Journal of Environmental Engineering

Various numerical modeling approaches, all based on computational fluid dynamics (CFD) solutions for the flow field, are studied for an ultraviolet disinfection system in which the lamps are oriented perpendicular to the flow direction. A two-dimensional model assumption is made in all simulations, for which turbulent flow solutions were obtained with commercial CFD software (FIDAP). Two modeling approaches were studied. A continuum Eulerian approach was taken in formulating an appropriate advection–diffusion equation which is solved for the viable micro-organism concentration. Alternatively, a Lagrangian approach, in which particles are numerically introduced into the flow and their trajectories through a spatially varying field of ultraviolet intensities were computed, was also investigated. The effect of modeling unsteady-flow features associated with vortex shedding and motion on the extent of disinfection was examined by comparing time-averaged results based on an unsteady-flow continuum model with the results from an analogous simulation assuming a steady flow. Under the steady-flow assumption, differences between predictions of the Eulerian continuum approach and the Lagrangian particle-trajectory approach were also considered. Both modeling approaches yielded similar predictions over a range of loadings, and tended to underestimate the extent of disinfection when compared to measurements at the pilot scale.

Ultraviolet (UV) disinfection of greywater has a number of advantages for small scale applications, but the UV disinfection efficiency can be impeded by high levels of particulates and chemicals in the greywater, micro-organism aggregation, and the geometry between the UV lamp and surrounding sleeve leading to suboptimal flow paths through the lamp assembly. Most process models for UV systems are empirical in nature and do not adequately represent the distribution of UV dose that is actually delivered to micro-organisms in a continuous flow system. This paper presents a model which incorporates: (1) variations in micro-organism sensitivity to UV radiation, (2) the variation of dose received in the UV reactor chamber, and (3) the shielding effect of part of the micro-organism population by the presence of particulates. The model is capable of predicting the asymptotic decay observed in bacterial survival curves when organisms are exposed to a UV dose in a greywater matrix and has been calibrated using experimental data on a series of synthetic greywaters of differing composition and validated against a series of real greywater samples. The model compares favorably to other UV disinfection models and allows the influence of water quality parameters such as turbidity, suspended solids, and UV absorbance to be examined. This allows water quality limits to be defined beyond which the UV disinfection of greywater becomes ineffective. Acceptable performance criteria are established for low power UV systems for the treatment of greywater, which have implications for the selection of suitable annular UV reactors.

During crossflow microfiltration, formation of cake layer on the membrane inhibits the filter performance. Previous studies on cake formation have focused on the monodisperse conditions, although most field applications are under the polydisperse conditions. In this study, microfiltration experiments were conducted to investigate the effect of particle size on cake formation, especially, at polydisperse conditions. Kaolin and two kinds of $\mathrm{Ca}\mathrm{C}{\mathrm{O}}_3$ were used as polydisperse particles and a polysulfon hollow fiber microfilter was used as the membrane for the experiment. To describe the effect of particle size on cake formation at polydisperse conditions, effective diameter for shear-induced diffusion (EDSD) was introduced as a representative particle size. Statistical analyses of the experimental results showed that EDSD can be used in quantifying the potential of cake formation at polydisperse conditions, and the larger the EDSD, the thinner the cake layer. EDSD was an imperative indicator which showed the potential of cake formation at polydisperse conditions quantitatively and can be applied to find efficient strategies for reducing the cake layer.

Five biofilm airlift suspension (BAS) reactors filled with ceramic materials as biocarriers were used to investigate the hydrodynamics, liquid mixing, and biofilm detachment kinetics in the BAS reactor. A mathematical model was developed to describe the internal liquid circulation within the BAS reactor. The Froude number was introduced to correlate the relationship between the Froude number and superficial gas velocity at different biocarrier concentrations. The validity of the empirical model was verified over a wide range of experimental conditions and the result shows that the internal liquid circulation velocity was proportional to the square root of the reactor height and the superficial gas velocity. Because the internal liquid circulation flow rate was much larger than influent flow rate, the BAS reactor had a strong capacity to resist shock loading caused by the change in influent organic matter concentration. Shock loading resistance increased with the height of a BAS reactor. Although biofilm detachment was a very complicated process which involved many mechanisms, dimensional analysis was employed to successfully analyze the biofilm detachment kinetics. It was found that the biofilm detachment rate was proportional to the first power of the superficial gas velocity and biofilm thickness, and to the $2∕3$ power of the number of biocarriers in the reactor, respectively. Use of the Froude number and dimensional analysis provide an effective and accurate method to study the characteristics of the BAS reactor.

A combined activated sludge–biofilm bioprocess called TNCU-I was developed by adding a rotating biological contactor to the aerobic zone of a traditional A2O process in order to solve the sludge retention time conflict between nitrifiers and phosphate accumulating organisms (PAOs), and the carbon source competition between denitrifiers and PAO. The TNCU-I process shows excellent carbon, nitrogen, and phosphate removal performance when treating synthetic wastewater. The process also achieved a more stable nitrification performance than the A2O process. The specific nitrification rate, the specific anoxic and aerobic phosphate uptake rates, the specific denitrification rate, and the specific anaerobic phosphate release rate were determined by a series of batch experiments. Such data were further analyzed to optimize the volume ratio of the TNCU-I anaerobic, anoxic, and aerobic tanks. The optimized process was also operated to confirm the performance. In addition, both Nitrosospira and Nitrospira were identified in the activated sludge and the rotating biological contactor biofilm by 16S rDNA based biotechnology.

The fate of tolyltriazoles, nonylphenol and nonlyphenol ethoxylates during anaerobic treatment of ethylene glycol (EG) based wastewater during batch or continuous upflow anaerobic sludge blanket reactors was investigated. Equilibrium sorption studies indicated that there was minimal sorption of benzotriazole (BT), 5-methyl-1 H-benzotriazole (MeBT), and 5,6-dimethyl-1 H-benzotriazole (DiMeBT) to anaerobic granules. Nonylphenol (NP), a reported biodegradation product of NP ethoxylates, had a higher sorption capacity to anaerobic biomass and was described by the Freundlich isotherm. Batch serum bottle EG degradation experiments indicated that BT, MeBT, DiMeBT, and the nonionic NP ethoxylate surfactant Tergitol NP-4 had no significant effects on acidogenesis and methanogenesis at the concentration levels studied. Significant inhibition of acetoclastic activity was observed for the biodegradation intermediate NP at $100\mathrm{mg}∕\mathrm{L}$ , with acetic acid consumption rate at 38% of the controls. No evidence for anaerobic degradation of benzotriazole and its derivatives was observed for both batch and continuously fed anaerobic systems. Continuously fed anaerobic experiments provided evidence that indicated that anaerobic degradation of nonylphenol ethoxylates and the biodegradation intermediate NP occurred.

Response of an aerobic upflow sludge blanket (AUSB) reactor system to the changes in operating conditions was investigated by varying two principle operating variables: the oxygenation pressure and the flow recirculation rate. The oxygenation pressure was varied between 0 and $25\mathrm{psig}$ (relative), while flow recirculation rates were between 1,300 and 600% correspondingly. The AUSB reactor system was able to handle a volumetric loading of as high as $3.8\mathrm{kg}$ total organic carbon $\left(\mathrm{TOC}\right)∕{\mathrm{m}}^3\text{day}$ , with a removal efficiency of 92%. The rate of TOC removal by AUSB was highest at a pressure of $20\mathrm{psig}$ and it decreased when the pressure was increased to $25\mathrm{psig}$ and the flow recirculation rate was reduced to 600%. The TOC removal rate also decreased when the operating pressure was reduced to 0 and $15\mathrm{psig}$ , with corresponding increase in flow recirculation rates to 1,300 and 1,000%, respectively. Maintenance of a high dissolved oxygen level and a high flow recirculation rate was found to improve the substrate removal capacity of the AUSB system. The AUSB system was extremely effective in retaining the produced biomass despite a high upflow velocity and the overall sludge yield was only $0.24–0.32\mathrm{g}$ VSS/g TOC removed. However, the effluent TOC was relatively high due to the system’s operation at a high organic loading.

This paper presents a novel approach to study and predict the removal of organic carbon in groundwater recharge systems by combining microbial community description with advanced methods for organic carbon characterization. Soil microbial biomass was characterized using three methods: dehydrogenase activity (general heterotrophic activity), substrate induced respiration (rapid mineralization potential), and phospholipid extraction (total viable biomass). These methods proved to be sensitive, robust, and relatively simple in their application for soils of various groundwater recharge sites. Findings indicated that microbial biomass was positively correlated to the organic carbon removal capacity of different laboratory-scale test systems. Organic carbon seems to be a limiting factor for biomass growth in recharge systems. Organic carbon removal rates are increased by higher initial organic carbon concentrations. The removal of three organic carbon fractions (natural organic matter, effluent organic matter, and glucose and glutamic acid) in soil column studies followed a first-order kinetic with distinctly different rate constants and correlated positively with respective total viable biomass in the column systems. These results supported the assumption that during groundwater recharge organic carbon is preferably removed by biological processes. The transformation of organic carbon fractions during travel through the subsurface became apparent in size-exclusion chromatograms indicating a shift to smaller molecular weight. The presented approach showed promise to reveal new insights into removal mechanisms of organic carbon and to serve as a tool to predict organic carbon removal in groundwater recharge systems to improve design and operation of vadose zone treatment.

Perchlorate $\left(\mathrm{Cl}{\mathrm{O}}_4^{-}\right)$ can be reduced by iron surfaces, suggesting that permeable reactive barriers may represent a useful groundwater remediation strategy. However, chloride produced by the reaction inhibits further perchlorate removal. Adsorption of chloride on iron filings was investigated as a potential mechanism of chloride interference. The effect of chloride on the removal of nitrate, another oxyanion reactive at iron surfaces, was also investigated to draw more general conclusions about anion competition when target compounds adsorb electrostatically. A triple layer adsorption model was used to describe chloride sorption isotherms on the iron filings using magnetite as the model surface and defining a single type of surface hydroxyl sorption site. The model considered electrostatic attraction, specific sorption, and the effect of adsorbed ${\mathrm{Fe}}^{2+}$ on chloride sorption. Experimental and modeling results indicate that chloride competition is probably not of concern for nitrate reduction in permeable reactive barriers. However, perchlorate reduction is significantly inhibited by chloride in both buffered and unbuffered solutions, possibly because the reactive sorbed ${\mathrm{Fe}}^{2+}$ sites may be preferentially occupied by chloride.

The use of permeable reactive barriers (PRBs) for groundwater remediation is based on two distinct mechanisms: sorption and transformation. With sorption as the main mechanism, contaminants sorb on the PRB materials and are retarded. With transformation as the main mechanism, the contaminants react with the PRB materials and then converted to less toxic or innocuous substances. In this study, we tested surfactant-modified zeolite/zero valent iron (SMZ/ZVI) pellets as a PRB material to retard and degrade perchloroethylene (PCE), utilizing both sorption and transformation processes. Batch PCE kinetic studies showed instantaneous PCE removal from the aqueous phase due to sorption and subsequent removal with time due to reduction. The separation of sorption from reduction can be used to obtain both the PCE distribution coefficient $\left(K_d\right)$ and the pseudofirst-order reduction rate constant $\left({\mu }_{\mathrm{obs}}\right)$ from a single batch experiment. The calculated $K_d$ and ${\mu }_{\mathrm{obs}}$ values are 3.0 and $0.5\mathrm{L}∕\mathrm{kg}$ and 0.14 and $0.05{\mathrm{h}}^{-1}$ for SMZ/ZVI and Z/ZVI pellets, respectively. Column experiments were performed at linear flow velocities of 0.07, 0.14, and $0.20\mathrm{cm}∕\min$ . The results were modeled using the one-dimensional advection–dispersion equation with linear sorption and first-order transformation. The $K_d$ values were $2.3\pm 0.4$ and $0.5\pm 0.1\mathrm{L}∕\mathrm{kg}$ for SMZ/ZVI and Z/ZVI pellets, respectively, in agreement with those of the batch study. The PCE transformation constants varied between 0.077 and $0.199{\mathrm{h}}^{-1}$ for the SMZ/ZVI pellets and between 0.037 and $0.144{\mathrm{h}}^{-1}$ for the Z/ZVI pellets, indicating that an enhanced transformation of PCE occurred with the sorbing SMZ/ZVI pellets. The PCE reduction rates were faster at slower flow rates, indicating that the reduction was not a mass-transfer-limited process.

The fate and transport of chemicals of concern released from field soils must be known to protect human and ecological receptors. A mechanistic approach to modeling chemical release from soil is advantageous to implement effective remediation strategies at an impacted site. The focus of this research was to gain an understanding of the processes causing slow release of polyaromatic hydrocarbons (PAHs) from field soils collected at sites with historical releases. A mechanistically based intraparticle diffusion model was applied to experimentally measured hydrocarbon release data and particle size distributions obtained from three field soils. For these field soils, the intraparticle diffusion model was able to describe the measured chemical release data. Fitted effective diffusion coefficients $\left(D_{\mathrm{eff}}\right)$ of the intraparticle diffusion model correlated to expected results. Trends were found to exist between the $D_{\mathrm{eff}}$ and both the molecular weight (MW) and the octanol–water partition coefficient $\left(K_{\mathrm{ow}}\right)$ of the PAH analyzed for the field soils with low organic carbon content. For these soils, the relationships suggest that intraparticle diffusion processes may be responsible for slow desorption and it may be possible to estimate $D_{\mathrm{eff}}$ values for a soil or contaminated media with similar intraparticle properties using a readily measured chemical characteristic such as MW and $K_{\mathrm{ow}}$ .

The expanded use of caps and cover systems is an important aspect of the U.S. Department of Energy Environmental Management’s strategy for restoration and long-term stewardship of sites throughout the complex. However, very little is available in terms of long-term monitoring of covers other than downstream groundwater or surface water monitoring. A novel methodology for verifying and monitoring subsurface barriers and cover systems has been developed. Gaseous perfluorocarbon tracers (PFTs) are injected on one side of the barrier and searched for on the opposite side of the barrier. The capability for leak detection in subsurface barriers using PFTs has been proven at multiple demonstrations. Adaptation of this concept to covers is a necessary step prior to full-scale demonstration. This paper discusses the PFT technology and a successful proof-of-principle test of the PFT technology as a leak detection tool for cover verification and monitoring.

Industrial fired heaters are a major source of nitrogen oxides ( ${\mathrm{NO}}_x$ ). On-line analyzers, kinetic models with computational fluid dynamics, and empirical predictive models have been developed to monitor ${\mathrm{NO}}_x$ emissions and analyze excessive ${\mathrm{NO}}_x$ emissions. However, previous approaches have been applied only to single heater systems, not to large-scale multiheater systems. This paper proposes a hierarchical monitoring and diagnosis procedure to monitor ${\mathrm{NO}}_x$ emissions from large-scale multiheater systems and to identify the root causes of excessive ${\mathrm{NO}}_x$ emissions as well as heater malfunctions. The procedure provides a functional three-layer hierarchy: (1) prediction of ${\mathrm{NO}}_x$ concentrations; (2) estimation of the influence of individual heaters on the predicted ${\mathrm{NO}}_x$ ; and (3) identification of the root causes by examining the detailed contributions of process variables to variations of the heater identified in step 2 as being the principal source of ${\mathrm{NO}}_x$ . An integrated multiblock partial least-squares (PLS) model, created by combining standard PLS and multiblock PLS, is employed to predict the ${\mathrm{NO}}_x$ emissions and estimate the influences of the heaters on the emissions. The validity of the proposed method is demonstrated through its application in two case studies.

Spatially independent Gaussian noise has been widely assumed in examining the Kalman filter (KF) properties in different areas of engineering practice. However, for subsurface modeling, it is more reasonable to consider both data and noise as regional. In this study, regional noises are employed in KF and finite-difference schemes in solving the subsurface transport problem. A KF is constructed as a data assimilation scheme for a subsurface numeric model. Also, a regional random field simulation scheme is proposed and employed to examine the impact on effectiveness of KF correction processes. The results indicate that the prediction error of the KF data assimilation scheme is 30% smaller than the error from the deterministic model. Furthermore, by applying a correct regional noise structure, the KF data assimilation scheme reduces the prediction error from 25 to 10 ppm in our model, indicating an improvement of 60% in prediction accuracy.

Methyl tert-butyl ether (MTBE) is frequently used as a gasoline additive to reduce carbon monoxide emissions from vehicles. Alternative fuel oxygenates are also used separately or in conjunction with MTBE including ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), diisopropyl ether (DIPE), tert-butyl alcohol (TBA), and ethanol (EtOH). Granular activated carbon (GAC) sorption is a proven technology for the removal of the ether oxygenates while the alcohols are not well adsorbed. In this research, Freundlich and Langmuir isotherms coefficients were developed based on linearized forms of the models for MTBE, ETBE, TAME, and DIPE $(R^2>0.97)$ on two common bituminous coal GACs:Calgon F400 and F600. No significant adsorption of either TBA or EtOH was observed on these carbons. The relative capacities on both Calgon F400 and F600 were $\mathrm{DIPE}>\mathrm{TAME}>\mathrm{ETBE}>\mathrm{MTBE}>\mathrm{TBA}$ , EtOH.

A master diagnostic curve (MDC) method is proposed for identifying the dispersion coefficient from observed breakthrough curve in soil–column experiments. The method uses matching of diagnostically plotted points to the MDC. Accurate identification of the dispersion coefficient is possible with a parallel shift of only one axis. Another advantage of the method is that the MDC is an invariant curve and once prepared, can be used for different data sets characterized by high Péclet number. The new method is simple, does not require large computations as in conventional least-squares approach, and yields a quick and accurate estimate of the dispersion coefficient. The new method does not require an initial guess for the dispersion coefficient. It can also yield a value of the dispersion coefficient from a single observed concentration. Although subjectivity is involved in matching, there is a transparent visual realization of the reliability of the estimated dispersion coefficient, and the points with substantial errors. The new method has several advantages over the least-squares approach and is suited for an advanced study on the subject. An estimate of the dispersion coefficient obtained using the new method is as good as obtained using a good optimization method.