Journal of Environmental Engineering

Adsorption is modeled when powdered activated carbon (PAC) is applied in continuous-flow reactors followed by membrane filtration units operated without carbon wastage between backwash events. Four reactor configurations are studied: (1) A membrane reactor dosed with a step input of PAC; (2) a continuous-flow stirred tank reactor dosed with a step input of PAC and followed by a membrane reactor; (3) a plug-flow reactor dosed with a step input of PAC and followed by a membrane reactor; and (4) a membrane reactor dosed with a pulse input of PAC at the beginning of the filtration cycle. A steady-state operation is considered to describe the adsorption process through the continuous-flow stirred tank reactor and plug-flow reactor, whereas adsorption in the membrane reactor is modeled as a non-steady-state process. Adsorption kinetics is assumed to occur by homogeneous surface diffusion, and adsorption equilibrium is described with the Freundlich isotherm model. Analytical solutions of the homogeneous surface diffusion model with no external mass transfer limitation are used to evaluate adsorbate concentrations in the solid phase as a function of time. Part II of this study presents model simulations and verification with experimental data obtained in a bench-scale apparatus.

The models developed in the first part of this study are applied to predict the removal of 4-nitrophenol by powdered activated carbon (PAC) in a bench-scale reactor. A series of continuous-flow filtration experiments were conducted with different carbon doses to verify the modeling approach when the activated carbon was added directly to the membrane reactor, either as step or pulse input, and when the carbon was dosed as a step input to a continuous-flow stirred tank reactor followed by the membrane reactor. The models predicted well the experimental data for all cases investigated. The verified model was used to investigate the effect of various operating parameters on the efficiency of the adsorption process. This analysis included the effect of filtration time, membrane reactor volume, dosing procedure, and the effect of dosing the carbon in reactors installed in series upstream of the membrane reactor.

Dust from production of steel in an electric arc furnace (EAF) contains a mixture of elements that pose a challenge for both recovery and disposal. This paper relates the leachability of six Canadian EAF dusts in four leaching tests [distilled water, Ontario Regulation 347 Leachate Extraction Procedure, Amount Available for Leaching (AALT), and pH 5 Stat] to their mineralogy. Chromium and nickel contaminants in EAF dust are largely unleachable (<5% available in AALT and pH 5 Stat), as they are found with the predominant spinel ferrite phase in EAF dust. However, even a small proportion of oxidized chromium can result in significant leachate concentrations of highly toxic chromate. The leachability of zinc (7–50% available), lead (2–17% available), and cadmium (9–55% available) can be significant, as large fractions of these contaminants are found as chlorides and oxides. The leaching of these metals is largely controlled by pH. The acid neutralization capacity of the EAF dusts appeared to be controlled by dissolution of lime and zincite, and results from regulatory leaching tests can be misleading because the variable acid neutralization capacity of EAF dusts can lead to very different final leachate pHs (5–12.4). A more informative approach would be to evaluate the total amounts of contaminants available in the long term, and the acid neutralization capacity.

In this paper, two different pesticide transport simulation models are presented and compared to carry out preliminary analysis on the applicability of those models in determining ground-water vulnerability to aldicarb contamination. The first model is a physically based analytical model that simulates 1D pesticide movement in soils, based on the concept of complete mixing and 2D advective-dispersive transport in the aquifer. The second model is a numerical simulation model that links the existing numerical codes PRZM2, MODFLOW, and MT3D to simulate pesticide transport in the subsurface. The concentrations of aldicarb residues in soil and in the aquifer calculated by the two models are found to be in good agreement. However, the analytical model tends to produce an earlier arrival of the peak concentration in each year due to the assumption of complete mixing. It is also found that the infiltrating water following aldicarb application plays a significant role on the leaching potential of aldicarb, which is also affected by various meteorological and hydrological factors as well as by agricultural practices.

One of the toxic and refractory pollutants formed during the color removal of fertilizer, chemical, and petroleum industrial effluents by chlorine is 2-chlorophenol (2-cp). The objective of this study is to investigate the effect of H₂O₂ and Fe²⁺ dosages on the decomposition of 2-cp using a coupled ultrasound/Fe²⁺/H₂O₂ process. The extent of 2-cp decomposition and mineralization depends on the dosages of H₂O₂ and Fe²⁺. More than 99% of 2-cp was decomposed and 86% of 2-cp was mineralized using the ultrasound/Fe²⁺/H₂O₂ process at Fe²⁺ of 10 mg/L and H₂O₂ of 500 mg/L. Oxidation-reduction potential (ORP) monitoring is a useful method for determining the decomposition efficiency of the target compound. There was a slight increase in the ORP values with increasing Fe²⁺ dosages, and an apparent increase with increasing H₂O₂ dosages was observed. The major intermediate formed during the decomposition of 2-cp was 2-chloro-p-benzoquinone. It was also readily decomposed using the coupled ultrasound/Fe²⁺/H₂O₂ process.

The purpose of this study was to optimize flocculation mixing created by single grids. Double and triple biplane grids were vertically oscillated within a standard 2 L jar. The turbulent velocities were measured using a 2D laser doppler anemometer. The particle removal performance was observed based on the settled water turbidity. When a larger number of grids were applied, the same average volume velocity gradient (G) could be achieved at lower vertical grid speeds. A uniform and more gentle mixing was therefore created, producing high particle contacts and low particle breakup. The minimum settled water turbidity was also achieved at lower G values. A larger number of grids, especially of high solidity ratio, produced a wider range of G values with low settled water turbidity. These findings showed that the grid mixing performance could be optimized by applying a larger number of high solidity ratio grids. It was also found that grids, at their best arrangement, had a better performance than a standard flat blade impeller.

The dissolved organic carbon parameter has typically been used as a measure of organic content in natural water. However, dissolved organic carbon is an aggregate parameter and does not provide information on the organic character of natural organic matter in water. Natural organic matter from New Jersey surface water sources was isolated and fractionated by resin adsorption into hydrophobic acid, hydrophobic neutral, hydrophobic base, hydrophilic acid, hydrophilic neutral, and hydrophilic base. The spectral fluorescent signature technique was developed for the identification of the six dissolved organic matter (DOM) fractions through a multiple linear regression model. High sensitivity, rapid identification, and quantification of DOM fractions are among the main advantages of this technique. The technique/model has spatial and temporal potential use for the rapid qualitative and quantitative measurement of the problematic DOM fraction(s) for source water characterization/assessment and water treatment process optimization.

This paper describes the construction and application of a numerical model representing mercury transformations and bioavailability in the aquatic environment of Clear Lake, Calif. The initial application described here provides the basis for more detailed fate and transport modeling of the lake. Results show that total Hg and MeHg concentrations in the lake may be reasonably modeled as functions of sediment total Hg. Calibrated rates of methylation and benthic exchange compare favorably with rates observed in the field and at other lakes. The model suggests the importance of accurately defining a biochemically “available” fraction of total Hg, and demonstrates that even a relatively small amount of available Hg in lake sediments can account for high levels of potentially toxic methylmercury in the water and sediment bed. Indications are that Clear Lake is experiencing a net loss of Hg at a rate of less than 2%/year. At such a remediation rate, mercury concentrations in the lake would meet current water quality criteria in a little over 200 years.

A series of refinements was added to a previously completed three-dimensional eutrophication model of Chesapeake Bay. Refinements included increased grid resolution in the western tributaries and in shallow littoral areas, extension of the grid onto the continental shelf, extension of the validation period to 1985–1994, and addition of living resources. Computations of zooplankton, submerged aquatic vegetation, and benthos compared successfully with observations aggregated over annual time scales and at spatial scales on the order of 100 km².

A 2-year study was conducted on the relationships between atypical colonies (AC) from total coliform (TC) tests and other bacterial indicators of water quality in a watershed mainly impacted by agricultural and urban animals. Eight representative sites were monitored for TC, feel coliforms (FC) and coliphage (CP) concentrations. Sampling sites included those impacted by raw sewage, agricultural runoff, urban runoff, and a mixture of urban and agricultural runoff. AC were found to be composed of coliforms (about 27%), noncoliforms (37%), and Aeromonas (36%). There was a clear pattern among the atypical concentrations, fecal pollution sources, and pollution levels. Correlation analyses found the densities of AC to be well associated with the densities of FC and not well associated with total CP (R_FC = 0.796 and R_CP = 0.575, respectively). A reference index defined as the ratio of AC to CP correlated well with degree of fecal pollution known to impact the sites. Results suggest that AC from TC tests using the membrane filter method and M-Endo medium may be used as supplemental indicators in conjunction with other microbial indicators for watershed monitoring.

White phosphorus (WP) has been identified as the cause of mortality to certain species of waterfowl at Eagle River Flats, a tidal marsh in Alaska, used as an ordnance impact area by the U.S. Army. A blend of calcium bentonite/organo clays, gravel, and binding polymers was tested for effectiveness as a barrier to reduce duck foraging and mortality. Following the application of the barrier to one of two contaminated ponds, we observed greater duck foraging and higher mortality in the untreated pond and no mortality in the treated pond after a year of tidal inundations and ice effects. Emergent vegetation recovered within a year of treatment. WP levels in the barrier were less than the method limit of detection, indicating no migration of WP into the material. Barrier thickness remained relatively stable over a period of 4 years, and vegetation was found to be important in stabilizing the barrier material.

Settling tanks are hydraulically designed on a settling velocity. Observations have indicated that out-of-the-basin sediment transport may be initiated by corner vortices, which are able to scour a sediment layer and significantly reduce the efficiency of sediment deposition. Using four different materials—with densities from close to water up to sand, and diameters from 0.55 to 3.0 mm—the various forms of vortex scour were experimentally determined. The densimetric particle Froude number could be identified as the scaling quantity that governs these processes. The scour process can be reduced by inserting so-called antivortex elements, by which the 3D corner flow characteristics are influenced to result in a more 2D flow over a wall. The location and length of these elements were found to be similar to elements recently recommended for standard gates.