Journal of Environmental Engineering

The single-collector removal efficiency based on the colloidal filtration model is widely used to quantify deposition of nanoparticles in porous media filtration. The validity of this theory for nanoparticles, especially at filtration rates used in water treatment, was evaluated. Granular media filtration experiments were performed under widely variant physical conditions. Chemical effects were minimized by selecting spherical branched polyethylenimine-capped silver nanoparticles as a positively charged nanoparticle to avoid electrostatic repulsion with the negatively charged silica filter media. The model and experimental results agreed well for 50- and 100-nm particles, but 10-nm particles were removed to a lesser extent than the model predicted. An updated Derjaguin–Landau–Verwey–Overbeek calculation was performed for the interaction energy between polymer-capped nanoparticles and the collector surface, under constant potential, constant charge, and mixed assumptions. The effect of particle size on these calculations was dramatic, leading to far less attractive energy for the smallest particles in the mixed case, and even repulsion in the constant charge case. These revised calculations are the primary means to explain the unexpected data.

The physicochemical and biological determinants of removal efficiencies in a variety of engineered and natural processes were explored for 55 frequently encountered trace organic compounds (TOrCs) in wastewater. Weak correlations between field observations and predicted TOrC biodegradabilities led to adoption of an empirical approach to prediction of compound removal during conventional wastewater treatment. The efficiencies of TOrC removals by UV photolysis (direct and indirect), activated carbon adsorption, membrane separation (reverse osmosis or nanofiltration), and sunlight photolysis were determined under representative process conditions. Results led to heuristic guidelines for the selection of sequenced treatment processes for TOrC management. Process- and compound-specific treatment efficiencies were sensitive to TOrC physicochemical properties and matrix effects.

This study investigates the significance of key design and operating variables on the dynamics of pollutant removal in laboratory-scale stormwater constructed wetland systems. Results show that total suspended solids were effectively removed irrespective of design and operating conditions, with reductions generally in excess of 85%. However, nutrient reduction was variable, and it was influenced by the wet and dry periods (for nitrogen) and primary media used (for phosphorus). Chromium and nickel were effectively removed irrespective of the design and operating conditions. Comparable performances were also achieved for copper, cadmium, lead, and iron. Results further indicate that for most metals, the choice of wetland-to-watershed area ratio did not appear to have a significant effect on their removal except for iron. Overall, the most-effective configuration was determined to be the system that had blast-furnace slag as the primary media, and which receives regular inflow (wet conditions). Final recommendations for configuring such systems based on the findings of this study are included. These findings will further contribute to a greater understanding of the treatment performance of stormwater constructed wetlands systems.

A municipal solid waste (MSW) landfill is a major source of odorous gases, such as hydrogen sulfide (${\mathrm{H}}_2\mathrm{S}$). To remove ${\mathrm{H}}_2\mathrm{S}$, a novel technique was studied using ground granulated blast furnace slag (GGBS). Laboratory column tests and regeneration tests were carried out to evaluate GGBS effectiveness. Loess soil was amended with 0, 10, or 30% GGBS, compacted to a bulk density ($1.54\mathrm{g}/{\mathrm{cm}}^3$) in a column, and then applied with a concentration of 1,000 ppm ${\mathrm{H}}_2\mathrm{S}$ from the column bottom. Test results showed that the concentration of ${\mathrm{H}}_2\mathrm{S}$ could be reduced to below the olfactory threshold (0.02 ppm). Breakthrough of ${\mathrm{H}}_2\mathrm{S}$ took three times longer when soil with 30% GGBS was used instead of unamended soil. Soil with 30% GGBS could achieve a removal capacity of $0.584\mathrm{mg}/\mathrm{g}$. After three cycles of regeneration enabled by air ventilation, the accumulated removal capacity was $1.44\mathrm{mg}/\mathrm{g}$. The fact that GGBS-amended soil can remove ${\mathrm{H}}_2\mathrm{S}$ efficiently and can be regenerated several times makes GGBS a cost-effective and environmentally friendly soil conditioner for reducing ${\mathrm{H}}_2\mathrm{S}$ concentration.

Urban stormwater runoff can promote eutrophication by discharging excessive nitrogen loads into downstream surface waters. Conventional stormwater biofiltration systems are inefficient in removing nitrate; however, a denitrifying biofilter containing a medium that includes an electron donor can be incorporated into these systems to enhance denitrification. This study presents a novel model for denitrifying stormwater biofilters that is compatible with existing stormwater modeling software. Processes that were incorporated into the model include water mixing, wood chip dissolution, and biological denitrification. The biokinetic model includes the effect of bioavailable organic substrate and dissolved oxygen concentration on denitrification. The model was calibrated and validated using experimental data from biofiltration column studies carried out with varying storm durations, antecedent dry conditions, hydraulic loading conditions, influent nitrate concentrations, and biofilter depths. The model accurately predicted nitrate mass removal efficiencies that were within 10% of the results from the experimental data. The model was validated with a high Nash-Sutcliffe efficiency coefficient (0.80) and coefficient of determination (0.85). This denitrifying biofilter model provides a practical tool for engineers to quantify nitrate removal as a function of biofilter characteristics as opposed to assumed percent removal efficiencies. Recommendations for future research include validating the model with field data and developing a total nitrogen removal model that includes additional nitrogen transformation processes.

The nonbiodegradable pollutants and high-strength nitrogen- and sulfur-containing compounds found in the wastewater from the thin-film transistor liquid-crystal display (TFT-LCD) screen industry are difficult to degrade. An electro-Fenton procedure has been developed to increase the efficiency of the ferric reduction. The organic compounds are ionized or oxidized by direct electrolysis on the anode in the electrolytic cell of the electro-Fenton process. The effects of operating parameters such as concentrations of ${\mathrm{Fe}}^{2+}$ and ${\mathrm{H}}_2{\mathrm{O}}_2$, pH, and current density on chemical oxygen demand (COD) removal were determined. The degradation of the TFT-LCD wastewater was faster by the electro-Fenton process than the conventional Fenton process. The highest COD removal efficiency was 100% at 120 min; $\mathrm{pH}=4$; ${[\mathrm{Fe}}^{2+}]=3.5\mathrm{mM}$; ${[\mathrm{H}}_2{\mathrm{O}}_2]=285\mathrm{mM}$; and $1.5{\mathrm{A}/\mathrm{dm}}^2$ of current density. The energy cost of the electro-Fenton process for treating TFT-LCD wastewater was approximately US$0.1/L.

Drying of wood causes airborne emissions that can be reduced by recirculating all or part of the drying medium. This favors both emission control and energy efficiency, but results in a condensate that contains significant amounts of organic compounds. Drying operations have been requested by municipal regulatory bodies to clean the condensate before release. The industry has tested biological treatment of condensate from biomass dryers, but maintaining the viability of microorganisms has been a challenge. In this study, the effect of drying gas temperature and the final wood moisture content on the chemical composition and acute toxicity of the condensate was tested. Results showed that whereas the condensate from wood drying was extremely toxic to Vibrio fischeri employed in Microtox assays, the undefined mixed culture present in biosludge from a pulp and paper mill treatment plant were considerably less affected.

The physicochemical characteristics of waste activated sludge (WAS) exposed to ${}^{60}\mathrm{Co}$ gamma-ray irradiation at doses of 0 to 15 kGy were investigated. Results showed that irradiation dose significantly influenced the physicochemical properties of WAS. Static sedimentation experiment indicated that the settleability was slightly improved after irradiation. Measurement of suspended solids showed that the sludge volume decreased. A vacuum filtration test demonstrated that 1 to 4 kGy would be potentially successful for dewaterability enhancement, and irradiation and cationic polyacrylamide (CPAM) coconditioning showed desirable synergistic effects. Decreased particle size and increased turbidity of supernatant, soluble chemical oxygen demand (SCOD), and content of soluble extracellular polymeric substances (EPS) indicated that irradiation doses above 4 kGy could efficiently disintegrate sludge flocs and cells. An optimal value for the complete disintegration of sludge was not determined, because irradiation dose higher than 15 kGy was not applied in this study. Possible mechanisms of irradiation were also discussed.

The modeling and monitoring of water-quality parameters is necessary because of the ever increasing use of water resources and contamination caused by sewage disposal. This study employs two data-driven methods for modeling water-quality parameters. The methods are the least-squares support vector regression (LSSVR) and genetic programming (GP). Model inputs to the LSSVR algorithm and GP were determined using principal component analysis (PCA). The coefficients of the LSSVR were selected by sensitivity analysis employing statistical criteria. The results of the sensitivity analysis of the LSSVR showed that its accuracy depends strongly on the values of its coefficients. The value of the Nash-Sutcliffe (NS) statistic was negative for 60% of the combinations of coefficients applied in the sensitivity analysis. That is, using the mean of a time series would produce a more accurate estimate of water-quality parameters than the LSSVR method in 60% of the combinations of parameters tried. The genetic algorithm (GA) was combined with LSSVR to produce the GA-LSSVR algorithm with which to achieve improved accuracy in modeling water-quality parameters. The GA-LSSVR algorithm and the GP method were employed in modeling ${\mathrm{Na}}^{+}$, ${\mathrm{K}}^{+}$, ${\mathrm{Mg}}^{2+}$, ${\mathrm{SO}}_4^{2-}$, ${\mathrm{Cl}}^{-}$, pH, electric conductivity (EC), and total dissolved solids (TDS) in the Sefidrood River, Iran. The results indicate that the GA-LSSVR algorithm has better accuracy for modeling water-quality parameters than GP judged by the coefficient of determination ($R^2$) and the NS criterion. The NS static established, however, that the GA-LSSVR and GP methods have the capacity to model water-quality parameters accurately.

The response surface method (RSM) was used to find out the best conditions for the nitrate removal by electrocoagulation (EC) process with aluminum electrodes. The independent variables were initial nitrate concentration, reaction time, initial pH, and cell voltage. A statistical analysis of variance (ANOVA) was performed for optimization of parameters obtained from the experimental data. A quadratic model was suggested as a good model for prediction of nitrate removal efficiency. The optimum conditions were obtained at pH 10, 17 V voltage, and 68 min when the initial nitrate concentration was found to be $226\mathrm{mg}/\mathrm{L}$. At the best conditions, the nitrate removal efficiency and energy consumption were obtained as 87.95% and $144.15\mathrm{kWh}/{\mathrm{m}}^3$, respectively. In terms of nitrate removal efficiency and energy consumption, the coefficients of determinations were found to be 0.95 and 0.99, respectively. The results indicate that the initial nitrate concentration, reaction time, and cell voltage were found to be the most important parameters. The results also show good agreement between experimental data and the predicted equation.

Transport of microbubbles and nanobubbles (MNBs) in porous media has drawn increasing attention as a promising technology for soil and groundwater remediation. Understanding the transport mechanisms of MNBs in soils is essential to optimize MNB-based remediation techniques. In this study, effects of flow rates and bubble gas species on transport characteristics of MNBs were investigated in columns packed with glass beads. Microbubbles and nanobubbles were created by either air or oxygen injection to the columns at different flow rates. All results showed marked entrapment of MNBs inside the columns and relatively higher retardation of MNBs with smaller bubble size. The entrapment was enhanced for air-based MNBs under lower flow rate. A convection-dispersion model including bubble attachment could well capture the obtained effluent curves for MNB transport at high flow conditions. For low flow conditions, a model including bubble attachment-detachment and straining terms best described the data. The fitted model parameters suggested that irreversible straining is an important deposition mechanism for MNB transport in porous media.

Migration potential of metal(loids) associated with small-arms ammunition fired into range berms under dynamic loading conditions was assessed using pilot-scale and field-scale live-fire lysimeters. Experimental impact media at both scales was sand or sand plus a commercial heavy metal sorption amendment. After firing, artificial rainwater was applied weekly to the pilot-scale system; the field-scale system received natural rainfall. Leachate collected from both systems was analyzed for total suspended solids, hydrogen ion concentration, antimony, and lead. In pilot-scale lysimeters, antimony constituted 0.52% of the total bullet mass, but comprised 91.5 and 17% of the dissolved leachate metal from control and amended lysimeters, respectively. Lead constituted 52% of the total bullet mass but made up only 8.5 and 5% of the total dissolved leachate metal from the control and amended lysimeters, respectively. Use of the live-fire lysimeters under dynamic loading conditions provided support for range design recommendations. Impact areas should be constructed using pure sand (low fines) along with antimony and lead sorbing amendment(s) in order to provide maximum protection from heavy metal transport off range.