Journal of Environmental Engineering

This paper presents a comprehensive review of the literature on electroremediation of soils. Laboratory studies of the technique are outlined, mechanisms of contaminant transport discussed, and major factors affecting the decontamination process examined. Enhancement techniques and hybrid processes are considered and examples of field trials and commercial applications described.

Recycling of spent filter backwash water is a widely practiced residual management approach throughout the United States for drinking water utilities. The United States Environmental Protection Agency (USEPA), under the 1996 Safe Drinking Water Act Amendments, has recently proposed regulations governing the recycle of this waste stream. Considering this new regulation, a comprehensive study was conducted by researchers at Colorado State University, and a suspended solids mass balance model was developed to characterize the impact of backwash water recycling on the overall treatment process. Online particle count data indicated that certain recycle practices could impact the overall treatment process. Data from pilot-scale experiments showed that total suspended solids (TSS) is a useful tool for characterizing the impacts of the backwash recycle processes. TSS can be used to assess whether solids loading or suboptimal coagulation conditions are the cause of recycle related issues. For the study described here, filter breakthrough occurred at about the same total influent solids load, regardless of the manner in which backwash recycling was performed, indicating that recycle of backwash solids did not impact the overall treatment process.

A side by side comparison of two 8,000 metric ton test cells was performed to evaluate the effects of leachate recirculation on refuse decomposition at Yolo County, CA. After about 3 years of operation, refuse was excavated in three borings from the enhanced cell (E1, E2, and E3) and two borings from the control cell (C1 and C2). Refuse moisture content data show that leachate recirculation resulted in an increase in refuse moisture content, but also show that the refuse in the enhanced cell was not uniformly wet. The average moisture content in E1, E2, and E3 was 38.8, 31.7, and 34.8%, respectively, while the average moisture content in C1 and C2 was 14.6 and 19.2%, respectively. Leachate recirculation resulted in both higher methane yields, (63.1 versus 27.9 L ${\mathrm{CH}}_4/\mathrm{wet}-\mathrm{kg}$ over 1231 days) and increased settlement (15.5% versus 3% of the waste thickness). The extent of decomposition of excavated refuse samples was determined by the biochemical methane potential (BMP) and the ratio of cellulose plus hemicellulose to lignin $\left[\right(C+H)/\mathrm{Li}]\text{.}$ Solids analyses showed the average BMP in the enhanced and control cells to be 24.0 and 30.9 mL ${\mathrm{CH}}_4/\mathrm{dry}-g\text{,}$ respectively. The corresponding $(C+H)/\mathrm{Li}$ ratios were 1.09 and 1.44, respectively. These data correlate well with the increased methane production in the enhanced cell. Thus laboratory and field data show more decomposition in the enhanced cell relative to the control cell. The refuse sampling program conducted for the Yolo County test cells, in concert with data on settlement, methane production, and the volume of liquid actually recycled, represents perhaps the most complete set of data available to date on a field-scale leachate recirculation landfill.

Solid waste from construction and demolition (C&D) activities is often disposed in unlined landfills. Leachate from unlined landfills poses a potential risk to groundwater quality. An understanding of the types of chemical constituents likely to be encountered in C&D waste landfill leachate and the concentrations at which they occur help assess this risk. An experiment was performed to characterize leachate from land-disposed residential construction waste. Four 54 m² (580 ft²) test cells were excavated, lined, and filled with waste. Leachate samples were collected and analyzed for a number of water quality parameters over a 6 month period. No volatile or semivolatile organic compounds were detected at elevated constituent levels in the leachate. Inorganic ions were found to account for the bulk of the pollutant mass leached. Calcium and sulfate were the predominant ions in the leachate, resulting from the dissolution of gypsum drywall. The concentrations of several leachate constituents were found to exceed water quality standards. These constituents included aluminum, arsenic, copper, manganese, iron, sulfate, and total dissolved solids. Arsenic was the only primary water quality standard exceeded. The arsenic was concluded to result from chromated copper arsenate (CCA)-treated wood. The potential risk of impacting groundwater was examined by comparing the measured constituent concentrations with the water quality standards to assess the amount of dilution and attenuation needed in the groundwater so that a water quality standard would not be exceeded. The water quality standard exceeded by the greatest magnitude was manganese, followed by iron.

Light nonaqueous phase liquids (LNAPLs) in subsurface systems may contain a relatively large amount of biodegradable organic material. During the biochemical oxidation of the organic compounds in the LNAPL, electrons are transferred to terminal electron acceptors (TEA) [i.e., $O_2\text{,}$ ${{\mathrm{NO}}_3}^{-}\text{,}$ Mn(IV), Fe(III), ${{\mathrm{SO}}_4}^{-2}\text{,}$ ${\mathrm{CO}}_2]$ via coupled redox reactions. A mass balance between the TEA required for mineralization of benzene, toluene, ethyl benzene, and xylene (BTEX) compounds contained in the subsurface (ground water, soil, LNAPL) and the total TEA available from the ground water and aquifer sediments is proposed and evaluated. The total TEA available is predominantly attributed to the solid phase material; the aqueous phase TEA constitutes a minor amount; and the TEA required for BTEX mineralization is predominantly from the LNAPL. Consequently, a TEA deficit exists in the LNAPL source area. Under these conditions, it may be invalid to assume an infinite supply of TEA and sustained bioattenuation rates. LNAPL removal is one remedial option to reduce the TEA deficit in the source area.

Conventional drinking water treatment processes were evaluated under typical water treatment plant conditions to determine their effectiveness in the removal of seven common antibiotics: carbadox, sulfachlorpyridazine, sulfadimethoxine, sulfamerazine, sulfamethazine, sulfathiazole, and trimethoprim. Experiments were conducted using synthetic solutions prepared by spiking both distilled/deionized water and Missouri River water with the studied compounds. Sorption on Calgon WPH powdered activated carbon, reverse osmosis, and oxidation with chlorine and ozone under typical plant conditions were all shown to be effective in removing the studied antibiotics. Conversely, coagulation/flocculation/sedimentation with alum and iron salts, excess lime/soda ash softening, ultraviolet irradiation at disinfection dosages, and ion exchange were all relatively ineffective methods of antibiotic removal. This study shows that the studied antibiotics could be effectively removed using processes already in use in many water treatment plants. Additional work is needed on by-product formation and the removal of other classes of antibiotics.

A laboratory chamber was designed and used to determine the headspace flux of the fungicide vinclozolin (3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-oxzoli-dine-2,4-dione) and its three degradation products from chamber surfaces, 20–30 mesh Ottawa sand, and sterilized and nonsterile North Carolina Piedmont aquic hapludult soils following fungicide spray applications. Results indicate that vinclozolin and its degradation products are influenced by the presence of soil particles, fluid-filled pore space, soil organic matter and clay content, and microbes. The formation of 2-[(3,5-dichlorophenyl)-carbamoyl]oxy-2-methyl-3-butenoic acid (“M1”), was highest in pore water with elevated pH levels, and the degradation is enhanced by the presence of microbes. M1 was also released from lower pH soil pore water, especially when the fungicide was incorporated into the soil. Unlike prior studies of vinclozolin degradation in solutions, this study found that, in soil, both M1 and 3^′,5^′-dichloro-2-hydroxy-2-methylbut-3-enanilide (“M2”) can be produced in the same soil column. These results indicate that engineering controls and agricultural practices following application can affect the amount and pathway of vinclozolin’s degradation.

Previous studies have shown that the dry deposition of semivolatile organic compounds to the Great Lakes can account for a significant fraction of their total inputs. However, there is no generally accepted method to directly measure dry deposition. In this study the particulate dry deposition of polycyclic aromatic hydrocarbons (PAHs) was measured using smooth surrogate surfaces during the winter of 1996–1997 in Chicago. Concurrently, ambient air samples were collected. Average particulate ${\Sigma }_{13}-\mathrm{PAH}$ fluxes and ambient concentrations were $120\pm 28\mu g/m^{2}d$ and $30\pm 16\mathrm{ng}/m^3\text{,}$ respectively. The measured particulate dry deposition fluxes were similar to those measured in other urban areas. Overall dry deposition velocities of PAHs calculated using the dry deposition fluxes and ambient concentrations averaged $4.5\pm 3.1\mathrm{cm}/s\text{.}$ This value is higher than values typically used to estimate PAH particulate deposition, however, it agrees well with values determined using similar techniques. The overall dry deposition velocity for individual PAHs generally decreased with increasing molecular weight. This finding is consistent with the previous experimental studies that have shown that a greater fraction of the higher molecular weight PAHs are associated with fine particles relative to the lower molecular weight compounds.

Cyclones are generally less efficient than other kinds of equipment, but their simple construction, low energy requirements, and ability to operate at high temperatures and pressures make them attractive for cleaning up gases. Despite the simplicity in construction and operation, complex mathematical formulations are used for predicting the collection efficiency of particles of a given diameter. These must be numerically integrated, along with the inlet particle-size-distribution functions that are appropriate in each application, in order to obtain the overall cyclone efficiency. In this paper, the above cumbersome procedure is simplified through nomographs allowing rapid, yet rigorous, estimation of the overall cyclone efficiencies based on two alternative and well-established approaches and on the sole assumption of a lognormal particle-size distribution. Along with the above, pressure drop and limiting inlet velocity correlations are also considered, and each of the above nomographs is combined with others, providing direct graphical representation of the so far obscure relationships among cyclone diameter, overall efficiency, and gas pressure drop or flow rate. The paper thus affords an overview of cyclone behavior over a wide range of conditions, offering direct solutions to both cyclone performance and optimal cyclone design problems.

A new catalyst, which was made of ${\mathrm{MnO}}_2$ impregnated with Pd for decomposition of high humidity ozone gas, was developed and its catalytic activity decrease was analyzed in a finite difference type fixed bed reactor. The activity of the catalyst was higher than that of other catalysts and an activated carbon and does not decrease so much for a long term. Therefore, its lifetime is very long. The reaction rate was shown as a first-order reaction equation for each catalyst in any operation time both under dry and wet conditions. The rate-determining step was considered to be a chemical reaction of ozone. The reaction rate constant $k_t$ decreased through two steps, fast in an early period and slowly afterward. Then, $k_t$ was analyzed as the function of operation time t and inlet concentration $C_0$ at each humidity. From the analysis, the ozone removal performance in any size of reactor and in any time became possible to predict.

This paper presents the results of a laboratory study on the effect of pH (2, 5, and 9) and gas-phase ozone concentration (1, 7, and 11 wt %) on the decolorization efficiency via ozonation for seven common textile dyes. Higher gas-phase ozone concentrations resulted in higher decolorization rates due to more rapid ozone transfer. Higher gas-phase ozone concentration, however, was also observed to have a positive, neutral, or negative effect on ozone dose requirements for different dyes. In general, greater ozone utilization efficiency was achieved at lower pH levels where direct ozone reactions predominate. It was observed that because ozonation can cause significant resolubilization of precipitated dyes, complete removal of dye precipitate should be accomplished prior to polishing via ozonation. The results point to the need for laboratory and/or pilot testing for dye-laden wastestreams to allow process optimization.