Journal of Environmental Engineering

Laboratory studies and model results were utilized to design packed tower and hollow fiber air stripping units which were field tested with a contaminant-laden surfactant stream. Field units were operated at a 1.9 liter/min liquid flow rate with air/liquid ratios ranging from 20 to 50 and system temperatures ranging from 10 to 37°C. Tri- and tetrachloroethylene were analyzed as the target components. When properly operated, the field units successfully met or exceeded the targeted 90% removal efficiency. As expected, high air to liquid flow rates and higher system temperatures achieved high removal efficiencies while solutions with high surfactant and contaminant concentrations were the most difficult to treat.

Hollow fiber (HF) and tubular membranes were installed at a dental clinic and used to treat dental wastewater (DWW) over a six-month period. Both membranes rejected the vast majority of the Hg (Tubular: 99% rejection and permeate Hg=20.8 μg/L; HF: 97% rejection and permeate Hg=6.6 μg/L). Permeate Hg concentration and flux were not adversely affected by concentrating the DWW indicating that the system can be operated indefinitely. Biological growth blocked the openings of the HF lumens necessitating frequent maintenance. The tubular membrane with its large channel diameter (2.53 cm versus 1 mm for the HF) did not experience channel blockage. Given the small volume of DWW that is produced at a dental facility (≈3 L/d), the packing density and footprint of the membrane unit are not a major concern, thus, HF module offers no real advantage over the tubular module. Additionally, the increase maintenance that is required with the HF module is a distinct disadvantage making the tubular module better suited for dental facilities.

Artificially contaminated water with aromatic compounds, including benzene, ethylbenzene, and xylenes, was exposed to dense medium plasma (DMP) environments in the presence of oxygen. This original plasma technique allows the volume exposure of liquid media to nascent plasma species under atmospheric pressure conditions. Analytical data resulting from gas chromatographic/mass spectroscopic evaluations of contaminated and plasma-exposed water, indicated that prior to any optimization the DMP technology can reduce contamination levels of 600–1,000 ppm to ppb values in treatment times as low as 1 min. It is suggested that hydroperoxide molecules generated as a result of the interaction of plasma-activated oxygen and water molecules, might play an essential role through the interaction of nascent OH free radicals with the contaminant molecules in the decontamination process. The reaction products (hydrocarbons and oxidized derivatives) have a significantly lower concentration relative to the starting contaminants (at least two to three orders of magnitude lower concentrations). This original plasma technology opens up new highways for efficient decontamination of water both under batch-type and continuous-flow system modes.

Performance stability of a biofilm airlift suspension reactor (BASR) was studied using ethanol as a substrate. The main objective of this research was to investigate the applicability of the reactor as a wastewater treatment process by examining the effects of soluble chemical oxygen demand (SCOD) loading rate and hydraulic retention time (HRT) on the performance of the reactor. SCOD removal of 90% or higher was achieved at an HRT of 45 min with loading rates from 10 to 18 kg $\mathrm{SCOD}/m^3 \mathrm{day}\text{.}$ Similar results were obtained at HRTs of 60 and 90 min and a SCOD loading rate of 10 kg $\mathrm{SCOD}/m^3 \mathrm{day}\text{.}$ Nitrification occurred in the system when the ratio of SCOD to ammonia nitrogen was changed from 10:1 to 6:1. The morphology of the biofilm in the BASR was denser and thicker when nitrifiers grew in the biofilm. Filamentous overgrowth was observed from time to time and proper chlorine dose successfully suppressed its growth. The oxygen uptake rate was an effective tool for monitoring the effect of chlorination.

Sedimentation tanks are used in the process industry to separate the solid particles from the slurry to get the clarified liquid. A detailed study of the hydrodynamics of sedimentation tanks is presented here using an Eulerian-Lagrangian approach to study the motion of solids in the tank. The model, in its present form, is applicable only to nonflocculent discrete (Type I) settling. It is shown that a typical particle-eddy interaction can be characterized by a lower cut-off size below which the particles would be entrained by the eddy; and an upper cut-off size above which the particle would continuously settle through the sedimentation tank in spite of the recirculation. The effect of inlet configuration on the flow field as well as on the settling characteristics has been investigated. The simulations show that both the upper and the lower cut-off sizes for a sedimentation tank are considerably reduced by providing a tulip type of inlet with a conical deflector as compared to a straight inlet.

A response alternative for floating vegetable oil spills based on sedimentation of negatively buoyant oil-mineral aggregates followed by anaerobic biodegradation in the sediments is under investigation. Sedimentation of floating canola oil by interaction with montmorillonite was demonstrated, and the oil-binding capacity of wet and dry clay was determined. Only two of the four factors that were investigated produced statistically significant effects on the sedimentation of floating oil: Clay was required for oil sedimentation to occur, and high mixing energy during the initial contact between oil and clay reduced the amount of oil that could be transported to the sediment compartment. The addition of ferric chloride as a coagulant and the mixing energy imparted during the flocculation period did not significantly affect the extent to which oil was transported to the sediment compartment. The maximum oil-binding capacity of dry high-surface-area (220–270 m²/g) clay was about three times higher than for wet clay (1 g oil/g dry clay versus 0.3 g oil/g wet clay). The oil-binding capacity of low-surface-area (20–40 m²/g) clay was less affected by prior interaction with water (0.7 g oil/g dry clay versus 0.6 g oil/g wet clay), but it was much less effective in promoting sedimentation of floating oil. The differences between the oil sedimentation abilities of these two types of clay suggest that the success of this remedial alternative requires a clear understanding of the nature of the oil-mineral interactions.

An acidic soil was deliberately contaminated with lead (Pb), cadmium (Cd), and chromium (Cr). The heavy metal speciation in the aged soil sample was analyzed using a sequential extraction procedure. A single-step extraction procedure was then employed to remove the heavy metals from the soil using sodium ethylenediaminetetraacetic acid, sodium nitrilotriacetic acid, and calcium trisodium diethylenetriaminepentaacetic acid. The extraction parameters were the type and concentration of chelating agent and the duration of extraction time. All the extractions that involved chelating agents were carried out at pH 7.0. The heavy metal extraction efficiencies of chelating agents were compared to those of ${\mathrm{HNO}}_3\text{,}$ ${\mathrm{CaCl}}_2\text{,}$ and deionized water. The extraction results showed that the chelating agents were more efficient in extracting Pb and Cd from the acidic soil than ${\mathrm{HNO}}_3\text{.}$ The extractable Pb and Cd were removed from the soil within 15 min of extraction time with the chelating agents. However, the chelating agents demonstrated a poor Cr extraction. The extraction efficiency seemed to be dependent on the heavy metal speciation in the solid phase. The extraction with a low chelating agent: metal molar ratio and short extraction time was proven to be optimal for Pb and Cd extractions. In contrast, an effective Cr extraction would require a high dosage of chelating agent and a long extraction time.

Numerous types of pipes and channels with spatially increasing flows in environmental engineering applications are identified by type and function and referred to as collection conduits. An overview of methods for designing and analyzing collection conduits is provided. Full conduits with nonuniform and uniform inflow are first considered. Dimensional analysis is then employed to demonstrate the relationship between variables for open channels; that leads to the identification of possibilities for generalized numerical solutions. Prior collection conduit applications are discussed within the framework of the dimensional analysis (which also pertains to some constant-flow applications). A previously unpublished generalized numerical solution for rectangular collection conduits is presented. Subsurface drains are addressed with particular emphasis, including the use of numerical methods to develop a new generalized chart and relation to other design methods. Among the important conclusions for subsurface drains is that the somewhat common practice of using Manning’s equation alone for such problems is not generally adequate. Examples and practical design suggestions are included, and the use of computer-based numerical methods is discussed more generally.

The environmental impact of various solid waste treatment methods being used in Korea was assessed to provide useful information for decision making in solid waste management strategy. Among the treatment methods considered, the incineration method and the anaerobic digestion method are the most environmentally friendly, while the landfill method has the highest environmental impact. Regarding the life cycle of the treatment methods, the environmental impact of the main treatment stage is the largest, contributing 46–94% of the total impact, depending on the treatment method. The environmental impact due to wastewater treatment was 6.2, 0.2, 4.1, and 9.0% for landfilling, incineration, composting, and anaerobic digestion, respectively. Among the environmental impact categories considered, global warming, eutrophication, and acidification are the key contributors to environmental impact, with a range of 53 to 91% of the total environmental impact depending on the selected treatment method. Of these key contributors, global warming has the largest contribution. Other contributors to environmental impact, such as photochemical oxidant creation, abiotic resource depletion, and ozone depletion, contribute little to the total environmental impact. These results make it possible to construct an environmental data set and examine the environmental impact of the life cycle of various waste treatment methods to support decision making in solid waste management strategy.

Flux decline with time is one of the most serious shortcomings of microfiltration and ultrafiltration membranes. It is highly desirable to have a membrane (fouling) testing procedure that is short in duration, utilizes a minimum amount of test solution, only requires a small membrane area, and is representative of the large-scale process. The objective of this study was to compare the results of the testing of a given membrane using a number of different test units (reverse osmosis, ultrafiltration, dead-end, and cross-flow cells) and testing procedures. It was of particular interest to determine if smaller cells used in the literature perform similarly to the Sepa CF cell, as it is a standard. During six-day runs the flux decline of the polyethersulfone membrane tested was mainly caused by membrane compaction and much less due to fouling. As various membrane materials compact to a different extent, studies into the fouling characteristics of different types of membranes should incorporate precompaction and pure water testing to quantify the contribution of membrane compaction and true fouling to the overall flux decline. The dead-end cell performed very differently from continuous cells, so their use is not recommended. The six-day continuous flow tests showed that the reverse osmosis (RO), ultrafiltration (UF), and cross-flow (CF) cells yielded very similar dissolved organic carbon removals and flux decline, despite UF and RO cells using membrane coupons eight times smaller than CF cells.

A custom designed pilot-scale photochemical remediation reactor is constructed for remediation of vapor-phase volatile organic halocarbons (VOHs), particularly chlorinated hydrocarbons such as PCE (tetrachloroethylene). Ultraviolet (UV) light, when emitted at an effective absorption frequency, cleaves a VOH’s carbon-chloride bond, transforming harmful contaminants to harmless products. The stainless steel reactor is of tubular-shape with an inner diameter of 32 cm and a length of 105 cm. The net volume of the reactor is approximately 73.7 L. Three stainless steel baffles are welded inside the reactor to create a well-mixed vapor phase and uniform UV contact time. Special low-pressure mercury amalgam UV lamps (Heraeus, Inc., Duluth, Ga.) are used as the photoenergy source. Two independent vapor-phase PCE destruction experiments are conducted using different influent contaminant concentrations. Both experiments show a PCE destruction efficiency of over 99%.

The extent of hydrogen sulfide transfer across the air-water interface plays a major role for odor and corrosion problems in sewer networks. One significant physical factor affecting the air-water transfer process is temperature. This study describes the temperature dependence of air-water transfer of hydrogen sulfide in terms of a temperature correction factor (temperature coefficient). The air-water transfer rate was found to increase with increasing temperature at a constant turbulence level. A mathematical expression for the transfer rate versus temperature was addressed following the Arrhenius equation. The temperature coefficient for air-water transfer of hydrogen sulfide was observed under acidic and neutral conditions (pH 4.5, 6.5, and 7.0), i.e., under conditions where only the molecular form of hydrogen sulfide was present (pH 4.5) and under conditions where both the molecular form and the ionized form existed (pH 6.5 and 7.0). The effect of temperature on air-water transfer of hydrogen sulfide decreased with increasing pH. The temperature coefficients found in this study were within the range reported in the literature for other substances transferring across the air-water interface such as oxygen, ozone, and krypton-85.