as a cathode purging solution resulted in significant contaminant migration towards the soil regions adjacent to the electrodes. Compared to low buffering capacity soils, such as kaolin, the removal of heavy metals from the glacial till soil was low, and this was attributed to the more complex composition of glacial till. Overall, this study showed that the selection of the purging solutions for the enhanced removal of heavy metals from soils should be primarily based upon the contaminant characteristics and the soil composition.

Trade-offs between precision of numerical solutions to deterministic models of the environment, and the number of model realizations achievable within a framework of Monte Carlo simulation, are investigated and discussed. A case study of a model of river thermodynamics is employed. It is shown that the tractability of Monte Carlo simulation relies on adaptation of the numerical solution time-step, giving results with a guaranteed error in the time domain as well as near-optimum speed of calibration under any chosen accuracy criteria. Time-step control is implemented using two adaptive Runge–Kutta methods: a second order scheme with first order error estimator, and an embedded fourth-fifth order scheme. In the case study, where the effects of sparse and imprecise data dominate the overall modeling error, both the schemes appear adequate. However, the higher order scheme is concluded to be generally more reliable and efficient, and has wide potential to improve the value of applying the Monte Carlo method to environmental simulation. The problem of reconciling spatial error with the specified temporal error is discussed.

This paper summarizes some of the recent trends in domestic water use in both developed and developing countries, so as to better identify the principal factors influencing the demand. The focus is on the adoption of a more microapproach to demand forecasting, rather than the traditional use of overall averages, so as to move towards more cost effective and resource efficient supply schemes. An important aim of the paper is to alert designers of new water supply schemes in developing countries to the need to apply caution to the belief that per capita water use will continue to increase in tandem with the general economic development of the area being served, to the extent that it reaches the levels experienced in more developed countries. Survey data are presented from a range of locations to illustrate the trends in domestic water use for both connected households and community standpipes.

This note presents a simple model to quantify the preloading effect of naturally occurring organic matter (NOM) in water on the adsorption capacity of activated carbon for a trace synthetic organic chemical (SOC). The model was developed from the Dubinin–Astakhov (DA) equation based on the assumption that the NOM preloading irreversibly reduced the limiting adsorption pore volume for the target SOC. Given that the DA-n value equal to one, the model reduces to a form similar to the one obtained by modifying the Freundlich equation directly. By assuming that the reduction of the limiting adsorption pore volume was proportional to the volume of NOM adsorbed, the NOM preloading effect was correlated directly to the amount of total organic carbon preloaded on the carbon. The resulting model was then compared with the experimental data in the literature. This simple model may be useful for certain practical applications that require only the estimation of the NOM preloading effect on the adsorption capacity of a target SOC from natural water.

In this study, an existing thermodynamic model was used to predict equilibrium phase partitioning behavior of a cosolvent in a two-phase nonaqueous phase liquid (NAPL)–water system. The activity coefficients are calculated using the universal quasichemical functional group activity coefficient (UNIFAC) method. We examined an assortment of cosolvent–NAPL pairs of environmental interest and compared the UNIFAC-predicted ternary phase diagrams against published experimentally derived ternary phase diagrams. Results show that the UNIFAC model is a promising method for predicting equilibrium cosolvent partitioning behavior in NAPL–water systems, and thus can be useful in estimating the potential for NAPL solubilization and mobilization in remediation processes. The cosolvent partitioning behavior is interpreted with regard to changes in the physical properties of the NAPL-water system. Changes in interfacial tension between the two phases were estimated using an existing correlation. A viscosity experiment was conducted for selected mixtures of ethanol, toluene, and water; and the viscosity was found to increase with increasing amounts of the cosolvent.

In aquatic toxicity testing, no single test species responds appropriately to all toxicants. Therefore test batteries consisting of several individual assays are becoming more common. The species comprising a test battery should be representative of the entire system of interest. Each assay should be complementary to other components in the test battery and the test battery should not include redundant tests. We studied the selection of test battery components for the assessment of the toxicity of organic chemicals to activated sludge. The assays considered were the continuous Shk1, Microtox, Polytox, activated sludge respiration inhibition, Nitrosomonas, and Tetrahymena assays. The correlations between the toxicity data obtained from these assays were analyzed by examining the correlation matrix and by principal component analysis. These statistical methods showed that the Nitrosomonas assay should be included in test batteries plus one of the remaining five assays for assessing toxicity of organic compounds to activated sludge.