Journal of Environmental Engineering

Sanitary sewer overflows (SSOs) are becoming of increasing concern as a health risk. Utilities and regulators have taken preventive measures but many overflows still occur and are not identifiable, especially in access-challenged locations. Several mathematical approaches are presented for detecting if a disruption in the system is impending or occurring based on measurements at one or more locations in the system. Time series analysis and neural networks are used as prediction tools for expected depths and flows for single measurement locations and a neural network is developed for a multiple monitor system. Control limit theory is applied in all cases for identifying significant deviations of measured values from the expected values that suggest a SSO is occurring. Data from Pima County Wastewater Management’s monitoring system are used in two case studies.

The purpose of a sanitary sewer is to carry the peak discharge at the end of the design period, and to transport suspended materials under all flow conditions to prevent deposition of solids, and hence, sewer blockages. To accomplish the latter, the liquid must provide for sufficient shear stress to suspend and transport the particles along the sewer. Published design criteria for critical shear stress in sanitary sewers vary significantly. However, the effect of biological film development on the internal pipe surface has been neglected. Experiments conducted utilizing a pilot-scale sanitary sewer installed in the Hydraulics Laboratory at the University of New Orleans, La., provide evidence that the shear stress to move particles of a given size is independent of slope and pipe diameter, but does depend on the effect of biological film on increasing the roughness coefficient. This critical shear stress, to achieve self-cleansing in sanitary sewers, was found to be in the range of $1.1–1.4\mathrm{N}∕{\mathrm{m}}^2$ , depending on the integrity of the biofilm. Based on this principle, a design procedure applicable to small-diameter PVC pipes with slopes between 0.1 and 0.5% was developed.

One-dimensional analytical mass transport models are familiar to environmental professionals because they are typically used as learning devices in undergraduate groundwater courses. The application of the models requires relatively certain knowledge of contaminant release to the saturated zone. However, release data are typically not reliably known at sites with uncontrolled contaminant releases. A mass balance approach has been developed to calculate contaminant release parameters based on site-specific groundwater concentration data. Standard numerical calibration and sensitivity analysis techniques were modified for use with the one-dimensional spreadsheet model. A groundwater concentration dataset from a Superfund site was used to evaluate three schemes for calculating the model initial concentration. The site application demonstrates how the spreadsheet model could be used for preliminary remediation system comparisons including restoration time estimating. The use of the spreadsheet model may reduce the effort associated with subsequent numerical modeling typically required for remedial design. The spreadsheet application highlights the importance of collecting physical data with groundwater concentration data.

The objective of this study was to investigate, through laboratory and numerical investigations, the effectiveness of a pulsed air sparging system for remediation of groundwater contaminated with trichloroethylene (TCE) in a sandy aquifer. In laboratory experiments, air was pulsed into TCE source zone on a daily basis in order to remediate TCE-contaminated groundwater. Most dissolved TCE was removed at the end of experiments although its concentrations fluctuated due to the air pulsing. The measured gaseous phase TCE concentration increased whereas the aqueous phase TCE concentration decreased during air sparging pulses. Experimental data were assessed by using a numerical code STOMP (subsurface transport over multiphases) with some modification based on the TCE dissolution kinetics. The unmeasured residual TCE mass was predicted through numerical simulations. Results show that aqueous concentrations for TCE are still much higher than the maximum contaminant level in spite of successful removal of 95% of residual TCE. It may imply that it would be more appropriate to apply air sparging combined with other remediation technologies such as bioremediation for remediation of TCE-contaminated groundwater.

This paper presents methodologies and demonstrates the need to couple bench-scale and intermediate tree-scale experiments, to fully understand the transport and fate of organic contaminants, specifically methyl tert butyl ether (MTBE), in mature trees. Bench-scale experiments showed MTBE to be optimally taken up by small poplar saplings with a transpiration stream concentration factor of approximately 1, little or no degradation in soils and, nearly $100\pm 20\%$ recovery in the coupled water-plant-air system, indicating no measurable phytodegradation at the bench-scale. A large $14\mathrm{ft}$ tree chamber was designed to evaluate MTBE transport and fate through intermediate-scale ( $12\mathrm{ft}$ tall) poplar trees. Abiotic MTBE volatilization tests conducted in the tree chamber showed $100\pm 20\%$ MTBE mass recovery, thereby demonstrating the integrity of the large chamber and its air monitoring technique. In contrast, replicate intermediate-scale experiments conducted with large $\left(12\mathrm{ft}\right)$ trees irrigated with a known mass of MTBE showed a deficit of MTBE mass recovery $(65\pm 20\%)$ in replicate soil-tree-air systems monitored over a 2-week period. More significantly, tert butyl alcohol (TBA), a degradation product of MTBE, was detected in increasing concentrations in leaf biomass while MTBE concentrations in leaf biomass decreased as the experiment progressed. The MTBE mass recovery deficit, coupled with the detection of increasing TBA in leaf biomass, provides preliminary evidence of MTBE degradation in mature trees.

Anaerobic pretreatment followed by aerobic posttreatment of municipal wastewater is being used more frequently. Recent investigations in this field using an anaerobic fluidized bed reactor/aerobic solids contact combination demonstrated the technical feasibility of this process. The investigation presented herein describes the use of a combined upflow anaerobic sludge bed (UASB)/aerobic solids contact system for the treatment of municipal wastewater and attempts to demonstrate the technical feasibility of using the UASB process as both a pretreatment unit and a waste activated sludge digestion system. The results indicate that the UASB reactor has a total chemical oxygen demand removal efficiency of 34%, and a total suspended solids removal efficiency of about 36%. Of the solids removed by the unit, 33% were degraded by the action of microorganisms, and 4.6% accumulated in the reactor. This low solids accumulation rate allowed operating the UASB reactor for three months without sludge wasting. The long solids retention time in this unit is comparable to the one normally used in conventional sludge digestion units, thus allowing the stabilization of the waste activated sludge returned to the UASB reactor. Particle flocculation was very poor in the UASB reactor, and therefore, it required postaeration periods of at least $100\min$ to proceed successfully in the aerobic unit. Polymer generation, which is necessary for efficient biological flocculation, was practically nonexistent in the anaerobic unit; therefore, it was necessary to maintain dissolved oxygen levels greater than $1.5\mathrm{mg}∕\mathrm{L}$ in the aerobic solids contact chamber for polymer generation to proceed at optimum levels. Once these conditions were attained, the quality of the settled solids contact chamber effluent always met the $30\mathrm{mg}$ BOD/L, $30\mathrm{mg}$ SS/L secondary effluent guidelines.

Hybrid-hollow-fiber membrane bioreactors were developed for the enhanced cometabolic biotransformation of phenol and 4-chlorophenol (4-cp) by Pseudomonas putida ATCC49451. Bioreactor performance was investigated, compared, and analyzed under batch and continuous operating modes. The spinning solutions contained polysulfone (PS), $N$ -methyl-2-pyrrolidone, and various weight ratios of granular activated carbon (GAC) (GAC: PS of 0, 1:4, and 1:2). The bioreactor fabricated with 1:2 GAC hybrid-hollow-fiber membranes demonstrated the best performance for the removal of phenol and 4-cp, both under batch and continuous operations. Under batch operation, $500\mathrm{mg}{\mathrm{L}}^{-1}$ phenol and 4-cp were completely removed within $23\mathrm{h}$ in the bioreactor, compared with 26 and $30\mathrm{h}$ for the 1:4 GAC and GAC free bioreactors. Sorption, biotransformation, desorption, and bioregeneration were identified as the four steps for substrate removal during batch operation. The 1:2 GAC hollow-fiber membrane bioreactor also manifested superiority over the other two during continuous operation for start up and the transient phase after shock loadings of the feed. $300\mathrm{mg}{\mathrm{L}}^{-1}$ phenol and 4-cp were completely removed in the 1:2 GAC hybrid-hollow-fiber membrane bioreactor whereas 4-cp was not completely removed in the other two bioreactors at a feed rate of $30\mathrm{mL}{\mathrm{h}}^{-1}$ . From the experimental results, it was inferred that at steady state, biotransformation was achieved through the dynamic equilibrium among sorption, desorption, and biotransformation rates established within the bioreactors.

Applications of artificial neural networks in the field of aeration phenomena in surface aerators, which are not geometrically similar, are explored to predict reaeration rates under varying dynamic as well as geometric conditions. The primary network for prediction is a feed forward network with nonlinear elements. The network consists of an input layer, an output layer, a hidden layer, and the nonlinear transfer function in each processing element. The network requires supervised learning and the learning algorithm is the back-propagation. As back-propagation learning is affected by local minima, and to get over this aspect various other modifications have been suggested like Levenberg-Marquardt, quasi-Newton, conjugate-gradient, etc. The present study suggests that the Levenberg-Marquardt modification is a very efficient algorithm in comparison with others like quasi-Newton and conjugate-gradient. In the situations when the dimension of the input vector is large, and highly correlated, it is useful to reduce the dimension of the input vectors. An effective procedure for performing this operation is principal component analysis. The best prediction performance is achieved when the data are preprocessed using principal components analysis before they are fed to a back-propagated neural network, but at the cost of losing the physical significance of experimental data. The model thus developed can be used to predict the reaeration rate for different sizes of geometric elements (like rotor diameter, sizes of rotor, aerators’ geometry, water depth, etc.) under various dynamic conditions, i.e., the speed of the rotor.

Chemical precipitation method utilizing calcium salts has been extensively used to treat fluoride-containing wastewater from semiconductor manufacturers. The major objective of this study was to investigate coagulation-flocculation of calcium fluoride precipitates $\left(\mathrm{Ca}{\mathrm{F}}_2\right)$ . Residual fluoride concentration of lower than $15\mathrm{mg}∕\mathrm{L}$ , the effluent standard, was found when molar ratio of calcium to fluoride, $[{\mathrm{Ca}}^{2+}∕{\mathrm{F}}^{-}]$ , was 0.5 and pH ranged from 6.5 to 8.5. The fine precipitates of $\mathrm{Ca}{\mathrm{F}}_2$ were further flocculated by polyaluminum chloride (PAC) and anionic polyelectrolyte, polyacrylic acid (PAA) with different molecular weight, to facilitate better solid-liquid separation. Experimental results indicated that both PAC and PAA with low to medium molecular weight could remove $\mathrm{Ca}{\mathrm{F}}_2$ precipitates effectively. Satisfactory removal efficiency was achieved at lower dosage when PAC and PAA were used in combination. Recycling of $\mathrm{Ca}{\mathrm{F}}_2$ precipitates or $\mathrm{Ca}{\mathrm{F}}_2$ sludge did not enhance removal of fluoride or $\mathrm{Ca}{\mathrm{F}}_2$ precipitates. Reaction mechanisms were discussed based on zeta potential and particle size distribution.

Sedimentation column studies and simulations using particle size distribution suggest that low removal efficiencies of smaller particles in highway runoff would be obtained using sedimentation if coagulation-flocculation is not performed. Coagulation-flocculation studies, using metal salts (alum and ferric chloride) and one organic polymer in three molecular weights, were evaluated over the 2004–2005 storm seasons. Only the first flush or approximately the first hour of runoff was coagulated. Efficiencies were quantified with particle size distribution measurements and turbidity. Results with low dosages of metal salts were ineffective and did not improve water quality. High dosages of metal salts using a sweep floc mechanism were effective in dramatically lowering runoff turbidity, but resulted in large quantities of sludge production and required pH control. A cationic organic polymer at low dosages $(<10\mathrm{mg}∕\mathrm{L})$ was effective in coagulating highway runoff and reducing particle charge. Extended mixing time was required to achieve low turbidities ( $\sim 5$ NTU). A combination of organic polymer, followed by small doses of alum $(<10\mathrm{mg}∕\mathrm{L})$ , reduced mixing time and produced high quality effluent.

Pesticide runoff loads from grass surfaces were estimated for 29 chemicals commonly applied to U.S. lawns and golf courses. Data on pesticide properties and typical application rates and schedules were developed and summarized as input parameters for the TurfPQ runoff model. Weather data for each of 9 U.S. cities were generated by the USCLIMATE model and modified by the addition of growing season irrigation. Simulation runs were made for each chemical, grass surface (lawns, greens, fairways), and city, and the results were summarized as mean annual and 1-in-10 year annual maximum daily pesticide loads. These loads varied greatly with pesticide, grass surface, and city, ranging from 0 to $875\mathrm{g}∕\mathrm{ha}$ for mean loads and 0 to $818\mathrm{g}∕\mathrm{ha}$ for 1-in-10 year daily loads. Mean annual loads averaged over the 29 chemicals and 3 grass surfaces were found to be closely related to growing season precipitation. Variations among the nine cities were well-captured by three general climate categories: Humid, characterized by abundant precipitation and warm temperatures, represented by Atlanta and Houston; temperate, with moderate precipitation and temperature, as with Albany, Columbus, Madison, and Olympia; and dry, with sparse precipitation, represented by Bismarck, Fresno, and Roswell. Mean annual pesticide runoff was 37, 9, and $2\mathrm{g}∕\mathrm{ha}$ in the humid, temperate, and dry regions, respectively.

This paper describes the influence of water outside a bay on water quality within the bay for a typical enclosed bay with a sill at its mouth. The influence of water outside Ohfunato Bay, Japan was expressed in a one-dimensional vertical dissolved oxygen (DO) model as the rate of seawater exchange caused by tides and the density difference between water inside and outside the bay. A nonhydrostatic, three-dimensional model was used to confirm the occurrence of density intrusions. A one-dimensional vertical DO model was used to examine long-term changes in DO concentrations in the bottom layer of the bay. Results indicated that seawater exchange caused by density differences had a significant effect on the formation and disappearance of anoxic water in the bay’s bottom layer.

An efficient venturi scrubber system combining a particle growth device and a traditional venturi scrubber was designed and tested in the laboratory. Before the venturi scrubber, saturated steam at $100°\mathrm{C}$ was mixed with normal temperature waste stream to achieve supersaturation conditions allowing submicron particles to grow into micron sizes. Hence the control efficiency of submicron particles was greatly enhanced at a reasonably low pressure drop as compared to that found in the literature. At a flow rate of $250\mathrm{L}∕\min$ and a liquid to gas ratio of $2.5\mathrm{L}∕{\mathrm{m}}^3$ , the control efficiency of the present venturi scrubber system for NaCl particles greater than $100\mathrm{nm}$ is greater than 90%, and pressure drop is only about $44\mathrm{cm}{\mathrm{H}}_2\mathrm{O}$ $\left(4.3\mathrm{kPa}\right)$ . In comparison, to remove only 50% of $0.6\mu \mathrm{m}$ particles at the same liquid to gas ratio, the pressure drop needed will be greater than $200\mathrm{cm}{\mathrm{H}}_2\mathrm{O}$ (or $19.6\mathrm{kPa}$ ). Theoretical calculation has also been conducted to simulate particle growth process and the control efficiency of the venturi scrubber considering the effects of mixing ratio (ratio of steam to waste stream by mass flow rate) and particle diameter. Theoretical results using Calvert’s theory (1970) were found to agree well with the experimental data for NaCl particles greater than $50\mathrm{nm}$ , and for $\mathrm{Si}{\mathrm{O}}_2$ particles greater than $150\mathrm{nm}$ .