Showing papers in "Journal of Environmental Engineering in 1997"

Partitioning and first flush of metals in urban roadway storm water

Abstract: Storm water runoff from urban roadways often contains significant quantities of metal elements and solids. These anthropogenic constituents are generated mainly from traffic-related activities. Metal elements partition into dissolved and particulate-bound fractions as a function of pH, pavement residence time, and solids concentration. Lateral pavement sheet flow from an experimental field site on a heavily traveled urban highway in Cincinnati was sampled during five rainfall runoff events in 1995. Results indicate that Zn, Cd, and Cu are mainly in dissolved form while Pb, Fe, and Al are mainly particulate-bound. Dissolved fractions of Zn, Cd, and Cu exhibited a strong first flush in lateral pavement sheet flow. Pb exhibited a weak first flush for all events. Event mean concentrations of Zn, Cd, and Cu exceed surface water quality discharge standards. Findings from this study will assist in the development of effective control strategies for the immobilization of metal elements and solids in urban runoff.

Nitrate Removal From Drinking Water—Review

Abstract: Nitrate concentrations in surface water and especially in ground water have increased in Canada, the United States, Europe, and other areas of the world. This trend has raised concern because nitrates cause methemoglobinemia in infants. Several treatment processes including ion exchange, biological denitrification, chemical denitrification, reverse osmosis, electrodialysis, and catalytic denitrification can remove nitrates from water with varying degrees of efficiency, cost, and ease of operation. Available technical data, experience, and economics indicate that ion exchange and biological denitrification are more acceptable for nitrate removal than reverse osmosis. Ion exchange is more viable for ground water while biological denitrification is the preferred alternative for surface water. This paper reviews the developments in the field of nitrate removal processes.

Characterization of Exocellular Protein and Its Role in Bioflocculation

Abstract: The relationship between exocellular biopolymer concentration and cation concentration was examined using laboratory scale activated sludge reactors with bactopeptone as a feed. An increase in the divalent cation concentration in the feed to the reactors was associated with an increase in the bound exocellular protein concentration, and high sodium concentrations resulted in a decrease in the bound protein concentration. The changes in bound biopolymer were explained according to the cation bridging model. Incubation of a laboratory activated sludge with a proteolytic enzyme resulted in deflocculation of the suspension as measured by an increase in the number of particles in the 5–40 μm range, which suggested that the exocellular protein was strongly involved in the aggregation of bacteria into flocs. SDS PAGE results revealed the presence of a single protein in the exocellular biopolymer extract from municipal, industrial, and laboratory activated sludge samples. The molecular weight of the protein was approximately 15 daltons. Amino acid analysis and amino acid sequencing results suggested the protein was a lectinlike protein, and binding site inhibition studies demonstrated that the protein had lectinlike activity.

Arsenic Removal from Drinking Water during Coagulation

Abstract: The efficiency of arsenic removal from source waters and artificial freshwaters during coagulation with ferric chloride and alum was examined in bench-scale studies. Arsenic(V) removal by either ferric chloride or alum was relatively insensitive to variations in source water composition below pH 8. At pH 8 and 9, the efficiency of arsenic(V) removal by ferric chloride was decreased in the presence of natural organic matter. The pH range for arsenic(V) removal with alum was more restricted than with ferric chloride. For source waters spiked with 20 μg/L arsenic(V), final dissolved arsenic(V) concentrations in the product water of less than 2 μg/L were achieved with both coagulants at neutral pH. Removal of arsenic(III) from source waters by ferric chloride was both less efficient and more strongly influenced by source water composition than removal of arsenic(V). The presence of sulfate (at pH 4 and 5) and natural organic matter (at pH 4 through 9) adversely affected the efficiency of arsenic(III) removal by ferric chloride. Arsenic(III) could not be removed from source waters by coagulation with alum.

NANOFILTRATION OF NATURAL ORGANIC MATTER: pH AND IONIC STRENGTH EFFECTS

Abstract: Studies were conducted to examine the effect of solution chemistry, defined here as pH and ionic strength, on the permeability of negatively charged polymeric nanofiltration membranes. Water permeation through the membrane was demonstrated to decrease at conditions of low pH and high ionic strength in the absence of organic macromolecules. The reduction in membrane permeability was attributed to a compaction of the membrane matrix resulting from charge neutralization at the membrane surface and electric double layer compression. An uncharged model organic macromolecule (polyethylene glycol) was used to quantify the effects of solution chemistry on membrane compaction and solute rejection capabilities of the charged membrane. Studies of membrane permeability and rejection were then repeated with solutions containing natural organic matter (NOM), enabling concurrent evaluation of the effects of electric double layer compression as well as changes in both membrane structure and the apparent macromolecular size of charged NOM macromolecules.

Removal of Lead and Chromium by Activated Slag—A Blast-Furnace Waste

Abstract: The blast-furnace waste generated in steel plants has been converted into a low-cost adsorbent. The resulting activated slag has been characterized and used for the removal of lead and chromium. The effect of pH, sorbent dosage, adsorbate concentrations, presence of other metal ions, temperature, and contact time on the sorption of lead and chromium were studied in batch experiments. Kinetic studies were undertaken to have an idea of the mechanistic aspects of the process. The uptake of lead is found to be greater than that of chromium. Adsorption on activated slag follows both Freundlich and Langmuir models. In addition, a series of fixed-bed experiments were performed in an attempt to simulate industrial conditions. The bed-depth-service-time (BDST) model proposed by Hutchins was successfully applied to the sorptive removal of lead. Some experiments were also performed with a view to recover Pb²\u+ and chemically regenerate the spent slag columns in situ.

Biofiltration: Fundamentals, design and operations principles and applications

Abstract: Biofiltration is a biological air pollution control technology for volatile organic compounds (VOCs). This paper summarizes the fundamentals, design and operation, and application of the process. Biofiltration has been demonstrated to be an effective technology for VOCs from many industries. Large and full-scale systems are in use in Europe and the United States. With proper design and operation, VOC removal efficiencies of 95–99% have been achieved. Important parameters for design and performance are empty-bed contact time, gas surface loading, mass loading, elimination capacity, and removal efficiency. Key design and operation factors include chemical and media properties, moisture, pH, temperature, nutrient availability, gas pretreatment, and variations in loading.

Particles, Metals, and Water Quality in Runoff from Large Urban Watershed

Abstract: Water quality, metals concentration, and particle size distributions were characterized in urban runoff. The distribution of metals in the macrocolloidal (0.45–20 μm) and dissolved (<0.45 μm) size fractions was determined from samples taken under both storm and background conditions. Concentrations of particle number, organic carbon, suspended solids, iron, and zinc increased during storms. The presence of zinc was highly correlated with organic carbon, each displaying significant concentrations in both size fractions. Iron existed almost exclusively in the macrocolloidal fraction. Differences in iron and zinc behavior suggest that sedimentation is not always an effective technique for metals removal. Data from two storms followed throughout their duration show individual materials eluting at different stages during storms. These measurements also indicated potential relationships between the zinc/organic carbon and iron/macrocolloid pairs. In addition, elevated contaminant concentrations and increased fl...

Modified clays for waste containment and pollutant attenuation

Abstract: In this study, the use of organically modified clay to remove the high-strength organic pollutants in leachate as well as reduce its liquid flow was investigated. Various physical and chemical factors that may affect the suitability of using the modified clay in removing and retarding the movement of contaminants have been examined. These factors include the structural stability of the modified clay, soil and swelling properties, sorption capacity for nonpolar and polar organics at different pH solutions, and chemical permeants on clay permeability under different effective stresses. The uptake of eight organics (benzene, toluene, o-xylene, ethylbenzene, phenol, 2-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol) by organoclay BB-40 is found to be significant and increases with an increase in their hydrophobicity. The hydraulic conductivities of organoclay BB-40 under an effective stress of 70 kN/m2 (∼10 psi) are 7 × 10−9 cm/s to tap water, 1.6 × 10−8 cm/s to landfill codisposal leachate, and 1...

Moisture Effect on Compaction and Permeability in Composts

Abstract: The effects of initial moisture content and compressive loads on the compactability and air permeability of two compost mixes, biosolids (primary) + bark + sawdust + recycled compost, and cow manure are described. Biosolids compost in the moisture range of 42–57% was subjected to compressive stresses of 0–43.2 kPa and the degree of compaction and pressure drops in the flow range of 0.05–0.20 m/s were measured. The relationship between air permeability and total air-filled porosity at different moisture levels was described using the Kozeny-Carman flow model. Biosolids showed significant compressive behavior and lower permeabilities with increasing moisture content (42–57%). Cow manure had a high moisture-retaining capacity and the differences in compaction behavior and air permeabilities were small when moisture levels were varied (57–73%). The model described the relationship between air permeability and effective free air space with a high level of accuracy (R2> 0.95) at all moisture levels and compacte...

GIS Technology for Vehicle Routing and Scheduling in Solid Waste Collection Systems

Abstract: Rapid improvements in the hardware and software for geographic information system (GIS) have enhanced its potential for solving various types of engineering and management problems. This study develops a multiobjective, mixed-integer programming model for collection vehicle routing and scheduling for solid waste management systems synthesized within a GIS environment. The integration of the mathematical programming model and the GIS were demonstrated through application to a specific site in Taiwan. The proposed interactive design procedure using GIS allows a decision maker to analyze many waste collection alternatives before selecting a final operational scenario. Such a system also has potential application in many other environmental planning and management problems.

Arsenic removal during precipitative softening

Abstract: Because utilities with hard waters tend to have higher concentrations of arsenic, removal of arsenic via precipitative softening processes was investigated in the context of the more stringent proposed arsenic regulation. Arsenic removal can be facilitated by a variety of solids formed during softening including CaCO3, Mg(OH)2, Mn(OH)2, and Fe(OH)3. The extent of As(V) removal is decreased in the presence of orthophosphate and carbonate. As(III) removal is much lower than As(V) removal. At typical solids concentrations, arsenic removal followed a linear isotherm for CaCO3, Mg(OH)2, and Fe(OH)3, with constant percentage arsenic removal regardless of initial arsenic concentrations. However, for Mn(OH)2 solids arsenic removal was sensitive to arsenic concentrations. A framework for predicting arsenate removal when multiple solids form during softening is presented.

Evaluation and Analysis of Soil Washing for Seven Lead-Contaminated Soils

Abstract: A bench-scale study of seven Pb-contaminated soils from actual sites was undertaken to determine the feasibility of soil washing to meet cleanup goals. In addition, soil characteristics and operational factors affecting washing performance were identified. Soils were characterized by a sequential extraction method and scanning electron microscopy (SEM). Following a treatment process that consisted of particle size and density separation, and batch soil washing, soil Pb treatment goals were met for five of the seven sandy soils. Toxicity characteristic leaching procedure (TCLP) limits were met for all soils. In soil washing, the most important factor affecting removal of Pb was pH, with greater removals observed at a lower pH. Ethylenediaminetetraacetic acid (EDTA) addition significantly improved soil-washing performance at pH 3, and the temperature and liquid-to-solid (L/S) ratio had a minimal effect for the range of conditions studied. Washing results were in qualitative agreement with expectations extrapolated from the soil-characterization data. However, definitive identification and distribution of the Pb-binding mechanisms in these real waste-site soils could not be ascertained from the sequential extraction or SEM data.

Temperature effects on physiology of biological phosphorus removal

Abstract: Phosphorus-removing sludge was enriched in an anaerobic-aerobic, acetate-fed, sequencing batch reactor at 20°C. Conversion of relevant compounds for biological phosphorus removal was studied at 5, 10, 20, and 30°C in separate batch tests. The stoichiometry of the anaerobic processes was insensitive to temperature changes. Some effect on aerobic stoichiometry was observed. In contrast, temperature had a strong influence on the kinetics of the processes under anaerobic as well as aerobic conditions. The anaerobic phosphorus-release (or acetate-uptake) rate showed a maximum at 20°C. However, a continuous increase was observed in the interval 5–30°C for the conversion rates under aerobic conditions. Based on these experiments, temperature coefficients for the different reactions were calculated. An overall anaerobic and aerobic temperature coefficient θ was found to be 1.078 (valid in the range 5°C

Evaluation of trickle bed air biofilter performance for BTEX removal

Abstract: Biofiltration of a gaseous stream contaminated with benzene, toluene, ethylbenzene, and the three xylene (BTEX) compounds was evaluated in this study. Experimental investigations were conducted on a pilot-scale biofilter containing randomly packed 6-mm R-635 Celite pellets as biological attachment media. The main focus of the study was to expand biofiltration technology to treat high volatile organic compounds (VOC) concentrations while maintaining consistently high removal efficiencies. Operational parameters investigated were BTEX loading, empty bed residence time (EBRT), backwashing frequency and duration, recovery of biofilter removal efficiency after backwashing, development of removal rate constants, and nutrient-phosphorous (nutrient-P) limitation as a biomass control. Periodic backwashing of the biofilter with medium fluidization was necessary for removing excess biomass and attaining stable long-term high removal efficiencies. Removal efficiencies above 99% were achieved for all the BTEX componen...

Identification of Monitoring Stations in Water Distribution System

Abstract: The location of water quality monitoring stations in a water distribution system should be such that the network is represented with the minimum number of monitoring stations. The present guideline...

Systematic evaluation of pollutant removal by urban wet detention ponds. authors' closure

Abstract: Three urban wet detention ponds in the Piedmont of North Carolina were monitored to investigate long-term pollutant removal as a function of surface to area ratios. Eleven storm events were monitored over a sampling period of 13 months. Urban runoff originating from the study area was characterized by event-mean concentrations for total suspended solids (135 mg/L), total Kjeldahl nitrogen (0.88 mg/L), total iron (6.11 mg/L), and total zinc (66 ug/L). Concentrations of copper and lead were consistently below the detection limits of 30 ug/L and 100 ug/L, respectively. The observed event-mean concentrations were generally lower than the national values reported by the Nationwide Urban Runoff Program. Particle sizes of sediment discharged in runoff were much finer than the national averages due to the predominant clayey soils in the region. This study demonstrates that surface to area ratio can be a useful predictor of wet pond performance. Utilizing 1--2% of the watershed area for the development of wet detention ponds at strategic locations could reduce pollutant loadings to meet targeted requirements of water quality improvement.

Depth of Fenton-Like Oxidation in Remediation of Surface Soil

Abstract: A series of soil columns was used to investigate the depth of Fenton-like reactions provided by the surface application of catalyzed hydrogen peroxide. Initial experiments examined the effect of fo...

Optimal Design of Water Distribution Systems Using an NLP Method

Abstract: In this study, a nonlinear programming approach using the successive quadratic programming optimization technique is developed for the optimal design of a pipeline network for water supply systems. The proposed method eliminates the equality constraints describing the hydraulics by a suitable choice of dependent and independent variables. The dependent variables are chosen based on graph theoretic decomposition of the network structure. This makes it possible to compute analytically the reduced constraints, objective function gradients, and reduced Hessian in a very efficient manner. This method of decomposition ensures that the nodal and loop balances are exactly satisfied and is robust for any initial starting point, able to handle incorrect initial flow directions. The method gives solutions comparable to the previous optimal solutions for the design of new as well as expansion of existing water distribution networks.

Estimating effective germicidal dose from medium pressure UV lamps

Abstract: Three methods of estimating effective germicidal ultraviolet (UV) dose in a collimated beam medium pressure UV system were analyzed: (1) A bioassay; (2) a mathematical model; and (3) a chemical actinometer. The bioassay was performed with MS2 phage. The mathematical model was used to estimate incident, average, and effective germicidal intensity. The chemical actinometer used was uridine, which contains a uracil nucleobase with an absorbance spectrum similar to that of MS2 phage. The average and effective germicidal intensity, terms often equated in low pressure UV systems, differed by 27% for the medium pressure UV system used in this research. The effective germicidal dose determined mathematically was within 10% of the dose estimated with the bioassay approach. For the uridine actinometry, when the differences in the relative absorbance spectras of the uridine actinometer and MS2 phage were accounted for, the actinometry and bioassay methods resulted in similar estimations of effective germicidal dose.

Transient behavior of biofilters: Start-up, carbon balances, and interactions between pollutants

Abstract: The work describes the aerobic biodegradation of volatile organic compound (VOC) mixtures from effluent air streams in laboratory-scale compost based biofilters. A rapid start-up of the system (3–5 d) was observed and 82% of the carbon in the influent pollutant (methyl ethyl ketone) was recovered as carbon dioxide in the exhaust air after this period. Biofilter performance and carbon dioxide production were also investigated during and after 0.5–1-h step inputs of 2–10 g m−3 of hexane, acetone, 1-propanol, and/or methyl isobutyl ketone (MIBK) during steady methyl ethyl ketone (MEK) treatment. Carbon dioxide patterns suggest that pulsed pollutants were first sorbed onto the packing material and subsequently degraded within 2–5 h. Hexane was not sorbed, and thus not degraded to a significant extent. Little effect was observed of the step inputs on the overall MEK removal process, mainly because the reactors were operated well below MEK breakthrough loading. However, the analysis of MEK profiles within the b...

GIS to estimate storm-water pollutant mass loadings

Abstract: In order to develop a monitoring program for the Santa Monica Bay, Calif., watershed, a land-use runoff model was developed using a geographic information system (GIS) coupled with an empirical runoff model. The GIS/model has simple data requirements as compared to more complex models that require routing information; and it is useful for predicting receiving-water loading on an annual basis or for single-storm events. Its approach can also be used to graphically present model results in simple and intuitive ways that provide better insight to managers and planners in evaluating pollution sources and control strategies. The GIS/model was used to locate monitoring stations in the most economical way. The model predictions can be used to improve the evaluation of best management practices to control pollutant discharges. Receiving-water pollutant contributions from point and nonpoint sources can be compared to develop more economical strategies for overall pollutant minimization.

Identification of Contaminated Soils by Dielectric Constant and Electrical Conductivity

Abstract: To develop effective decontamination methods, characterization and identification of contaminated soils are needed. However, current methods of environmental soil characterization involve either soil sampling and analysis for targeted species in the laboratory or soil electrical conductivity measurements. Soil sampling and analyzing in the laboratory involves the risk of sample contamination during handling and testing. Furthermore, it is destructive. To overcome deficiencies of current identification and characterization methods, the use of dielectric constant and electrical conductivity of the soil-fluid system has been suggested. However, little is known about the dielectric behavior of a contaminated soil-fluid system. Thus, the objective of this study is to investigate the possibility of using dielectric constant and electrical conductivity to characterize and identify contaminated fine-grained soils. To investigate the usefulness of the preceding concept, the dielectric constant and electrical conductivity of kaolinite, bentonite, and a local soil are determined at various ion concentrations, organic liquids, and moisture content. Results show that both dielectric constant and electrical conductivity of soil-fluid system are mainly controlled by those of pore fluid.

Sorption of organic compounds in the aqueous phase onto tire rubber

Abstract: Batch sorption tests were conducted to investigate the sorption capacity of organic compounds by ground tire and to assess the effects of the presence of other organic compounds, ionic strength, pH, ground tire particle size, and temperature on sorption. None of the factors were significant under the conditions tested. m-Xylene had the highest partition coefficient (977 L/kg), followed by ethylbenzene, toluene, trichloroethylene, 1,1,1-trichloroethane, chloroform, and methylene chloride (13 L/kg). The partition coefficients had a logarithmic linear relationship with the octanol-water partition coefficients. The diffusion coefficients of the compounds tested were in the range of 10−8 cm2/s. The diffusion coefficients did not correlate well with the physical/chemical properties, such as molecular size, of the compounds tested. The heat of solutions of the compounds tested had relatively low values (<2.5 kJ/mol/K). Thus, the sorption may not be affected significantly by temperature change. Organic compounds ...

Capillary Barriers and Subtitle D Covers: Estimating Equivalency

Abstract: 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.

Observations on Flow in Vertical Dropshafts in Urban Drainage Systems

Abstract: Exploratory physical-model studies were made of the hydraulics of stormwater dropshafts in the city of Edmonton. Under certain conditions, it is necessary to provide a curved inlet at the top of the dropshaft to increase its carrying capacity. Except for very small discharges, the falling water in the dropshaft does not form a coherent central jet but takes the form of a complex jet with a spreading flow around the periphery of the dropshaft. Such a flow also forms a pool at the bottom of the shaft. The energy loss in the dropshaft is significant. For the case studied, with the diameter of the shaft (Ds) equal to about twice the diameter (D) of the inflow sewer and a fall of 6.6Ds, and over a wide range of flow rates, the relative energy loss in the dropshaft was about 80–95%. Further, the air flow Qa required by the falling water, relative to the water flow rate Q, decreased from about 1.4 to 0.5 as Q* increased from 0.1 to about 1.0. Q*=Q/(gD5).Q= water discharge and g= acceleration due to gravity.

Continuous Classification of Moisture Content in Waste Activated Sludges

Abstract: Bound water content is generally taken as an index for differentiating the moisture content in a sludge. However, some recent works have demonstrated that such an index is an operationally defined value differing markedly when different techniques are employed. In this study, the continuous moisture distribution in waste activated sludge is constructed on the basis of the combined thermal gravimetry analysis (TGA) and differential thermal analysis (DTA). The water-solid bond strength is considered here to be an adequate classification index. The bound water contents measured via filtration, drying, or expression are interpreted as the portion of moisture displaying a bond strength higher than the threshold energy that could be provided by filtration, drying, or expression tests. Employing one of these bound water measurement methods is thereby equivalent to setting a threshold bond strength to divide the continuous moisture distribution into bound water and free water. Moreover, the effects of a freeze/thaw treatment on the continuous moisture distribution are discussed.

Modeling Chlorine Inactivation Requirements of Cryptosporidium parvum Oocysts

Abstract: Chlorine and monochloramine inactivation of Cryptosporidium parvum oocysts was studied using bench-scale experiments in 0.05-M phosphate buffer at pH 6 and 8 at 22°C. Animal infectivity using neonatal CD-1 mice was used as the criterion for oocyst viability. Inactivation data were fitted to a robust kinetic model, the incomplete gamma Hom (I.g.H.) which can account for first-order disinfectant decomposition. For chloramination a two-step disinfection approach was evaluated in which chlorine species were applied sequentially with free chlorine followed by ammonium chloride and preformed monochloramine (if necessary). Increasing levels of free chlorine pretreatment were shown to reduce the subsequent monochloramine concentration and/or contact time required for a given level of inactivation thereby demonstrating synergism. Incomplete gamma Hom models were used to generate design graphs that can aid engineers in establishing disinfection requirements for controlling Cryptosporidium parvum in drinking water.

Performance of a pilot-scale compost biofilter treating gasoline vapor

Abstract: A pilot-scale compost biofiltration system was operated at a gasoline soil vapor extraction site in Hayward, Calif. for one year. The media was composed of equal volumes of compost and perlite, a bulking agent. Supplements added included nitrogen (as KNO3), a gasoline degrading microbial inoculum, buffer (crushed oyster shell), and water. The biofiltration system was composed of four identical units with outside dimensions of 1.2 × 1.2 × 1.2 m (4 × 4 × 4 ft) operated in an up-flow mode. The units were configured in parallel during the first eight months and then reconfigured to two parallel systems of two units in series. Air flux values ranged from 0.29 to 1.0 m3/m2 per min. Inlet total petroleum hydrocarbon (TPHgas) concentrations ranged from 310 to 2,700 mg/m3. The average empty bed contact time was 2.2 min. Following start-up, performance of the individual biofilters varied considerably for a seven-month period. The principal factor affecting performance appeared to be bed moisture content. Overall TP...

Dynamic Model for UASB Reactor Including Reactor Hydraulics, Reaction, and Diffusion

Abstract: A dynamic model has been developed to describe upflow anaerobic sludge blanket (UASB) reactors from several aspects including reactor hydraulics, biological reaction kinetics, and mass transfer within anaerobic granules. A flow model of a nonideal continuously stirred tank reactor (CSTR) followed by a dispersion plug flow reactor (PFR) was used to simulate the reactor hydraulics as observed from a LiCl tracer study. The dynamic model based on this flow model was then evaluated by a set of acetate impulse data and verified with a data set from a two-step acetate feed increase experiment from a bench-scale UASB reactor. The model describes UASB reactor performance well. Simulation results indicate significant effects of reactor nonideal flow, diffusional resistance, as well as degradation kinetics on overall substrate utilization rate. Sensitivity analyses on model parameters Ks, km, KL, D, R, and nonideal flow factors revealed granule size has a strong impact on the reactor performance. The effect of KL is...