Journal of Environmental Engineering

Remediation of landfill wastes, mine land wastes, and oil shale residues normally includes a cover over the waste. Nearly all currently used landfill covers (caps) employ barrier-type systems. The authors discuss innovative vegetative landfill covers that use no barriers. They consist of a layer of soil covered by native grasses to control infiltrating precipitation as follows: (1) the soil stores infiltrating water; and (2) natural evapotranspiration empties the soil water reservoir. The vegetative cover concept has been extensively verified in the field. Because they are natural, they should perform better than conventional covers over decades or centuries and they are less expensive to build and maintain. The concept has been proven and it should be widely used. The authors propose that the name evapotranspiration cover should be associated with correctly designed and constructed vegetative covers.

Sewerage involves the major portion of the cost of a wastewater system. In the design of a sewerage system the sewer line is the basic unit occurring repeatedly in the design process. Any savings during the design of this unit will affect the overall cost of the sewerage system. A survey of the literature showed that the present status of sewer line design algorithms use linear programming and dynamic programming. The linear programming, using piecewise linearization of the objective function and constraints in every cycle, requires substantial computer time. On the other hand, dynamic programming algorithms are subjected to the “curse of dimensionality,” thus requiring large amounts of computer memory. In this paper, using a dimensionally consistent resistance equation, the sewer line design problem is formulated as a minimization of the cost function subjected to tight and loose constraints. The problem is solved by iterative application of the Lagrange-multiplier method.

A fully quantitative cellular automaton (CA) biofilm model was developed. The model describes substrate and biomass as discrete particles existing and interacting in a specified physical domain. Substrate particles move by random walks, simulating molecular diffusion. Microbial particles grow attached to a surface or to other microbial particles, consume substrate particles, and duplicate if a sufficient amount of substrate is consumed. The dynamics of the system are simulated using stochastic processes that represent the occurrence of specific events, such as substrate diffusion, substrate utilization, biofilm growth, and biofilm decay and detachment. The ability of the CA model to predict substrate gradients and fluxes was evaluated by comparing model simulations to predictions from a traditional differential equations model. One and 2D CA models were evaluated. In general, CA model predictions of steady-state flux, biofilm thickness, and substrate gradients inside the biofilm fitted well the differential equations model results; the 2D model had a better agreement at high substrate concentrations. Fully quantitative CA biofilm models offer an alternative approach to simulate biofilm activity and development. Specific advantages of CA modeling include the ability to simulate growth of heterogeneous biofilms with irregular boundary conditions, and the possibility of developing computationally efficient parallel processing algorithms for the quantitative simulation of biofilms in two and three dimensions.

The development, calibration, and application of a dynamic two-dimensional mass balance model for dissolved oxygen (DO) for rivers are documented for the first time accommodating the oxygen demand associated with zebra mussels. The test system is a short (2.3 km) phytoplankton-rich section of the Seneca River, N.Y., which is believed to represent an upper bound of the impact of this exotic invader on oxygen resources because of the unusually high population densities and limited turbulent mixing that prevail. Model calibration is supported by comprehensive measurements of DO, which resolve diurnal and seasonal patterns, and various forcing conditions over a four-month period. Wide temporal variations in the areal consumption rate of DO by zebra mussels [zebra mussel oxygen demand (ZOD), g⋅m⁻²⋅day⁻¹] were determined through model calibration. These determinations are supported by closure with earlier estimates based on simple DO budget calculations, and with laboratory biomass-specific oxygen consumption rates published in the scientific literature. Values of ZOD at times (e.g., >50 g⋅m⁻²⋅day⁻¹) were an order of magnitude greater than the sediment oxygen demand associated with organically enriched deposits. The model performs well in simulating important features of the complex patterns of DO observed, including (1) DO depletion across the study section; (2) vertical DO stratification; and (3) diurnal changes. ZOD was the dominant sink for DO over the river study section; it was entirely responsible for the substantial observed DO depletion, and it was the major cause of the DO stratification during periods of low flow. A preliminary extension of the model is demonstrated to be successful in simulating the persistence of DO depletion 15 km downstream. The model is expected to have management utility for this and other phytoplankton-rich rivers that have been, or will be, invaded by zebra mussels.

The biodegradable strong transition metal chelant [S,S] stereoisomer of ethylenediamine disuccinate was investigated for its applicability for the washing extraction of heavy metals from soil, sewage sludge, and harbor sediment. Heavy metals Pb, Zn, Cu, and Cd were extracted from authentically polluted samples by means of an ex situ washing procedure at the laboratory scale. The exposure time necessary to achieve maximum metal extraction from the authentically polluted solids used in this study was longer than that reported elsewhere with solids polluted artificially in the laboratory. Required exposure time was 1 day for the extraction of Pb, 3 days for Zn, and 6 days for Cu, irrespective of solid type. Speed and extent of metal extraction were increased by facilitating mass transfer from the solids to the liquid (e.g., by lowering calcium concentration, increasing temperature, adding fatty acid soap, and most of all, by using intermittent but intense agitation). Slightly alkaline pH was necessary to eliminate the interference by iron. This pH effect as well as observed metal selectivity was explained with a speciation model. It was feasible to achieve 70–90% extraction of Zn, Pb, and Cu from all three solids tested. These extraction efficiencies were equal or superior to those obtained with the benchmark chelants, ethylenediamine tetraacetic acid and nitrilotriacetate, provided extraction time was sufficient.

Recently, microbial leaching of heavy metals from contaminated soils with indigenous iron-oxidizing microflora has been successfully applied in flask experiments. However, the long hydraulic residence time (HRT) required and the batch mode are not well suited for an industrial scale process. Therefore, this research focused on bioleaching of Zn, Cu, and Mn from a contaminated soil in the semicontinuous mode. Metal leaching experiments were carried out in an 8 L semicontinuous stirred tank reactor (SCSTR) with a soil concentration of 100 g/L, as well as in 500 mL shake flasks. It was found that bioleaching in the SCSTR entails a reduction of treatment duration (from 10 to 2 days) and an increase in the solubilization efficiency. Metal solubilization efficiency in the SCSTR was 40% for Zn, 47% for Cu, and 34% for Mn. When the volume of the soil suspension remaining in the SCSTR between transfers was small (20% instead of 50%), corresponding to a shorter HRT (2.5 days instead of 4 days), the solubilization efficiencies were reduced. The volumetric oxygen transfer coefficient and the oxygen uptake rate were calculated in the SCSTR for both HRTs tested. The dissolved oxygen concentration below which the microflora does not grow was found to be 0.2 to 0.3 mg/L, and the concentration below which oxygen is limiting was 0.8 mg/L.

This bench scale experiment investigated the mineralization of crude oil at cold temperatures. Biodegradation rates of Alberta Sweet Mix crude oil at 5°C and at ambient temperatures (21°C) were compared. The experimental design consisted of 14 soil columns. Off-gas samples for each column were analyzed every second day using a gas chromatograph to determine CO₂ production rates. The run lasted for 219 days, at which time the soil columns were sacrificed for analysis. Oil mineralization values were modeled by a number of methods, including CO₂ production determination from GC measurements and gravimetrically determined hydrocarbon loss using soxhlet extraction. The results of the experiment suggested that temperature only affected the biodegradation rates of crude oil in the initial phase of the biodegradation process. After approximately 3 months, the degradation rates of crude oil at 5°C and 21°C were similar at about 11 mg hydrocarbon/kg dry soil/day. The conclusion of this study was that significant mineralization of Alberta Sweet Mix crude oil can occur at cold temperatures.

Acidification of lactose in wastewater was conducted in four series of experiments in an upflow reactor to investigate individual effects of hydraulic retention time (HRT) (2–24 h), lactose concentration in wastewater (2–30 g COD/L), pH (4.0–6.5), and temperature (20°–60°C). Optimum acidification was found at pH 5.5 and 55°C. Acidification increased with HRT, but with the decrease of lactose concentration in wastewater. Degradation of lactose followed the Michaelis-Menten model with a maximum specific degradation rate of 4.39 g/g VSS⋅day and a half-rate concentration of 1.97 g/L. Production of volatile fatty acids, in general, favored lower lactose concentrations and higher pH, but was not sensitive to HRT and temperature. Distribution of individual volatile fatty acids/alcohols was dependent on lactose concentration, pH, and temperature, but less sensitive to HRT. Under most conditions acetate, propionate, and ethanol were the predominant products. Biogas produced under all test conditions was composed of mostly hydrogen and carbon dioxide, but no detectable methane. Sludge yield was estimated as 0.230 ± 0.021 g VSS/g COD.

The water-quality parameters influencing the performance of a UV disinfection system in the tailing region (typically apparent at doses greater than 30 mW⋅s/cm² in wastewater secondary effluents) are the inactivation rate coefficient (k) and the number of particles with associated coliform bacteria (N_p). In this research, the natural variations of k and N_p in a wastewater secondary effluent and the relative impact of filtration on reducing the variability of these two parameters was investigated. The coefficient of variation (COV) of k in the effluent of a secondary clarifier, a sand filter, and a disc filter was roughly 39% for all three effluents. The sand and disc filters reduced the COV of N_p in the secondary effluent from 112% to 63% and 68%, respectively. Thus, filtration can be used to reduce the variability in N_p to improve the long-term performance of a UV disinfection system. The type of filtration system necessary was found to be dependent on the average log reduction in N_p required to meet the discharge requirement at the wastewater treatment plant.

This study investigates the denitrification/phosphate uptake and denitrification/phosphate release characteristics among denitrifying phosphate accumulating organisms (DNPAO), denitrifier, and nondenitrifying phosphate accumulating organisms (non-DNPAO) in a biological nutrient removal process named TNCU-I, using a series of anoxic batch experiments with and without added acetate under high/low intracellular polymer conditions. The results showed 47% phosphate uptake in the anoxic tank of the TNCU-I process. Additionally, due to the combined attribution of denitrifier and DNPAO, the experiments with both added acetate and phosphate produced higher denitrification rates than experiments with only acetate added. Furthermore, DNPAO contributed 42% of the denitrification reaction. The sludge exhibited simultaneous phosphate uptake and release under anoxic conditions when acetate was added. When no acetate was added, the specific phosphate uptake rate for the high intracellular polymer level was higher than that found at the low intracellular polymer level. Moreover, the phosphate uptake rate of non-DNPAO was observed to be 2.46 times greater than that of the DNPAO. The phosphate uptake per unit polyhydroxyalkanoates (PHA) consumption $\left({\gamma }_{{\mathit{PO}}_{\mathit{4}}\mathit{/}\mathit{PHA}}\right)$ for the non-DNPAO was 1.08 times greater than that of DNPAO. Thus, this study demonstrates that the utilization efficiency of PHA by non-DNPAO is not significantly different with the utilization efficiency of PHA by DNPAO.

To determine the role of diverse groups of bacteria in the decolorization of a monoazo dye C. I. Reactive Orange 96 (RO 96), batch experiments with an anaerobic mixed culture were made using the selective inhibitors molybdate and 2-bromoethanesulfonic acid (BES). In the presence of acetate and sulfate, inhibition of sulfate reducing bacteria (SRB) by molybdate (8 mmol/L) caused a significant decrease in the decolorization rate of RO 96. Increases in the SRB inhibitor concentration (20, 38 mmol/L) led to slower decolorization of RO 96, confirming the contribution of SRB to the decolorization. Inhibition of methane producing bacteria (MPB) with BES (10, 20 mmol/L), however, did not significantly influence the decolorization, indicating that MPB took no part in the decolorization. In the presence of lactate and sulfate, SRB also contributed to the decolorization of RO 96. The mechanism of decolorization of azo dyes based on extracellular chemical reduction with sulfide was postulated. Sulfide produced via sulfate respiration by SRB chemically decolorizes azo dyes.

This study investigated the spatial distribution of biofilm extracellular polymeric substances (EPS) with depth in biofilms. Heterotrophic biofilms were grown in a rotating drum biofilm reactor fed with synthetic wastewater with a COD of 150 mg/L. Biofilm was found to be heterogeneously structured, represented not only by the spatial distribution of EPS yields but also by clearly defined aerobic/anoxic zones, increased density, decreased porosity, decreased soluble COD concentrations, and decreased viable biomass concentrations along the biofilm depth. Thicker biofilms exhibited greater soluble COD concentrations, EPS yields, and viable biomass than thinner biofilms. The net EPS yields in the biofilms are proportionally related to the amount of viable biomass present, and viable biomass loses its ability to produce EPS at the deeper sections because of its lower microbial activity resulting from lower nutrient availability. Also, it is possible that the naturally produced EPS was consumed as a substrate in the deeper layers, where more readily degradable organics were absent. The results of the spatial distribution of EPS yields gained in this paper provide helpful information to achieve a more complete description of heterogeneous biofilm structure. New biofilm models need to be developed to incorporate the EPS information to accurately reflect the heterogeneity of biofilms.

Multiple route, multiple media distributions of exposure to chlorpyrifos and diazinon and associated uncertainties are investigated using the database generated by the National Human Exposure Assessment Survey in Arizona (NHEXAS-AZ). Exposure to pesticides and associated uncertainties may be estimated using either deterministic or probabilistic methods. This paper employs probabilistic models to estimate the 90th percentile of inhalation, dietary ingestion, dermal, and nondietary ingestion exposures to chlorpyrifos and diazinon. Questions associated with the uncertainty of exposure estimates for the two pesticides are also investigated. Probabilistic models are used to formulate distributions of exposures to each of the two pesticides for several subpopulation groups. Parameter uncertainties associated with the 90th and other percentiles of population and subpopulation groups are addressed in this paper. Highly exposed subpopulations have been defined as those with route-specific 90th percentile exposure that is higher than the population 90th percentile. All subjects exposed to levels above the 90th percentile of inhalation exposure live in dwellings with carpeting covering over 50% of their floor areas. The relative uncertainty of the 90th percentile of dermal exposure is larger than corresponding uncertainties for inhalation, dietary ingestion, and nondietary exposure.