Journal of Environmental Engineering

Chlorinated solvents are the most prevalent organic contaminants in groundwater because of their extensive and widespread use as cleaning agents and metal degreasers, and they have become a significant threat to groundwater supplies. Groundwater contamination by chlorinated solvents has proven difficult and costly to remedy because of the physicochemical properties of the solvents. This study was conducted to examine the effectiveness of treating contaminated groundwater containing chlorinated solvents using air stripping, advanced oxidation, and activated carbon adsorption processes. The results showed that the stripping instrument could effectively transfer chlorinated solvents into the gas phase within several minutes at an airflow rate of $5.0\mathrm{L}/\min$ and a temperature of 298 K. The residual chlorinated solvents were further oxidized into harmless by-products by the subsequent ${\mathrm{O}}_3/{\mathrm{H}}_2{\mathrm{O}}_2$ process, and the off-gas generated from the previously-mentioned processes were collected and absorbed by four types of activated carbon [i.e., Shanghai coconut, Shanghai fruit, Taixi coal ($12*40$) and Taixi ZJ-15 (cylinder)]. Shanghai coconut exhibited the greatest adsorption capacity, at $0.5\mathrm{g}/\mathrm{g}$. Two types of contaminated groundwater containing chlorinated solvents from contaminated sites were successfully treated by the coupled process at bench scale with the effluent concentrations of chlorinated solvents complying with the target values standard for groundwater regulated by the Dutch Ministry of Public Housing. Overall, the study found that the proposed coupled process is a viable method for efficiently and effectively remediating shallow contaminated groundwater containing chlorinated solvents in southern China.

Electrochemical oxidation has been studied in a series of bench-scale tests as a physico-chemical oxidation technique for on-site treatment of very complex polluted groundwater containing pharmaceuticals, chlorinated solvents, volatile organic compounds present in petroleum derivatives, and inorganic salts. Two different cells were applied, one with $\mathrm{Ti}/{\mathrm{Pt}}_{90}-{\mathrm{Ir}}_{10}$ and the other with Si/boron-doped diamond anode material, representing two different classes of anode materials for organic oxidation. Chemical oxygen demand and total organic carbon analysis were used to assess performance, and the influence of changing recirculation flow and applied current density was studied. Si/boron-doped diamond exhibited the highest instantaneous current efficiency of 0.17 at $50\mathrm{mA}{\mathrm{cm}}^{-2}$, but further optimization at lower currents closer to the limiting values are needed for the process to be economically attractive. Si/boron-doped diamond exhibited a superior total organic carbon removal, resulting in full mineralization of the organic groundwater contaminants, relative to the higher degree of partial oxidation obtained by $\mathrm{Ti}/{\mathrm{Pt}}_{90}{-\mathrm{Ir}}_{10}$. Model consideration demonstrated the importance of bulk oxidation by generated oxidants using the $\mathrm{Ti}/{\mathrm{Pt}}_{90}-{\mathrm{Ir}}_{10}$ anode, in addition to the high dependence of this process on the flow conditions and applied current.

Controlled titanium dioxide (${\mathrm{TiO}}_2$) thin films were deposited on stainless steel surfaces using the flame-aerosol synthetic technique, which is a one-step coating process that does not require further calcination. Solid state characterization of the coatings was conducted by different techniques, including X-ray diffraction (XRD) spectrum, scanning electron microscope, and atomic force microscope. The coated thin films were used in a gas phase photoreactor for the partial oxidation of hydrocarbons to alcohols and ketones as an alternative production method for the highly sought oxygenates. For this purpose, the oxidation reaction of cyclohexane to form cyclohexanol and cyclohexanone was chosen as a model reaction. The effects of the film thickness, anatase-to-rutile ratio, and particle morphology on the reactivity of the catalyst were studied. Experimental results revealed that there is an optimal film thickness (between 400 and 700 nm) for the photooxidation process that gave a maximum rate of reaction. The yield and selectivity of ${\mathrm{TiO}}_2$ increased with the increase of the film thickness up to 350–400 nm. The activity decreased with a further increase in thickness. The influence of the crystallographic structure of ${\mathrm{TiO}}_2$ on the partial oxidation of cyclohexane showed that the catalyst efficiency increased almost linearly with the increase of the anatase fraction between 20 and 95%. The coating technique that formed highly porous and soft aggregated ${\mathrm{TiO}}_2$ thin films with rough morphology showed lower photoactivity than the technique that formed fine particle and transparent thin film.

The rising trend of converting conventional activated sludge processes to membrane bioreactor (MBR) processes for water reuse requires studying the start-up performance of bioreactors, during which mixed liquid suspended solids concentrations increase significantly. One conventional activated sludge MBR (CAS-MBR) and one modified Luzack-Ettinger (MLE) type MBR (MLE-MBR) with mixed liquor recirculation were evaluated for their performance on organic and nutrient removal, membrane fouling, biomass characteristics, and bacterial activities during the start-up period. The two bench-scale MBRs had identical reactor volume (7.2 L) and were operated under continuous flow conditions with no sludge wasting during the start-up operation. It took approximately 130 days for the MBR biomass concentrations to increase from initial 2,500 mg biomass $\text{chemical oxygen demand (COD)}/\mathrm{L}$ to a final concentration of $\mathrm{13,000}\mathrm{mg}\mathrm{COD}/\mathrm{L}$ with net specific biomass growth rates of $0.0125{\mathrm{day}}^{-1}$ and $0.0127{\mathrm{day}}^{-1}$ for the CAS-MBR and MLE-MBR, respectively. The total nitrogen removal efficiency of the MLE-MBR was 73%, higher than that of the CAS-MBR (44%), whereas both MBRs had excellent organic removal ($>99\%$) soon after the start-up operation. Because of sequencing anoxic and aerobic operations, the biomass of the MLE -MBR exhibited higher heterotrophic and autotrophic respiration activities and better sludge settling than that of the CAS-MBR. Furthermore, the MLE-MBR experienced less membrane fouling than the conventional MBR. Results of the start-up performance suggest alternating anoxic/aerobic MBR operations improve wastewater nutrient removal, increase bacterial activities, and reduce membrane fouling.

Batch adsorption experiments were conducted using environment-friendly prepared chelating ethylenediaminetetraacetic sodium modified polystyrene-based (PS-EDTA) resins as an adsorbent to adsorb ${\mathrm{Cd}}^{2+}$ from aqueous system in which experimental parameters were studied including solution pH, adsorbent dose, contact time, initial metal concentration and temperature. The Langmuir, Freundlich, and Dubinin-Radushkevich (DR) isotherm models were employed to analyze the experimental data among which Freundlich isotherm model was found to be suitable for ${\mathrm{Cd}}^{2+}$ adsorption. In addition, ${\mathrm{Cd}}^{2+}$ adsorption on PS-EDTA resins fitted well to the pseudo-second-order kinetic model. Intraparticle diffusion studies revealed that surface adsorption and intraparticle diffusion were both involved in the adsorption of ${\mathrm{Cd}}^{2+}$ ions. Thermodynamic parameters such as Gibbs free energy ($\Delta G°$), enthalpy change ($\Delta H°$), and entropy change ($\Delta S°$) were calculated and indicated that adsorption of ${\mathrm{Cd}}^{2+}$ ions onto PS-EDTA resins was a spontaneous and endothermic process. The effects of various salts and coexisting heavy metal ions on ${\mathrm{Cd}}^{2+}$ ions adsorption were also investigated. Moreover, the results from the sequential adsorption–desorption cycles showed that PS-EDTA resins held good reusability and this could be a potential application in the fixed-bed continuous-flow column for the removal of heavy metals.

For more than two decades, an HSPF-based watershed model has been used to simulate nutrient and sediment load delivery to the Chesapeake Bay. Over time, the watershed model has increased in complexity commensurate with the management challenges in Chesapeake Bay restoration. The increased complexity poses challenges to the standard application of HSPF for efficient operation of the model in a large-scale watershed, as well as difficulties in incorporating changes in best management practices (BMPs) and land uses over time. In response, the U.S. Environmental Protection Agency’s Chesapeake Bay Program Office developed a software solution that enhances the existing HSPF model structure. The software system, consisting of preprocessors, an external transfer module, and postprocessors, was devised to conveniently generate and update parameter files essential to operations of a large and complex watershed-modeling system and to implement land-use and non-point-source-pollution management changes on any timescale greater than or equal to daily. The developed model system is demonstrated through comparison of the hydrologic calibrations of the current Phase 5 model and the previous Phase 4.3 model at 14 stations, as well as by several key scenario runs. The results show that the combined upgrades in segmentation, input data, and functionality improved model calibration; however, simply incorporating changes in land use did not significantly improve model calibration. The developed software provides a means to represent the key forcing functions in more detail and to address issues of flexibility that are difficult to manage in traditional HSPF applications.

Remediation of a contaminated site to site-specific cleanup standard requires a good understanding of the geochemical characteristics of the site. In this study, the groundwater hydrochemical characteristics of a fuel-contaminated mine site in the Northwest Territories (Canada) was evaluated to understand the active geochemical processes and assess the groundwater quality in comparison to guidelines for the protection of freshwater aquatic life. Groundwater samples were taken from installed monitoring wells across the site and analyzed by field and laboratory methods for dissolved metals; ions; and benzene, toulene, ethylbenzene, and xylenes (BTEX) organic constituents. The results showed that the groundwater is $\mathrm{Ca}\text{-}{\mathrm{SO}}_4$ type because of ubiquitous occurrence of gypsum dissolution and carbonate weathering. The last sampling at the site showed that the BTEX constituents of interest were above the guideline limits in some locations, but other geochemical indicators showed biodegradation is occurring at the site. The inorganic parameters of interest were generally less than the limits studied with few outliers except iron, aluminum, and nickel. Iron and aluminum have background concentrations above the studied limits. This study underscores the importance of mineralogical composition of the native bedrock on groundwater geochemical processes.

As the use of constructed storm water wetlands to treat storm water runoff becomes more frequent, strategies for maintaining or increasing their pollutant removal over time must be examined. One potential strategy is plant harvesting at the water surface to remove nutrients that would otherwise be deposited back into the wetland during senescence. This technical note presents a first look at this strategy from a storm water management perspective. Vegetation was harvested from two storm water wetlands located in Smithfield and Pactolus, North Carolina, to evaluate the ability of five wetland plant species to sequester nitrogen. Biomass samples were collected from the following species of emergent vegetation: Pontederia cordata (Pickerelweed), Saururus cernuus (Lizard Tail), Scirpus cyperinus (Wool Grass), Sagittaria latifolia (Arrowhead), and Schoenoplectus tabernaemontani (Softstem Bulrush). Samples were collected immediately prior to senescence in September and October 2007 and analyzed for nitrogen content on a percent of biomass basis. At the Pactolus wetland the Pontederia cordata, Scirpus cyperinus, and Schoenoplectus tabernaemontani biomass retained significantly ($p<0.05$ ) more nitrogen than Sagittaria latifolia and Saururus cernuus. At the Smithfield wetland, Pontederia cordata and Sagittaria latifolia biomass retained significantly more nitrogen than Scirpus cyperinus and Saururus cernuus. Wetland maturity appears to have a direct relationship to harvestable nitrogen, which could explain why the relative amount of nitrogen sequestered in Scirpus cyperinus and Sagittaria latifolia varied between the two wetlands. A positive relationship existed between the density of harvested biomass and nitrogen removal for two species. To estimate the relative amount of harvestable nitrogen, a model for estimating total nitrogen loading in Coastal Plain watersheds in North Carolina was used to compare estimated inflow nitrogen mass to that which could theoretically be harvested. The harvestable N mass was greater than 20% of inflow nitrogen on an annual basis. Storm water wetland plant harvesting as a maintenance activity has potential to supplement wetland nitrogen removal.

Hydrodynamic and water quality codes have been frequently linked. These have typically been linked with both the hydrodynamic and water quality models using similar explicit time steps, but for long-term simulations implicit models are required. The water quality codes linked to these hydrodynamic codes are forced to perform their computations using the hydrodynamic time step even though utilizing the same might result in drifting of the water quality solution. This technical note presents the development and testing of an operator splitting–derived method for linking hydrodynamic and water quality codes with adaptive time stepping. The resulting method provides high-fidelity solutions that compare well with analytic solutions and lends itself for extension to various other transported quantities.

The present paper proves the uniqueness of the superposition solution regarding tracer or buoyancy for parallel multiple (plane or round) turbulent buoyant jets with positive buoyancy in general, which are discharged vertically upwards into a still environment from sources of relatively short spacing. The multiple plane buoyant jets are of infinite length, whereas the multiple round buoyant jets may form groups of any arrangement shape. The proof is based on the observation that the partial differential equation of tracer or buoyancy conservation becomes linear with respect to the mean tracer or buoyancy fluxes of single plane or round turbulent buoyant jets, which simultaneously satisfy the aforementioned equation. Alternatively, the validity of similar assumptions to the Reichardt’s hypothesis, for either plane or round turbulent buoyant jets, has been verified. Findings denote that the solution of a group of interacting buoyant jets with respect to the tracer or buoyancy fluxes can be uniquely obtained by superimposing the particular solutions corresponding to each single buoyant jet of the group. In addition, the superposition method is suitably applied to predict the profiles of the tracer or buoyancy flux above a finite two-dimensional or three-dimensional source.