Showing papers in "Journal of Environmental Engineering in 1989"
TL;DR: In this paper, analytical and numerical groundwater flow models are used to evaluate the results of a field gas extraction test, and results of these evaluations indicate groundwater models can provide an efficient and readily accessible tool to aid in designing vapor extraction systems.
Abstract: Vapor extraction systems have recently been used in a variety of environmental engineering applications, including controlling methane migration and remediating problems associated with spills of volatile and semi-volatile organic compounds. The differential equations that govern pressure flow of gas and vapor in soil are nonlinear in that gas density depends upon gas pressure. However, if the maximum pressure difference between any two points in the flow field is less than approximately 0.5 atmospheres, the differential equations developed to model groundwater flow provide good approximations to gas transport. Vapor extraction systems generally operate under pressure differences on the order of 0.2 atmospheres. Analytical and numerical groundwater flow models can therefore be used to model vapor and gas transport if the proper set of input variables is defined. Analytical groundwater flow models are used to evaluate the results of a field gas extraction test. The results of these evaluations indicate groundwater models can provide an efficient and readily-accessible tool to aid in designing vapor extraction systems.
203 citations
TL;DR: In this article, the extent to which the chemical constituents of refuse degrade is investigated, and it is shown that the degradation rate depends on the degree of decomposition of the refuse.
Abstract: Methane production from the decomposition of municipal refuse is well documented. However, there is little information on the extent to which the chemical constituents of refuse degrade. Decomposit...
173 citations
TL;DR: In this article, a simple model for membrane fouling is proposed, where fouants capable of entering membrane pores are aggregated to produce particles that are rejected at the membrane surface.
Abstract: The deposition of small colloids or macromolecules in membrane pores and the subsequent irreversible fouling of the membrane is considered using a simple model for membrane fouling. As a strategy for avoiding pore fouling, it is proposed that foulants capable of entering membrane pores be aggregated to produce particles that are rejected at the membrane surface. Considerations in filtering suspensions of particles on membranes are discussed with emphasis on particle transport mechanisms as a function of particle size. It is concluded that particles larger than 3 μ\Nm should not contribute significantly to membrane fouling at permeate fluxes that are currently feasible. For many membrane configurations, particles between 0.1 and 1 μ\Nm will be most likely to contribute to fouling on membrane surfaces. Batch flocculation and membrane filtration experiments were conducted to test the feasibility of manipulating flocculation conditions to control particle size and fouling. Conditions that produced particles with a zeta potential near zero minimized fouling by reducing foulant penetration into pores, increasing the porosity of the deposited cake, and increasing the transport of potential foulants away from the membrane.
136 citations
TL;DR: The state of the art in denitrification of drinking water has been surveyed in this article, where various unit processes have been used including biofilters, fluidizedbed and packedbed reactors, packed towers containing cells immobilized in polymer gels, and completely mixed reactors with cells attached to bouyant porous carriers.
Abstract: Voluminous research has been published regarding the denitrification of drinking water. Most of this work has been done in Europe. Unfortunately, much of the European literature has not been translated into English, and as a consequence there may be a gap in the understanding of the international state of the art with regard to drinking‐water denitrification. Numerous substrates have been evaluated including methanol, ethanol, acetic acid, methane, carbon monoxide, hydrogen, and various sulfur compounds. Various unit processes have been utilized including biofilters, fluidized‐bed and packed‐bed reactors, packed towers containing cells immobilized in polymer gels, and completely mixed reactors with cells attached to bouyant porous carriers. There are several commercial facilities currently providing drinking water to European communities. Most include post‐treatment with flocculation, filtration, and disinfection. A common concern in denitrification operations is the minimization of nitrite accumulation. ...
112 citations
TL;DR: Wet air oxidation is ideally suited to liquid wastes which are too dilute to be incinerated and too refractory to be handled by chemical or biological oxidation as discussed by the authors, but it relies on high tempera...
Abstract: Wet air oxidation is ideally suited to liquid wastes which are too dilute to be incinerated and too refractory to be handled by chemical or biological oxidation. This process relies on high tempera...
101 citations
TL;DR: In this paper, a model for single species gas flow inside a nonisotropic porous medium, within which gas is continuously generated, was developed for single-species gas flow, incorporating Darcy's law, and a linear parabolic equation was derived to express the internal pressure variations in terms of the permeability, gas production rate and boundary conditions of a site when a series of extraction wells are present.
Abstract: A model, incorporating Darcy’s law, is developed for single-species gas flow inside a nonisotropic porous medium, within which gas is continuously generated. A linear parabolic equation is derived to express the internal pressure variations in terms of the permeability, gas production rate, and boundary conditions of a site when a series of extraction wells are present. The model is used to determine the gas fluxes within a site of rectangular cross section, into which an arbitrary number of horizontal extraction pipes have been installed. This solution is used to predict the consequences of cumulative failures within a complex pumping system, and hence estimate the circumstances under which gas is first able to escape from a site. Using the results of the model some brief guidelines are offered for designing such installations. The analytical solution technique is contrasted with purely numerical methods for similar problems, and the speed and accuracy of each are compared. An efficient computer implementation for preliminary design studies is suggested.
80 citations
TL;DR: In this article, the dynamics of adsorption for various adsorbate-adsorbent systems have been predicted successfully using the homogeneous surface diffusion model (HSDM), where external film mass transfer and surface diffusion coefficients are defined in order to solve the mathematical model.
Abstract: The dynamics of adsorption for various adsorbate-adsorbent systems have been predicted successfully using the homogeneous surface diffusion model (HSDM). External film mass transfer and surface diffusion coefficients, as well as adsorption equilibrium parameters must be defined in order to solve the mathematical model. Simple batch experiments are usually performed to determine the mass transfer coefficients, whereas bottle tests are employed to obtain the equilibrium data. The parameter search procedure presented in this paper uniquely determines these parameters for the HSDM. No limitations are imposed on this search due to the dominance of one mass transport mechanism over the other, such as cases limited by either external film or surface diffusion resistance. Simple residual plots are used to examine the reliability of the estimated parameters and to judge whether the HSDM is the appropriate model for describing specific adsorption data.
70 citations
TL;DR: An event-based computer model, GRAPH, was developed to simulate phosphorus (P) transport in grass buffer strips (GBS) by incorporating submodels into SEDIMOT II, a stormwater and sediment transport model developed for strip mine reclamation.
Abstract: An event-based computer model, GRAPH, was developed to simulate phosphorus (P) transport in grass buffer strips (GBS) by incorporating submodels into SEDIMOT II, a stormwater and sediment transport model developed for strip mine reclamation. GRAPH considers the effects of advection processes, infiltration, biological uptake, P desorption from the land surface to runoff, adsorption of dissolved P to suspended solids in runoff, and the effects of changes in sediment size distribution on P transport. Required input data include: rainfall intensity and duration, an inflow hydrograph, a sediment graph, sediment size distribution, GBS dimensions and hydraulic characteristics, inflow graphs for dissolved P, P desorption and adsorption reaction coefficients for soil and plant matter, and the P content of each soil particle size class. GRAPH simulates time varying infiltration, runoff discharge, sediment yield, particle size distribution, and dissolved and sediment-bound P discharge along with sediment and P trapping efficiencies in GBS. GRAPH was verified using data from experimental field plots. Model predictions and observed P transport in the GBS compared favorably.
67 citations
TL;DR: In this article, the bactericidal action of solar radiation was investigated in pilot scale waste stabilization ponds under the tropical climate of Dar es Salaam, Tanzania, and the disappearance rate of faecal coliforms for samples incubated at the pond surface and at a depth of 1.0 m was 1.66 d\u-¹ and 0.37 d/u¹ respectively.
Abstract: The bactericidal action of solar radiation was investigated in pilot scale waste stabilization ponds under the tropical climate of Dar es Salaam, Tanzania. Bacterial reduction was observed to proceed with increasing direct solar intensity and hydraulic detention time. The mortality rate of faecal coliforms used as test micro-organisms was higher in samples incubated near the surface and decreased rapidly when the samples were incubated at greater depths in the pond. The disappearance rate of faecal coliforms for samples incubated at the pond surface and at a depth of 1.0 m was 1.66 d\u-¹ and 0.37 d\u-¹ respectively. Faecal coliforms were also found to be reduced rapidly in shallow ponds. The mortality rate in 1.0 m and 1.5 m deep ponds was respectively 0.43 and 0.32 d\u-¹. The die-off rate constant was observed to vary significantly with pond depth but was independent of hydraulic detention time.
64 citations
TL;DR: In this paper, a linear programming, diameter discretization, heuristic approach is presented for the optimum design of large gravity sewer networks, which contains a nonlinear convex function relating pipeline diameter and slope, which is approximated by piecewise linear segments.
Abstract: A linear programming, diameter discretization, heuristic approach is presented for the optimum design of large gravity sewer networks. The mathematical model contains a nonlinear convex function relating pipeline diameter and slope, which is approximated by piecewise linear segments. This approach uses a modified Hazen‐Williams hydraulic model at part‐full flow conditions, along with a newly developed universal expression to determine the coefficient of roughness. Moreover, the hydraulic formulation contains a regression equation to determine Darcy's friction factor based on the depth of flow in the pipe. The developed model has been extensively and successfully used to design several large sewer networks.
63 citations
TL;DR: In this article, individual carbon particles were examined using a programmable and computerized image analyzer to determine their size and shape characteristics, and power-law correlations were developed to indicate the effect of batch adsorber parameters and particle size on the external mass transfer coefficient.
Abstract: Individual carbon particles were examined using a Quantimet‐720‐23A programmable and computerized image analyzer to determine their size and shape characteristics. Particles in a given sieve size fraction are well represented by the log‐normal distribution. The use of the Sauter mean of particle diameters from projected area measurements is recommended to account for the effects due to the variations in particle size and shape. The solid phase diffusion coefficient estimated from batch reactor analysis, is found to be invariant with this particle diameter. Power‐law correlations are developed to indicate the effect of batch adsorber parameters and particle size on the external mass transfer coefficient.
TL;DR: In this paper, the physical requirements of a lightweight concrete in terms of unit weight, strength, heat-insulating properties, and fire resistance were investigated using sludge ash as a potential source of suitable lightweight aggregates.
Abstract: Sludge is an inevitable by‐product of wastewater treatment. Its abundance poses disposal problems that can be drastically reduced if sludge can be converted for economical uses in construction as substitute materials. Digested and dewatered sludge, after incineration at a high temperature, yields a hard, cellular, porous mass with low unit weight. This hardened mass of sludge ash can be crushed to smaller‐sized aggregates, which, when graded in suitable proportions, manifest the basic attributes required of lightweight aggregates. When used as aggregates in the production of lightweight concrete, experimental results show that the resulting concrete satisfies the physical requirements of a lightweight concrete in terms of unit weight, strength, heat‐insulating properties, and fire resistance, thus indicating that sludge ash could be a potential source of suitable lightweight aggregates.
TL;DR: In this article, a Monte Carlo simulation model is used to generate a series of water quality responses that lead to the formulation of a constraint set for the optimization model, which yields a distribution for the required treatment cost.
Abstract: A modeling technique for water‐quality management that incorporates both simulation and optimization is presented. The proposed methodology should be of use in the allocation of waste load for a number of dischargers located on a water body. A Monte Carlo simulation model is utilized to generate a series of water quality responses that lead to the formulation of a constraint set for the optimization model. Repeated solution of the optimization model, using an appropriate mathematical programming technique, yields a distribution for the required treatment cost. Additionally, the distribution for the required pollutant removal fraction at each of the point source locations is obtained from the combined use of simulation and optimization. From the treatment cost distribution function, attractive alternatives can be identified for further analysis prior to the implementation of a water‐quality management plan. Elements of the proposed methodology are illustrated through an example of allocating biochemical ox...
TL;DR: The ability of the modified clay to remove benzene decreases at doses higher than 150% of the CEC of the clay as discussed by the authors, and the adsorption isotherm constants on TMA-bentonite are calculated from equilibrium studies for benzene, toluene, and o−xylene.
Abstract: The natural cation in Wyoming bentonite is exchanged with Tetramethylammonium (TMA+) ions. The adsorptive properties of TMA‐bentonite increase in direct proportion to the exchange reaction below 60% of the CEC of the clay. The ability of the modified clay to remove benzene decreases at doses higher than 150% of the CEC of the clay. Adsorption isotherm constants on TMA‐bentonite are calculated from equilibrium studies for benzene, toluene, and o‐xylene. The selectivity of the TMA‐tailored bentonite follows the following order: benzene » toluene > o‐xylene. Solute equilibrium concentration is attained within fiveminute contact time. Solution pH plays a secondary role on the adsorptive nature of TMA‐bentonite.
TL;DR: In this article, a time series analysis approach was applied to model 21 years of mean monthly water quality data in the Guangzhou reach of the Pearl River in southern China, where the basic properties of the water quality time series were determined, time and frequency-domain analyses were carried out, and the dependent stochastic component was represented by various stochastically models.
Abstract: A time series analysis approach was applied to model 21 years of mean monthly water quality data in the Guangzhou reach of the Pearl River in southern China. The basic properties of the water quality data time series were determined, time‐ and frequency‐domain analyses were carried out, and the dependent stochastic component was represented by various stochastic models. Synthetic water quality data were generated by using the probability distribution of the independent residuals, and forecasting of future water quality data was done using a Box‐Jenkins‐type difference model. Eighteen years of data were used for model development, while the model performance was compared with the data for the remaining three years. The comparisons were found to be satisfactory.
TL;DR: In this paper, a sludge freezing bed is proposed for dewatering sludges produced by treatment facilities in cold regions, which uses natural freezethaw to condition the sludge.
Abstract: A new unit operation called a sludge freezing bed is proposed for dewatering sludges produced by treatment facilities in cold regions. This unit operation uses natural freezethaw to condition the s...
TL;DR: In this paper, a predictive mathematical model that describes the adsorption and biodegradation phenomena in recycle fluidizedbed (RFB) adsorbers was developed and solved by a combinatorial technique involving the methods of orthogonal collocation and finite differences.
Abstract: A predictive mathematical model that describes the adsorption and biodegradation phenomena in recycle fluidized‐bed (RFB) adsorbers was developed. The model incorporated liquid film transfer, biodegradation and diffusion in the biofilm, adsorption onto activated carbon, and biofilm growth. The model equations were solved by a combinatorial technique involving the methods of orthogonal collocation and finite differences. Computer simulations of the model were used for adsorber performance predictions from parameters obtained from adsorption equilibrium and kinetic studies, biokinetic experiments, and correlation techniques. Sensitivity tests were also performed to determine the effect of physical and biological parameters on model profiles. Recycle fluidized adsorber experiments were conducted to test the predictive capability of the model. Two ideally biodegradable compounds, glucose and sucrose, as well as two actual wastewaters, a dairy waste and a landfill leachate, were used to compare the predicted m...
TL;DR: A model for calculation of ICN values based on animal infectivity data is developed, based on first-order kinetics, that relates chlorine concentration, pH, and temperature to disinfection levels and predictions are compared to laboratory data.
Abstract: Amendments to the Safe Drinking Water ACt (PL-93-523) highlight the continuing problem of waterborne disease by mandating the EPA to promulgate: (1) Criteria by which filtration will be required for surface water supplies; and (2) disinfection requirements for all water supplies in the United States. There is interest on the part of the EPA in applying the \IC\N·\N\It\N concept for determining the inactivation of \IGiardia lamblia\N cysts as a key criterion for determining exceptions to the filtration rule. If a utility, in addition to meeting other requirements, can demonstrate that through effective disinfection, manifested by a sufficient \IC\N·\N\It\N value, it can reduce \IGiardia\N levels by 99.9%, then it will be exempted from surface water filtration. In this paper, a model for calculation of \IC\N·\N\It\N values based on animal infectivity data is developed. The model, based on first-order kinetics, relates \IC\N·\N\It\N values to chlorine concentration, pH, and temperature. The model predictions are compared to laboratory data.
TL;DR: In this article, a PC-based continuous stirred tank reactor (CSTR) model is used to depict the response of lake water quality to loadings associated with a variety of development options ranging from impervious cover of 10-40%.
Abstract: Extensive land use, nonpoint source (NPS), and lake water quality data are used to determine the interaction of lake water quality and watershed development in the Lake Austin watershed. Historical trends in total suspended solids and total phosphorus are examined over the 1979–84 period, during which impervious cover increased by 79% in the lake watershed. A PC‐based continuous stirred tank reactor (CSTR) model is used to depict the response of lake water quality to loadings associated with a variety of development options ranging from impervious cover of 10–40%. The reliability of the model is supported by the unusually simple lake hydraulics, exclusive NPS loading, and extensive data base. Model results are used to create a set of recommendations that should protect the water quality of the lake.
TL;DR: In this article, the authors designed and monitored an experimental on-site watewater disposal system with nitrogen-reducing capability, which incorporated two fixed-film reactors: a nitrification/denitrification (N/D) tank, and a polishing filter.
Abstract: One of the enironmental concerns associated with on‐site wastewater disposal is nitrate contamination of groundwater. The purpose of this study was to design and monitor an experimental on‐site watewater disposal system with nitrogen‐reducing capability. Incorporated into the system are two fixed‐film reactors: a nitrification/denitrification (N/D) tank, and a polishing filter. Recirculated denitrified effluent sprayed onto the sand filter portion of the N/D tank is nitrified and the nitrified effluent is then mixed with septic tank effluent in the submerged gravel section for denitrification. The remaining portion of the denitrified effluent enters a polishing filter before final discharge into groundwater. With a recirculation ratio of 3.3, the overall reduction in total nitrogen through the N/D tank was approximately 70%. The N/D component of the system also achieved a reduction in BOD, COD, and suspended solids of 87, 80, and 84%, respectively. With the polishing filter, further enhanced removal of th...
TL;DR: A steady-state biofilm can tolerate bulk substrate concentrations greater than greater than \IS\N\dm\da\dx, because the inner layers of the biofilm are exposed to substrate concentrations less than less than this, due to mass transport resistance and substrate utilization in the outer layers ofthe biofilm.
Abstract: Numerical simulations were performed that examined the utilization of inhibitory substrates by steady-state biofilms. Based on kinetic and energetic constraints, the growth of a monolayer of cells into a steady-state biofilm requires that substrate concentrations be between \IS\N\dm\di\dn and \IS\N\dm\da\dx. The continued exposure of a monolayer or dispersed cells to substrate concentrations less than \IS\N\dm\di\dn or greater than \IS\N\dm\da\dx will not lead to the development of a self-perpetuating biological treatment process. However, once developed, a steady-state biofilm can tolerate bulk substrate concentrations greater than \IS\N\dm\da\dx, because the inner layers of the biofilm are exposed to substrate concentrations less than \IS\N\dm\da\dx due to mass transport resistance and substrate utilization in the outer layers of the biofilm. In such situations, maximal rates of substrate utilization and microbial growth occur in the middle or at the inner surface of the steady-state biofilm. The simulations also indicated that there are two sets of steady-state biofilms: one associated with \IS\N\dm\di\dn (stable steady-state solutions) and the other associated with \IS\N\dm\da\dx (unstable steady-state solutions).
TL;DR: In an attempt to simulate the mitigation of chemical contamination by microbial enrichment in existing unsaturated soil systems, two important characteristics, i.e., the influence of microorganisms on soil water flow and chemical removal rates, were incorporated into a mathematical model (BIOSOIL).
Abstract: In an attempt to simulate the mitigation of chemical contamination by microbial enrichment in existing unsaturated soil systems, two important characteristics, i.e., the influence of microorganisms on soil water flow and chemical removal rates, were incorporated into a mathematical model (BIOSOIL). Variablestep and variable‐order Gear's Method was employed as a numerical approximation to solve the set of four differential equations. The resulting mathematical model described the behavior of the biosoil system under varying input condititons. From this modeling study of chemical removal, the following conclusions were drawn: (1) The depth of the unsaturated soil zone, a significant consideration in waste disposal practices, seems to be less crucial under bioremediation than generally thought; and (2) microbial distribution in a vertical column of soil is as important as the total population size of soil microorganisms. Study results suggest a guideline for the development of vertically well distributed bio...
TL;DR: In this article, an acoustic wave is projected through a subsurface cross section to a hydrophone array located vertically in a borehole, and amplitude versus time signal of the propagating wave is collected at each hydrophone.
Abstract: A new geophysical tool for high resolution subsurface imaging has been developed which has numerous applications in the field of hazardous waste management. The primary steps of the technique are: (1) An acoustic wave is projected through a subsurface cross section to a hydrophone array located vertically in a borehole; (2) the amplitude versus time signal of the propagating wave is collected at each hydrophone; and (3) the reduced wave equation and theory of backpropagation tomography are invoked to reconstruct the subsurface features from the collected data. The development of this emerging technology is highlighted beginning with its theoretical conception, through system development and field testing, to an examination of its future applications in environmental engineering.
TL;DR: In this paper, an equation of iso-percentage curves as a function of settling time and depth is developed which is applicable both to discrete and flocculent suspensions and an expression for the solids removal ratio of quiescent settling suspensions is obtained.
Abstract: In this study an equation of iso-percentage curves as a function of settling time and depth is developed which is applicable both to discrete and flocculent suspensions. Using this model, an expression for the solids removal ratio of quiescent settling suspensions is obtained. Results of the proposed expression are found to be in good agreement for most cases when predicted and reported solids removal ratios are compared. Observed differences are interpreted as results of manual interpolation of iso-percentage curves and as assumptions made in graphical evaluations of solids removal efficiencies in the literature. It is concluded that the presented expression can be used as a numerical approach in the evaluation of ideal settling column test results of suspensions.
TL;DR: In this paper, the dependency of parameter values on the level of model discretization was investigated, and results of different levels of discretisation were compared to observed hydrograph volume and peak runoff.
Abstract: Stormwatrer models, which are used extensively for stormwater drainage design and management, require calibration. The parameters usually estimated by calibration include infiltration and roughness. Parameters that can be determined by measurement include catchment area, slope, and length of flow path. The dependency of parameter values on the level of model discretization was investigated. Experiments were performed on a small urban catchment, and results of different levels of discretization were compared to observed hydrograph volume and peak runoff. The only factor found to require adjustment based on the level of discretization and the size of subcatchment was the overland flow time. Small-scale discretization required a longer flow path or a higher Manning roughness coefficient than coarse discretization to predict lag times correctly.
TL;DR: In this article, fixed-film nitrification was studied in a pilot-scale fluidized bed treating municipal secondary effluent, where a mechanistic mathematical model incorporating reaction stoichiometry, diffusion, multisubstrate kinetics with product inhibition, fluidization, and a reactor model developed from the observed residence-time distribution, was developed to predict the steady-state and short-term dynamic performance of the reactor.
Abstract: The authors discuss fixed-film nitrification studied in a pilot-scale fluidized bed treating municipal secondary effluent. A mechanistic mathematical model incorporating reaction stoichiometry, diffusion, multisubstrate kinetics with product inhibition, fluidization, and a reactor model developed from the observed residence-time distribution, was developed to predict the steady-state and short-term dynamic performance of the reactor. The model equations were solved using orthogonal collocation with trial functions tailored to the spherical-shell biofilm geometry, and a semi-implicit third-order Runge-Kutta integration technique. The steady-state model closely fit measured concentration profiles using the maximum specific growth rates for Nitrosomonas and Nitrobacter as adjustable parameters. The dynamic model predicted observed responses to set and impulse changes in ammonium and nitrite concentrations to within 3 mg/L without further parameter adjustment. The fluidization model predicted the observed fluidized bed height within 1 cm.
TL;DR: In this article, a microporous hollow-fiber membrane/oil stripping system is used to separate volatile organic contaminants from water using an air-filled gas-permeable membrane.
Abstract: Separation of volatile organic contaminants from water using a microporous hollow-fibermembrane/oil stripping system is evaluated. Countercurrent flow of water and oil on opposite sides of an air-filled gas-permeable membrane is used to concentrate the contaminants in the oil phase. The rate of mass transfer under varying conditions is measured and compared to existing full- and laboratory-scale air-stripping processes, to membrane-extraction processes, and to predictions based on known empirical and theoretical correlations. The correlations can be used as the basis for system design and scale-up. This process incorporates the advantages of other membrane-stripping processes, such as a high surface area to volume ratio for transfer, and independent control of the separate liquid phases. It also overcomes several disadvantages of extraction and stripping processes. There is no contact between the liquid phases and thus no potential for cross-contamination or emulsion formation. The membrane separation of phases prevents flow channeling and flooding present in air-stripping towers. Finally, materials used in this process may be recovered aand recycled, preventing further environmental contamination.
TL;DR: The aerated fluidized bed biofilm reactor (FBBR) was evaluated for treatment of a corn starch wastewater at food-to-microorganism (F/M) ratios ranging from 0.4 to 1.61 g 5-day biochemical oxygen demand (BOD\d5/g( total volatile solids (TVS)-day) as discussed by the authors.
Abstract: The aerated fluidized bed biofilm reactor (FBBR) was evaluated for treatment of a corn starch wastewater at food-to-microorganism (F/M) ratios ranging from 0.4 to 1.61 g 5-day biochemical oxygen demand (BOD\d5/g( total volatile solids (TVS)-day. Laboratory results indicated that good combined carbon oxidation-nitrification, with removal efficiencies greater than 90%, could be achieved providing that F/M ratio and mean cell residence time (MCRT) were maintained at greater than 1.0 g BOD/d4/g TVS-day and fewer than five days, respectively. More than 95% of reactor biomass in an aerated FBBR was immobilized on the fluidized media. Depending on the BODd5 loadings applied, between 25 to 75 mg TVS could be immobilized per gram of sand. Good oxygenation performance, with bulk-liquid DO concentrations consistently greater than 3.0 mg/L, was achievable because the fluidization requirementsof media controlled the air injection rate. Both BOD\d5 removal and nitrification kinetics exhibited a pattern suggesting that mass transfer resistances of substrates could be significant within the region of low bulk-liquid concentrations.
TL;DR: In this article, three commonly accepted mathematical techniques (integral, differential, van't Hoff) for the analysis of rate data are employed, and the results indicate that when single-order dependencies are used to model autocatalytic reactions, time variable behavior of the rate constant and order is exhibited.
Abstract: Experimental data and hypothetical process behavior are analyzed in an attempt to elucidate the kinetics of aqueous phase ozone decomposition reactions. Three commonly accepted mathematical techniques (integral, differential, van't Hoff) for the analysis of rate data are employed. The results indicate that when single‐order dependencies are used to model autocatalytic reactions, timevariable behavior of the rate constant and order is exhibited. This can partially explain existing controversy within the scientific community regarding the apparent order of ozone decomposition reactions. A simple autocatalytic rate expression is developed that accurately describes the decomposition rate data. The conclusions from the work have implications not only for development of an understanding of ozone decomposition kinetics, but for the analysis of rate data derived from nonelementary reactions in general.