Journal of Environmental Engineering

An integrated mathematical model for propylene glycol (PG) degradation in an anaerobic fluidized bed bioreactor is described. Special attention is put on biomass distribution, bed expansion, and bed segregation, associated with the biofilm accumulation process. In order to interpret the segregation of the bed during the initial development of the biofilm, the model postulates various mixing intensities along the bed height and thereby different exchange rates of microbial cells between the biofilm and the bulk liquid. The model incorporates stoichiometry of PG methanization, hydrodynamics, and reaction kinetics for elucidating microscopic interaction among microbial trophic groups inside the biofilm as well as the macroscopic behavior of the reactor such as bed expansion. A biofilm diffusion mechanism is also taken into account focusing on the spatial distribution of multiple species of micro-organisms. Employing moving boundaries makes the model flexible in computation, which permits simplifying the implementation of the biofilm accumulation and the bed expansion phenomena.

This paper examines the influence of bed segregation on the performance of an anaerobic fluidized bed bioreactor (AFBR) using both an integrated mathematical model previously described in Part I of this study, and experimental data obtained from a laboratory-scale AFBR continuous flow system and batch serum vial tests. Local hydrodynamics within the bed are shown to determine mixing intensities and patterns of bioparticles thereby controlling biofilm thickness and composition along the bed height. Results of the model simulations and the experimental data indicate that shallow biofilms that allow full substrate penetration are dominantly populated with faster growing micro-organisms. The internal mass transfer resistance in thicker biofilm significantly influences population distribution resulting in the increase of population of slower growing micro-organisms in a deeper layer of the biofilm. The serum bottle tests also confirm that microbial distribution inside a multispecies biofilm is determined by the hydrodynamic condition of the reactor. This study illustrates the importance of hydrodynamic regimes in the AFBR, and demonstrates the impact of bed segregation on bioparticle properties and total system performance.

Propylene glycol-based aircraft deicing fluid (ADF) is sprayed on aircraft during cold weather to remove ice and snow or prevent ice formation. A large fraction of the fluid typically falls to the pavement where it mixes with stormwater. Since airport stormwater containing ADF can exert a high biochemical oxygen demand, biological treatment may be required. The objective of this study was to determine and compare the rates of ADF chemical oxygen demand (COD) removal in anaerobic complete-mix stirred tank reactors (CMSTRs), anaerobic filters (AFs), and anaerobic fluidized bed reactors (FBRs) treating acidified and nonacidified propylene glycol ADF at temperatures between 35 and 11°C. The AF and FBRs were initially operated in a continuous-flow mode. Subsequently, kinetic data were collected when the reactors were operated in batch mode. Maximum specific removal rates of 0.93, 0.30, and 0.045 g COD per g volatile solids per day were determined at temperatures of 35, 24, and 11°C, respectively. The rates of acidified and nonacidified ADF COD removal were not significantly different. An Arrhenius equation temperature correction coefficient (θ) of 1.11 was determined. The most significant increase in overall COD removal rates (mg COD/L-day) were a result of biomass immobilization and increased biomass concentration in AFs and FBRs. Final COD concentration in the CMSTR were chronically high (circa 700 mg/L), and did not decline after five additional days of batch reaction time, whereas no chronically high final COD concentrations were observed in AFs and FBRs.

Mixed liquor pH and temperature are two parameters that affect the growth rate of nitrifying bacteria and therefore the minimum solids retention time required to achieve nitrification. The objective of this study was to determine the consequence of low mixed liquor pH, and to determine if pH depression could be alleviated by recovering alkalinity through denitrification in a pure oxygen activated sludge system. The study was conducted at the University of Manitoba using laboratory scale, pure oxygen activated sludge reactors, fed with primary effluent. The results indicated that when denitrification was not included in the process, the concentration of ${\mathrm{CO}}_2$ in the headspace of the pure oxygen reactors increased to as high as 15% due to carbon oxidation and endogenous respiration. The high ${\mathrm{CO}}_2$ concentration in the headspace combined with low alkalinity caused by nitrification resulted in bulk mixed liquor pHs below 5.5. In order to maintain complete nitrification at a temperature of 24°C and a mixed liquor pH of 5.5, a solids retention time (SRT) of 12 days was required. In comparison, when denitrification was included in the process the pH of the mixed liquor was increased to 6.4 allowing for full nitrification at an SRT of 5.6 days at a temperature of 24°C. The increase in pH in the denitrification trains was attributed to three factors: recovery of alkalinity through the denitrification process, the conversion of influent carbon to ${\mathrm{CO}}_2$ in the anoxic reactor allowing the ${\mathrm{CO}}_2$ to escape to the atmosphere, and the recycle of mixed liquor super saturated with ${\mathrm{CO}}_2$ from the pure oxygen reactor to the anoxic reactor allowing the ${\mathrm{CO}}_2$ to escape to the open atmosphere. It was determined that the nitrifier growth rate at 12°C was approximately 50% of the rate measured at 24°C. At mixed liquor pHs between 6.0 and 6.3 at a temperature of 12°C, the specific nitrifier growth rate was between 0.12 and $0.15d^{-1}\text{,}$ while at 24°C, the specific nitrifier growth rate was between 0.25 and $0.30d^{-1}$ at pHs ranging from 5.0 to 6.1

A mathematical model was developed for the decomposition of halogenated compounds in water and applied for tetrachloroethylene (PCE) in a flow-through photosonolysis reactor. To develop the model, a series of differential equations were formulated based on the principles of conservation of mass and mass action for hypothetical parent and daughter species, which were then solved analytically. The model sensitivity analysis was performed to determine if the model gives intuitive results. In support of the modeling effort, experiments were conducted. In a flow-through bench-scale reactor, simulated groundwater contaminated with PCE was irradiated with ultraviolet light and ultrasound concurrently in the presence of titanium dioxide $\left({\mathrm{TiO}}_2\right)\text{.}$ The model was calibrated against the concentrations of PCE, trichloroethylene, methylene chloride, and chloride ion, obtained from the experiments. The proposition for the rate constants is based on fitting the model result to the experimental data. The model was further verified by comparing the model results against a different set of experimental data. The model results against available data indicated good agreement within experimental variations. The modeling suggests that PCE is more susceptible to the C-C double bond cleavage than the C-Cl bond cleavage. The results also support the assumptions that chlorinated methane compounds can be degraded at higher rates than chlorinated ethylene and that the values of the degradation rate constants increase with a decreasing number of chlorine atoms attached to the hydrocarbon compound.

Groundwater contamination by chlorinated ethenes is a widespread environmental problem. Shortcomings in conventional remediation methods have motivated research into novel treatment technologies. A palladium/alumina catalyst in the presence of molecular hydrogen gas (referred to hereafter as the $\mathrm{Pd}/H_2$ system) has been demonstrated to destroy chlorinated ethenes in contaminated groundwater. This study presents a model for aqueous-phase destruction of chlorinated ethenes in contaminated groundwater using the $\mathrm{Pd}/H_2$ system that includes catalyst deactivation and regeneration. The model is validated using published data from laboratory column experiments from Stanford University. The model is then coupled with an analytical groundwater flow model to simulate application of in-well $\mathrm{Pd}/H_2$ reactors for in situ treatment of chlorinated ethene contaminated groundwater in a recirculating horizontal flow treatment Well (HFTW) system. Applying the model under realistic conditions results in approximately 130 days of HFTW system operation without significant catalyst deactivation. This suggests catalyst deactivation will not significantly affect system performance in a real remediation scenario. The model presented in this study, which simulates deactivation kinetics and regeneration of an in-well catalyst that is a component of a recirculating well system designed for in situ treatment of contaminated groundwater, represents an important step in transitioning the $\mathrm{Pd}/H_2$ technology to the field.

A novel approach toward the removal of iron and nonferrous metals from typical South African acid mine drainage (AMD) waters was investigated. The approach involves the controlled oxidation of ferrous-containing AMD water at ambient temperatures in the presence of magnetite seed. The resulting oxidation product is the ferrite $\left({\mathrm{M1}}_2^{3+}{\mathrm{M2}}^{2+}{O}_4\right)$ magnetite $\left({\mathrm{Fe}}_3{O}_4\right)$ which has the capacity for nonferrous metal removal by cation substitution. Mössbauer spectroscopy, x-ray diffraction, and scanning electron microscopy analyses confirmed the precipitant to be magnetite. The effects of four parameters are reported: airflow rate, seed concentration, pH, and temperature. All of these independently affect the % ferrous in the final precipitant. In all experiments, the airflow rate was found to be rate limiting with respect to the kinetics of ferrous removal. The retention time for the complete removal of 1,200 mg Fe/L was 0.3–1.6 h (corresponding to airflow rates of 0.05–0.6 L/min, respectively). The precipitant settled well and showed complete stability at pH 5. The total iron concentration in the raw effluent was always less than 1 mg/L, representing an iron removal efficiency of greater than 99.9%.

Quantitative methods for characterizing both variability and uncertainty are applied to case studies of nitrogen oxides $\left({\mathrm{NO}}_x\right)$ and total hydrocarbon air pollutant emission factors for construction, farm and industrial engines. A database was developed and statistical methods were used to identify statistically significant categories, including gasoline engines, two-stroke diesel engines, and four-stroke diesel engines. Emissions were not found to be statistically significantly different for older versus newer nonroad diesel engines nor when comparing naturally aspirated and turbocharged engines. Interengine variability in emissions was quantified using Weibull, gamma, and lognormal distributions. Bootstrap simulation was used to characterize confidence intervals for the mean. The 95% confidence intervals for the mean emission factors were as small as −10 to +11% and as large as −48 to +49%, with an average range of −26 to +27%. Asymmetry in the confidence intervals is attributable to small sample sizes and skewness in the data. Estimates of uncertainty convey information regarding the quality of the emission factors and serve as a basis for calculation of uncertainty in emission inventories.

This paper presents a new approach to analyze the performance of outfalls with single buoyant plumes in flowing ambient sea water, taking into account all three dilution mechanisms: the initial, the dispersion, and the effective dilution due to the decay of nonconservative substances. Simultaneous consideration of all dilution mechanisms, study of their functional relationships, sensitivity analysis of outfall behavior, and graphical presentation of the results, allows recognition of patterns of practical importance that remain otherwise obscure. The generated graphs afford an overview of the relative performance of outfalls with a single port and perpendicular line diffusers over a broad range of operating conditions, and portray the sensitivity of the single-port outfall behavior. The results show that, contrary to common belief, outfalls with a single port outperform those with perpendicular line diffusers over a broad range of operating conditions. They also show that higher rather than lower current speed is the critical factor in the design of single-port outfalls. These findings affect the construction cost of outfall systems and bear a significant impact on the sizing of new outfalls as well as on the performance evaluation of existing ones.

The present paper provides some evidence regarding the thermal electrical power production sector of Greece evaluating performance indicators as signposts of sustainability. The methodology used was data envelopment analysis applied for each one of the yearly activities of thermal electrical power production sector. In the present study two evaluations are carried out. The first one takes into account only corporate data (i.e., inputs and outputs of production process), though in the second one environmental impact data (i.e., ${\mathrm{NO}}_x$ and ${\mathrm{SO}}_2$ emissions) are also included. According to the results, in the late 1980s the performance of Public Power Corporation, the exclusive electricity producer, was efficient compared to the previous yearly activities considered here.

In situ apparent oxygen uptake rate (OUR) measurements of laboratory bioreactors open to atmospheric air are practical and useful, but atmospheric oxygen transfer into the reactor may significantly underestimate the actual values of OUR. The effects of the atmospheric oxygen transfer were quantitatively assessed using an oxygen mass transfer model. A factor Ψ representing the degree of underestimation of actual OUR by the in situ apparent OUR $\left({\mathrm{OUR}}_a\right)$ technique was introduced. The Ψ factor for the primary settling tank effluent of a local water pollution control plant was found to be unity in the beginning of reaction period when the microbial activity was high $({\mathrm{OUR}}_a=27$ mg/L h), but decreased to 76% at the end of reaction period when the microbial reaction rate was low $({\mathrm{OUR}}_a=2$ mg/L h).