In unsaturated soil, methane and volatile organic compounds can significantly alter the density of soil gas and induce buoyant gas flow. A series of laboratory experiments was conducted in a two-dimensional, homogeneous sand pack with gas permeabilities ranging from 110 to 3,000 darcy. Pure methane gas was injected horizontally into the sand and steady-state methane profiles were measured. Experimental results are in close agreement with a numerical model that represents the advective and diffusive components of methane transport. Comparison of simulations with and without gravitational acceleration permits identification of conditions where buoyancy dominates methane transport. Significant buoyant flow requires a Rayleigh number greater than 10 and an injected gas velocity sufficient to overcome dilution by molecular diffusion near the source. These criteria allow the extension of laboratory results to idealized field conditions for methane as well as denser-than-air vapors produced by volatilizing nonaqueous phase liquids trapped in unsaturated soil.
Many water treatment technologies for arsenic removal that are used today produce arsenic-bearing residuals which are disposed in non-hazardous landfills. Previous works have established that many of these residuals will release arsenic to a much greater extent than predicted by standard regulatory leaching tests (e.g. the toxicity characteristic leaching procedure, TCLP) and, consequently, require stabilization to ensure benign behavior after disposal. In this work, a four-step sequential extraction method was developed in an effort to determine the proportion of arsenic in various phases in untreated as well as stabilized iron-based solid matrices. The solids synthesized using various potential stabilization techniques included: amorphous arsenic-iron sludge (ASL), reduced ASL via reaction with zero valent iron (RASL), amorphous ferrous arsenate (PFA), a mixture of PFA and SL (M1), crystalline ferrous arsenate (HPFA), and a mixture of HPFA and SL (M2). The overall arsenic mobility of the tested samples increased in the following order: ASL > RASL > PFA > M1 > HPFA > M2.
Two sediment cores were collected from a marina in the San Francisco Bay to characterize historical sediment contamination resulting from the direct discharge of industrial wastewater from Naval Air Station Alameda. Depth profiles of trace metals, petroleum hydrocarbons, and radionuclides were determined with a 12-cm spacing down to a depth of 120 cm. The chronology of sediment accumulation is established by depth profiles of sedimentary time markers in conjunction with information on site history. The traditional approach of determining sediment accumulation rates by measuring atmospheric (210)Pb deposition was obscured by a larger source of (210)Pb in the sediments from the decay of anthropogenic (226)Ra, likely from luminescent paints used at this facility and released to the marina. The sedimentation rates inferred from the data indicate that the greatest amount of contamination by trace metals and petroleum hydrocarbons took place between 1940 and 1960. In addition, anthropogenic (226)Ra activities are positively correlated with some of the contaminants in the sediments, allowing the wastewater discharged from the facility to be distinguished from baywide contamination. In locations such as this, where there is a complex history of contaminant deposition, a source-specific tracer may be the only feasible method of attributing historical contamination to a point source.
Synthetic musk fragrances are common personal care product additives and wastewater contaminants that are routinely detected in the environment. This study examines the presence eight synthetic musk fragrances (AHTN, HHCB, ATII, ADBI, AHMI, musk xylene, and musk ketone) in source water and the removal of these compounds as they flow through a Midwestern conventional drinking water plant with lime softening. The compounds were measured in water, waste sludge, and air throughout the plant. HHCB and AHTN were detected in 100% of the samples and at the highest concentrations. A mass balance on HHCB and AHTN was performed under warm and cold weather conditions. The total removal efficiency for HHCB and AHTN, which averaged between 67% to 89%, is dominated by adsorption to water softener sludge and its consequent removal by sludge wasting and media filtration. Volatilization, chlorine disinfection, and the disposal of backwash water play a minor role in the removal of both compounds. As a result of inefficient overall removal, HHCB and AHTN are a constant presence at low levels in finished drinking water.
Horizontal infiltration experiments were performed to validate a plug flow model that minimizes the number of parameters that must be measured. Water and silicone oil at three different viscosities were infiltrated into glass beads, desert alluvium, and silica powder. Experiments were also performed with negative inlet heads on air-dried silica powder, and with water and oil infiltrating into initially water moist silica powder. Comparisons between the data and model were favorable in most cases, with predictions usually within 40% of the measured data. The model is extended to a line source and small areal source at the ground surface to analytically predict the shape of two-dimensional wetting fronts. Furthermore, a plug flow model for constant flux infiltration agrees well with field data and suggests that the proposed model for a constant-head boundary condition can be effectively used to predict wetting front movement at heterogeneous field sites if averaged parameter values are used.
Electrokinetic extraction is an emerging technology that can be used to remove contaminants from heterogeneous fine-grained soils in situ. Contaminants in the subsurface are removed by the application of a direct-current electric field across the contaminated soil. The primary contaminant transport and removal mechanisms are electroosmotic advection and ionic migration. However, there are many complex physicochemical reactions occurring simultaneously during the process that may enhance or retard the cleanup process. Nonetheless, the viability of the technology has been established by results obtained from many bench-scale and large-scale laboratory and pilot-scale field experiments performed on various soils. This paper will review the fundamental concepts of the technology and discuss some important practical aspects and design criteria of the technology for field implementations. An example on cost analysis of the technology is also presented to demonstrate the use of various equations presented in the paper and to illustrate the cost-effectiveness of the technology.
: Accurate mean concentrations of volatile organic compounds (VOCs) can easily and economically be obtained from a single VOC analysis by using proven methods of collecting representative, discrete water samples and compositing them with a gas-tight syringe. The technique can be used in conjunction with chemical analysis by a conventional laboratory, field-portable equipment, or a mobile laboratory. The type of mean concentration desired depends on the objectives of monitoring. For example, flow-weighted mean VOC concentrations can be used to estimate mass loadings in wastewater and urban stormwater and spatially-integrated mean VOC concentrations can be used to assess sources of drinking water (e.g. reservoirs and rivers). The mean error in a discrete sample due to compositing is about 2 percent for most VOC concentrations greater than 0.1 g/L. The total error depends on the number of discrete samples comprising the composite sample and precision of the chemical analysis. ____________...
: A numerical model of gravity sedimentation and thickening was developed from the governing two-phase flow equations for the liquid and solid phases. The inertial and gravity terms in the solid and liquid momentum equations were retained in the gravity sedimentation and thickening model. An implicit, spacestaggered finite-difference algorithm was developed for the resulting coupled partial differential equations. Constitutive relationships describing the physical properties of the slurry were required to solve the numerical model. These constitutive properties describing the relationship between effective stress and porosity and between permeability and porosity were determined experimentally and by model calibration. The model was calibrated and verified using the data of dynamic porosity profiles of gravity sedimentation and thickening of kaolin suspensions in distilled water. INTRODUCTION A large fraction of the current cost of wastewater treatment is from the treatment and dispos...
Lagrangian actinometry represents a new method of photochemical reactor characterization. The method is based on an application of dyed microspheres, which were developed by attachment of (E)-5-[2-(methoxycarbonyl)ethenyl]cytidine (hereafter referred to as S) to polystyrene microspheres. S is a non-fluorescent molecule that when subjected to UV irradiation yields a single product, 3-β-D- ribofuranosyl-2,7-dioxopyrido[2,3-d]pyrimidine (hereafter referred to as P), which displays a strong fluorescence signal. Dyed microspheres were subjected to UV irradiation under a collimated-beam and using a single-lamp (low pressure Hg), continuous-flow reactor. In parallel with these experiments, a biodosimetry experiment was conducted using Bacillus subtilis spores as the challenge organism.
Particle-specific fluorescence intensity measurements were conducted on samples from the collimated-beam experiments and the flow-through reactor experiments by flow cytometry. Estimates of the dose distribution delivered by the flow-through reactor for each operating condition were developed by deconvolution of data resulting from flow cytometry analysis of these samples.
In conjunction with these experiments, a numerical model was developed to simulate the behavior of the reactor system. A commercially available computational fluid dynamics package was used to simulate the flow field, while line-source integration was used to simulate the irradiance field. A particle-tracking algorithm was employed to interrogate the flow and intensity field simulations for purposes of developing particle-specific (Lagrangian) estimates of dose delivery.
Dose distribution estimates from the microspheres assays and the numerical simulations were combined with the measured dose-response behavior of B. subtilis spores to yield estimates of spore inactivation in the flow-through experiments. For the range of operating conditions used in these experiments, predictions of spore inactivation based on dose distribution estimates from both methods were in good agreement with each other, and with the measured spore inactivation behavior.
Lagrangian actinometry is capable of yielding accurate, detailed measurements of dose delivery by continuous-flow UV systems. This method represents a substantial improvement over existing experiment-based methods of UV reactor characterization (e.g., biodosimetry) in that it yields a measurement of the dose distribution for a given operating condition. This method also represents an improvement over existing methods for validation of numerical simulations. Specifically, because this method yields a measurement of the dose distribution, it is possible to compare these measurements with predicted dose distributions from the numerical simulation. When used in combination with conventional biodosimetry, the analysis of a reactor system becomes extremely robust.
In subtropical coastal waters around Hong Kong, algal blooms and red tides have been frequently observed over the past two decades. In particular, in March-April 1998, a massive red tide invaded the northeastern and southern coastal waters of Hong Kong. The devastating red tide resulted in the worst fish kill in Hong Kong's history, the most significant impacts being at the Lo Tik Wan and Sok Kwu Wan fish culture zones on Lamma Island. This work reports the first scientific investigation of the cause of this massive red tide. A calibrated three-dimensional (3D) hydrodynamic model for the Pearl River Estuary, Delft3D, is applied to study the advective transport of red tides. Based on the tidal boundary conditions and the measured wind data for a typical spring season, the 3D flow field is computed and extensive surface drogue tracking performed for releases in different parts of the coastal waters and for different tidal and wind conditions. The results show that a bloom initiated in Mirs Bay (Nan Au or Tap Mun) in the northeastern water would likely be transported to the southern coastal waters under the combined action of tidal current and wind. The computed bloom tracking patterns are generally supported by observations and are consistent with the temporal and spatial patterns of individual fish kill events in the 1998 red tide. We conclude that the major cause of the bloom being transported into the southern waters and East Lamma Channel (and causing the massive fish kill) is the generally strong wind in March-April 1998 and the change in wind direction in early April under almost diurnal tidal conditions. Further, it is most probable that the red tide originated in Mirs Bay rather than from outside Hong Kong. The findings provide a firm basis for environmental and fisheries management.
Iron oxide impregnated onto an activated carbon (FeAC) has a high arsenic (As) removal capacity with the potential to be used in existing activated carbon column systems. Objectives of this research were to investigate As(V) removal from aqueous-phase systems using fixed-beds packed with FeAC and to determine if the triple layer model (TLM) with the homogeneous surface diffusion model (HSDM) could describe As(V) removal in the columns. Rapid small-scale column tests (RSSCT) were conducted at various empty bed contact times (EBCT). Effluent As(V) breakthrough (10μg∕L) was incipient for the 0.20-min EBCT experiment, whereas ∼2300 bed volumes of water at 1-mg/L inlet concentration of As(V) was treated at an EBCT of 2.1min before breakthrough occurred. The TLM with three As(V)-FeAC surface reactions coupled with the HSDM provided accurate prediction of As(V) removal in the RSSCT.
In recent years, risk assessment models have become widely used as aids in the decision-making process related to contaminated soils. The Monte Carlo method is a popular method for incorporating uncertainty relative to parameter values in risk assessment modeling. But risk assessment models are often used as screening tools in situations where information is typically sparse and imprecise. In this case, it is questionable whether true probabilities can be assigned to parameter estimates, or whether these estimates should be considered as simply possible. This paper examines the possibilistic approach of accounting for parameter value uncertainty, and provides a comparison with the Monte Carlo probabilistic approach. The comparison illustrates the conservative nature of the possibilistic approach, which considers all possible combinations of parameter values, but does not transmit through multiplication the uncertainty of the parameter values onto that of the calculated result. In the Monte Carlo calculation, on the other hand, scenarios that combine low probability parameter values have all the less change of being randomly selected. If probabilities are arbitrarily assigned to parameter estimates, without being substantiated by site-specific field data, possible combinations of parameter values (scenarios) will be eliminated from the analysis as a result of Monte Carlo averaging. This could have a detrimental impact in an environmental context, when the mere possibility that a scenario may occur can be an important element in the decision-making process.
Applications of artificial neural networks in the field of aeration phenomena in surface aerators, which are not geometrically similar, are explored to predict reaeration rates under varying dynamic as well as geometric conditions. The primary network for prediction is a feed forward network with nonlinear elements. The network consists of an input layer, an output layer, a hidden layer, and the nonlinear transfer function in each processing element. The network requires supervised learning and the learning algorithm is the back-propagation. As back-propagation learning is affected by local minima, and to get over this aspect various other modifications have been suggested like Levenberg-Marquardt, quasi-Newton, conjugate-gradient, etc. The present study suggests that the Levenberg-Marquardt modification is a very efficient algorithm in comparison with others like quasi-Newton and conjugate-gradient. In the situations when the dimension of the input vector is large, and highly correlated, it is useful to reduce the dimension of the input vectors. An effective procedure for performing this operation is principal component analysis. The best prediction performance is achieved when the data are preprocessed using principal components analysis before they are fed to a back-propagated neural network, but at the cost of losing the physical significance of experimental data. The model thus developed can be used to predict the reaeration rate for different sizes of geometric elements (like rotor diameter, sizes of rotor, aerators’ geometry, water depth, etc). under various dynamic conditions, i.e., the speed of the rotor.
Biodegradation of trichloroethylene (TCE) was studied using a mixed culture of aerobic, phenol-induced organisms. Abiotic experiments showed that sorption of TCE to biomass was negligible in the systems studied. The effects of influent phenol and TCE concentration on the TCE degradation capacity of the culture were studied using chemostats. A relationship exists between the influent phenol/TCE ratio and TCE biodegradation. TCE transformation yields ranged from 0.052 to 0.222 mg TCE removed/mg phenol removed. Monod kinetic coefficients for phenol degradation were determined. Monod kinetic coefficients were also determined for TCE biotransformation by resting cells. The concept of transformation capacity was used to model the decrease in active biomass concentration caused by TCE transformation. In mineralization studies using ¹⁴ C-labeled TCE, 22% of the degraded mass of TCE was transformed to carbon dioxide, 8.8% was incorporated into biomass, 42% was transformed to nonvolatile products, with the remaining, unrecovered 27% most likely transformed into volatile or semivolatile products.
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 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 kg total organic carbon (TOC)/m(3) day, with a removal efficiency of 92%. The rate of TOC removal by AUSB was highest at a pressure of 20 psig and it decreased when the pressure was increased to 25 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 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 g VSS/g TOC removed. However, the effluent TOC was relatively high due to the system's operation at a high organic loading.
Stepped waterways are commonly used as river training, debris dam structures, storm water systems and aeration cascades. The present study was focused on analysis of basic air-water flow properties on a low gradient stepped chute, combined with dissolved oxygen measurements. The oxygen aeration efficiency was found to be about 30% for 12 steps with a total drop in invert elevation of 1.4 m, nearly independently of the inflow conditions. Detailed air-water flow measurements, including void fraction, velocity, bubble count rate and interface area, were used to integrate the mass transfer equation and to estimate the aeration potential of the waterway. Direct comparisons with dissolved oxygen measurements showed good agreement between the two methods.
A new theoretical model to analyze the measurements obtained from a typical soil column venting experiment is proposed. The principles of mass transfer, Darcy's law, and air compressibility in the form of pressure-volume relationships were coupled to calculate the contaminant concentration in the gas phase (air), and the rate of contaminant removal. The proposed model relates soil air permeability with the contaminant removal and is capable of calculating the variation of soil air permeability with time during the venting process. The contaminated sand sample was idealized as a system of straight capillary tubes in the direction of flow, lined by the liquid contaminant. A closed-form solution for radial diffusion of the contaminants in a cylinder, coupled with axial advection of air, was used to model contaminant removal. The results from the mass transfer model were then used to trace the change of soil air permeability with time. The model also uses, as an alternative approach, a modified form of Darcy's law for compressible flow.
Algae grown on wastewater media are a potential source of low-cost lipids for production of liquid biofuels. This study investigated lipid productivity and nutrient removal by green algae grown during treatment of dairy farm and municipal wastewaters supplemented with CO2. Dairy wastewater was treated outdoors in bench-scale batch cultures. The lipid content of the volatile solids peaked at Day 6, during exponential growth, and declined thereafter. Peak lipid content ranged from 14-29%, depending on wastewater concentration. Maximum lipid productivity also peaked at Day 6 of batch growth, with a volumetric productivity of 17 mg/day/L of reactor and an areal productivity of 2.8 g/m2/day, which would be equivalent to 11,000 L/ha/year (1,200 gal/acre/year) if sustained year round. After 12 days, ammonium and orthophosphate removals were 96 and >99%, respectively. Municipal wastewater was treated in semicontinuous indoor cultures with 2-4 day hydraulic residence times (HRTs). Maximum lipid productivity for the municipal wastewater was 24 mg/day/L, observed in the 3-day HRT cultures. Over 99% removal of ammonium and orthophosphate was achieved. The results from both types of wastewater suggest that CO2-supplemented algae cultures can simultaneously remove dissolved nitrogen and phosphorus to low levels while generating a feedstock potentially useful for liquid biofuels production.
A multiobjective optimization model is presented to determine the efficient aggregation of land parcels for use as a solid- or hazardous-waste landfill. In this work, a new constraint for measuring compactness and contiguity of the selected subregion is introduced. This constraint measures compactness and contiguity as a function of the subregion’s outside perimeter and area. The model optimally selects and sizes the landfill site from multiple bundles of available discrete and irregularly shaped land parcels. Each bundle consists of several individual and irregular land parcels and is disjoint from all other bundles. The model is multiobjective in nature, addressing land purchase cost, compactness, and contiguity considerations. The quantity of land required is determined by a projection of the flow of waste from the communities, commercial areas, and industries the landfill serves. To illustrate the model, a case study is presented using the landfill-site search process in Orange County, North Carolina.
A novel optical technique is used to investigate the dynamics of coagulation of particle suspensions with aluminum salt. The relative size of aggregates formed during coagulation, expressed as a ''coagulation index,'' can be continuously measured by this technique. Coagulation of clay particles with aluminum sulfate is examined at various aluminum concentrations, solution pH, and mixing intensities. Results indicate that the coagulation index provides valuable information about aggregate dynamics and coagulation mechanisms with aluminum salts.
The effects of media specific surface area, porosity, pore size as well as the role of suspended biomass on the performance of upflow anaerobic packed-bed reactors (APBRs) treating synthetic protein-carbohydrate waste were examined in the laboratory. The results showed that the reactor packed with media of the largest media pore size and porosity demonstrated the highest chemical oxygen demand (COD) removal efficiencies at loading rates of 8, 12, and 16 g COD/L/d. An increase of over 40% in specific surface area in an APBR had not improved the removal efficiency, instead it produced 16% lower in COD removal efficiency at loading rate of 16 g COD/L/d. The superiority in treatment performance of the media having the largest porosity and pore size indicates that, a substantial amount of the COD removal was associated with the suspended biomass entrapped at the interstitial void spaces within the media. The amount of methane production associated with the suspended biomass determined from a batch serum bottle test was as high as 56% at 12 g COD/L/d and increased to 58% at higher loading rate of 16 g COD/L/d. The results suggest that media pore size and porosity play a more significant role than media specific surface area in the performance of upflow APBRs.
A single unit anaerobic granular bed baffled reactor (GRABBR) is proposed as an alternative to a separately operated two-phase anaerobic digestion system. This overcomes the problems related to wastewater treatment at high loading rates which usually results in accumulation of intermediate acid products, and consequently inhibits methanogenesis. This study was carried out to evaluate the stability of a five compartment GRABBR system when treating synthetic glucose wastewater at various operational conditions. The reactor was started with volumetric organic loading rate (OLR) of 1 kg chemical oxygen demand (COD)/m³ day, equivalent to 120 h hydraulic retention time (HRT), and loading rates were gradually increased at suitable intervals to up to 20 kg COD/m³ day (6 h HRT). At steady state, the overall soluble COD (SCOD) removal was over 95% under all applied loading conditions. At lower loadings, the reactor operated as a completely mixed system, and most of the treatment was achieved in the first compartment. At higher loadings, the entire system transformed into different phases, acidogenesis being dominant near the influent point, whilst methanogenesis was the main activity in the compartments near the effluent point. Granule breaking and flotation was observed in the acidogenic zone, whilst the methanogenic zone retained its original granular form. High assimilation rate of influent nitrogen was observed in the first compartment with the formation of nongranular biomass, identified as Klebsiella pneumoniae. The success of GRABBR as a single unit two-phase anaerobic digestion system could save the cost of an extra unit traditionally employed to achieve similar goals in treatment of high strength wastewaters.
Microalgal biomass production offers a number of advantages over conventional biomass production, including higher productivities, use of otherwise nonproductive land, reuse and recovery of waste nutrients, use of saline or brackish waters, and reuse of CO2 from power-plant flue gas or similar sources. Microalgal biomass production and utilization offers potential for greenhouse gas (GHG) avoidance by providing biofuel replacement of fossil fuels and carbon-neutral animal feeds. This paper presents an initial analysis of the potential for GHG avoidance using a proposed algal biomass production system coupled to recovery of flue-gas CO2 combined with waste sludge and/or animal manure utilization. A model is constructed around a 50-MW natural gas-fired electrical generation plant operating at 50% capacity as a semibase-load facility. This facility is projected to produce 216 million k·Wh/240-day season while releasing 30.3 million kg-C/season of GHG-CO2. An algal system designed to capture 70% of flue-gas CO2 would produce 42,400 metric tons (dry wt.) of algal biomass/season and requires 880 ha of high-rate algal ponds operating at a productivity of 20 g-dry-wt/m2-day. This algal biomass is assumed to be fractionated into 20% extractable algal oil, useful for biodiesel, with the 50% protein content providing animal feed replacement and 30% residual algal biomass digested to produce methane gas, providing gross GHG avoidances of 20, 8.5, and 7.8%, respectively. The total gross GHG avoidance potential of 36.3% results in a net GHG avoidance of 26.3% after accounting for 10% parasitic energy costs. Parasitic energy is required to deliver CO2 to the algal culture and to harvest and process algal biomass and algal products. At CO2 utilization efficiencies predicted to range from 60-80%, net GHG avoidances are estimated to range from 22-30%. To provide nutrients for algal growth and to ensure optimal algae digestion, importation of 53 t/day of waste paper, municipal sludge, or animal manure would be required. This analysis does not address the economics of the processes considered. Rather, the focus is directed at determination of the technical feasibility of applying integrated algal processes for fossil-fuel replacement and power-plant GHG avoidance. The technology discussed remains in early stages of development, with many important technical issues yet to be addressed. Although theoretically promising, successful integration of waste treatment processes with algal recovery of flue-gas CO2 will require pilot-scale trials and field demonstrations to more precisely define the many detailed design requirements.
The design of repository seals for deeply buried high-level radioactive wastes incorporates densely compacted clayey barriers around metallic waste canisters. In this paper, a mathematical model that is based on conservation of thermal energy and mass is developed to describe the locations of moisture and temperature fronts within a barrier, around a cylindrical waste canister of 1-meter radius, containing radionuclides with half-lives that range from 100 – 10,000 years. The solution developed is axisymmetric: the moisture fraction, w, and temperature T, vary only with time t, and radial distance r from the axis of the cylindrical waste canister. The model produces parabolic partial differential equations (PDEs). The spatial domain is discretized such that ordinary differential equations (ODEs) that result are solved. Computations using a uniform mesh of 0.1 meters and a cooling coefficient of 6.7 x 10 -2 with assumed but typical data on material properties, indicate that coupling of transport processes would be negligible in the case of radionuclides with long half-lives. Also, a quasi-steady vaporization front can form and propagate outward over the course of several decades after waste emplacement. The evolution of the front is somewhat insensitive to the half-life used and the permeability of the clayey barrier material.
The city of Hanford, California, relies on ground water for its municipal water supply. Arsenic concentrations in local wells frequently exceed the current drinking water standard (50 μg/L), although some dilution is achieved within the distribution system. Water samples were collected from municipal water supply wells and storage tanks in July and December 1996. Total arsenic concentrations ranged from 9 to 75 μg/L. Arsenic was found to occur predominantly in the +III oxidation state. Lower contributions of As(III) to total arsenic concentrations were found in three wells and one storage tank. In all other samples, the percent As(III) was 89 ± 6%. The very low values of %As(III) in one storage tank (1% in July and 14% in December) indicate that As(III) oxidation occurs within the distribution and storage system. | The city of Hanford, California, relies on ground water for its municipal water supply. Arsenic concentrations in local wells frequently exceed the current drinking water standard (50 μg/L), although some dilution is achieved within the distribution system. Water samples were collected from municipal water supply wells and storage tanks in July and December 1996. Total arsenic concentrations ranged from 9 to 75 μg/L. Arsenic was found to occur predominantly in the +III oxidation state. Lower contributions of As(III) to total arsenic concentrations were found in three wells and one storage tank. In all other samples, the percent As(III) was 89 ± 6%. The very low values of %As(III) in one storage tank (1% in July and 14% in December) indicate that As(III) oxidation occurs within the distribution and storage system.
This study employed pilot-scale filters to examine the fate of Mn in MnOx(s)-coated filter media as a function of filter-applied pH and backwash conditions. A key operational issue for continuous efficient Mn(II) removal was maintenance of appropriate levels of free chlorine to ensure coated media regeneration. Neutral or slightly acidic pH promoted Mn(II) sorption and subsequent oxidation on MnOx(s)-coated media. Alkaline influent pH (pH > 7) allowed some soluble Mn(II) oxidation by free chlorine prior to filtration, resulting in significant Mn removal by MnOx(s) particle filtration. Increased backwash rates removed greater amounts of MnOx(s) from the filter media. The combination of MnOx(s) accumulation on filter media during filtration and its partial removal during backwash maintained a net amount of MnOx(s) coating sufficient for catalyzing further soluble Mn(II) removal, yet it did not significantly alter the size of the media.
Accurate knowledge of the quantity and quality of runoff is required to assess the impacts of runoff on the environment and to develop appropriate mitigation technologies. Water quality of highway runoff in the Austin, Texas, area was determined by monitoring runoff at three locations on the MoPac Expressway. Daily traffic volumes, surrounding land uses, and highway drainage system types were different at each site. The concentrations of constituents in runoff at all sites were similar to median values compiled in a nationwide study of highway runoff quality. A grassy swale at one site was effective in reducing the concentrations of most constituents in runoff. The lower runoff coefficient at this site is attributable to infiltration of runoff into the grassy swale. The pollutant loads discharged from the pipe draining the swale were lower than those observed at the sites where runoff drained directly from the pavement. A first flush effect (i.e., higher pollutant concentrations at the beginning of an event) was evident during selected events, but was generally limited to a small volume. The overall effect was negligible when all monitored events were considered.
Most previous studies of bacterial reduction of chromium have been done with pure cultures that are not likely to be found in ground water, and at hexavalent chromium concentrations much greater than typically present in contaminated ground water. Further, most previous work has been performed with complex laboratory substrates that would not be suitable for in situ application. In this study, mixed cultures were enriched from three diverse soil sources: surface soil, subsurface soil, and river sediment. The enrichment medium contained 10 mg Cr⁶⁺/L and sucrose as the carbon source. The three mixed cultures obtained from the diverse soil samples were transferred to batch reactors and exhibited similar chromium reduction enzyme kinetics at stationary phase. The maximum specific reduction rates were between 0.98 and 3.3 mg Cr⁶⁺/(g dry cellss˙h) and the half velocity constants were between 0.39 and 1.48 mg Cr⁶⁺/L. The relatively narrow range of values for kinetic parameters suggests that a conservative engineering design for in situ remediation could be applied over a wide range of contaminated sites at the Cr(VI) concentrations examined.
Accumulating data on traditional compacted soil-surface covers are demonstrating that they are likely to degrade and have reduced effectiveness as long-term barriers; therefore, suitable alternatives are being examined. One possible alternative that is receiving increased attention is capillary barriers. The U.S. Environmental Protection Agency (USEPA) allows for alternatives to be used, but requires that they achieve infiltration and erosion protection equivalent to that of designs contained in design guidance documents. A method of comparing a capillary barrier to a design that features a compacted soil layer that meets the minimum requirements for a solid-waste landfill cover (so-called Subtitle D) under identical, transient conditions is introduced in the present paper, allowing equivalency to be demonstrated. The approach uses daily climatic data rather than monthly or yearly averages, which can provide misleading results. The concept of adding a "transport layer" at the fine/coarse interface of the capillary barrier to laterally drain water and reduce the moisture content is also presented. Numerical modeling results for a variety of climates show that the capillary barriers may be equivalent (or better) compared to a Subtitle D cover at many locations. The inclusion of a transport layer may significantly improve capillary barrier performance.
Laboratory tests were conducted to determine the effect of soil gas oxygen concentration on the degradation and mineralization of spiked Â¹â´C-pentachlorophenol and nonlabeled pentachlorophenol (PCP) present in soil taken from a prepared-bed land treatment unit at the Champion International Superfund Site in Libby, Mont. This soil was contaminated with wood preserving wastes including creosote and PCP. Degradation rates of Â¹â´C-PCP and nonlabeled PCP were found to be enhanced under soil gas oxygen concentrations between 2 and 21% in the contaminated soil. Between 48 and 64% of Â¹â´C-PCP spiked onto the soil was mineralized after 70 days at soil gas oxygen levels between 2 and 21%. No statistically significant mineralization of PCP was found to occur at 0% oxygen concentrations. Mineralization of Â¹â´C-PCP in contaminated soil poisoned with mercuric chloride was determined to be less than 0.2%. Degradation of indigenous nonradiolabeled PCP in the nonpoisoned soil was statistically significantly greater than in poisoned soil. These results indicated that degradation of PCP was biological and would occur under low oxygen concentrations. Soil gas oxygen concentrations necessary for PCP biodegradation (2--5%) could be maintained, for example, using bioventing technology in order to achieve continued treatment of buried lifts of soil while new lifts are added, thus decreasing the total time for soil remediation of the prepared bed.
In this paper the effect of operating parameters on biotrickling filter performance degrading chlorobenzene and o-dichlorobenzene mixture were studied. The large laboratory scale biofilter, total volume 40 L, filled with inert packing material was used. The biomass adaptation and cultivation were performed in a batch fermentor and were used to inoculate the biotrickling filter. After a starting period, the influence of the substrate load increase, liquid recirculation flow rate, and empty bed retention time on elimination capacity and removal efficiency were found. The most important recirculation liquid parameters were analyzed every day, that is: concentration of metabolites, dissolved organic carbon, nitrate, chloride, and biomass. A good correlation was found between intermediate concentration and the removal efficiency of the biotrickling filter. The measurements of the absorbance, very easy and rapid, can be used as a control parameter of the biofiltration efficiency.
The Water Poverty Index (WPI) was created as an interdisciplinary indicator to assess water stress and scarcity, linking physical estimates of water availability with the socioeconomic drivers of poverty. This index has found great relevance in policy making as an effective water management tool, particularly in resources allocation and prioritization processes. Two conceptual weaknesses exist in the current index: (1) inadequate technique to combine available data and (2) poor statistical properties of the resulting composite. The purpose of this paper is to propose a suitable methodology to assess water poverty that overcomes these weaknesses. To this end, a number of combinations to create the WPI have been considered, based on indicators selection criteria, simple aggregation functions and multivariate analysis. The approach adopted has been designed for universal application at local scale. To exemplify the utilization of each alternative method, they have been piloted and implemented in the Turkana District (Kenya) as a case study. The paper concludes that the weighted multiplicative function is the most appropriate aggregation method for estimation of water poverty. It is least eclipsing and ambiguous free function, and it does not allow compensability among different variables of the index Postprint (published version)
The sorptive capabilities of soils for organic contaminants can be greatly enhanced by treatment with cationic surfactants, and this has been suggested as a potential in situ approach for contaminant plume management. The hydraulic properties of soils modified by injection of hexadecyltrimethylammonium (HDTMA) were investigated using soil columns and a fixed-ring consolidometer. Oshtemo soil (87% sand, 10.5% clay, 2.5% silt) under two different effective stresses, was equilibrated with 1mMNaCl and treated by recirculation of two different HDTMA soil concentrations, one above and one below the cation exchange capacity. No statistically significant changes in hydraulic conductivity occurred as a result of HDTMA treatment at any of the experimental conditions studied. These results suggest that sorptive zones created in situ with HDTMA may be hydraulically feasible.
A range or arsenic containing compounds, including arsenic trioxide, pentoxide and a lead arsenate insecticide have been stabilized using formulations of cement alone, cement + lime and cement + ferrous sulfate and subsequently exposed to a range of leaching regimes in order to compare their effectiveness for metal stabilization. Leaching tests used were two regulatory tests, the Toxicity Characteristic Leaching Procedure (TCLP) and the Australian Bottle Leaching Procedure (ABLP), as well as column leaching. Arsenic leachate concentrations from cement-stabilized lead arsenate insecticide were similar when subjected to either the TCLP or ABLP using the same leachant. Lead, known to be immobilized by means different to that of arsenic, yielded varying leachate concentrations when using either of the regulatory tests, even though the leachant was of the same type. The leaching of calcium influences the filtered arsenic leachate, whereas the leaching of lead is greatly affected by leachate pH. As expected, both regulatory tests generally proved to be very severe in terms of the masses of the hazardous constituents leached when compared to conceptually more realistic column leaching scenarios. Sodium arsenate-containing formulations behaved anomalously, with column leaching tests resulting in larger arsenic masses being leached than the regulatory tests. Sodium arsenate, known to inhibit cementation reactions, serves as a reminder of the perils that can be faced when generalizing the results obtained from leaching tests.
This paper summarizes the results of an investigation into the use of neural networks to analyze data collected from the literature regarding the interaction of wastes and hydraulic binders in, and final properties of, cement-solidified wastes. Neural network models were constructed for prediction of the effects of contaminants on setting time, unconfined compressive strength, and leachate pH. It was found that construction of successful models was possible, with prediction errors approaching experimental error, and that modeling was useful for generalizing about the relative effects of the input variables on the outputs using the results from the different studies. The work has shown that the potential for practical implementation of models of this type in prediction of key properties related to long-term behavior, and/or formulation design in waste treatment facilities clearly exists, but more detailed definition of the data space by experimentation, with more complete harmonization of methods and reporting of experimental results, will be necessary to develop reliable commercial models.
Wind produces turbulence facilitating the exchange of pollutants and other environmentally important trace gases such as oxygen and greenhouse gases between stationary water bodies and the atmosphere. Whereas wind speeds continuously vary, different wind speed monitoring and characterization procedures have been used for the gas exchange studies. We assessed the impact of measurement time intervals, logarithmic wind speed profiles, and surface roughness values on wind characterizations. The Weibull probability density function effectively characterized yearly and seasonal wind speed distributions. It was not affected by various averaging time intervals (1-60 min). However, averaging time interval of <10 min was necessary for reliable characterizations of shorter-periods (<3-5 days). Vertical wind speed variations were effectively described by logarithmic profile irrespective of atmospheric stability conditions. Interestingly, use of the logarithmic profile allowed the actual U10 to be predicted with reasonable accuracy for a wide range of surface roughness values. This was true under all stability conditions. Thus, small time intervals and the logarithmic profile appear to be very robust and widely useful techniques.
The river inflow in a natural lake with important suspended sediment load during floods, can impact water quality by mobilizing dissolved matters like phosphorous from deep to surface waters. Generally due to thermal stratification in prealpine lakes, the water column is stable. It does not mix vertically unless acted on by outside forces, for example, currents or winds. Since Lake Lugano has a strong thermal stratification, river inflow exhibits different modes of density currents, from surface flows and thermocline intrusion to bottom currents. Turbidity currents are the direct cause of the downward water flow, and at the same time at the origin of upward directed flow. In this study, the impact of river born turbidity currents in Lake Lugano under varying ambient conditions was investigated using field measurements at the inflow river and inside the lake, together with a full three-dimensional numerical model of the entire lake. The paper characterizes the induced circulation of the turbidity plume and gives some indications on the relevance of turbidity currents on the lake.
A semidistributed watershed model is applied over the Mahantango Creek catchment in Pennsylvania to estimate future changes in direct runoff under 22 different climate scenarios. It is shown how different subcatchments of the watershed may respond to possible changes in the precipitation and temperature regimes. Subcatchments with the most unfavorable future runoff responses can be identified where possible changes in land use management practices may be suggested.
The addition of ferrous salts is a commonly used strategy for sulfide control in sewer networks. The Fe(2+) dosing requirement in rising main sewers which takes into account of the effect of anaerobic sewer biofilms on the dosing demand is investigated. A laboratory-scale rising main sewer, consisting of four biofilm reactors in series and fed with real sewage, was operated for over 12 months, during which FeCl(2) was dosed at several locations and at various dosing rates. The experimental results consistently revealed that approximately 0.7 mol of Fe(2+) was required to precipitate sulfide formed from the reduction of 1 mol of sulfate by anaerobic sewer biofilms. This ratio is significantly lower than the ratio expected from reaction stoichiometry (molar ratio of 1:1), and also the Fe(2+) to sulfide ratio (1.07-1.10 mol:1 mol) observed in batch tests conducted with real wastewater in the absence of sewer biofilms. Biofilms adapted to Fe(2+) addition were found to contain a substantially higher amount of elemental sulfur than biofilms not receiving Fe(2+) dosage. This suggests Fe(2+) addition might have altered the final product of sulfate reduction by anaerobic sewer biofilms. The study also showed that the addition of ferrous salts at the inlet of a rising main sewer can effectively control sulfide throughout the whole system despite of the presence of competing anions in wastewater. Phosphate precipitation with ferrous iron in anaerobic rising main sewers is negligible.
The study presented is an example of the assessment of the relative sustainability of either option for disposal of domestic sanitary waste, either via the toilet or via the solid waste route. This required an evaluation of the total (social, economic, environmental, and technical) benefit/cost of implementing and adopting the alternative routes and an assessment of public responsiveness to encouragement to change sanitary waste disposal practices. It illustrates how, even for an apparently straightforward either/or question, the assessment of relative sustainability is complex and the amount of data needed to quantify sustainability indicators is prodigious. The study also provides an appraisal of the effectiveness of public campaigns to reduce waterborne disposal. Important information regarding public attitude and behavior in relation to wastewater systems has been acquired and lessons for ways of encouraging behavioral change to more sustainable ways of living have been gleaned.
Long-term spatial and temporal variations in temperatures have been investigated in covers, wastes, and liners at four municipal solid waste landfills located in different climatic regions: Alaska, British Columbia, Michigan, and New Mexico. Temperatures were measured in wastes with a broad range of ages from newly placed to old (up to 40 years). The characteristic shape of waste temperature versus depth relationships consisted of a convex temperature profile with maximum temperatures observed at central locations within the middle third fraction of the depth of the waste mass. Lower temperatures were observed above and below this central zone, with seasonal fluctuations occurring near the surface and steady and elevated values (above mean annual earth temperature) near the base of the landfills. Heat gain and long-term temperatures were directly affected by placement temperatures. Sustained concave temperature profiles were observed for winter waste placement. The highest heat gain and resulting high temperatures were observed in Michigan followed by British Columbia, New Mexico, and Alaska. The high heat gain in Michigan was attributed to coupled precipitation/moisture content and waste density. The time-averaged waste temperature ranges were 0.9–33.0, 14.4–49.2, 14.8–55.6, and 20.5–33.6°C in Alaska, British Columbia, Michigan, and New Mexico, respectively. Temperature increases occurred rapidly (over multiple years) in British Columbia and then dissipated for tens of years. Longer periods of temperature increase were observed at the other sites. Temperatures, temperature increases, and heat gain were higher during anaerobic decomposition of wastes than aerobic decomposition. A parametric study indicated that use of insulating materials over covers decreased temperature variations compared to uninsulated conditions for prevention of frost penetration or desiccation and for optimum methane oxidation. Overall, thermal regime of landfills is controlled by climatic and operational conditions.
Dewatering and drying of residuals are extremely energy intensive processes, which are necessary to reduce the quantity of wet residuals produced from the water and wastewater treatment operations. Meteorological conditions are a major factor in the drying of residuals, which can greatly affect the drying period. A mathematical model is developed for the process of drying of water treatment residuals. A steady-state heat-balance equation is applied for a control volume of residuals that takes into account the heat transfer by radiation, convection, and evaporation. The mathematical model was validated using drying experiments conducted in a wind tunnel as well as other experiments conducted in an open environment equipped with a weather monitoring station. Good agreement was obtained between model predictions and experimental observations. The model can be used to predict the drying time of a given application of water treatment residuals with the knowledge of meteorological conditions.
Evolving environmental legislation has received increased attention worldwide in the last two decades, reported by Bradfield, Schultz, and Stone in 1996 in Environmental management in the Australian minerals and energy industries. The focus of concern by the industry, environmental regulatory agencies, and members of the public is the potential impacts associated with unstable landscapes which sometimes lead to slope failures, especially in hillside development. Engineered landscape profiles, though stable at the end of construction, may deteriorate over time due to erosion. There is thus a need to increase the base of knowledge on the existing practices of engineered profile design, hillside development, reshaping practices, and erosion control. With escalating production costs and the keen competitiveness in the industry world wide, the necessity to increase the efficiency of engineered profile development is further gaining prominence. This paper reviews the advancement of erosion management research in the industry, economics of landscape profiling, the practical application of the Point Estimate probabilistic technique, and the optimum design selection for the systematic planning and reshaping of engineered landscape profiles. The probabilistic engineering design erosion nomographs developed is useful in determining and illustrating quantitatively the reliability of final engineered landscape designs and the reshaping costs involved for different soil texture types. Landscape designs, which meet environmentally acceptable levels of reliability against erosion failure at optimum earth-moving reshaping costs, can be obtained using this probabilistic engineering design approach whilst satisfying environmental standards and community expectations for erosion minimisation.
A methodology developed by the U.S. Environmental Protection Agency (U.S. EPA) for evaluating the mass transport potential of hazardous organic compounds through environmental pathways is used to determine the potential mobility of eight chlorinated and organophosphorus pesticides in soil systems. Soil treatability studies are conducted to determine first-order degradation constants. Partition coefficients among water, soil, and air phases are calculated. Results of the treatability study along with calculated partition coefficients are used as input to a finite difference mathematical model to evaluate mass transport potential, including amount and extent of movement, through environmental pathways to groundwater and to the atmosphere. Application of the model using results of the treatability studies provides a methodology for predicting the behavior of hazardous constituents in soil systems, and for ranking chemicals with regard to the need for management and control for protection of public health and the environment.
This paper describes the verification of the flux model using independent pilot data obtained with variable water quality under worst case, laminar flow conditions. The original model accurately predicted iron release for this independent verification data, with an overall R-squared of 0.80. For laminar flow conditions, the increase in iron concentration is proportional to the flux and the hydraulic residence time, and is inversely proportional to the pipe diameter. Ce document décrit la vérification du modèle de flux en utilisant des données de projet pilote indépendantes obtenues avec qualité de l'eau variable dans les conditions les plus défavorables de flux laminaire. Le modèle original a pu prédire avec précision le rejet de fer de ces données de vérification indépendantes, avec un écart type global de 0,80. Dans le cas des conditions de flux laminaire, l'augmentation de la concentration en fer est directement proportionnelle au flux ainsi qu?au temps de séjour hydraulique, et inversement proportionnelle au diamètre du tuyau. RES
Various mesoporous catalysts with titanium loadings between 0.5 and 4 Ti wt. % and surface areas between 600 and 1,600 m(2)/g were synthesized using the molecular designed dispersion technique. These catalysts were tested using toluene oxidation in a fixed bed reactor at temperatures between 300 and 550degreesC. The reaction products were found to be CO2 and CO with selectivity towards CO2 above 80% for all catalysts. The catalytic activity of the catalysts increases with titanium loading. The total conversion at 550degreesC was not affected by the textural porosity, but increased textural porosity did significantly reduce the ignition temperature by up to 50degreesC. The Thiele modulus was calculated to be much less than one for all these materials indicating that the reaction rate is not diffusion, limited.
Fisherman Islands is an area of reclaimed land at the mouth of the Brisbane River in Queensland, Australia. Ongoing groundwater monitoring has found elevated concentrations of hydrogen sulfide (H2S) in the groundwater on the island. The presence of H2S on Fisherman Islands is of concern because of its toxic nature, the potential for acid sulfate soil formation, and its noxious odor. The aim of this study was,to, identify the sources of H2S within the groundwater on Fisherman Islands. It was hypothesized that the H2S is being formed by sulfate reducing bacteria acting on sulfate from seawater, rather than the introduction of sulfide with the dredge sediments. Groundwater and soil samples were collected and analyzed for sulfide, sulfate, and organic carbon contents. Elevated concentrations of sulfides coincide with,elevated concentrations of sulfate in the groundwater and elevated concentrations of organic carbon in the sediments, supporting the hypothesis that sulfide formation is the result of heterotrophic, sulfate reducing organisms.
The anaerobic hydrolysis rate of organic solid waste was studied at fixed volatile fatty acid (VFA) concentrations ranging from 3 to 30 g COD/L and fixed pH values between 5 and 7. For separate control of both VFA and pH, a special completely mixed reactor was designed. In this way, it was possible to distinguish between the inhibitory effects of pH, total VFA, and undissociated VFA on anaerobic hydrolysis. It was shown that hydrolysis of the organic solid waste followed first-order kinetics. Using a statistical analysis, it was found that the hydrolysis rate constant was pH dependent but was not related to the total VFA and undissociated VFA concentrations
An index for ranking the mobility of organic compounds in soil systems is presented. The index is defined as the ratio of time required for an organic constituent to travel through a given depth of soil (e.g., soil treatment zone), and the constituent half-life due to degradation assuming a first-order degradation rate. The mobility and degradation index (MDI) has been evaluated as a function of the constituent retardation factor in soil and degradation half-life for several soil textures. This approach is useful for the design and management of hazardous waste land treatment systems, as well as for treatment of previously contaminated soil.