High Rates of Ammonia Removal in Experimental Oxygen-Activated Nitrification Wetland Mesocosms

While constructed treatment wetlands are very efficient at polishing nitrate from secondary effluent, they are much less effective at removing ammonia. A key factor that limits ammonia oxidation via biological nitrification in vegetated wetlands is low levels of dissolved oxygen. This study evaluated the effectiveness of side-stream oxygenation to enhance ammonia removal in replicate surface-flow experimental mesocosms containing wetland sediment and plants (Typha spp.). Mesocosms had a water volume of 29.5 L, a hydraulic retention time of 5 days, and a hydraulic loading rate of 4.3 cm/d, and were loaded with synthetic secondary effluent contain 10 mg-N/L of ammonia. Relative to nonoxygenated controls, oxygenation increased ammonia removal rates by an order of magnitude. Areal removal rates increased from 40?mg-N/m2/d to 450?mg-N/m2/d, concentration removal efficiency increased from 10 to 95%, and area-based first-order removal rates increased from <2?m/year to 50–75 m/year. Ammonia removal rates in oxygenated mesocosms were 2- to 4-fold higher than rates reported for full-scale constructed wetlands treating secondary effluent. Results show that oxygen-activated nitrification wetlands, a hybrid of conventional oxygenation technology and wetland ecotechnology, hold promise in economically enhancing rates of ammonia removal and shrinking the wetland area needed to polish ammonia-dominated secondary effluent. Further study is needed to confirm that oxygenation can promote high rates of ammonia removal at the field scale.     

Simulating the Effect of Liquid CO2 on Cryptosporidium parvum Oocysts in Aquifer Material

The effects of liquid CO2 injection on the viability of Cryptosporidium parvum oocysts were evaluated. A laboratory study was designed to test the effects of saturated CO2, freeze–thaw cycles and different freezing protocols on C. parvum oocysts in aquifer material. Oocysts were exposed to a saturated solution of CO2 at room temperature for 1-, 4-, 8-, and 12-h intervals and their viability was compared with controls. One- and three-cycle freeze–thaw experiments on oocyst survival were conducted. Inactivation of oocysts was assessed for: (1) rapid freezing and rapid thawing and (2) gradual freezing and rapid thawing. Exposure to 1 atm of CO2 in water at room temperature had a negligible effect on oocyst viability. Average oocyst viability after the one- and three-cycle freeze–thaw experiments was 24.7 and 2.7%, repsectively. The average oocyst viability associated with the rapid freeze–thaw and gradual freeze–thaw experiments was 11.3 and 26.2%, respectively. Freezing associated with injection of liquid CO2 into aquifers would be the factor inactivating oocysts; to cause a 3-log decrease in oocyst viability multiple injections may be required.     

Spatial Variation of Sediment Sulfate Reduction Rates in a Saline Lake

Devils Lake in North Dakota is a terminal, multibasin, saline lake with an overall surface area that is currently approximately 44,520?ha (110,000?acres). Lake elevation has increased by more than 7?m within 10?years, and vast areas of prairie and cropland have been flooded. The lake is rich in sulfate, and water column sulfate concentrations are relatively uniform within each of the five major basins, but increase from 3.1?mM (300?mg/L) in West Bay to 31?mM (3,000?mg/L) in East Devils Lake. Sediment cores were collected from three of the basins at different water depths, and used in laboratory studies to evaluate the spatial distribution of sulfate-reducing bacteria (SRB) activity in the lake sediments. The high sulfate concentrations within the experimental sediment cores suggest that the activity of SRB is limited by the availability of suitable electron donors rather than by the availability of sulfate and that SRB activity can be defined by a zero-order volumetric rate constant (K0). Experimentally determined K0 values ranged from 11?to?88?mmol SO42? m?3?day?1. The water depths from which sediment cores were collected in Devils Lake are related to the elapsed time since inundation by the rising lake level. It was found that time since inundation influences the observed K0 value. Mean K0 values for cores from an average depth of 4.8?m (submergence time of about 5?years), and 9.4?m (submergence time of about 28?years) were 62 and 17?mmol SO42? m?3?day?1, respectively. The significant difference (two-tailed t-test, p<0.05) suggests that SRB activities in the Devils Lake sediments change with submergence times. A uniform sulfate reduction rate applied to all Devils Lake sediments is therefore only a crude approximation of reality.     

Evaluating Four Storm-Water Performance Metrics with a North Carolina Coastal Plain Storm-Water Wetland

Storm-water best management practices (BMPs) are typically assessed using the performance metric of pollutant concentration removal efficiencies. However, debate exists whether this is the most appropriate metric to use. In this study, a storm-water wetland constructed and monitored in the coastal plain of North Carolina is evaluated for water quality and hydrologic performance using four different metrics: concentration reduction, load reduction, comparison to nearby ambient water quality monitoring stations, and comparison to other wetlands studied in North Carolina. The River Bend storm-water wetland was constructed in spring 2007 and was monitored from June 2007 through May 2008. Twenty-four hydrologic and 11 water quality events were captured and evaluated. The wetland reduced peak flows and runoff volumes by 80 and 54%, respectively. Reductions were significant. Concentrations for the following pollutants increased: total kjeldahl nitrogen (TKN), NH4–N, total nitrogen (TN), and total suspended solids (TSS); inflow and outflow concentrations did not change for total phosphorus (TP), while only NO2–3–N and orthophosphorus (OP) concentrations were lower at the outlet. Using a load reduction metric, results were strikingly different, showing positive load reductions of 35, 41, 42, 36, 47, 61, and 49% for these respective pollutants: TKN, NO2–3–N, NH4–N, TN, TP, OP, and TSS. When comparing the effluent concentrations from the wetland to ambient water quality in the Trent River, all effluent nitrogen species concentration were either similar or lower. TP and TSS concentrations leaving the wetland were higher than ambient water quality data. Finally, by comparing pollutant concentrations among different North Carolina wetlands, it is apparent the River Bend wetland received relatively “clean” water and released water with pollutant concentrations comparable to all other studies examined. Major conclusions from this study include: (1) storm-water wetlands sited in sandier soils (such as those of the North Carolina coastal plain) should be considered a low impact development tool and (2) the selection of performance metric has a pronounced bearing on how a BMP’s performance is perceived. Sole reliance on a concentration reduction metric is discouraged.     

Effect of Water Addition Frequency on Oxygen Consumption in Acid Generating Waste Rock

The oxygen decay coefficient is a key parameter used to predict the distribution of oxygen concentrations spatially and temporally in a waste rock pile. The present study proposes a new equation to calculate the oxygen decay coefficient based on the oxidation rate (sulfate release rate) of the waste rock, dry density, and equivalent porosity for oxygen transport. The equation gave oxygen decay coefficients that were of the same order of magnitude as those obtained from a semianalytic solution to the modified Fick’s law with an oxygen consumption term. Values were in the range of 3.74×10?8?s?1 for air dry waste rock and 3.99×10?7?s?1 for moist waste rock. The effect of water addition frequency on the oxidation rate and the oxygen decay coefficient was investigated through four column experiments with various flushing rates and a laboratory case simulating actual precipitation at a specific site. The results indicated that the oxygen decay coefficient was dependent on not only the oxidation rate but also on the physical characteristics of the waste rock, such as porosity and dry density. The flushing rate had a significant influence on the oxidation rate of the waste rock and the calculated oxygen decay coefficient. The oxidation rate of the waste rock decreased from 1.19×10?6 to 5.32×10?7?s?1 with an increase in flushing intervals from 1 week to 4 weeks. When the drying period was longer than 3 weeks, the oxidation rate decreased very slowly with an increase in drying period for the tested waste rock.     

National Assessment of Pesticide Runoff Loads from Grass Surfaces

Pesticide runoff loads from grass surfaces were estimated through simulation experiments for 37 chemicals registered for use on U.S. lawns and golf courses. Simulation runs were made for each chemical and surface (lawns, greens, fairways) using 100-year weather records generated for nine U.S. cities. Results were summarized as mean annual and 1-in-10?year annual maximum daily pesticide loads. These loads varied greatly with pesticide, grass surface, and city, ranging from less than one to over 400??g/ha for mean annual loads and from less than one to over 500??g/ha for 1-in-10?year maximum daily loads. Mean annual loads averaged over the 37 chemicals and three grass surfaces were found to be closely related to growing season precipitation. Variations among the nine cities were well-captured by three general climate categories: humid, represented by Atlanta and Houston; mesic, as with Albany, Columbus, Madison, and Olympia; and dry, represented by Bismarck, Fresno, and Roswell. Mean annual pesticide runoff was 19, 6, and 2??g/ha in the humid, mesic, and dry regions, respectively.     

Modeling Nonpoint Source Pollutant Losses from a Small Watershed Using HSPF Model

Hydrologic models play an important role in the assessment of nonpoint source (NPS) pollution, which is essential for the environmental management of water resources. The present study has been undertaken to evaluate the applicability of a physically based continuous time scale, hydrological, and water quality computer model—Hydrologic Simulation Program-Fortran (HSPF)—in simulating runoff and sediment associated NPS pollutant losses from a small mixed type (land under agriculture, shrubs and forest, rocks, grasses) watershed of the Damodar Valley Corporation, Hazaribagh, India. Water soluble NO3–N, NH4–N, and P were considered as pollutants and their concentrations in the runoff were measured at the outlet of the watershed, randomly for 15 dates during the monsoon season (June–October) of 2000 and 2001. The model calibration and validation results reveal that the seasonal trend of HSPF simulated runoff, sediment yield, and NPS pollutants compared reasonably with their measured counterparts. Although the concentrations of pollutants were generally overpredicted for NO3–N and underpredicted for NH4–N and water-soluble P in the month of June when fertilizers releasing NH4–N and P are applied in rice fields, the differences in the mean concentration were not significantly different at a 95% level of confidence. Variation in the simulated losses of water soluble N and P species between the years occurred largely due to differences in the amount and distribution of rainfall. These results indicate that the HSPF model can be used as a tool for simulating runoff and sediment associated NPS pollution losses from the study area.     

Modeling of Cadmium Removal from Domestic Wastewater in Constructed Wetlands Using STELLA Simulation Program

A mathematical model was developed to simulate cadmium removal from wastewater in free water surface (FWS) and subsurface flow (SF) constructed wetlands using STELLA simulation program. The model simulated the accumulation of cadmium in soil (Cds), uptake by plants (Cdp), and residual concentration in effluent (Cdww_eff). The model was calibrated using one-half of the experimental data for the adjustment of the coefficients and the remaining data for model verification. The comparison of simulated and experimental values of Cds, Cdp, and Cdww_eff showed good agreement. The results indicated that the developed mathematical model could be useful for predicting the fate of cadmium when treating domestic effluents in constructed wetlands.     

Pesticide Runoff Loads from Lawns and Golf Courses

Pesticide runoff loads from grass surfaces were estimated for 29 chemicals commonly applied to U.S. lawns and golf courses. Data on pesticide properties and typical application rates and schedules were developed and summarized as input parameters for the TurfPQ runoff model. Weather data for each of 9 U.S. cities were generated by the USCLIMATE model and modified by the addition of growing season irrigation. Simulation runs were made for each chemical, grass surface (lawns, greens, fairways), and city, and the results were summarized as mean annual and 1-in-10 year annual maximum daily pesticide loads. These loads varied greatly with pesticide, grass surface, and city, ranging from 0 to 875?g/ha for mean loads and 0 to 818?g/ha for 1-in-10 year daily loads. Mean annual loads averaged over the 29 chemicals and 3 grass surfaces were found to be closely related to growing season precipitation. Variations among the nine cities were well-captured by three general climate categories: Humid, characterized by abundant precipitation and warm temperatures, represented by Atlanta and Houston; temperate, with moderate precipitation and temperature, as with Albany, Columbus, Madison, and Olympia; and dry, with sparse precipitation, represented by Bismarck, Fresno, and Roswell. Mean annual pesticide runoff was 37, 9, and 2?g/ha in the humid, temperate, and dry regions, respectively.     

Models Quantify the Total Maximum Daily Load Process

Mathematical models have been used for many years to assist in the management of water quality. The total maximum daily load (TMDL) process is no exception; models represent the means by which the assimilative capacity of a water body can be quantified and a waste load allocation can be determined such that the assimilative capacity is not exceeded. Unfortunately, in many TMDLs, the use of models has not always adhered to the best modeling practices that have been developed over the past half-century. This paper presents what are felt to be the most important principles of good modeling practice relative to all of the steps in developing and applying a model for computing a TMDL. These steps include: Problem definition and setting management objectives; data synthesis for use in modeling; model selection; model calibration and, if possible confirmation; model application; iterative modeling; and model postaudit. Since mathematical modeling of aquatic systems is not an exact science, it is essential that these steps be fully transparent to all TMDL stakeholders through comprehensive documentation of the entire process, including specification of all inputs and assumptions. The overriding consideration is that data richness and quality govern the level of model complexity that can be applied to a given system. The model should never be more complex than the data allow. Also, in applying a model, one should always attempt to quantify the uncertainty in predictions. In general, quantifying uncertainty is easier with simple models, which is another reason to begin with a simple framework.     

Removal of Inorganic Mercury from Polluted Water Using Structured Nanoparticles

This paper presents a process for the removal of inorganic mercury from aqueous solutions using alumina nanoparticles, which were prepared by the sol-gel method. Different amounts of mercury were added to the particles until a critical concentration was achieved, thus inducing the alumina sol flocculation. Particle growth was monitored during the process using dynamic light scattering. The amount of metal ion adsorbed on the surface of the alumina sols was determined by atomic absorption spectroscopy. Initial mercury concentrations ranging between 50 and 100 ppm decreased to below 1 ppb in a short time.     

User-Friendly Mathematical Model for the Design of Sulfate Reducing H2/CO2 Fed Bioreactors

This paper presents three steady-state mathematical models for the design of H2/CO2 fed gas-lift reactors aimed at biological sulfate reduction to remove sulfate from wastewater. Models 1A and 1B are based on heterotrophic sulfate reducing bacteria (HSRB), while Model 2 is based on autotrophic sulfate reducing bacteria (ASRB) as the dominant group of sulfate reducers in the gas-lift reactor. Once the influent wastewater characteristics are known and the desired sulfate removal efficiency is fixed, all models give explicit mathematical relationships to determine the bioreactor volume and the effluent concentrations of substrates and products. The derived explicit relationships make application of the models very easy, fast, and no iterative procedures are required. Model simulations show that the size of the H2/CO2 fed gas-lift reactors aimed at biological sulfate removal from wastewater highly depends on the number and type of trophic groups growing in the bioreactor. In particular, if the biological sulfate reduction is performed in a bioreactor where ASRB prevail, the required bioreactor volume is much smaller than that needed with HSRB. This is because ASRB can out-compete methanogenic archaea (MA) for H2 (assuming sulfate concentrations are not limiting), whereas HSRB do not necessarily out-compete MA due to their dependence on homoacetogenic bacteria (HB) for organic carbon. The reactor sizes to reach the same sulfate removal efficiency by HSRB and ASRB are only comparable when methanogenesis is inhibited. Moreover, model results indicate that acetate supply to the reactor influent does not affect the HSRB biomass required in the reactor, but favors the dominance of MA on HB as a consequence of a lower HB requirement for acetate supply.     

Effect of Long Internal Waves on the Quality of Water Withdrawn from a Stratified Reservoir

The properties of water withdrawn from a stratified reservoir are investigated in a field study conducted in Lake Burragorang, Australia. It is shown that temperature and turbidity fluctuations of the extracted water are directly correlated to the vertical displacement of the thermal structure of the reservoir immediately in front of the offtake and the thickness of the selective withdrawal layer. Scaling of the unsteady withdrawal revealed that the timescale associated with the formation of selective withdrawal is an order of magnitude smaller than the typical period of the internal wave. This means the withdrawal layer is acting as a filter, extracting water of a particular quality as it is swept past the outlet by the internal seiches; the steady-state theory of the selective withdrawal can be used to predict outflow temperature fluctuations in reservoirs where long internal waves are present. To correctly interpret other outflow water parameters, such as turbidity or dissolved oxygen, it is important not only to know the stratification conditions in front of the offtake, but also to understand the local flow dynamics in the lower reaches of the reservoir.     

Simplified Databased Total Maximum Daily Loads, or the World is Log-Normal

The total maximum daily load (TMDL) approaches that have relied mostly on deterministic modeling have inherent problems with considerations of a margin of safety and estimating probabilities of excursions of water quality standards expressed in terms of magnitude, duration, and frequency. A tiered probabilistic TMDL approach is proposed in this paper. A simple databased Tier I TMDL that uses statistical principles has been proposed for watersheds that have adequate water quality databases enabling statistical evaluations. Studies have shown that for many pollutants, event mean concentrations in runoff, wastewater loads, and concentrations in the receiving waters follow the log-normal probability distribution. Other probability distributions are also applicable. Tier II Monte Carlo simulation, using a simpler deterministic or black box water quality model as a transfer function, can then be used to generate time series of data, which fills the data gaps and allows estimation of probabilities of excursions of chronic standards that are averaged over periods of 4 or 30 days. Statistical approaches, including Monte Carlo, allow replacement of an arbitrary margin of safety by a quantitative estimation of uncertainty and enable linking the model results to the standards defined in terms of magnitude, frequency, and duration.     

Simulating Sediment Transport in a Flume with Forced Pool-Riffle Morphology: Examinations of Two One-Dimensional Numerical Models

One-dimensional numerical sediment transport models (DREAM-1 and DREAM-2) are used to simulate seven experimental runs designed to examine sediment pulse dynamics in a physical model of forced pool-riffle morphology. Comparisons with measured data indicate that DREAM-1 and -2 closely reproduce the sediment transport flux and channel bed adjustments following the introduction of fine and coarse sediment pulses, respectively. The cumulative sediment transport at the flume exit in a DREAM-1 simulation is within 10% of the measured values, and cumulative sediment transport at flume exit in a DREAM-2 simulation is within a factor of 2 of the measured values. Comparison of simulated and measured reach-averaged aggradation and degradation indicates that 84% of DREAM-1 simulation results have errors less than 3.3?mm, which is approximately 77% of the bed material geometric mean grain size or 3.7% of the average water depth. A similar reach-averaged comparison indicates that 84% of DREAM-2 simulation results have errors less than 7.0?mm, which is approximately 1.7 times the bed material geometric mean grain size or 11% of the average water depth. Simulations using measured thalweg profiles as the input for the initial model profile produced results with larger errors and unrealistic aggradation and degradation patterns, demonstrating that one-dimensional numerical sediment transport models need to be applied on a reach-averaged basis.     

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.     

Biphasic Decay Kinetics of Fecal Bacteria in Surface Water Not a Density Effect

The decay of fecal bacteria in surface water often follows a biphasic pattern with the apparent first-order rate constant relatively high during a first phase and lower in a second one. This could be the result of population heterogeneity in resistance due to various mechanisms (different strains, genetically or nongenetically differentiated cells, different growth or cell cycle stage, clumping, hardening), or the specific decay rate could be directly or indirectly affected by the cell density (e.g., quorum sensing). All these mechanisms can theoretically produce a biphasic decay pattern and are consistent with the literature. However, they are fundamentally different and lead to different behavior of mechanistic total maximum daily load models, so identifying the correct mechanism is important. This technical note presents the results of a study aimed at determining if a density effect is involved. Laboratory decay experiments with pure strain Escherichia coli cells in phosphate buffer were conducted over a range of initial densities. The results show that the rate constant changes after a certain time, rather than at a certain density, which is inconsistent with a density effect. As the experiments were performed with a pure strain, the resistant fraction cannot be attributed to a different strain. Further research is needed to identify the mechanism responsible for the population heterogeneity.     

Calibration of a Continuous Simulation Fecal Coliform Model Based on Historical Data Analysis

Since 1984, the major water reclamation plants discharging to the Chicago Waterway System (CWS) have not disinfected their effluents. The possible addition of disinfection at these plants is the subject of an ongoing use attainability analysis (UAA). For the UAA, Escherichia coli (E. coli) is used as the indicator of bacterial contamination. However, only a few years of E. coli data are available for the CWS and the treatment plants discharging to the CWS. Thus, it was decided to develop a model based on fecal coliforms for which more data are available and to develop a relation between fecal coliform and E. coli counts for the CWS. A 1:1 relation was found between fecal coliform and E. coli counts in the CWS by Limnotech (2004, written communication) as part of the UAA. In order to evaluate the effects of possible disinfection measures on fecal coliform and related E. coli counts in the CWS, a simple first-order fecal coliform decay model was added to the continuous-simulation flow-water quality model DUFLOW applied to the CWS system. Due to the limited amount (monthly samples) of measured fecal coliform concentration data for the CWS, a reasonable calibration of the model would have been difficult to achieve based on the traditional trial and error method. In this paper, a new concept of model parameter estimation based on historical data analysis and its application to model calibration is presented. The fecal coliform decay rate k was estimated for every reach of the CWS based on analysis of historical data (1990–2003) between each two consecutive sampling locations and the related travel time between these stations. The fecal coliform decay rate then was determined on the basis of many years (14 years, in this case) of monthly fecal coliform samples rather than the few monthly samples taken in a typical calibration period. The results obtained indicate that the calibration process was successful, and a good match between measured and simulated fecal coliform concentrations at almost all locations along the CWS is achieved with one model run for several multiple month periods in 1998, 1999, 2001, and 2002.     

Effect of Aeration on the Quality of Effluent from UASB Reactor Treating Sewage

The treatment of effluent of pilot- and full-scale upflow anaerobic sludge blanket (UASB) reactors operating at steady state was studied in an aeration-settling system. The fine pore submerged diffusers were used to aerate the effluent of UASB reactors under different operating conditions. Forty to 55% of the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) removal efficiencies were achieved by the direct aeration of the UASB effluent in the laboratory. The maximum removal efficiencies were achieved at 30?min hydraulic retention time (HRT) and a dissolved oxygen (DO) of 5–6??mg/L or high KLa (vigorous aeration). Batch experiments on nitrogen purging and the aeration of sulfides, volatile organic compounds (VOCs), and nonpurgeable organic carbons (NPOCs) were performed to ascertain the mechanism of BOD/COD removal. During aeration, BOD and COD were reduced by the stripping of H2S and VOCs and by the chemical oxidation of total sulfides and organic carbon. The stripping and chemical oxidation depended on the HRT and DO. The performance of a full-scale surface aeration system was compared to the performance of a pilot-scale diffused aeration system. Final sedimentation was effective only in removing the solids from the effluent of the aeration system. The results were confirmed by organic mass balance.     

Evaluation of a Fast Large-Eddy-Simulation Model for Indoor Airflows

A three-dimensional large-eddy-simulation computational fluid dynamics (CFD) program, developed for studying the transport of smoke during a fire in an enclosure, is applied to four flow problems relevant to nonfire situations. This evaluation is relevant to the use of the program for indoor air quality modeling as well as its use in modeling the early phases of smoldering fires. The program uses finite-difference techniques to solve the Navier-Stokes equations, with an approach emphasizing high spatial resolution and efficient flow-solving techniques. Subgrid scale effects are addressed with the Smagorinsky model. The flow problems include simple geometries, with forced, natural, and mixed convection flows as well as a realistic test room with a displacement ventilation system and tracer gas release. Grid effects and computing time are investigated. Results are compared with the experimental data, and issues important to defining the problems in CFD are highlighted. In general the program predicts the experimental data reasonably well, with very fast computing times. However, care must be taken in defining convection from heated surfaces, and adequate grid resolution is needed to model the dispersion of a tracer gas in the enclosure.