Journal of Environmental Engineering

A dynamic model was developed to predict activated-sludge aeration basin temperature. The model accounts for hourly or more frequent changes in weather conditions and input parameters such as wastewater temperature, aeration, and biological reaction. The model was verified using data from full-scale treatment plants located across the United States. The various heat transfer terms are evaluated, and the relative contribution from each is shown. Evaporation from aeration can be a major component. Surface aerators cool the basin much more than diffused aeration systems. Diffused aeration systems are preferred for cold climates. The heat of biological reaction is small, except for very high rate processes. The effect of changing weather conditions, such as a cold front, can be predicted. Local relative humidity has a major impact on cooling. The impact of design changes, such as covering an aeration basin, insulating walls, or changing retention times, can be determined using the developed model.

Measuring the sediment oxygen demand rate in deep water can be difficult. Yet this parameter can be a significant component in ecological models of deep water systems. The results of a study to characterize the oxygen demand in the benthos of more than 210 km (130 mi) of the Tennessee-Tombigbee Waterway are presented here. Sampling was performed with a modified Shelby tube apparatus, which allowed the collection of samples at depths of more than 7 m (25 ft) without the use of divers. Results of in-situ analyses performed by the U.S. Environmental Protection Agency (EPA) are correlated with data from a sampling and laboratory methodology developed for this project. The laboratory setup used a sealed, cylindrical chamber through which water was continuously recirculated. The results of both procedures were statistically equivalent throughout the majority of the waterway. Only in areas where the channel bottom consisted of extremely porous media did the sampling and laboratory methodology yield questionable results. The results obtained indicate that sediment oxygen demand of the section of the waterway studied ranged between 0.5 g O ₂ /m ² -day and 1.5 g O ₂ /m ² -day.

A simple time series describing nitrate-nitrogen concentrations percolating from a sludge-amended forest is presented for the case where applications are made at several-year intervals. The time series converges to a quasi–steady-state solution that can be solved for an application rate limited by percolating nitrate-nitrogen concentrations. A chance constraint incorporates uncertainty associated with precipitation and evapotranspiration, the most important factors in determining the excess water available for leaching. Design loading rates for eight New York state forest regions are discussed. If applications occur at 3-year intervals, rates range from 0.2 to 5.3 Mg/ha dry weight depending on the design confidence level, local excess water patterns, forest nitrogen uptake, sludge type, and atmospheric nitrogen deposition rates. Results are compared to predictions made with FORSENTO, a comprehensive model for simulating sludge applications to northern hardwood forests. FORSENTO simulations suggest that mature hardwoods need only 12 kg/ha to support annually perennial material growth and that atmospheric nitrogen deposition may eventually meet or exceed needs of trees so that landspreading may not be sustainable indefinitely in some areas.

In metropolitan areas and highly populated cities the volume of sludge produced by wastewater treatment plants is enormously high. Incineration of sludge is a common practice to reduce its volume, through a burning process that converts it into ash. Still, a considerable amount of ash is produced, which creates serious disposal problems. Attempts have been made to study the feasibility of using sludge ash as a substitute for a portion of fine aggregates in concrete. The results indicate that it could be possible to replace up to 30% by weight of fine aggregate by sludge ash in a concrete mix for normal practice.

Laboratory studies were conducted to determine the feasibility of injecting and mixing hydrogen peroxide (H ₂ O ₂ ) solutions into clay soils contaminated with trichloroethylene (TCE) to achieve in-situ chemical oxidation. Bench-scale slurry studies were conducted first using 0.3 L slurry reactors and TCE concentrations in the 1.9 to 34 mg/kg range. TCE reductions as high as 98% of the initial concentration were achieved with a H ₂ O ₂ dose of 28 g H ₂ O ₂ /kg soil. TCE degradation increased with increasing hydrogen peroxide strength and appeared independent of the initial TCE concentration. Column studies were conducted with an apparatus fabricated to simulate in-situ mixing and chemical oxidant injection. Stainless steel columns 20 cm in diameter and 23 cm long, which were packed with clay soil, were mixed with an auger blade while H ₂ O ₂ solutions were injected through orifices at the back of the mixing blade. The H ₂ O ₂ doses for the column studies were 1.2 and 2.5 g H ₂ O ₂ /kg soil, based on an injection concentration of 5% weight H ₂ O ₂ at volumetric additions of 5% and 10% of the soil volume treated. TCE reductions of 88% and 75% were achieved at the two dosing rates. Based on the results of these laboratory studies, in-situ chemical oxidation of contaminated soils appears to be a viable soil remediation technique that is dependent on the efficient delivery and distribution of H ₂ O ₂ throughout the region to be treated.

The binding behaviors of five metals (cadmium, copper, nickel, lead, and zinc), individually at pH 6 and collectively at pHs 6 and 3, to deoxycholic acid (DCA) and taurocholic acid (TCA) were compared with those of sodium dodecyl sulfate (SDS) using a continuous diafiltration method. DCA and SDS have been successfully applied in micellar-enhanced ultrafiltration (MEUF) for metal removal from water. In this study, SDS exhibits the strongest binding in the single-component experiments while DCA binds the most in the multicomponent trials. TCA does not show any significant binding compared with DCA and SDS. Overall the molar binding ratios of the mixture at pH 3 were well below those of the other two solutions. This diafiltration technique quantifies the binding characteristics of a surfactant by generating sorption isotherms and determining the intrinsic association constants with corresponding number of binding sites. These parameters can be useful in designing an efficient MEUF system.

Granular activated carbon (GAC) columns that were used for Pb removal were regenerated using several regeneration schemes. Acid type (HCl and HNO ₃ ), regenerant concentration (0.1 N or 1 N), acid reuse, and a NaOH-only rinse were studied. Column performance was assessed using the Pb surface loading (X/M) at exhaustion, and the number of bed volumes (BVs) treated at breakthrough and exhaustion. The type of acid used did not affect column performance. Increasing the regenerant concentrations from 0.1 N to 1 N increased the surface loading at exhaustion and the BVs treated at breakthrough by 20% and 25%, respectively. Acid reuse did not significantly affect column performance, although desorption efficiencies decreased with the run number. The insensitivity of Pb removal to desorption efficiency indicates that the dominant removal mechanism is precipitation on the carbon surface or in the carbon pore, not adsorption. All measures of column performance deteriorated slightly when base-only regeneration was employed. However, column performance for the 1 N NaOH experiments were similar to the 0.1 N HCl-0.1 N NaOH studies.

A land-farming project to remove diesel fuel from soil, which showed extremely variable total-petroleum-hydrocarbon (TPH) concentrations, is presented. Experiments showed that the variability was not an artifact of the TPH analytical method, but reflected the random distribution of contaminant in the soil. It was found that the data were well fit by a lognormal distribution. The implications of the sampling statistics on the remediation standard are discussed using the data, the lognormal distribution, and the remediation standard imposed on this particular remediation project.

A two-dimensional (2D) theoretical analysis of the dissolved-oxygen (DO) concentration in rectangular channels is performed. It was assumed that the dissolved-oxygen concentration was affected by constant longitudinal advection, constant transverse diffusion, consumption by dissolved biochemical oxygen demand (BOD) and reaeration. The solution obtained presents the same behavior as conservative constituents and first-order decay constituents when expressed in the nondimensional form given by the ratio between the concentration and the cross-sectional concentration for the corresponding cross section. An order-of-magnitude analysis of the constants involved suggests that the location of maximum DO deficit for a bank discharge occurs in a region of the channel where the dissolved oxygen is almost completely mixed across the transverse direction. In this case, both one-dimensional (1D) and 2D dissolved oxygen models yield similar values for the location and value of the critical DO deficit. This solution may be useful as a first estimate of what happens in real situations as well as to provide a way to assess the performance of algorithms that numerically solve the DO transport equation.