Simulating the Effect of Sulfate Addition on Methylmercury Output from a Wetland

The watershed analysis risk management framework (WARMF) model was applied to Wetland S6 of the Marcell Experimental Forest, using the data from a field experiment, conducted to investigate the effect of sulfate additions on mercury methylation in the wetland. The wetland was modeled as interconnected land catchments. Actual meteorology data and mercury and sulfate concentrations of precipitation were input to the model. To simulate the sulfate sprinkling, the experimental section of the bog was irrigated with sulfate water on the actual dates of sulfate additions. The model simulated wetland outflows that matched the measured outflows with an R-square of 0.856. WARMF also simulated other phenomena observed in the experiment: higher sulfate and MeHg levels at the wetland outlet after every sulfate addition, and higher sulfate and MeHg levels in the pore water of the bog after only the May addition, not the July and September additions. According to WARMF, the low groundwater table in May allowed the sprinkled sulfate to percolate to the soil stratum 10–30 cm below the ground level of the bog, where the pore water was sampled. In July and September, the sulfate could not reach that zone because the percolation was blocked by high groundwater tables. The sampled soil stratum was not the site of methylation that contributed MeHg to the wetland outlet. The saturated zone of the top 10 cm of bog was the site that produced MeHg, which was flushed to the outlet after all sulfate additions. WARMF predicted that quadrupling the sulfate deposition would increase the MeHg output by 216%, which might become lower with more data and better model calibration.     

Aerobic Biodegradation of Methyl Tert-Butyl Ether in Gasoline-Contaminated Aquifer Sediments

Intrinsic biodegradation of methyl tert-butyl ether (MTBE) in aquifer sediments under oxic conditions was investigated using laboratory microcosms. Aquifer samples were collected from three different areas (source area, upgradient, and downgradient) of a shallow gasoline-contaminated aquifer within the Atlantic Coastal Plain Province located in Virginia. Biodegradation of MTBE was observed in the source-area microcosms in which MTBE declined from a starting concentration of 2.7 to 0.28 mg/L over a 58-day period, following an initial lag period of 20 days. The same set of microcosms was respiked with MTBE to an initial concentration of 4.8 mg/L and MTBE concentrations declined to 0.20 mg/L over a 52-day period with no lag in biodegradation. First-order MTBE biodegradation rates for the first and second periods were 0.037±0.003 and 0.063±0.003 day?1, respectively. When another set of source-area microcosms was spiked with MTBE (5 mg/L), toluene and ethylbenzene (1 mg/L each), the initial lag period increased to 33 days but there was no significant change in the MTBE biodegradation rate (0.065±0.026 day?1) and MTBE was not detected after 134 days. Biodegradation of MTBE was also observed in the microcosms constructed using aquifer sediment with only limited exposure to MTBE but the degradation rate was lower and statistically different (0.022±0.005 day?1) than the source area microcosms. Biodegradation of MTBE ceased when oxygen was depleted. Methyl tert-butyl ether did not biodegrade in the uncontaminated, upgradient microcosms; however, rapid biodegradation of toluene was observed. Methyl tert-butyl ether biodegradation appears to be limited in the absence of dissolved oxygen and in aquifer sediments where petroleum hydrocarbons including MTBE were not previously observed.     

Remediation of TCE-Contaminated Groundwater in a Sandy Aquifer Using Pulsed Air Sparging: Laboratory and Numerical Studies

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.     

Effects of Primary Substrate Concentration on NDMA Transport during Simulated Aquifer Recharge

N-nitrosodimethylamine (NDMA) is known to be highly carcinogenic and is present in drinking water, wastewater, and a variety of foods. Because of its presence in chloraminated water at nanogram per liter concentrations, NDMA has become an emerging issue for reclaimed water which may be used for aquifer recharge or irrigation. This research investigated the fate of NDMA in two soil column systems used to simulate subsurface transport. One column system was operated under aerobic conditions with increasing primary substrate concentration where the biodegradable organic carbon (BDOC) in reclaimed water was used as the primary substrate. The reclaimed water content in the influent was increased from 0 to 25% in the column to increase the BDOC concentration. Negligible NDMA removal was observed at 0% reclaimed water and increasing the primary substrate in the influent resulted in NDMA removal suggesting that biodegradation of NDMA might be a cometabolic process. The effects of redox conditions on NDMA fate was studied by operating a second column system with 100% reclaimed water under anoxic conditions and then changing the conditions to aerobic. It was observed that NDMA removal was similar under both aerobic and anoxic condition, however, much lower effluent concentrations were observed under aerobic conditions. Under anoxic condition, a normalized mass removal rate of 254 ng NDMA/mg DOC was observed which increased to 273-ng NDMA/mg DOC under aerobic conditions. The majority of NDMA and substrate removal occurred in the first of three columns in series column under both aerobic and anoxic conditions. Normalized mass removal rates of NDMA after the first, second, and third columns were 372, 30, and 20 ng NDMA/mg DOC, respectively. Since the majority of dissolved organic carbon was also removed in the first column, NDMA biodegradation was consistent with cometabolic activity. Batch tests verified the biodegradation removal potential of NDMA. Addition of a methylotrophic substrate, methanol and an aromatic substrate, toluene, did not increase NDMA removal.     

Comparative Study of SVMs and ANNs in Aquifer Water Level Prediction

In this research, a data-driven modeling approach, support vector machines (SVMs), is compared to artificial neural networks (ANNs) for predicting transient groundwater levels in a complex groundwater system under variable pumping and weather conditions. Various prediction horizons were used, including daily, weekly, biweekly, monthly, and bimonthly prediction horizons. It was found that even though modeling performance (in terms of prediction accuracy and generalization) for both approaches was generally comparable, SVM outperformed ANN particularly for longer prediction horizons when fewer data events were available for model development. In other words, SVM has the potential to be a useful and practical tool for cases where less measured data are available for future prediction. The study also showed high consistency between the training and testing phases of modeling when using SVM compared to ANN. While for the proposed SVM model the relative error of mean square error increased by an average of 42% from the training phase to testing the phase, the corresponding testing error of the ANN model raised by approximately seven times the training error.     

Coupled Reactive Transport Model for Heat and Density Driven Flow in CO2 Storage in Saline Aquifers

In this paper, a novel reactive diffusion-convection transport model is proposed to investigate the flow during different CO2 trappings in deep saline aquifers. Dissolved and immiscible CO2 have trapping times ranging from 1?million to several million years. The mineral trapping has a much longer temporal scale than the solubility trapping. The fine resolution of diffusion-to-advection characteristics is mapped by a corresponding implementation of finite-element numerical simulation. The diffusivity and reaction rate has prominent effects on diffusion-convection-reaction behaviors of the CO2-brine system. The 2-D numerical solutions give insight into the trapping evolution of injected CO2 in a deep subsurface environment.     

Estimation of the Maximum Consumption of Permanganate by Aquifer Solids Using a Modified Chemical Oxygen Demand Test

Knowledge of the consumption of permanganate by naturally occurring reduced species associated with aquifer materials is required for site screening and design purposes to support permanganate in situ chemical oxidation (ISCO) applications. It has been established that this consumption is not a singled-valued quantity, but rather is kinetically controlled. Current methods to determine this permanganate natural oxidant demand (NOD) involve the use of well-mixed batch tests, which are time consuming and subject to test variables (e.g., concentration, mass of oxidant to solid ratio, reaction duration, and mixing conditions) that significantly affect the results. In this paper, we propose a modified chemical oxygen demand (COD) test using permanganate, which can be used to determine the maximum permanganate NOD of an aquifer material. As an initial point of comparison, we tested aquifer materials collected from eight potential ISCO sites using this modified or permanganate COD method, the traditional dichromate COD method, and a method based on well-mixed batch reactors. The results from this comparison indicated that there was no statistically significant difference (α = 5%) between the results of the permanganate COD test and the maximum NOD from the well-mixed batch reactors, while on average the dichromate COD test overestimated the maximum NOD by 100%. The permanganate COD test results were highly correlated to the batch-test maximum NOD data (r = 0.996), and to the total organic carbon and amorphous Fe content of the aquifer materials (r = 0.91). A limited sensitivity investigation of this proposed permanganate COD test revealed that the suspected formation of manganese oxides, a reaction byproduct, may lead to increased experimental variability. However, in spite of this concern we recommend that this proposed permanganate COD method is a quick and economical approach for estimating the maximum permanganate NOD for aquifer materials to support permanganate ISCO site screening and initial design purposes.     

Water Table Fluctuation in the Presence of a Time-Varying Exponential Recharge and Depth-Dependent ET in a Two-Dimensional Aquifer System with an Inclined Base

An analytical solution is presented for water table fluctuation between ditch drains in presence of exponential recharge and depth-dependent evapotranspiration (ET) from groundwater table in a two-dimensional gently sloping aquifer. The groundwater head above the drain is small compared to the saturated thickness of the aquifer. A sound mathematical transformation is devised to transform the two-dimensional groundwater flow equation into a simple form, which makes possible to obtain an analytical solution. The transient midpoint water table variations from the proposed solution compare well with the already existing solutions for horizontal aquifer. A numerical example is used to illustrate the combined effect of depth-dependent ET coupled with a time-varying exponential recharge on the water table fluctuation. The inclusion of a depth-dependent ET in the solution results in water table decline at a faster rate as compared to the case when ET is not considered. With an increase in slope of the aquifer base, water table profiles become asymmetric and the water table divide shifts towards the lower drain. The height of the water table profiles increases on moving away from the boundary of the aquifer and the highest level of the ground water table is obtained in the central portion of the aquifer basin due to the presence of drainage ditches on the aquifer boundary. When the effect of ET is incorporated in combination with recharge, the analytical solution results in accurate and reliable estimates of water table fluctuations under situations subjected to a number of controlling factors. This study will be useful for alleviation of drainage problems of the aquifers receiving surface recharge and surrounded by streams.     

Inactivation of Cryptosporidium Oocysts in a Pilot-Scale Ozone Bubble-Diffuser Contactor. II: Model Validation and Application

The axial dispersion reactor (ADR) model developed in Part I of this study was successfully validated with experimental data obtained for the inactivation of C. parvum and C. muris oocysts with a pilot-scale ozone-bubble diffuser contactor operated with treated Ohio River water. Kinetic parameters, required to model the effect of temperature on the decomposition of ozone in treated Ohio River water and oocyst inactivation, were determined from batch and semibatch ozonation experiments. The ADR model was used to simulate the effects of operating conditions (feed-gas ozone concentration, liquid flow rate, and gas flow rate), and water quality related parameters (fast ozone demand, first and second order ozone decomposition rate constants, and temperature) on the performance of the pilot-scale contactor. The model simulation provided valuable insight into understanding the performance of ozone disinfection systems and recommendations for ozone contactor design and optimization. For example, the simulation revealed that meeting inactivation requirements for C. parvum oocysts would be more challenging at relatively lower temperatures.     

Modeling the Sorption of Fluoride onto Alumina

Fluoride is a potentially toxic ion that occurs in aquifers both naturally and as a result of anthropogenic activity. Sometimes remediation of the aquifer is required. One potential aquifer decontamination strategy is an “interception-sorption trench”—one of a number of “reactive wall” technologies. This remediation strategy relies upon natural hydraulic gradients to transport the fluoride through the aquifer to the interception-sorption trench where it partitions onto a strong sorbent—alumina. In this paper, the focus is on the development and calibration of an equilibrium-based geochemical model that will be employed in the development of a quantitative reactive transport model, which in turn will be used for the design of an interception-sorption trench. The geochemical model described here takes into account a variety of ions likely to be present in a sandy aquifer, chemical activities, and the surface charge on the alumina. The model is calibrated over a wide pH range and for high initial fluoride concentrations using experimental results obtained from batch tests. It is found that pH dependent equilibrium constants are needed to capture the behavior of the experimentally observed fluoride sorption. The presence of sodium sulfate in solution is investigated, and it is found that sodium significantly interferes with the sorption of fluoride onto alumina under alkaline conditions. The geochemical model indicates that under acidic conditions, the alumina may release potentially large and unacceptable concentrations of aluminum into the aquifer. As a way of managing this potential problem, it is proposed that aluminum concentrations in the pore fluid may be mitigated by the inclusion of tree bark within the interception-sorption trench.     

Effect of pasteurization on infectivity of Cryptosporidium parvum oocysts in water and milk

Cryptosporidium parvum is a major cause of diarrheal disease in humans and has been identified in 78 other species of mammals. The oocyst stage, excreted in feces of infected humans and animals, has been responsible for recent waterborne outbreaks of human cryptosporidiosis. High temperature and long exposure time have been shown to render oocysts (suspended in water) noninfectious, but for practical purposes, it is important to know if high-temperature--short-time conditions (71.7 degrees C for 15 s) used in commercial pasteurization are sufficient to destroy infectivity of oocysts. In this study, oocysts were suspended in either water or whole milk and heated to 71.7 degrees C for 15, 10, or 5 s in a laboratory-scale pasteurizer. Pasteurized and nonpasteurized (control) oocysts were then tested for the ability to infect infant mice. No mice (0 of 177) given 10(5) oocysts pasteurized for 15, 10, or 5 s in either water or milk were found to be infected with C. parvum on the basis of histologic examination of the terminal ileum. In contrast, all (80 of 80) control mice given nonpasteurized oocysts were heavily infected. These data indicate that high-temperature--short-time pasteurization is sufficient to destroy the infectivity of C. parvum oocysts in water and milk.     

Effect of Temperature on Ozone Inactivation of Cryptosporidium parvum in Oxidant Demand-Free Phosphate Buffer

Ozone inactivation of Cryptosporidium parvum oocysts was studied at bench-scale in 0.05 M phosphate buffer at 1 to 37°C, pH 6–8. Animal infectivity using neonatal CD-1 mice was used for evaluation of oocyst infectiousness following treatment. Survival curves of ozone inactivation were characterized by a tail-off effect, with an initial shoulder most evident at low temperature. Temperature was a critical factor for ozone inactivation kinetics with a significant decrease of ozone efficacy at low temperature. Accounting for ozone residual stability at different pH conditions, pH was found to have no significant effect on the activation of C. parvum by ozone. Inactivation kinetics at different temperatures were expressed as an Incomplete gamma Hom model with different reaction rate constants, adjusted for water temperature using the van't Hoff-Arrhenius relationship. Between 1 and 37°C, for every 10°C decrease in the water temperature, the inactivation rate constant decreased by a factor of 2.2, corresponding to activation energy of 51.7 kJ∕mol. Ozone disinfection design criteria for 1.0 and 2.0 log-units of inactivation of Cryptosporidium were developed for various water temperatures, and 90% confidence intervals are also provided.     

方坯连铸液体流动模拟实验

通过水模拟实验装置，对方坯连铸过程中的液体流动行为进行了实验和分析，结晶器内的液流状态分为冲击区和层流区，冲击区占据了结晶器的主要部分。     

Role of the Material Constitutive Model in Simulating the Reusable Launch Vehicle Thrust Cell Liner Response

The reusable launch vehicle thrust cell liner, or thrust chamber, is a critical component of the space shuttle main engine. It is designed to operate in some of the most severe conditions seen in engineering practice. These conditions give rise to characteristic deformations of the cooling channel wall exposed to high thermal gradients and a coolant-induced pressure differential, characterized by the wall’s bulging and thinning, which ultimately lead to experimentally observed “dog-house” failure modes. In this paper, these deformations are modeled using the cylindrical version of the higher-order theory for functionally graded materials in conjunction with two inelastic constitutive models for the liner’s constituents, namely Robinson’s unified viscoplasticity theory and the power-law creep model. Comparison of the results based on these two constitutive models under cyclic thermomechanical loading demonstrates that, for the employed constitutive model parameters, the power-law creep model predicts more precisely the experimentally observed deformation leading to the “dog-house” failure mode for multiple short cycles, while also providing much improved computational efficiency. The differences in the two models’ predictions are rooted in the differences in the short-term creep and relaxation responses.     

Generalized Analytical Solutions for Groundwater Head in a Horizontal Aquifer in the Presence of Subsurface Drains

Generalized analytical solutions for groundwater head in horizontal aquifers in the presence of parallel subsurface drains are obtained considering a transient rate of recharge as a power series (polynomial) function and depth-dependent rate of evapotranspiration. A function, new to analytical drainage studies, is proposed for correctly representing the depth-dependent rate of evapotranspiration. The solutions are obtained considering the practical situation of drains placed at a shallow depth in a considerable depth of aquifer. Two conditions of large and small saturated thicknesses in comparison to the changes in groundwater head are considered. A mathematical criterion is proposed to distinguish between large and small saturated thicknesses.     

Synergistic Effect of N and Ni2+ on Nanotitania in Photocatalytic Reduction of CO2

Nitrogen and nickel codoped nanotitania (N-Ni/TiO2) photocatalysts for producing methanol by photocatalytic reduction of CO2 were prepared by an improved sol-gol method. The catalysts were characterized by XRD, HRTEM, DES, FTIR, TG-DSC, and UV-Vis, respectively. The experimental results indicated that nano-N-Ni/TiO2 had better properties than the pure nanotitania (TiO2), N doped titania (N/TiO2), and Ni2+ doped titania (Ni/TiO2), considering their performance of photoresponse and photocatalytic reduction of CO2. The methanol yield could reach 482.0μmol/g-cat under optimal conditions. Additionally, the synergetic effect of N and Ni2+ on nano-TiO2 in photocatalytic reduction of CO2 was explained, and the mechanism of photocatalytic reduction CO2 on N-Ni/TiO2 catalyst was proposed.     

Water Reuse/Recycling and Reclamation in Semiarid Zones: The Israeli Case of Salination and “Hard” Surfactants Pollution of Aquifers

The essence of three case studies in relation to the global problem of surface and groundwater contamination by inorganic salts and biodegradation-resistant (“hard”) nonionic surfactants (APEOs) is presented and the results analyzed as far as the long-term consequent water salt and APEO profiles are concerned. The main conclusion derived is that sustainable large-scale reuse/recycling and reclamation in semiarid zones requires a combined desalination-biological treatment of APEO-free sewage/wastewaters before their reuse. This should be done without delay in order to ensure the quality of the supplied water from the scarce resources and to avoid, most probably, an irreversible process of aquifer contamination in these zones.     

CO/CO2气氛对Fe3C形成的影响规律

利用X-ray衍射和失重法研究了CO/CO2混合气体还原氧化铁过程中Fe3C的生成规律,得到3Fe 2CO=Fe3C CO2的反应标准自由能表达式为:△G°= -151 470 168.78T,绘制了碳化铁生成热力学平衡图,与实验结果基本吻合.     

Effect of Na2O on the Reduction of Fe2O3 Compacts with CO/CO2

Compacts of Fe₂O₃ and Fe₂O₃ doped with varying amounts of Na₂O were isothermally reduced at several temperatures, using CO/CO₂ mixed gas in a vertical resistance furnace. To determine the effect of Na₂O on the reduction of Fe₂O₃ compacts, the mass loss due to oxygen removal was continuously recorded, from which the reduction rate and rate constant were obtained. Na₂O was found to retard the reduction of Fe₂O₃ compacts. The apparent activation energy (E _a) of reaction and the mathematical relationship for pore gas diffusion suggested that the reduction behavior at the initial stages was controlled by a combination of pore gas diffusion and interfacial chemical reaction. At the intermediate and late stages of reduction, pore gas diffusion was the sole contributing factor. Morphological examination of the reduced compacts showed the formation of a liquid phase during the reduction process, which appeared to lower the rate of reaction.     

Inactivation of Adenovirus Types 2, 5, and 41 in Drinking Water by UV Light, Free Chlorine, and Monochloramine

A bench-scale study was conducted to determine the inactivation of adenovirus (Ad) types 2, 5, and 41 by ultraviolet (UV) light, chlorine, and monochloramine. The motivation for this study was to determine whether UV disinfection followed by chlorine or monochloramine for a very short contact time (e.g., a minute) could satisfy regulatory requirements for four-log virus inactivation. In order to overcome the difficulty Ad 41 presents for enumeration of the virus in cell culture, a technique was used that combined immunofluorescent staining of viral antigen with traditional scoring of cytopathic effect. A UV dose of 40?mJ/cm2 (millijoules per square centimeter) (applied using a collimated beam apparatus) achieved approximately one-log inactivation of adenovirus types 2, 5 and 41, confirming previous research. Ad 41 was found to be more UV resistant to UV light than Ad 2 or Ad 5 at UV doses >70?mJ/cm2 to a statistically significant degree (95% confidence); however, at lower UV doses there were no statistically significant differences. Experiments with Ad 5 and Ad 41 at 5°C and pH 8.5 showed that chlorine was very effective against Ad 5 and Ad 41, with a product of disinfectant concentration and contact time (CT) of 0.22?mg min/L providing four-log inactivation. Monochloramine was less effective against these adenoviruses, with a CT of 350?mg min/L required to achieve 2.5-log inactivation of Ad 5 and 41 at 5°C and pH 8.5.