Journal of Environmental Engineering

Bench-scale reactor experiments were performed to study the dissolution of a binary naphthalene-in-nonane mixture nonaqueous phase liquid (NAPL) pool over a wide range of average pore water velocities, $v_x$ (≈0.1–60 m/day). Experimental NAPL pool dissolution flux values were determined using a steady-state mass balance approach. The experimental flux data were compared to model predictions made assuming either local equilibrium or mass-transfer limited conditions. The local equilibrium model could describe the trends in the average effluent concentration and dissolution flux with $0.1<v_x<10m/\mathrm{day}\text{,}$ but greatly overpredicted the data for $v_x>10m/\mathrm{day}\text{.}$ Data determined to be under mass-transfer limited conditions were fit to the nonequilibrium model to estimate values for an overall mass-transfer coefficient. The calculated overall mass-transfer coefficients had an average value of 0.407 m/day and showed no correlation with $v_x\text{,}$ probably due to mass-transfer resistance becoming dominated by the diffusional resistance in the NAPL. These results suggest that the nonequilibrium approach is better suited for describing high velocity $(v_x>10m/\mathrm{day})$ dissolution of multicomponent NAPL pools, and that flushing of groundwater at very high velocities may not be an effective approach for enhancing NAPL-pool dissolution flux.

${\mathrm{NO}}_x$ removal from gas streams via dielectric barrier discharges (DBDs) has been experimentally evaluated. This paper investigates the effect of injecting $C_2{H}_4$ as an additive with respect to the $\mathrm{De}-{\mathrm{NO}}_x$ chemistry and the effect of gas composition on $\mathrm{NO}/{\mathrm{NO}}_x$ removal efficiencies. Experimental results indicate that both removal efficiencies of NO and ${\mathrm{NO}}_x$ are enhanced with increasing applied voltage, gas temperature, and water vapor. Water vapor in gas streams has a distinct influence on ${\mathrm{NO}}_x$ removal by generating OH radicals to convert ${\mathrm{NO}}_2$ to form ${\mathrm{HNO}}_3\text{.}$ ${\mathrm{NO}}_x$ removal decreases with increasing oxygen content although NO removal increases with increasing oxygen content. As high as 100% of NO and 57% of ${\mathrm{NO}}_x$ are removed at 140°C for the gas stream containing $\left[\mathrm{NO}\right]:\left[C_2{H}_4\right]:\left[H_2{O}_{\left(g\right)}\right]:\left[O_2\right]:\left[N_2\right]=0.05:0.2:3.0:5.0:91.75\text{.}$ Major mechanisms for NO and ${\mathrm{NO}}_x$ removals in DBD processing with $C_2{H}_4$ as an additive are described in the text.

In this study, a pilot-scale pulse-jet baghouse is utilized to control the particulate emission of an oil-fired boiler. The operating and design parameters, such as filtration velocity, initial tank pressure, and nozzle diameter, were varied to evaluate the cleaning effect of the pulse-jet baghouse. Two different cleaning types, (1) high initial tank pressure and one bag cleaning; and (2) low initial tank pressure and two consecutive bag cleanings, are used to compare the bag-cleaning performance in this study. It is found that the cleaning effect increases with the initial tank pressure. However, the cleaning intensity (overpressure) does not increase with the nozzle diameter. There exists an optimum nozzle diameter to achieve higher cleaning intensity and a better cleaning effect. This phenomenon results from the small volume of the baghouse compartment in this study. If an industrial size baghouse was used, it suggests that a nozzle diameter larger than 13 mm and initial tank pressure greater than 2.5 kg/cm² should be adopted to achieve a higher cleaning effect. Between the two cleaning types, type 2 is found to be more effective to clean the bag and the energy consumption for compressed air is reduced significantly from type 1. Therefore, type 2 bag cleaning is suggested to be a better method to clean the baghouse.

Field, laboratory, and engineering data confirmed the efficacy of chemical reduction and air stripping as a low concentration mercury treatment concept for water containing Hg(II). The process consists of dosing the water with low levels of stannous chloride [Sn(II)] to convert the mercury to elemental mercury $\left({\mathrm{Hg}}^0\right)\text{.}$ ${\mathrm{Hg}}^0$ can easily be removed from the water by air stripping or sparging. We studied this concept for groundwater containing initial mercury concentrations of approximately 138 ng/L (0.00069 μmol/L). In undosed samples, sparging removed 0% of the initial mercury. Removal in the treated samples varied by reagent dose. Low reagent doses, with Sn:Hg stoichiometric ratios <1, showed little removal. High reagent doses, with Sn:Hg stoichiometric ratios greater than about 5 to 25, showed relatively complete removal (>94%) and yielded final mercury concentrations <10 ng/L (<0.00005 μmol/L). At intermediate doses, mercury removal was a function of the dose. A kinetic study indicated that addition of the Sn(II) reagent resulted in rapid reduction of Hg(II) to ${\mathrm{Hg}}^0\text{.}$ When combined with standard supporting engineering techniques (e.g., treating the purge air) as needed, a simple system of chemical reduction and stripping may be useful and cost effective.

A combined system composed of three sequentially arranged reactors, anaerobic-anoxic-aerobic reactors, was used to treat the wastewater generated in the tuna cookers of a fish canning factory. These wastewaters are characterized by high chemical oxygen demand (COD) and nitrogen concentrations. The anaerobic process was performed in an upflow anaerobic sludge blanket reactor operated in two steps. During Step I different influent COD concentrations were applied and organic loading rates (OLRs) up to 4 g COD/(L⋅d) were achieved. During Step II hydraulic retention time (HRT) was varied from 0.5 to 0.8 days while COD concentration in the influent was constant at 6 g COD/L. The OLRs treated were up to 15 g COD/(L⋅d). When HRTs longer than 0.8 days were used, COD removal percentages of 60% were obtained and these values decreased to 40% for a HRT of 0.5 days. The denitrification process carried out in an upflow anoxic filter was clearly influenced by the amount of carbon source supplied. When available carbon was present, the necessary COD/N ratio for complete denitrification was around 4 and denitrification percentages of 80% were obtained. The nitrification process was successful and was almost unaffected by the presence of organic carbon (0.2–0.8 g TOC/L), with ammonia removal percentages of 100%. Three recycling ratios $(R/F)$ between the denitrification and nitrification reactors were applied at 1, 2, and 2.5. The overall balance of the combined system indicated that COD and N removal percentages of 90% and up to 60%, respectively, were achieved when the $R/F$ ratio was between 2 and 2.5.

We propose a model of the development of a periphyton community in a stream under the influence of nutrients and light. Coupling the model with a nutrient transport model clarified the longitudinal distribution of both periphyton community and nutrients. The thickness of the periphyton mat, an important factor regulating nutrient exchange between the mat and overflowing water, was determined from water velocity and the periphyton biomass. We compared the results of this study with three observational data sets to overall validate our proposal: (1) a comparison of electrical conductance in two channels with different periphyton biomasses validated the model in the mass exchange between stationary and flowing water zones; (2) a comparison of the temporal variation in periphyton biomass and nutrient concentration in a once-through and a re-circulated water channel, validated the relationships among the periphyton biomass, the nutrient uptake rate, and the nutrient concentrations in the stationary water zone; and (3) a longitudinal distribution of the algal species composition of Stigeoclonium and Chamaesiphon, and the nutrient concentrations of a 140 m reach was reproduced and compared with measured data. The light intensity indirectly controlled the nutrient gradients along the stream by the periphyton biomass in the third application.

In water distribution systems containing PVC pipe manufactured in the “early era” (prior to 1977), vinyl chloride can leach into drinking water resulting in vinyl chloride concentrations exceeding the 2 μg⋅L⁻¹ maximum contaminant level. Field testing of dead-end segments of water distribution systems consisting of early-era PVC pipe was conducted to examine their initial intrapipe vinyl chloride monomer (VCM) concentrations based on a Fickian-diffusion-based leaching model. The experiments showed a wide range of VCM concentrations within early-era PVC pipe ranging from less than 50 to more than 600 mg⋅kg⁻¹. Based on the diffusion modeling approach, a protocol was designed that provides a means for utility managers to calibrate the model for specific dead-end lines. The paper delineates procedures to determine which dead ends require flushing to control vinyl chloride, examines the effects of system parameters such as temperature on vinyl chloride leaching, and provides a method to devise flush schedules and volumes. Through a properly designed, tested, and maintained flush protocol such as that developed in this research, public water systems with dead-end lines consisting of early-era PVC pipe can control vinyl chloride concentrations using either manual or automatic flush valves.

The contamination of turfgrass by bacteriophages MS-2 and PRD-1 was assessed in the field under sprinkler irrigation (SI) and subsurface drip irrigation (SDI). No contamination of turfgrass by MS-2 was observed using SDI in the summer or winter seasons. In the summer, PRD-1 was detected in low numbers in SDI turfgrass; however, at significantly lower numbers than in SI turfgrass $\left(p<0.05\right)\text{.}$ In contrast, SI turfgrass was readily contaminated with MS-2 and PRD-1 during both seasons. Column experiments showed that viral migration was greater in sandy soil than in clay soil. Descending viral transport was more pronounced than upward migration, but only significantly greater $\left(p<0.05\right)$ in sandy soil. The survival in soil of MS-2 and PRD-1 was compared with that of poliovirus 1 and enteric adenovirus 40. MS-2 showed shorter survival in comparison to the other viruses $\left(p<0.05\right)\text{.}$ The results obtained in this study suggest that SDI used to irrigate turfgrass with wastewater may effectively reduce the risk of contamination by potential viral pathogens.

Soil and groundwater contamination can pose a variety of impacts and risks to communities. Identification of management schemes with sound environmental and socio-economic efficiencies is desired. Before any decisions regarding site remediation actions can be made, three major questions may have to be answered. They are namely “What happened underground?”, “What will happen in the future under the given remediation scenarios?”, and “Are there specific risks to the surrounding community?”. In this study, an integrated modeling and risk assessment method is developed for effectively managing petroleum-contaminated sites through technically answering the above questions. It presents an integral concept that integrates issues of multicontaminant transport simulation, biodegradation modeling, health risk assessment, and site remediation for real-world problems within a general decision support framework. The developed method is applied to a petroleum-contaminated groundwater system in western Canada for identifying cost-effective management schemes with improved environmental and socio-economic efficiencies. The research outputs are directly useful for the decision maker to gain insight into the site and to make remediation decisions.

Soil vapor extraction (SVE) has become an acceptable method of removing volatile organic compounds from soil. However, determining the length of time these systems should operate has been historically difficult. This paper presents a procedure for determining this length of operation. The procedure incorporates principles of uncertainty analysis, contaminant transport, and decision theory. An example is provided to illustrate the use of the procedure. Additional analysis of the results shows that a simple calculation can be made that will determine if a SVE system that has been operating for a period of time and is in the later stages of contaminant removal should continue to operate. This calculation consists of dividing the cost of treating the remaining contaminated soil with an alternative method (e.g., ex situ biological treatment) by the annual operation and maintenance cost and comparing this ratio to the inverse of the interest rate. If this ratio is less than the inverse of the interest rate the system should be shut off.

The use of a bioengineered bioluminescent bacterium (Shk1) for monitoring zinc toxicity was evaluated with samples from a municipal activated sludge wastewater treatment plant and in a bench-scale activated sludge system. Bioluminescent measurements were compared with oxygen uptake rates of activated sludge samples. In batch experiments with activated sludge, the Zn ${\mathrm{EC}}_{50}$ for Shk1 bioluminescence was 16 mg/L, while the Zn ${\mathrm{EC}}_{50}$ for activated sludge OURs was approximately 58 mg/L. In the bench-scale system, the influent Zn concentrations tested were 50 and 200 mg/L in toxic shock loads of about 4 h duration. Soluble Zn transport through the influent, aeration basin, and clarifier was able to be monitored by the decrease in Shk1 bioluminescence. However, bioluminescence in samples from the aeration basin decreased faster than activated sludge specific oxygen uptake rates. Differences in responses of Shk1 and the activated sludge community may be due to differences in the assay conditions, the growth forms, physiology of the organisms, or previous cultivation conditions.