Journal of Environmental Engineering

In four successive studies at Jefferson City, Mo., seasonal temperature change has been observed to result in major changes in water treatment plant microbiological efficiency. The present study (1989) was directed at estimating the relative numbers of particles of potential health significance transmitted through the Jefferson City water distribution system during cold and warm water periods. In addition, the contribution of aftergrowth to the number of particles generated or recruited during distribution was estimated. Seasonal variations in turbidity, coliform, heterotrophic plate count organisms, total bacteria, planktonic bacteria, and particle-associated bacteria were observed in finished water and distribution system samples. Direct microscopic counting was used to enumerate the total number of particles larger than 3 μm, as well as algal cells, long bacterial rods, activated carbon particles, and nematodes. All measurements confirmed the dominant effect of water temperature in influencing water treatment plant process efficiencies and the number of specific particles observed in the distributed drinking water. The results indicate that water treatment plant process efficiencies should be evaluated under low temperature conditions employing analytical techniques that are sufficiently sensitive to detect the impairment of removal of particles of potential health concern.

Federal regulations restrict land application of all but “exceptional quality” biosolids (sewage sludges) to “agronomic rates.” When municipal biosolids are applied to farmland over time, soil organic nitrogen accumulates, reducing the design application rates in succeeding years. This paper describes a simple linear algorithm useful for designing agronomic rates under such non–steady-state conditions. Designs are primarily determined by biosolids nitrogen content, crop nitrogen demand, and site denitrification rates. Percolating ground water can be incorporated, but the advantages of doing so are generally modest. This paper also describes how the economic sustainability of a site can be predicted. Examples are described for a Wellsboro, Pennsylvania, cornfield and for dryland wheat in Hemet, California. Over a 20-year planning period, cumulative applications in Wellsboro ranged from 120 to 162 Mg/ha dry weight, depending on the design approach. Systems are economically sustainable for from 13 to 16 years. Hemet values ranged from 43 to 96 Mg/ha dry weight.

Small landfills are exempt from compliance with Resource Conservation and Recovery Act Subtitle D standards for liner and leachate collection. We investigate the ramifications of this exemption under western Kansas semiarid environments and explore the conditions under which naturally occurring geologic settings provide sufficient protection against ground-water contamination. The methodology we employed was to run water budget simulations using the Hydrologic Evaluation of Landfill Performance (HELP) model, and fate and transport simulations using the Multimedia Exposure Assessment Model (MULTIMED) for several western Kansas small landfill scenarios in combination with extensive sensitivity analyses. We demonstrate that requiring landfill cover, leachate collection system (LCS), and compacted soil liner will reduce leachate production by 56%, whereas requiring only a cover without LCS and liner will reduce leachate by half as much. The most vulnerable small landfills are shown to be the ones with no vegetative cover underlain by both a relatively thin vadose zone and aquifer and which overlie an aquifer characterized by cool temperatures and low hydraulic gradients. The aquifer-related physical and chemical parameters proved to be more important than vadose zone and biodegradation parameters in controlling leachate concentrations at the point of compliance.

In the design of an ultraviolet (UV) disinfection system for a wastewater treatment plant (WWTP), the number of lamps necessary to meet the permit requirements must be determined. Factors influencing the required number of lamps include the wastewater characteristics, the variability in the wastewater characteristics, and the permit requirements. In this paper, a probabilistic approach is described for designing a disinfection facility and is contrasted with the conventional, nonprobabilistic approach. The approaches are illustrated using data collected from both collimated beam and pilot-scale UV disinfection studies conducted at a major Northern California WWTP. The advantages and disadvantages of each approach are discussed along with criteria for selecting a suitable approach for a particular WWTP.

A theoretical model describing the various kinetic reactions occurring in a biological fluidized-bed reactor is presented. It covers both the unsteady and steady conditions of the process, taking into account the bulk liquid biomass activity and adopting Rittmann's (1982) shearing model. It is the result of four mass balance equations dealing with the state of the process. The state was defined by: (1) the substrate in bulk liquid medium; (2) the substrate in the biofilm; (3) the suspended microorganisms in the bulk liquid medium; and (4) the microorganisms attached to the solid media. The sensitivity of each of the four state variables to various biological parameters, and system design variables were investigated at steady-state conditions. The sensitivity analysis showed that the main factors affecting the process state variables were fluidization velocity, size of the solid media, initial bed porosity, specific yield, and a maximum rate of substrate utilization.

A one-dimensional clarifier model employing a concentration and feed velocity dependent dispersion coefficient was coupled with an algorithm for predicting sludge blanket height. The model was successfully calibrated using blanket heights; effluent suspended solids and return activated sludge concentrations; and the Vesilind parameters V₀ and b . These data were collected from one of the secondary clarifiers at a full-scale activated sludge plant. Model validity was confirmed by comparing predictions of the calibrated model against separate sets of data collected from the same clarifier. The model outperformed other well-known models in predicting clarifier overloading. Better performance of the present model can be attributed to its ability to portray, through a dependence of dispersion coefficient on feed velocity, the detrimental effect of increasing hydraulic loading (for any given applied solids flux) on clarifier performance.

Dry deposition and air sampling were undertaken, simultaneously, in the ambient air of an urban site and a petrochemical-industry (PCI) plant by using several dry deposition plates and PS-1 samplers from January to May 1994 in southern Taiwan. The dry deposition plate with a smooth surface was always pointed into the wind. Twenty-one polycyclic aromatic hydrocarbons (PAHs) were analyzed by a gas chromatography/mass spectrometer (GC/MSD). The dry deposition flux of total-PAHs in urban and PCI sites averaged 166 and 211 μg/m ² $\dot{s}$d, respectively. In general, the PAH dry deposition flux increased with increases in the PAH concentration in the ambient air. The PAH pattern of dry deposition flux in both urban and PCI sites were similar to the pattern measured by the filter of the PS-1 sampler and completely different from the PAH pattern in the gas phase. The higher molecular weight PAHs have higher dry deposition velocities. This is due to the fact that higher molecular weight PAHs primarily associated with the particle phase are deposited mostly by gravitational settling, while the gas phase PAHs are deposited mainly by diffusion. The dry deposition velocities due to gravitational settling are much higher than those due to diffusion. When the dry-deposition-velocity ranges of gas phase PAHs were between 0.001 and 0.010 cm/s, only the lower molecular-weight PAHs—Nap and AcPy—had a significant fraction of dry deposition flux contributed by the gas phase. All the remaining higher molecular-weight PAHs had more than 94.5% of their dry deposition flux resulting from the particle phase. This is due to the fact that higher molecular weight PAHs have a greater fraction in the particle phase and the dry deposition velocities of particulates are much higher than those of the gas phase.

Steady-state models of biological degradation, representative of situations found in the treatment of difficult to degrade wastes, are studied in conjunction with chemical pretreatment. Multiple reactor configurations and inhibitory biological kinetic regimes are utilized to study a reaction network where a nonbiodegradable compound is chemically oxidized to yield biodegradable intermediates. The simulations show that the combined reactor system can achieve higher mineralization efficiencies than either reactor alone and demonstrate specific cases and operating regions where enhancement of mineralization occurs. Optimal operating regions are identified under given design constraints. Overall efficiency and achievement of process treatment objectives are functions of the waste characteristics, kinetic regimes present, and the reactor configurations used. A key element in effectively mineralizing the waste is operation in regions not subject to biomass washout. Pretreatment of inhibitory compounds in the chemical reactor or biomass recycling can stabilize the bioculture and lead to increased mineralization and a broader range of high-conversion operating regions.

Immiscible liquids when spilled into the ground or leaked from underground storage tanks tend to remain trapped in the form of discrete ganglia due to strong capillary forces. These ganglia often have low solubility in water and may remain in the subsurface over long periods of time creating a continuous source of pollution. Previous studies, which were exploratory in nature, showed that creation of localized vibrations could recover high percentages of trapped ganglia. In this paper, the mechanisms involved in the vibratory destabilization of ganglia are analyzed using results from two sets of experimental studies. It is postulated that, when vibrations result in compaction of sands, viscous pressures tend to destabilize the ganglia by splitting them whereas buoyancy pressures increase the maximum sustainable lengths. The roles of viscous and buoyancy pressures are reversed when vibrations result in increased porosities due to expansion (dilation) of soil. The volumes of trapped ganglia recovered during the experiments are consistent with these postulates. Experimental results also indicate significant recoveries in the cases where the ganglia are supposed to remain stable. These recoveries are attributed to the transient particle rearrangement during vibrations, which is concluded to be an important mechanism.

For the estimation of moments from pulse-tracer experiments, prior workers have used trapezoidal rule integration as well as a generalized moment of inertia approach. In this technical note, these two methods are compared, and it is shown that the latter method produces biased estimators of the mean, particularly the variance of the residence time distribution, while the trapezoidal rule is substantially less biased under usual conditions. Therefore, the trapezoidal rule should be applied for the analysis of such data.