Journal of Environmental Engineering

As a unit operation, filtration generally requires flow equalization and primary clarification. This study examines the separation of runoff particulate matter (PM) in a volumetric clarifying filter (VCF). The VCF is a detention/retention vault integrating filtration after sedimentation. A paved source area $\left(\mathrm{1,088}{\text{m}}^2\right)$ directly loaded the vault $\left(4.2{\text{m}}^3\right)$ with five radial filters ( $4{\text{m}}^2$ of filtration surface area). PM separation was examined for 19 runoff events through monitoring of influent and effluent granulometric fractions. During the monitoring phase no maintenance was conducted and subsequent to the 19 events a measured material balance of the sedimentation vault and the radial cartridge filters generated a 94% recovery of PM. During 5 months of monitoring and PM mass, suspended sediment concentration (SSC) was reduced from 334 to 34 mg/L (90% reduction) with effluent sediment $\left(>75\mu \text{m}\right)$ of $<3\text{mg}/\text{L}$ , settleable of 14 mg/L, suspended PM $\left(<25\mu \text{m}\right)$ of 17 mg/L as event mean concentrations; with turbidity reduced from 96 to 23 NTU (76% reduction). Based on separate PM recovery from the vault and filters, 77% of the PM separation was sedimentation in the vault and 23% as filtration. Captured particle-size distributions are heterodisperse with a $d_{50\text{m}}$ of 300 μm in the vault and a $d_{50\text{m}}$ that ranged from 34 to 63 μm with filter depth. Filter forensics indicated PM capture was nonuniform, with the bottom and middle most heavily loaded by PM as compared to the upper third of the filter. While paired testing of automatic and manual sampling produced similar median effluent SSC, automatic sampling significantly misrepresented the median influent PM as SSC $\left(p⩽\alpha =0.05\right)$ .

This study examines in situ phosphorus treatment using a combined unit operation and process, a volumetric clarifying filter (VCF). Urban rainfall-runoff transports phosphorus in dissolved and particulate phases with the latter phase distributed across the particulate matter (PM) gradation. From a clean initial condition, the VCF was monitored across 19 events without maintenance, to examine partitioning and phosphorus distribution on PM. For the monitoring period, site influent total phosphorus (TP) is 0.342 mg/L of which 0.081 mg/L is dissolved; and subsequently reduced to 0.095 and 0.031 mg/L, respectively, by the VCF. PM-bound phosphorus is categorized as suspended, settleable and sediment fractions based on PM size and separation behavior. Site influent PM-based concentrations (mg/g) are 0.22 for sediment, 0.42 for settleable and 3.27 for the suspended fraction with each fraction further enriched in the VCF, based on effluent monitoring. A categorical analysis and odds ratio testing of PM-based phosphorus specific capacities (mg/g) indicate that a significant fraction of phosphorus can bind to suspended PM preferentially over settleable and sediment PM as a PM-based concentration. At the end of the event-based monitoring the inter-event change in phosphorus and nitrogen, chemistry is examined as a function of runoff storage time. Runoff retention generates nitrate reduction and ammonia $\left({\text{NH}}_3+{\text{NH}}_4^{+}\right)$ production; predominately as ammonium. Phosphorus partitioning is stable during runoff storage with a dissolved fraction between one fourth to one-third of TP. Predominant species are ${\text{H}}_2{\text{PO}}_4^{-}$ for a $\text{pH}<7$ and ${\text{HPO}}_4^{2-}$ for a $\text{pH}>7$ .

In practice, the challenge of storm-water low-impact-development (LID) design is often related to how to quantify the effectiveness of a LID layout. In this study, the watershed imperviousness was chosen as a basis to evaluate the performances of various LID designs. Often, LID designs apply cascading planes to drain the runoff flow from the upstream impervious area to the downstream pervious area. In this study, the conventional area-weighting method is revised with a pavement-area-reduction factor (PARF) to produce the effective imperviousness. PARF is employed as an incentive index to quantify the on-site runoff volume reduction and cost savings from downsized sewers. Two sets of PARF are derived: conveyance-based and storage-based LID designs. The conveyance-based LID approach is to drain runoff flows on various porous surfaces while the storage-based LID approach is to temporarily store runoff flows in an on-site basin. For a specified LID layout, the PARF provides a consistent basis to translate the infiltration and storage effects into the reduction on the area-weighted imperviousness. The nondimensional governing equation derived in this paper indicates that the PARF depends on the ratio of the soil infiltration rate to rainfall intensity, the ratio of receiving pervious area to upstream impervious area, and the on-site storm-water storage capacity. The PARF serves as a basis for the engineers, planners, and/or developers to select a LID design and also for regulatory agencies to assess meritorious credits for cost savings.

In this study, daily Escherichia coli measurements at six locations in an urban watershed in Houston, were undertaken over a period of 12 weeks, and were analyzed using time series and fractal analyses. The time series analysis revealed that the E. coli data series were nonrandom in nature and were characterized by a lack of periodicity. Shorter E. coli time series data sets (on the order of 10 days or less) exhibited a fractal structure, suggesting that micro scale time series may be fractal in nature in urban environments, a finding that has significant implications for bacteriological water quality monitoring. Although stormflow E. coli concentrations were significantly higher than baseflow levels, the range of variability in E. coli concentrations both during dry and wet weather conditions was comparable, indicating the residual impacts of rain events on bayou water quality. While other studies in the literature have shown that afternoon E. coli levels were lower than morning levels, the results from this study demonstrate the complexity of this phenomenon and its dependence on flow, turbidity, total suspended solids, temperature and the location/land use of the monitoring point (upstream or downstream and rural/urban). Spatial variability was highly correlated to land use with key differences between grassland and urban uses: urbanized sites exhibited higher overall E. coli concentrations, experienced rebound in E. coli levels during and after a rain event, exhibited no correlations between total suspended solids and E. coli, and exhibited less daily variability in bacteria concentrations.

An urban watershed in Raleigh, North Carolina, was monitored for indicator bacteria during 20 rain events. Results showed elevated levels of E. coli, enterococci, and fecal coliform. Samples were compared based on seasonality and were found to be statistically different $\left(p<0.05\right)$ , with pairwise comparisons indicating significantly lower concentrations of E. coli and fecal coliform during the winter $\left(p<0.05\right)$ . Enterococci concentrations were substantially lower in the winter and fall, but no significant differences were found between seasons during pairwise comparisons $\left(p<0.05\right)$ . Correlation analyses showed multiple significant relationships between antecedent climate parameters, flow characteristics, and indicator bacteria concentrations. More detailed multiple linear regression yielded explanatory variables related to antecedent climate conditions. Variables were generally related to temperature and moisture conditions in the atmosphere and soil. The results of this study show indicator bacteria concentrations significantly vary based on season; however, this variability can partially be explained by antecedent climate data.

This work investigates the leachability-related properties of acid tars treated with portland cement (CEM I), with the addition of high carbon fly ash (HCFA), as a novel binder for the immobilization of hydrocarbons. The leachate pH, acid neutralization capacity (ANC), and leaching of metals and sulfates from the treated acid tars were investigated. The effect of acid tar type, CEM I:HCFA ratio, and curing time on hydrocarbon leaching was also studied using factorial design experiment. ANC results show that acid tars had detrimental effect on the formation of cement hydration products. The overall results indicate that metal was not released in high concentration from the stabilized/solidified acid tars; hence their leaching is not of great environmental concern. The amount of leached sulfates was significantly lower than untreated acid tars and was attributed to ettringite formation. Factorial analyses show that all studied factors significantly affected hydrocarbon leaching. HCFA addition resulted in reduction in hydrocarbon leaching but led to an increase in sulfate leaching. This work shows that HCFA improved the immobilization of hydrocarbons and may represent an inexpensive binder for stabilization/solidification of wastes containing organic contaminants.

Groundwater from the aquifers of Birimian system in the northern and southern sections of the country was sampled for the concentrations of the major ions in the area. The objective was to determine the spatial groundwater associations which will in turn be used to infer the position of each groundwater group in the flow system. In addition, this study intended to determine the major sources of variation in the hydrochemistry and the suitability of groundwater from aquifers of the Birimian system for irrigation activities. R-mode factor and Q-mode hierarchical cluster analyses were used together with conventional graphical techniques. This study revealed four groundwater associations (clusters) representing three major groundwater types in the Birimian System: the $\text{Ca}–{\text{HCO}}_3$ water types which make up Clusters (groups) 1 and 2 members; the Na-K-Cl water types comprising cluster 3 members, and $\text{Mg}–{\text{HCO}}_3$ water types comprising Cluster 4 members. Cluster 2 has the lowest average electrical conductivity of 194 mS/m with total dissolved solids (TDS) ranging between 50 and 250 mg/L. This is the freshest groundwater type in the area and is typical of groundwater in recharge areas of the groundwater flow system. Cluster 1 members range in salinity between 50 and 500 mg/L. The highest average salinity is contained in Cluster 3, with TDS in the range of 300 to 1,000 mg/L, which is characteristic of groundwaters in discharge areas of the groundwater flow system. Members of this group are also characterized by high fluoride concentrations; average fluoride concentration in this group is 4.60 mg/L. Cluster 3 is the least desirable of the four clusters, for domestic water supply. Cluster 4 has TDS in the range of 300 and 1,000 mg/L, with low fluoride content. This study finds that the hydrochemistry of groundwater in the terrain is controlled by three major factors: silicate mineral weathering and cation exchange, carbonate mineral weathering, and chemical fertilizers from farms in the area. All the groundwater clusters have low sodium content and will not pose the sodium hazard when used for irrigation. However, as a result of high permeability indices, all but one of the Cluster 2 members plot within the class III region of the Doneen’s chart and are therefore unsuitable for irrigation on these grounds. Clusters 3 and 4 members are the best water types, while Cluster 1 members are equally distributed between Classes II and III categories.

This paper investigates the ability of olive stone to remove chromium (VI) ions from aqueous solution in a packed bed up-flow column with an internal diameter of 1.5 cm. The experiments were performed with a bed height of 15 g (13.4 cm) and a flow rate of 2 mL/min. To predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design, four kinetic models; Adams-Bohart, Thomas, Yoon-Nelson, and Dose-Response models were applied to the experimental data. All models were found suitable for describing the whole or a definite part of the dynamic behavior of the column. The simulation of the whole breakthrough curve was effective with the Dose-Response model, but the initial part of the breakthrough was best predicted by the Adams-Bohart model. On the other hand, the results indicated that, at pH values of this work, approximately 50% of Cr (VI) is biosorbed by olive stone and the other 50% is reduced to Cr (III), both processes being of equal importance. Therefore, a two-stage biosorption process was developed. The goal of these final experiments was to confirm that Cr (III) [the Cr (VI) reduction product] was also effectively sorbed by olive stone in a second column.

The present study attempts to clean up 1,2,4-trichlorobenzene (TCB) vapor of the flue gas from the laboratory-scale bubbling reactor. Experiments were carried out to examine the effects of input TCB vapor concentration, pH of reaction medium, reaction temperature, and the other experimental conditions on TCB removal efficiency. The optimum experimental conditions for removing 1,2,4-TCB are that the ratio of ${\text{NaClO}}_2/\text{NaClO}$ in complex absorbent is 2, reaction temperature is $50°\text{C}$ , and pH of reaction medium is 8. TCB removal efficiency above 90% was achieved under the optimized conditions. The reaction products were determined by gas chromatograph/mass spectrometer, as such, the reaction route was revealed, 4-methyl-1-pentanol and succinic acid are considered to be the major intermediate products.

FeCoCu/zeolite 5A was used as a catalyst for microwave catalytic desulfurization and denitrification and for microwave catalytic reduction of ${\text{SO}}_2$ and ${\text{NO}}_x$ with ammonium bicarbonate $\left({\text{NH}}_4{\text{HCO}}_3\right)$ as a reducing agent. Microwave catalytic desulfurization and denitrification efficiency attained 99.5 and 86.1%, respectively. The reaction efficiencies of microwave catalytic reduction of ${\text{SO}}_2$ and ${\text{NO}}_x$ could be up to 95.8 and 95.1% separately; the optimal microwave power and empty bed residence time on microwave catalytic reduction of ${\text{SO}}_2$ and ${\text{NO}}_x$ simultaneously are 280 W and 0.358 s, respectively. Microwave accentuates catalytic reduction treatment, and microwave addition can increase the ${\text{SO}}_2$ and ${\text{NO}}_x$ removal efficiency. The microwave catalytic ${\text{SO}}_2$ and ${\text{NO}}_x$ removal follows the Langmuir-Hinshelwood model.

Use of clayey soil has been explored in the laboratory scale experiment as a low cost adsorbent for the removal of copper from wastewater. The influence of metal ion concentration, weight of adsorbent, stirring rates, influence of temperature, pH are also evaluated and the results are fitted using adsorption isotherm models. From the experimental results it is observed that almost 90–99% copper can be removed from the solution using clay at optimized pH 5.5. Langmuir adsorption isotherm, Freundlich isotherm and Tempkin isotherm model have been used to describe the distribution of copper between the liquid and solid phases in batch studies and it has been observed that Langmuir isotherm better represents the phenomenon. From the experimental results rate constant, activation energy, Gibbs free energy, enthalpy, and entropy of the reaction are calculated to determine the mechanism of the sorption process. Thomas, Adams-Bohart, and Yoon-Nelson models are applied to the experimental data to determine the characteristic parameters of the column for process design.

Catalytic decomposition of dichlorodifluoromethane (CFC-12) in the presence of water vapor and oxygen was studied over a series of solid super acids ${\text{Mo}}_2{\text{O}}_3/{\text{ZrO}}_2$ that had different ${\text{ZrO}}_2$ content by using a fixed-bed reactor. ${\text{CO}}_2$ and ${\text{CClF}}_3$ were the main products and no CO was detected as by-product. The decomposition activity of solid super acid largely depended on the content of ${\text{ZrO}}_2$ and the calcination temperatures of ${\text{Mo}}_2{\text{O}}_3/{\text{ZrO}}_2$ . The optimal calcination temperature and content of ${\text{ZrO}}_2$ for preparing ${\text{Mo}}_2{\text{O}}_3/{\text{ZrO}}_2$ with the highest activity for catalytic decomposition of CFC-12 were $450°\text{C}$ and 20–40 wt %, respectively. Adopting a low concentration of oxygen and CFC-12 together with a high concentration of water vapor was preferable for having the high conversion efficiency of CFC-12 and the selectivity for ${\text{CO}}_2$ . The catalytic activity of ${\text{Mo}}_2{\text{O}}_3/{\text{ZrO}}_2$ remained steady for 100 h in continuous operation.

This paper discusses the modeling framework and identifies a number of parameters relevant when setting up a computational fluid dynamics simulation of a dissolved air flotation (DAF) tank. The selection of a turbulence model, the choice between performing two-dimensional (2D) or three-dimensional (3D) simulations, the effects of the design of the flow geometry and the influence of the size of the air bubbles are addressed in the paper. The two-phase flow of air and water is solved in the Eulerian-Lagrangian frame of reference. The realizable $k\text{-}\epsilon$ model with nonequilibrium wall functions is suggested as a compromise between a need to effectively resolve the flow and the cost of the simulations. There is a discussion on the conditions for which the steady-state simulations are appropriate. We demonstrate that a steady 2D model can simulate a stratified flow pattern. Our results show that 2D models require adjustments in geometry (e.g., substitution of the outlet pipes to an outlet distributed over the total width of the tank) and in the parameters governing the flow in order to account for the true 3D nature of some of the flow patterns. In addition, we show that the bubble size has a larger influence on the flow in the separation zone than in the contact zone.

Storm-water runoff has been identified as a major cause of coastal water quality degradation. Storm-water outfalls, common in many coastal towns, convey bacteria and other pollutants into the ocean and estuaries. In an effort to minimize this impact, the Town of Kure Beach, North Carolina, installed Dune Infiltration Systems (DIS) at two storm-water outfalls to receive storm-water runoff and allow infiltration beneath the beach dunes. A laboratory column experiment was performed to supplement this installation and determine the potential hydraulic and bacterial removal efficiency of the sand comprising the Kure Beach dunes. Columns constructed using sand collected at different depths of the dune were used to analyze the affect of bacteria application on infiltration and to examine the changes in bacteria removal that occur as infiltration rates are affected by bacteria-laden water application. Sand columns were loaded over a 60-day period with either bacteria-free storm water or storm water spiked with Escherichia coli. The seepage rate for the bacteria-spiked storm-water treatment was significantly lower $\left(p<0.05\right)$ than the seepage rate of the bacteria-free treatment, particularly toward the end of the study. Bacteria application likely compounds the impact of sediment clogging at the sand/storm-water interface. This study indicates the need for maintenance when implementing a DIS or similar sand filter to maintain design infiltration rates, especially if reduced infiltration rates are not planned for in the design. However, a decrease in seepage rate was correlated with a decrease in effluent bacteria concentration in the bacteria-spiked storm-water sand columns. Thus, optimization is required to provide maximum infiltration of storm-water while maintaining bacteria removal efficiency.

The effects of pollutants in runoff on the environment have forced the development of several water treatment systems with the aim of reducing this kind of pollution before its final discharge. Nevertheless, many of these systems do not behave satisfactorily and, additionally, there is a low level of confidence in the treatment performance. This paper introduces the results of research on the long-term performance of a laboratory prototype of a system for catchment, pretreatment, and treatment (SCPT) designed to deal with the polluted runoff water. Solid and oil treatment efficiency were the focus of the study. After 14 consecutive simulated rain events, the treatment efficiency levels achieved by the prototype are higher than 80% of solids and 90% of oils.

Emissions of polycyclic aromatic hydrocarbons (PAHs), elemental carbon (EC), organic carbon (OC), and size distributions of particulate matter from summer tire-concrete road interaction were studied. Based on particle size distribution, particles were categorized in three groups: (1) ${\text{PM}}_{10}\left(0.02\mathrm{\%}\right)$ ; (2) ${\text{PM}}_{10–100}\left(44.20\mathrm{\%}\right)$ ; and (3) ${\text{PM}}_{100–2,000}\left(55.78\mathrm{\%}\right)$ . The emission factor for total of four PAHs [fluoranthene, phenenthrene, pyrene, and benzo(ghi)perylene] was estimated as $378\text{ng}{\text{tire}}^{-1}{\text{km}}^{-1}$ for small cars (engine displacement $\text{volume}⩽\mathrm{1,000}{\text{cm}}^3$ ; $\text{load}⩽170\text{kg}{\text{tire}}^{-1}$ ). Out of eight PAHS analyzed in particles (all sizes), the main PAH compounds were pyrene (54%) and benzo(ghi)perylene (21%). Emission factors for EC and OC were 1.46 and $2.37\text{mg}{\text{tire}}^{-1}{\text{km}}^{-1}$ .