Journal of Environmental Engineering

A modified version of the electro-Fenton process was evaluated for the degradation of phenol in an aqueous solution with bipolar graphite electrodes and activated carbon. The effects on reaction parameters including the pH value of the solution, the dosage of ferrous ion, and the current density within the solution on the removal of phenol and ${\mathrm{COD}}_{\mathrm{Cr}}$ at various reaction times were evaluated for the treatment of wastewater containing phenol of $100\mathrm{mg}/\mathrm{L}$ and granular activated carbon (GAC) of $333\mathrm{g}/\mathrm{L}$ at $25\pm 1°\mathrm{C}$. Removal mechanisms were also investigated by analyzing intermediate products by using high performance liquid chromatography (HPLC) and Gas chromatography-mass spectrometry (GC-MS). Results showed that removal efficiencies of phenol and ${\mathrm{COD}}_{\mathrm{Cr}}$ were 93 and 65%, respectively at a pH of 3.0, a current density of $3.75\mathrm{mA}/{\mathrm{cm}}^2$, a dosage of ferrous ion of $0.10\mathrm{mM}$, and a reaction duration of 60 min. When the reaction time was increased to 180 min, the phenol concentration in the wastewater was below the detection limit. Phenol removal efficiency decreased significantly when ${\mathrm{Na}}_2{\mathrm{CO}}_3$, a hydroxide radical scavenger, was added in the reactor. This indicates that both electro catalytic oxidation and radical oxidation contributed to the degradation of phenol. The removal efficiency of phenol achieved 39, 65, and 93% at a reaction time of 60 min when the traditional electrolysis, the traditional electro-Fenton process, and the modified electro-Fenton process were used, respectively.

The absorption behavior of ${\mathrm{Hg}}^0$ was studied experimentally by using sodium chlorite (${\mathrm{NaClO}}_2$) as the absorbent in a bubble reactor. Primary influencing factors on the removal of ${\mathrm{Hg}}^0$ such as ${\mathrm{NaClO}}_2$ solution concentration, solution hydrogenion concentration (pH), reaction temperature, the concentration of ${\mathrm{Hg}}^0$, and other components in the flue gas, such as ${\mathrm{O}}_2$, ${\mathrm{SO}}_2$, and NO, were investigated. Approximately 65% removal of elemental mercury can be achieved under optimal experimental conditions. The removal mechanism of ${\mathrm{Hg}}^0$ was proposed by analyzing ${\mathrm{Hg}}^{2+}$ concentration in the spent absorption solution and comparing the electrode potentials between ${\mathrm{NaClO}}_2$ species and ${\mathrm{Hg}}^{2+}/{\mathrm{Hg}}^0$.

A countercurrent two-stage hybrid powdered activated carbon-submerged membrane (PAC-SM) system for atrazine removal was simulated numerically in the present work. The simulation of the system performance at different operating conditions confirms that the adsorption capacity of the powdered activated carbon (PAC) can be further utilized and a stable product water quality can be maintained in the countercurrent two-stage mode as compared with the concurrent single-stage operations. For instance, the utilization of the PAC adsorption capacity was enhanced by 28% in the countercurrent two-stage operation at a flux of $60\mathrm{L}/{\mathrm{m}}^2\mathrm{h}$, and 21% of enhancement was obtained at a flux of $100\mathrm{L}/{\mathrm{m}}^2\mathrm{h}$ by more frequent PAC replacement. Therefore, the adsorption capacity utilization is also dependent on the membrane filtration flux. Moreover, if the final effluent concentration was controlled at a higher level (e.g., $C_2^{*}=0.1$ instead of $C_2^{*}=0.05$), a further 5% of the PAC adsorption capacity can be utilized. In addition, reducing the replacement rate (RR) will make the operation similar to a system with continuous PAC dosing (pseudo-steady-state) by presenting nearly constant product water quality. This study sheds some light on the performance of a countercurrent multistage hybrid PAC-SM system for its further applications and system optimization.

The aim of this study was to develop a fundamental understanding of the association between lead (Pb) species and leachability behavior in the simulated municipal solid waste incinerator (MSWI) fly ash during the thermal treatment process. Two main factors that influence this process, temperature and the carbon content in the simulated ash, were also studied. In the sequential extraction results, the main distribution pattern of Pb in treated simulated ash was carbonate fraction with different temperatures when the carbon content was 3.5%. The chief fraction of the raw simulated ash ($\mathrm{\text{carbon content}}=0\%$) was carbonate and that of raw simulated ash when carbon content was increased was Fe-Mn oxide Electron spectroscopy for chemical analysis (ESCA) results showed that Pb (element) in treated simulated ash could increase the toxicity characteristic leaching procedure (TCLP) concentration of Pb when temperatures reached 700°C. With a temperature of 900°C, ${\mathrm{PbSiO}}_3$ was present in the treated simulated ash and reduced the TCLP concentration of Pb. A comparison of different carbon contents showed that $\mathrm{PbO}\mathrm{\text{-}}{\mathrm{SiO}}_2$-related compounds were present in the raw simulated ash and caused the distribution patterns of Pb to become stable as carbon content was increased.

Turbidity measurements at high temporal resolution from several sites within the distribution network gave a more complete record of the variability of turbidity than previously possible, showing that there are frequent movements of sediment at low concentrations. Knowledge of the availability of sediment was shown to be important to the prediction of turbidity, as the correlation of hydraulic disturbance (indicated by pressure change) alone with changes in turbidity was weak. These data sets also showed with greater confidence than previously possible that mains flushing frequently resulted in the incomplete removal of sediment. Given that knowledge of sediment availability is required to reduce uncertainty in the prediction of turbidity, measurements at high temporal and spatial resolutions were used to calculate sediment mass balances and determine sediment distribution within the study area. A net accumulation of 0.923 kg of sediment was observed within 2,482 m of the main, equivalent to $5.212\mathrm{g}{\mathrm{m}}^{-1}{\mathrm{y}}^{-1}$; it was also possible to identify the impact of hydraulic disturbance in changing sediment sinks to sources during the monitored period. In addition, the sediment fluxes gave some insight into the processes of deposition and resuspension. The former was shown to be unaffected by sediment concentration, and an increase in the latter was seen to persist for several days following a hydraulic disturbance of $<15\min$. High-resolution monitoring may be useful for improving the targeting and evaluation of current reactive maintenance strategies for reducing discoloration and may also form the basis of more proactive strategies. The latter may be possible by using sediment budgets in conjunction with operational intervention to actuate mild hydraulic disturbances to encourage sediment throughput and maintain the discoloration risk below a critical limit.

Determining the optimal location and quantity of waste bins for the collection of municipal solid wastes is challenging because it influences service coverage and public satisfaction, and is often influenced by economic and environmental constraints. This study develops a framework that applies a geographic information system for siting municipal waste bins and determines the optimum quantity of waste bins using an analytic hierarchy process. The framework was applied to a neighborhood in a developing world city (Ilorin, Nigeria). The spatial performance of specific quantities of waste bins was evaluated for social, economic, and environmental effects, as determined from $p$-median solutions using field-collected solid waste generation data and operational data for the collection vehicles. For the study site, the most optimal solution is five waste bins whose spatial location utilized their capacities and produced less comparative negative effects. The result represents a starting point for extension to larger urban areas by considering the smallest basic unit for spatial and multicriteria analysis. The approach is promising for improvement of municipal solid waste management in developing world cities.

The aim of this study is to examine the accuracy of two different artificial neural network (ANN) techniques, the multilayer perceptron (MLP) and radial basis neural network (RBNN), to estimate dissolved oxygen (DO) concentration. The ANN results are compared with multilinear regression (MLR) model. The neural network model is developed using experimental data collected from the upstream (USGS Station No: 07105530) and downstream (USGS Station No: 07106000) stations on Foundation Creek, CO. The input variables used for the ANN models are water pH, temperature, electrical conductivity, and discharge. The determination coefficient ($R^2$), mean absolute error (MAE), and root mean square error (RMSE) statistics are used for the evaluation of the applied models. The MLP and RBNN models are also compared with MLR model in estimating the DO of the downstream station by using the input parameters of the upstream station. Comparison results indicate that the RBNN model performs better than the MLP and MLR models.

Environmental conflicts of interest are important to account for when environmental policies are designed. This paper explores the quantitative connection between urban wastewater treatment, coastal eutrophication, and fish biomass in the mesotrophic Gulf of Riga (northern Europe). The probable effect on the water quality from one clearly defined abatement measure, improved urban sewage treatment, has been studied. The implementation cost and the likely effect on total fish biomass also have been assessed. Computer simulations by using the previously published model CoastMab suggested that good water quality according to the European Union (EU Marine) Strategy Framework Directive could be achieved if urban sewage treatment would be upgraded to Nordic and German standards, and not only around the Gulf of Riga but also in the whole Baltic Sea drainage basin. The Secchi depth would double according to these simulations, whereas total phosphorus and summer chlorophyll concentrations would decrease by 54% and 53%, respectively. The total fish biomass should be expected to decrease by approximately 42% if good water quality (as defined in EU directives) should be achieved. However, changes in total fish biomass also could be offset by changes in other important determinants, such as climate-related variables or fishing pressure. The study estimated that it could take approximately 20–40 years after abatement action for the trophic state in the Gulf to stabilise again. Upgrading urban sewage treatment to this extent would cost 468–1,118 million Euro per year. Treatment could have substantial positive effects on the water quality of the Gulf but could also have adverse side effects on the total fish biomass.

Understanding the size distribution of stormwater particulates and the pollutants associated with each size fraction is becoming an increasingly important aspect of stormwater management. This paper evaluates the accuracy of the Laser In Situ Scattering and Transmissometry (LISST 100x) particle analyzer and describes the adaptation of the instrument for use in urban stormwater assessment. The accuracy of the instrument was evaluated with known particle size standards of 5, 20, and 100 µm. While the mode of the size distribution corresponded with the average particle size indicated by the manufacturer, the weighted mean was 131%–141% of the average particle size of the standards. Measured concentrations of screened natural sediment ($<63\mu \mathrm{m}$) ranged from 71 to 120% of the nominal value, with a variation in replicate measurements of 3% (coefficient of variation). The pumping regime used to transport stream water to the instrument gave results that compared well with those obtained using a depth-integrated grab sampler. Bubbles in the pumped samples, which could be interpreted by the instrument as particles, were reduced using a modified filter device. Transmission of the laser through the samples was greatly improved using a reduced-volume flow-through cell. Field results using the adapted technique compared well with those obtained with a laboratory Coulter Counter, with a median relative percent difference between the two techniques of 8% for the silt and clay fraction and 20% for very fine and fine sands. With application of protocols outlined in this study, the LISST provides a new tool for continuous in situ analysis of stormwater particulates.

The purpose of this project was to characterize runoff and pollutant export from three commercial sites: one with no storm water control measures (NoTreat), one with a wet detention basin (WetBasin), and one with low impact development (LID) measures. The sites were located in the Piedmont and Coastal Plain physiographic regions of central North Carolina. Rainfall, runoff, and pollutant concentrations were monitored at each site for more than one year by using automated rain gauges and samplers. The storm event mean concentrations (EMCs) of total kjeldahl nitrogen (TKN), nitrate+nitrite nitrogen (${\mathrm{NO}}_x\mathrm{\text{-}}\mathrm{N}$), and total phosphorus (TP) in runoff were generally less than corresponding EMCs for many other urban areas in the United States. Also, EMCs were similar to those found for eight parking lots in North Carolina. Storm runoff to rainfall ratio was greatest for the NoTreat site and least for the WetBasin site, which was anticipated because the NoTreat site had no detention/storage and the WetBasin site had the greatest detention/storage. Export of TKN, ammonia nitrogen (${\mathrm{NH}}_3\mathrm{\text{-}}\mathrm{N}$), TP, and total suspended solids (TSS) was lowest for the LID site, whereas export of ${\mathrm{NO}}_x\mathrm{\text{-}}\mathrm{N}$ and TN was lowest for the WetBasin site. Although by no means definitive, the monitoring data indicated that the LID site with its multiple LID measures was more effective at reducing export for most pollutants than the WetBasin site with its wet detention basin.

Two infiltrating low-impact development (LID) practices configured in-series, pervious concrete and bioretention (PC-B), were monitored for 17 months to examine the hydrologic and water quality response of this LID treatment train design. For the first LID practice, 0.53 ha of pervious concrete was installed to treat direct rainfall and run-on from 0.36 ha of asphalt parking lot. The pervious concrete was installed over a gravel subsurface storage basin, which was designed to store 25 mm (1 in.) of runoff from the parking lot before draining into the second LID practice, which was a 0.05 ha bioretention cell. The bioretention cell was conventionally drained, had a media depth of 0.5 m (1.6 ft), and was constructed at a location with a high water table. Outflow was only generated in 33 out of 80 monitored events, and over the course of the entire monitoring period, the total outflow volume reduction was 69%. The large outflow reduction subsequently led to high pollutant load reductions for total nitrogen (49%), total phosphorus (51%), and total suspended solids (89%). However, when the contribution of base flow was included in the calculation, the total nitrogen load discharged from the bioretention cell was 64% higher than that of the runoff load because of nitrite and nitrate, ${\mathrm{NO}}_2^{-}$ and ${\mathrm{NO}}_3^{-}$(${\mathrm{NO}}_{2,3}\mathrm{\text{-}}\mathrm{N}$), which were present in the base flow. The total nitrogen (TN) loads of runoff, storm flow (total outflow minus base flow), base flow, and outflow (total) were 7.70, 3.94, 8.69, and $12.64\mathrm{kg}/\mathrm{ha}·\mathrm{year}$, respectively. Of the $8.69\mathrm{kg}/\mathrm{ha}·\mathrm{year}$ TN in the base flow, 92% was in the form of ${\mathrm{NO}}_{2,3}\mathrm{\text{-}}\mathrm{N}$. This study demonstrated the hydrologic benefits (peak flow and outflow reduction) gained by having two infiltration LID practices in-series. When compared with a single treatment practice (bioretention) that was monitored at the same site, the two LID practices in-series treated an additional 10% of annual runoff volume, discharged approximately one-half as much outflow volume, and discharged significantly lower peak outflow rates. However, the water quality results were not as promising because of the influx of groundwater in the bioretention cell and the lack of denitrifying conditions in either the bioretention cell or pervious concrete system. This study also quantified increased TN and ${\mathrm{NO}}_{2,3}\mathrm{\text{-}}\mathrm{N}$ export to surface waters from a bioretention cell that was situated in an area with a high water table.

Bioretention is one of the most commonly used stormwater control measures (SCMs) in North America and Australasia. However, current design is not targeted to regulatory need, often reflecting an outdated understanding of how and why bioretention works. The purpose of this manuscript is to synthesize research to recommend a suite of design standards focused on the purpose of bioretention SCM. Both hydrologic (peak flow mitigation, infiltration, annual hydrology, and stream stability) and water quality [total suspended solids (TSS) and particulates, pathogen-indicator species, metals, hydrocarbons, phosphorus, nitrogen, and temperature] regulatory and stream ecology needs are addressed. Bioretention cells designed to meet a prioritized subset of those measures would be substantially different than cells that are designed for a different subset of needs. Designers have the ability to adjust bowl volume, media composition, media depth, underdrainage configuration, and vegetation type. This study examines how each of those design parameters can be adjusted such that a “one size fits all” approach is no longer the norm.