Journal of Environmental Engineering

A model is developed using classical thermodynamics to characterize pore size distributions (PSDs) of materials containing micropores and mesopores. The thermal equation of equilibrium adsorption (TEEA) is used to provide thermodynamic properties and relate the relative pore filling pressure of vapors to the characteristic pore energies of the adsorbent/adsorbate system for micropore sizes. Pore characteristic energies are calculated by averaging of interaction energies between adsorbate molecules and adsorbent pore walls as well as considering adsorbate-adsorbate interactions. A modified Kelvin equation is used to characterize mesopore sizes by considering variation of the adsorbate surface tension and by excluding the adsorbed film layer for the pore size. The modified-Kelvin equation provides similar pore filling pressures as predicted by density functional theory. Combination of these models provides a complete PSD of the adsorbent for the micropores and mesopores. The resulting PSD is compared with the PSDs from Jaroniec and Choma and Horvath and Kawazoe models as well as a first-order approximation model using Polanyi theory. The major importance of this model is its basis on classical thermodynamic properties, less simplifying assumptions in its derivation compared to other methods, and ease of use.

A parametric waste-specific study was conducted to develop a more mechanistic understanding of the tubular ultrafiltration system using a surrogate metalworking (MW) fluid as a model waste stream. An average gel layer concentration of 31% oil was calculated and the gel layer concentration was determined to be independent of transmembrane pressure and cross-flow velocity. The thin-film model adequately described limiting flux data collected in this study, due to the use of discrete cross-flow velocity/MW fluid concentration experiments; thus, an improved mechanistic understanding was achieved. Mass transfer and thus the pressure-independent “limiting” permeate flux were generally comparable to values observed in a high-shear rotary UF system, for oil concentrations <26%. However, a decrease in net permeate flux was observed in the tubular ultrafiltration (UF) system at high feed oil concentrations; thus, a hybrid system (conventional tubular followed by high-shear rotary UF) is proposed for treatment applications where high concentrations are desired.

Utilization of dissolved organic matter in a 1.5 km section of a sanitary gravity concrete sewer with an inner diameter of 450 mm constructed on a slope of 0.0075 was studied. Continuous measurements of dissolved organic carbon (DOC), suspended solids, dissolved oxygen, and flow rate were performed along the sewer. About 14% of the DOC was removed in an 18-min retention time. A slower flow rate in the sewer would favor higher DOC removal efficiency because it offers a longer retention time. Oxygen was not a limiting factor as the dissolved oxygen level was at least 1 mg/L. Batch tests using raw sewage and either suspended solids or settled sediments yielded specific DOC rates of 1.3 mg and 2.6 mg DOC/mg dry wt/day for the sewage phase and sediment phase, respectively. Adenosine triphosphate content analysis of the suspended solids and sediment samples confirmed that both contained substantial amounts of active biomass. In the 1.5-km sewer system, it is estimated that 39.13 kg of DOC can be stabilized/day; the sewage phase contributes 40% while the sediment phase contributes 60%.

Bayesian belief networks are probabilistic knowledge-based expert systems that predict the probability of an event occurring or diagnose the most probable causes of specific problems. Although Bayesian belief networks calculate the probabilities of events both before and after the introduction of evidence and are particularly useful for complicated systems with nonlinear relationships between causes and effects, they have not been widely applied to wastewater treatment systems. A Bayesian belief network for diagnosing upsets in an anaerobic wastewater treatment system was developed using the anaerobic sequencing batch reactor as a model system. A new approach for determining the conditional probabilities of the states of the variables was developed using a microbial kinetics model in conjunction with Monte Carlo simulation. The completed network suggests the most probable cause of upsets to the anaerobic sequencing batch reactor and updates its suggestions as more evidence is provided. The approach used is general and may be applied to other anaerobic treatment systems.

A pilot-scale, first-stage, autothermal thermophilic aerobic digestion reactor was used to study the effect of microaerophilic conditions on sludge solids destruction, volatile fatty acids (VFA) production, and phosphorus release. For the aeration rates of 0–100 mL/min and the reactor sludge volume of 72 L, with a primary to secondary sludge ratio of 35:65, the solids destruction efficiency ranged between 19.5 and 23.8%, as measured by total suspended solids (TSS). The maximum increase in VFA concentration (483 mg/L as acetic acid) occurred at the low airflow rate of 25 mL/min. The unit VFA production ranged from 0.009 to 0.183 mg of VFA generated/mg of TSS destroyed, with the dominance of acetic acid. The milligrams of phosphorus released per milligrams of TSS destroyed was from 0.018 to 0.0312, with the maximum measured when no air (nitrogen) was supplied; but the maximum ratio of VFA to PO₄ (equal to 8.2) was measured when the air supply was at 25 mL/min.

The atmospheric reaeration prediction equation of Thackston and Krenkel was recalibrated, using additional values of the reaeration coefficient that have been measured since 1969, in addition to the original values. The recalibration corrected a tendency of the original equation to overpredict reaeration coefficients at low Froude numbers. The basic form of the equation was kept intact, but the coefficient involving the Froude number was revised. Accuracy improved in the low Froude number range by 20% and stayed about the same in the remainder of the range.

A silty loam soil treated with 1-allyl-2-thiourea as an inhibitor of autotrophic nitrification, and sulfide as an inhibitor of nitric oxide reductase in respiratory denitrification, was studied to evaluate the respective contribution of these two microbial processes to the nitric oxide (NO) flux from the soil. Soil samples were either unamended or amended with ammoniated fertilizer or biosolids from a wastewater treatment plant at an application rate of 100 lb-nitrogen/acre. Water-filled pore space and temperature were maintained within respective ranges of 22 ± 2% and 22 ± 1°C. NO fluxes from unamended, chemically fertilized, and biosolids-amended soil samples increase in that order, and autotrophic nitrification accounts for 80, 84, and 92% of the NO flux, respectively. The suggested Jousset-Peirce index Ψ, which shows the contribution of respiratory denitrification with respect to heterotrophic nitrification and chemodenitrification, decreases by a factor of 3.3 and 5.6 from unamended to chemically fertilized soil samples and from unamended to biosolids-amended soil samples, respectively. An ancillary finding reveals the dramatic sensitivity of denitrification to the presence of sulfide.

Nitric oxide (NO) in combustion flue gasses can be converted to higher oxidation states by the injection of aqueous solutions of hydrogen peroxide (H₂O₂) into the hot flue gases. The NO is oxidized to NO₂, HNO₂, and HNO₃, which can then be removed in a wet scrubber. A pilot plant system that was designed, constructed, and operated at Kennedy Space Center confirmed previous results that H₂O₂ is very effective at oxidizing NO; conversions of NO above 90% were obtained at temperatures of about 500°C (930°F) using mole ratios of H₂O₂:NO_x slightly above 1.0. The mole ratios of H₂O₂/NO_x needed to obtain high conversions of NO were significantly lower in the pilot plant that they had been in previous laboratory studies, demonstrating that this process can be an economically feasible method for NO_x control. The position of the injector and the type of atomization were very important to the efficient utilization of peroxide. When SO₂ was present in the flue gas, both NO and SO₂ were oxidized without increasing the demand for peroxide.

Laboratory experiments were completed to compare the treatment efficiency of KMnO₄ with H₂O₂ (alone or with amendments) for sand and silty clay soil contaminated with either a mixture of volatile organic compounds (VOCs) [trichloroethylene (TCE), tetrachloroethene (PCE), and 1,1,1-trichloroethane (TCA)] or semivolatile organic compounds (SVOCs) (naphthalene, phenanthrene, and pyrene). The relatively treatment effects of soil type, oxidant loading rate and dosing, and reaction period, as well as the use of surfactant or iron amendments and pH adjustment were examined using batch experiments with contaminated soil slurries. When KMnO₄ was applied to low organic carbon, acidic, or alkaline soils, at loading rates of 15–20 g/kg it was found to degrade consistently 90% or more of the alkene VOCs (TCE and PCE) and 99% of the polyaromatic SVOCs (naphthalene, pyrene, and phenanthrene). H₂O₂ was more sensitive to contaminant and soil type and VOC treatment efficiencies were somewhat lower as compared with KMnO₄ under comparable conditions, particularly with the sandy soil and even when supplemental iron was added. In clay soil, H₂O₂ with iron addition degraded over 90% of the SVOCs present compared with near zero in sandy soil, unless the pH was depressed to pH 3 and iron amendments were increased, whereby the treatment efficiency in the sandy soil was increased slightly. With both H₂O₂ and KMnO₄, treatment efficiency increased to varying degrees as the oxidant loading rate (g/kg) and reaction time (h) were increased. Multiple oxidant additions or surfactant addition were not found to have any significant effect on VOC treatment efficiency. Also, very limited TCA treatment was observed with either H₂O₂ or KMnO₄.

Six metal-contaminated soil samples were submitted to physical methods of treatment. A wet magnetic separator, Wilfley shaking table, and jig gravimetric separator were used on different soil fractions. A mineralogical model describing lead-bearing particles with and without iron oxide has been proposed. A significant part of the selected metals from each of the soil samples were removed by physical treatment. Linear regression analyses gave many relationships predicting the efficiency of the separation processes. The most useful variable to predict the magnetic process efficiency is the proportion of magnetic fraction removed. The density of fraction being removed was the most significant factor predicting the performance of the Wilfley table or the jig. The most significant variable predicting lead, copper, tin, and zinc removal was the initial metal concentration entering the process. Positive relationships between the results of the mineralogical study and the removal efficiency were found. These different relations confirm that the proposed scheme and the associated quantitative mineralogical study (identification of lead-bearing phase, carrying phase, and mean surface ratio of lead-bearing phase on total surface of lead-bearing particles) proved to be useful.

This project was conducted to evaluate the performance and leaching of controlled low strength materials (CLSM) incorporating fly ash and foundry sand. Two different CLSM (or flowable slurry) reference mixtures (equivalent to available production CLSM mixtures) were proportioned for unconfined compressive strength levels in the range of 0.3–0.7 MPa (50–100 psi), at 28 days, using two sources of ASTM Class F fly ash. For each reference mixture, other mixtures were proportioned using two sources of foundry sand (molten metal-casting mold sand) as a replacement for fly ash in the range of 30–85%. The ingredients of the slurry mixtures—fly ash, clean foundry sand, and used foundry sand—were tested for their physical and chemical properties and their leachate characteristics. Portland cement used as the primary binder was also tested for its properties. All CLSM mixtures made with and without foundry sand were evaluated for settlement, setting and hardening characteristics, compressive strength, permeability, and leachate characteristics. The leachate results of these CLSM-making materials were below the enforcement standards (ES) of the Wisconsin Department of Natural Resources (WDNR) ground-water quality standards (GWQS). They also met practically all the parameters of the drinking water standards. A number of CLSM mixtures incorporating fly ash and foundry sand are recommended for construction applications.

A 2D numerical investigation of the relationships between building height, gap distance, and wind velocity for flow in a street canyon is conducted using the computational fluid dynamics technique. The numerical scheme is first applied to a backward-facing step flow over a wide range of Reynolds numbers. Good agreement with experimental data from literature is found. It is then applied to study the flow around two rectangular buildings with various building heights, gap distances, and approaching wind velocities. Simulations show that the wind profile upstream of buildings is similar under different inflow wind velocities for a fixed building height. The maximum wind velocity in the street canyon largely depends on the configuration of the buildings. It increases dramatically when the gap-to-height ratio (G/H) of the buildings is increased from 0.75 to 1.0 but increases only mildly for G/H rising from 1.0 to 1.5. No significant increase in velocity can be found for a further increase in G/H. The flow pattern in the street canyon becomes more complex with an increasing height-to-gap ratio (H/G), particularly at low inflow velocity. Two or more stable recirculation vortices, which stack vertically in the street canyon, are found for H/G ≥ 3. For those simulations with nonidentical buildings, natural ventilation tends to be better in the case of the higher building located upstream.