Journal of Environmental Engineering

This study investigates the elution of trichloroethylene (TCE), tetrachloroethylene (PCE), and 1,1,1‐trichloroethane (TCA) from a sandy soil in a soil column system. Each chemical is applied to one of three soil columns. A fourth soil column serves as a control. Chemicals are applied to the soil in a nonaqueous form to simulate an accidental spill or discharge. The chemicals are then eluted from the soil with water, which was applied intermittently over a 68‐day period. The three chemicals investigated in this study achieve a 1% breakthrough in the following order: (1) TCE; (2) TCA; and (3) PCE. In terms of overall elution from the soil, the percentage of TCE leached through the soil (20.4%) is greater than the percentage for TCA (10.7%) and PCE (2.3%). The sequence and rate of elution of the three chemicals agrees best with predictions based on the octanol‐water distribution coefficient and the Henry's constant of each chemical. Volitalization of the chemicals has a major impact of the overall elution patterns of the chemicals.

The precision and accuracy of estimating the oil and grease content of petroleum‐contaminated soil using acidification, followed by Soxhlet extraction with trichlorotrifluoroethane (freon) and methylene chloride, are compared. Stock oil‐soil mixtures prepared with vegetable oil, no. 2 and no. 6 fuel oil, SAE 30 nondetergent motor oil, and an oily petroleum waste are analyzed. The analytical results obtained using freon are more precise. Using freon, the coefficient of variation for all oil‐soil mixtures analyzed never exceeds 4%, compared to 9% when methylene chloride was used as the solvent. Percent recovery varies with oil type, with freon providing more accurate estimates of vegetable oil and no. 2 fuel‐oil concentrations, and methylene chloride giving a more accurate estimate of no. 6 fuel‐oil concentration. Recoveries slightly exceed 100% for both motor oil using freon and the oily petroleum waste using methylene chloride. The results suggest that either freon or methylene chloride can be used to provide reasonably precise and accurate estimates of the oil and grease content of contaminated soils.

Electrical energy consumption was documented for five wastewater treatment facilities with average flows of less than $0.2m^3/s\text{.}$ Three of the plants employed activated sludge, one used trickling filter/solids contact, and one had parallel activated‐sludge and trickling‐filter trains. All digested sludge aerobically. Most of the larger motors at the facilities (5 kW or more) were operated within a load range giving optimum efficiency. Smaller motors were generally operated in very inefficient load ranges. Aeration for secondary processes or (aerobic) sludge digestion was the greatest single consumer of electrical energy, accounting for 49–97% of total plant requirements. Unit energy consumption at the facilities ranged from 0.39 to $1.17\mathrm{kWh}/m^3$ of wastewater treated, and from 3.7 to 7.2 kWh/kg ${\mathrm{BOD}}_5$ removed. This parameter varied inversely with the percentage of design capacity at which the plants were operated. The peaking factor for electrical demand ranged from 1.2–1.9.

A method for determining chemical dosing based on multiple regression analysis is presented. Due to smaller operating budgets, small plants often lack the full‐time laboratory technicians and testing equipment necessary to assess rapidly changing influent conditions. Therefore, this method is particularly applicable to small treatment utilities. It was found that alum and prelime dosage levels can be predicted from correlations with dosage levels of other chemicals in the treatment operation, physical parameters describing the influent conditions, and previous values of the dosage. From the confidence limits of the predicted dosage, it is also possible to assign dosage levels based upon the risk of underdosing. A comparison with the effectiveness of streaming current detectors indicates several influent conditions under which the regression approach may be more appropriate. By basing treatment decisions on statistical models of previous successful treatment operation, plant efficiency will be maximized—resulting in fewer plant upsets and more consistent water quality.

The homogeneous surface diffusion model (HSDM) has been used extensively to model the dynamics of adsorption of organic compounds onto porous media in natural and engineered systems. A modified finite‐difference solution to the HSDM is developed in this paper for multicomponent adsorption in fixed beds. The primary difference between the algorithm presented here and that advanced previously is the alternate selection and structuring of the adsorbent particle boundary conditions. The resulting numerical solution addresses the problems of limited stability and computational inefficiency of the original finite‐difference scheme as illustrated in one‐, two‐, and five‐component sample simulations. Comparative sensitivity testing with respect to space and time‐step sizes also demonstrates a more clearly defined convergence for the modified solution. The computational speed and ease with which the algorithm can be adapted to a personal‐computer code also make it an attractive option alongside more sophisticated, though powerful, numerical techniques such as orthogonal collocation.

Limestone contactors can mitigate corrosion in small water‐supply systems that use dilute, acidic water. As water is transported through a packed bed of crushed limestone, ${\mathrm{CaCO}}_3$ dissolves and the pH, calcium‐ion concentration, and alkalinity increase. Operation of a contactor can be effectively modeled by considering the rate of dissolution and interfacial transport of calcium ions. The steady‐state model developed and tested in this study relates the depth of limestone required in the contactor to the desired effluent water chemistry, influent water chemistry, limestone‐particle size and shape, bed porosity, water temperature, and superficial velocity. The magnitude of the rate constant that describes the release of calcium ions from the calcite surface varies with the pH at the particle surface. When this pH is less than about 9.5, the rate constant for the surface reaction becomes large, and the rate of dissolution tends to be controlled solely by the transport of calcium ions away from the interface.

Kinetics of manganese(II) oxidation with chlorine as well as the effects of chlorine dose and the presence of complexing agents are evaluated. Mn(II) oxidation is facilitated by excess chlorine at $\mathrm{pH}=8\text{.}$ An autocatalytic model analogous to that for Mn(II) oxidation by $O_2$ is developed in which the major mechanism for Mn(II) removal is heterogeneous Mn(II) adsorption onto newly precipitated ${\mathrm{MnO}}_2\text{.}$ The same model also describes the effects of pH and the external addition of ${\mathrm{MnO}}_2$ on Mn(II) removal. The model applications in water treatment and acid mine drainage control for Mn(II) removal with chlorine are discussed. Mn(II) oxygenation in the presence of equimolar ligand indicated the following: complete inhibition in the Mn‐ethylenediaminetetracetic acid (Mn‐EDTA) system, moderate inhibition in the Mn‐iminodiacetic acid (Mn‐IDA) system, and slight inhibition in the Mn‐glycine (Mn‐GLY) system. The degree of inhibition, similar to that previously found for Fe(II) oxidation, follows the Mn‐ligand complex affinity. However, Mn(II) removal in these systems occurs differently with chlorine as the oxidizing agent. Mn‐EDTA accelerates the reaction while both Mn‐IDA and Mn‐GLY retards the reaction. The catalytic effect of the Mn‐EDTA complex is discussed. Mn(II) oxidation kinetics in terms of complexation stability constant, ligand/Mn(II) ratio, and chlorine dose are described.

The estimation of energy content of municipal solid waste (MSW) is normally done by the use of modified Dulong equation (MDE). The MDE requires changing all MSW components to percentages of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S), which is very time-intensive effort. An easier-to-use and more practical new equation is presented, which directly uses the percentages of MSW components. The validity of the new equation is checked against MDE by utilizing MSW component data for 35 countries and 86 international cities. A linear regression coefficient (R²) of 0.97 between energy content values (Btu/lb) for the new equation and MDE indicates an excellent closeness. The new equation energy values are about 1–10% higher than the MDE values. The energy content of developing and underdeveloped countries is a half to one-third of those for the developed and highly industrialized countries. About 50–70% of the energy content of MSW is due to the paper component. The new equation offers a good tool in assessing energy content of MSW.

A simple procedure for designing large, shallow basins to ensure adequate treatment time and reduce their costs is derived and explained. It considers the cost of perimeter and internal (baffle) dikes, the cost of land, and the retention time, as affected by hydraulic efficiency. Two examples are provided. They illustrate that sometimes a designer can increase treatment (retention) time cheaper by introducing internal spur dikes or baffles to increase hydraulic efficiency than it would cost to increase the size of the basin.