Journal of Environmental Engineering

Chlorinated ethanes are contaminants commonly found in soil and groundwater. The potential of nanoscale bimetallic $(\mathrm{Fe}∕\mathrm{Pd})$ particles for the hydrodechlorination of seven chlorinated ethanes $\left({\mathrm{C}}_2{\mathrm{H}}_{6-x}{\mathrm{Cl}}_x\right)$ was evaluated in batch experiments. Hexachloroethane (HCA) $\left({\mathrm{C}}_2{\mathrm{Cl}}_6\right)$ , pentachloroethane (PCA) $\left({\mathrm{C}}_2{\mathrm{HCl}}_5\right)$ , 1,1,2,2-tetrachloroethane (1,1,2,2- $\mathrm{TeCA}$ , ${\mathrm{C}}_2{\mathrm{H}}_2{\mathrm{Cl}}_4$ ), and 1,1,1,2-tetrachlorethane (1,1,1,2- $\mathrm{TeCA}$ , ${\mathrm{C}}_2{\mathrm{H}}_2{\mathrm{Cl}}_4$ ) were rapidly hydrodechlorinated (9–28 min half-lives) at a nanoparticle loading of 5 g/L. End products were ethane (61–87%) and ethylene (6–16%). Only one chlorinated intermediate, a corresponding $\beta$ -elimination product, appeared temporarily during the reactions. Reductive dechlorination of 1,1,1-trichloroethane (1,1,1-TCA, ${\mathrm{C}}_2{\mathrm{H}}_3{\mathrm{Cl}}_3$ ) to ethane was completed at a relatively slower rate with half-life at 44.9 min. Little reduction of dichloroethane $\left({\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{Cl}}_2\right)$ was observed within 24 h. The Pd/Fe bimetallic nanoparticles generally exhibit much higher reactivity when compared with conventional micro- and millimeter scale iron powders. The hydrodechlorination reactions are more complete, with a much higher yield of ethane and lower yield of chlorinated byproducts. A kinetic model incorporating a transition state species was proposed. Results from this work suggest that the Pd/Fe bimetallic nanoparticles may represent a treatment alternative for in situ remediation of chlorinated ethanes.

The hydraulic characteristics of horizontally installed sorbent wick sampling devices were evaluated through wick tracer studies and laboratory soil column experiments to assess the influence of horizontal wick length and sampler interface design on sampling pore water in unsaturated soils. The nominal sampler design consisted of a cylindrical porous metal interface packed with granular-activated carbon encapsulating the end of a fiberglass wick that extended 100 cm horizontally from the interface before dropping 100 cm vertically to a collection vessel. The maximum sampling rate of horizontally installed wick systems declines exponentially with increasing horizontal wick length, while the vertical length influences the range of soil–water pressures that may be sampled. The nominal design sampled pore water from clay loam laboratory columns at 8 to 14 $\mathrm{mL}{\mathrm{h}}^{-1}$ under steady-state infiltration conditions and 2 to 5 $\mathrm{mL}{\mathrm{h}}^{-1}$ under draining conditions across a −10 to −45 $\mathrm{cm}$ ${\mathrm{H}}_2\mathrm{O}$ soil–water pressure range. Sampling rates in medium-grained sand under similar flow conditions were less than that of the clay loam due to reduced water content and reduced interface/soil contact area. An analysis of observed sampling velocities versus calculated soil water contents and hydraulic conductivities indicated that the design performs best when the soil water content is greater than 0.15 and unsaturated hydraulic conductivity is greater than 0.2 $\mathrm{cm}{\mathrm{h}}^{-1}$ . A hydraulic model was developed that estimates the sampling velocity of the nominal design based on sampler interface pressure, which was linearly correlated with soil pressure.

Experiments investigated the chemical capture and quantitative recovery of chlorinated hydrophobic organic compounds (HOCs) sampled from the pore-water of unsaturated soils with a new in situ sorbent wicking device. The sampling device is comprised of an annular porous stainless-steel interface encasing granular-activated carbon and a fiberglass wick. Laboratory column studies using Ottawa sand spiked with tri- and tetrachlorobenzenes evaluated the accuracy of the sampling device in assessing average pore-water concentrations. The findings from these experiments showed that the sorbent-wick sampler provided reliable and repeatable estimates of the pore-water concentrations of the chlorobenzenes in the unsaturated soil columns at pore-water concentrations as low as several parts per billion. Field trials were conducted in a land biotreatment unit containing industrial soil/sludge materials to assess the availability of trace levels of aqueous-phase polychlorinated biphenyls (PCBs). The land treatment unit had undergone $5\text{years}$ of intrinsic remediation and the test results indicated that the samplers were able to replicate the aqueous-phase PCB homolog pattern measured in ex situ aqueous extraction tests. Orthosubstituted PCBs were dominant in sorbent-wick samples and aqueous extracts; these PCBs appear relatively recalcitrant in land biotreatment units. The sorbent-wicking device offers the ability to obtain time-averaged mass and volumetric flux rates of HOCs in land treatment units.

The high explosive (HE) compounds royal demolition explosive or hexahydro-1,3,5-trinitro-1,3,5-triazocine (RDX) and high melting explosive or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have been detected as groundwater contaminants at many military facilities. This research evaluated adsorption of RDX and HMX with granular activated carbon (GAC) to provide guidance for the design and operation of GAC adsorbers for treatment of HE-contaminated groundwater. Five GACs were screened using rapid small-scale column tests (RSSCTs), after which additional tests were performed with the two GACs that most effectively treated mixtures of RDX and HMX (Calgon F400 and Northwestern LB-830). GAC service life as a function of empty-bed contact time (EBCT) was determined using RSSCTs for a range of simulated full scale EBCTs with influent concentrations of 2,200 μg RDX/L and 350 μg HMX/L. Increasing the influent concentration of either contaminant significantly reduced the predicted service life, as did preloading GAC with groundwater natural organic matter. In batch isotherm tests, RDX was less adsorbable than HMX under all conditions studied. Concurrent loading of natural organic matter reduced the Freundlich K for RDX, whereas adsorption of HMX was not affected. Of the GACs tested, Calgon F400 most effectively removed RDX and HMX.

Treatment of lead-contaminated material focuses on the reduction of leached lead concentrations in laboratory leaching tests. There has been little study on the chemical stability of treated materials after waste disposal. To investigate the effects of weathering on several solidification/stabilization chemistries, lead-contaminated soil was treated with various agents (cement, phosphates, dithiocarbamate, calcium hydroxide, calcium carbonate, and metallic iron) and subjected to natural weathering for one year. Lead concentrations and pH values in field percolates and leachates from toxicity characteristic leaching procedure (TCLP) and water leaching tests were used to evaluate changes in the treatment effectiveness. Weathering altered the treatment chemistry of several additives—alkaline additives were neutralized, while reduced additives were oxidized. Lead concentrations in field percolates from the untreated soil were around $1.0\mathrm{mg}∕\mathrm{L}$ , and did not vary over one year of weathering time. After one year of weathering, lead concentrations in field percolates from most samples were reduced to low levels (<0.15 mg/L). Weathering also affected lead concentrations in the TCLP and water leach test leachates from the treated wastes. Treated wastes in which the alkaline additives were neutralized or reduced additives oxidized gave higher TCLP lead concentrations after weathering than before, in contrast to the decreasing lead concentrations in the field percolates. Water leaching tests on the alkaline treated wastes had lower lead concentrations after weathering than before.

Samples of sediment found on an urban road in Aberdeen (Scotland) were collected by washing designated surfaces. This method, called the “wet” method, was capable of collecting sediment of the smallest particle size range that is normally left behind by traditional sampling techniques using dry vacuuming. Over 17 months (mainly on a weekly basis), 66 samples were collected and analyzed for sediment loading, particle size distribution, concentration of heavy metals (Zn, Cu, Pb, Cd) in four sediment size fractions, and several dissolved pollutants in the effluent collected from washing ( $\mathrm{NO}_3{}^{-},\mathrm{SO}_4{}^{2-},\mathrm{PO}_4{}^{3-},{\mathrm{Cl}}^{-},{\mathrm{F}}^{-},\mathrm{NH}_4{}^{+}$ , total organic carbon, total carbon). Standard statistical methods, including multiple regressions, were used to determine relationships amongst different sediment characteristics. It was found that sediment loading, as well as concentrations of ${\mathrm{Cl}}^{-}$ and ${\mathrm{SO}}_4^{2-}$ , were highest in the winter months, especially when snow was present on the road surface. It was observed that 66% of total road sediment loading was found within a 0.5 m strip next to the curb. The average sediment particle sizes found were smaller than those previously recorded in the literature. As expected, the concentrations of heavy metals were highest in the smallest particle size fraction analyzed $(<63\mu \mathrm{m})$ , and this occurred during the summer months when less sediment was available on the street surface. The antecedent dry weather period had a very weak and negative influence on the loading rate of the smallest particle size fraction next to the curb.

The marshland upwelling system (MUS) was installed on private camps in the Grand Bay National Estuarine Research Reserve, Moss Point, Mississippi. The system was evaluated for its effectiveness in removing fecal coliforms from settled, raw wastewater. A suite of studies was performed at flow rates of 1.9, 2.8, and 5.5 L/min and an injection frequency of 30 min every 3 h to investigate fecal coliform removal. An additional study was performed at a flow rate of 2.8 L/min and an injection frequency of 15 min every hour. Overall, the MUS consistently maintained fecal concentrations below effluent regulatory standards for shellfish harvesting waters (14 most probable number of colonies per 100 mL). Mean influent concentrations of 55,269±2,218,016 colony forming units (CFU)/100 mL were reduced to effluent counts of 2.7±14.07 CFU/100 mL (observed in the 1.5 m wells). Three- to four-log reductions in influent counts were observed over the initial 1.4 $\text{vector}\mathrm{m}$ from the injection well. The overall removal followed a first-order decay relationship with respect to vector distance, resulting in removal rate constants ranging from 5.6 to 6.6/m and predicted surface concentrations approaching 0 CFU/100 mL. The 2.8 L/min for 30 min every 3 h treatment provided the best effluent quality.

The American Dye Manufactures’ Institute (ADMI) 3 and 31 wavelength (WL) methods are the most well-known analytical methods for measuring wastewater true color. However, these two methods use a spectrophotometer as the measurement device. The measurements thus must be conducted in the laboratory and cannot provide on-line monitoring data for process control. This study applies the digital image analysis (DIA) method to develop an effective and economical method for on-line monitoring of the wastewater true color. The DIA method was used to measure three types of colored samples including the platinum-cobalt color standard solutions, synthetic colored samples and real colored samples. Experimental results show that the DIA method performed not only with good accuracy and precision but also high sensitivity in the measurement of true color. However, the DIA values present different linear relationship with the ADMI 3 and 31 WL values for different sample hues. Direct substitutions of DIA, ADMI 3 and 31 WL values may be inappropriate. Finally, a back-propagation neural network (BPNN) was proposed to calibrate the DIA, ADMI 31 and 3 WL values. The BPNN models were proven to be highly effective for the calibrations among the ADMI 3, 31 WL, and DIA values.

The ability to measure network strength is important in sludge conditioning and dewatering applications. Previous research has mostly focused on determining sludge floc strength indirectly through measuring other parameters such as floc size, floc density, and dewaterability of sludge. Few methods were developed for direct measurement of floc strength but these methods are not very practical for sludge applications. For the purpose of sludge characterization, it is more appropriate to determine the overall network strength of sludge rather than determining the strength of individual sludge flocs. This is because individual floc strengths will vary greatly, especially during conditioning, and therefore network strength is a more meaningful measurement compared to floc strength. This paper refers to raw or conditioned sludge as “network,” and provides a protocol to measure “network strength” which can be used to evaluate the dewaterability of water and wastewater sludges. The proposed protocol uses rheology, a fundamental character of sludge, to measure network strength in terms of energy required to break up the structure of a certain volume of sludge. Two methods are presented to directly measure network strength using either torque or concentric cylinder rheometers. A mathematical derivation showed that the area under a shear stress–shear rate or a torque–time rheogram is representative of the energy dissipation within the sludge system, and the total dissipated energy is related to the network strength. This study does not intend to measure the absolute network strength, rather a comparative strength of different sludges using the same instrument and measurement conditions.

The effect of the substrate nitrogen/chemical oxygen demand (N/COD) (mg/mg) ratio on the formation and characteristics of aerobic granules for simultaneous organic removal and nitrification were studied in four sequencing batch reactors operated at different substrate N/COD ratios ranging from 5/100 to 30/100. Results showed that aerobic granules formed at the substrate N/COD ratios studied, and both nitrifying and heterotrophic activities of aerobic granules were governed by the substrate N/COD ratio. The nitrifying activity was significantly enhanced with the increase of the substrate N/COD ratio, while the heterotrophic activity decreased. By determining elemental compositions of aerobic granules cultivated at different substrate N/COD ratios, it was revealed that the cell hydrophobicity was inversely related to the ratio of cell oxygen content to cell carbon content of aerobic granule. The production of extracellular polysaccharides showed a decreasing trend as the substrate N/COD ratio increased. This is probably due to enriched nitrifying population with the high N/COD ratios. This study clearly demonstrated that an aerobic granule-based sequencing batch reactor would have a great potential for simultaneous organic oxidation and nitrification.

A numerical and analytical investigation is performed on a dissolved air flotation (DAF) pilot tank by using the residence time distribution (RTD) of the conservative dye rhodamine measured with a fluorometer. The experiments are numerically analyzed with regard to the total volume of the DAF tank separation zone in order to detect differences between observed separation zone flow structures in previous studies. The mean hydraulic detention time, the variance, and the estimated number of completely mixed tanks $\left(N_{\mathrm{cstr}}\right)$ in a series model are calculated. The variance is found to relate to the flow structure and the $N_{\mathrm{cstr}}$ is used for characterizing the occurrence of a stratified flow structure, which is beneficial for particle separation by DAF. The result shows a significant difference in RTD depending on expected flow structure. Analytically, a conceptual model is defined by dividing the DAF tank into an upper and a lower layer. In the upper layer, the water flow is horizontal and in the lower the water flow is vertical. The hypothesis is that mixing of the tracer takes place in the upper layer and that there is no significant mixing in the lower layer. Two simple mixing models are evaluated for the upper layer; the completely mixed tanks in series model, characterized by the number of tanks, and the dispersed plug flow model, characterized by the Peclet number. The models show good agreement with the experiments when the stratified flow structure is expected, but less agreement when the flow deviates from the stratified flow structure. The dispersed plug flow model shows the best fit with the experiments. The completely mixed tanks in series model is less sensitive, generating greater changes to the modeled RTD curve, which makes it more difficult to fit the model to the experiments.

This paper reports the effectiveness of the photocatalysis ${\mathrm{TiO}}_2$ in degrading Lanasol Blue CE. A flat-plate reactor (FPR) with a reactor area of 0.37 ${\mathrm{m}}^2$ and ultraviolet (UV) light source of six 36 W blacklight lamps was used in the study. Operating variables including dosage of the photocatalyst, flow rates through the FPR, UV intensity, and tilted angle of the reactor were investigated to degrade Lanasol Blue CE. Results showed that the photocatalytic process can efficiently remove the color in textile dyeing effluent. The degradation process was approximated using first-order kinetics. The photocatalytic apparent reaction rate increased with the increasing UV intensity received by the photocatalyst ${\mathrm{TiO}}_2$ in slurry. The liquid flow rate and tilted angle influenced the film thickness. The apparent reaction rate constant was mainly determined by the liquid film thickness, UV intensity, and the dosage of the photocatalyst. The findings of this research can be utilized as preliminary input for potential solar photocatalytic applications on color removal from dye solutions.

A mathematical model was developed to estimate the efficacy of coagulation–flocculation treatment for removing neutral hydrophobic organic chemicals from raw drinking water. The model assumed that the only significant removal mechanism was the destabilization and settling of organic matter containing sorbed anthropogenic organic compounds. The model was validated with standard jar tests using compounds with a range of hydrophobicities $(\log K_{\mathrm{ow}}=1.89\text{to}5.48)$ , including contaminant candidate list chemicals, pesticides, pharmaceuticals, and endocrine disrupting chemicals. Final concentrations of test compounds after coagulation and flocculation were in good agreement with model estimations for synthetic waters composed of Aldrich (Milwaukee, WI) humic acid solutions. The final compound concentrations in coagulated natural waters from two drinking water reservoirs were about 80% lower than those estimated with the model. Overestimations of treated water concentrations by the model were attributed to an increase in sorption by natural organic matter when coiled in aluminum hydroxide flocs, compared to sorption to dispersed natural organic matter in untreated water.

The effects of monochloramine application techniques, chlorine-to-ammonia-N (Cl:N) ratios, water matrices, and bacterial origins on fecal coliform bacteria inactivation behavior in the monochloramination range were studied in ammoniacal bacteria suspensions and wastewater samples containing either naturally occurring or reseeded laboratory-cultured fecal coliform bacteria. The time-dependent chlorine residual concentrations and the bacteria counts were measured. The inactivation behavior was strongly affected by the monochloramine application techniques and the initial chlorine and ammonia concentrations and ratios. When dosing free chlorine to the ammoniacal solution, a “two-stage” pattern that coupled initial inactivation by transitory free chlorine and extended inactivation by forming monochloramine was observed at a Cl:N ratio of 3:1, while, at a high initial ammonia concentration $(20\mathrm{mg}∕\mathrm{L})$ , synergy without initial inactivation was found instead. The difference is explained with calculations of the free-chlorine CT values. The inactivation behavior of laboratory-cultured suspensions differed from that of wastewater effluents, which was primarily attributable to the variations in the water matrix, not to the bacterial origins. Conducting dose-response studies using autoclaved wastewater samples reseeded with field-isolated, laboratory-cultured bacteria was proposed as the solution.

Many rivers in the Western U.S. suffer from high salinity content due to both natural and human-induced causes. Computer simulation models are often used to estimate future salinity levels and identify mitigation needs. To date, estimation of future natural salt loading has utilized linear relationships between natural flow and natural salt. We develop a nonparametric regression technique to fit a functional relationship between natural flow and natural salt. The main advantages of the nonparametric technique are: (1) No prior assumptions have to be made as to the underlying form of the relationship and (2) any arbitrary relationship (linear or nonlinear) can be modeled. In addition, we develop a resampling scheme to provide confidence intervals of the natural salt estimates from the nonparametric model. We apply this model to data from a stream gauge at Glenwood Springs, Colo., on the Colorado River. We show that the new natural salt model reduces the average overprediction of salt mass shown in the existing natural salt model for the period 1941–1995 by approximately 15% $\left(\mathrm{78,000}\text{metric}\text{tons}\right)$ .

This study examines the air temperature/stream temperature relationship at a geographically diverse set of streams. We evaluate the general temperature relationships (both linear and nonlinear) that apply to these streams, and then examine how changes in stream temperature associated with climate variability or climate warming might affect dissolved oxygen levels. The majority of streams showed an increase in water temperature of about 0.6–0.8°C for every 1°C increase in air temperature, with very few streams displaying a linear 1:1 air/water temperature trend. For most of the streams, a nonlinear model produced a better fit than did a simple linear model. Understanding the relationship between air temperature and water temperature is important if people want to estimate how stream temperatures are likely to respond to anticipated future increases in surface air temperature. Surface water temperature in many streams will likely increase 2 to 3°C as air temperature increases 3 to 5°C. At sites with currently low dissolved oxygen content, an increase in summer stream temperatures could cause the dissolved oxygen levels to fall into a critically low range, threatening the health of many aquatic species.

A new dynamic model of water quality, ${\mathrm{Q}}^2$ , has recently been developed, capable of simulating large branched river systems. This paper describes the application of a generalized sensitivity analysis (GSA) to ${\mathrm{Q}}^2$ for single reaches of the River Thames in southern England. Focusing on the simulation of dissolved oxygen (DO) (since this may be regarded as a proxy for the overall health of a river); the GSA is used to identify key parameters controlling model behavior and provide a probabilistic procedure for model calibration. It is shown that, in the River Thames at least, it is more important to obtain high quality forcing functions than to obtain improved parameter estimates once approximate values have been estimated. Furthermore, there is a need to ensure reasonable simulation of a range of water quality determinands, since a focus only on DO increases predictive uncertainty in the DO simulations. The ${\mathrm{Q}}^2$ model has been applied here to the River Thames, but it has a broad utility for evaluating other systems in Europe and around the world.

Soluble manganese (II) and amorphous and crystalline manganese (IV) oxides were investigated as catalysts for the Fenton-like decomposition of hydrogen peroxide into oxidants and reductants. 1-Hexanol was used as a hydroxyl radical probe and carbon tetrachloride (CT) was used as a reductant probe. Soluble manganese (II)-catalyzed reactions at acidic pH resulted in $>99\%$ degradation of 1-hexanol and no measurable transformation of CT, indicating that hydroxyl radicals were generated but reductants were not. However, when these reactions were conducted at near-neutral pH, an amorphous manganese oxide precipitate formed and 89% of the CT degraded in $60\min$ , while 1-hexanol degradation was negligible. Using an amorphous manganese oxide synthesized in a separate reactor, CT was rapidly degraded while 1-hexanol oxidation was undetectable. Reactions catalyzed by the crystalline manganese oxide pyrolusite $\left(\beta \text{-}\mathrm{Mn}{\mathrm{O}}_2\right)$ at near-neutral pH also resulted in significant CT degradation, indicating that reductants are generated by both the crystalline and amorphous manganese oxide-catalyzed decomposition of ${\mathrm{H}}_2{\mathrm{O}}_2$ . The presence of manganese oxides in the subsurface and their ability to catalyze the generation of reductants in modified Fenton’s reactions has important implications for hydrogen peroxide stability and contaminant transformation pathways during the in situ Fenton’s treatment of contaminated soils and groundwater.

Dissolution is one of the key physiochemical processes controlling subsurface remediation of nonaqueous phase liquid (NAPL) pools. One process that can accelerate NAPL pool dissolution is in situ biodegradation. The bioenhancement of NAPL pool dissolution has been studied previously using an analytical solution for the case of first-order biodegradation kinetics. However, data suggest that at typical NAPL source zone concentrations, mathematical description of dissolution bioenhancement may require biokinetic models ranging from first to zero order. In this work, it was determined that an $n\text{th}$ -order approximation could be derived using the first-order case and bioenhancement was compared under first- and zero-order conditions. Two example scenarios demonstrate that predictions of the potential magnitude of the bioenhancement effect are erroneously high when the first- and zero-order cases are incorrectly applied.