VTechWorks Repository :: Browsing by Author "Randall, Clifford W."

Browsing by Author "Randall, Clifford W."

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Anaerobic / Aerobic Digestion for Enhanced Solids and Nitrogen Removal
Banjade, Sarita (Virginia Tech, 2008-12-04)
Anaerobic digestion of wastewater sludge has widely been in application for stabilization of sludge. With the increase in hauling cost and many environmental and health concerns regarding land application of biosolids, digestion processes generating minimized sludge with better effluent characteristics is becoming important for many public and wastewater utilities. This study was designed to investigate the performance of anaerobic-aerobic-anaerobic digestion of sludge and compare it to anaerobic-aerobic digestion and single stage mesophilic digestion of sludge. Experiments were carried out in three stages: Single-stage mesophilic anaerobic digestion (MAD) 20d SRT; Sequential Anaerobic/Aerobic digestion (Ana/Aer); and Anaerobic/Aerobic/Anaerobic digestion (An/Aer/An). The Anaerobic/Aerobic/Anaerobic digestion of sludge was studied with two options to determine the best option in terms of effluent characteristics. The two sludge withdrawal options were to withdraw effluent from the anaerobic digester (An/Aer/An – A) or withdraw effluent from the aerobic digester (An/Aer/An – B). Different operational parameters, such as COD removal, VS destruction, biogas production, Nitrogen removal, odor removal and dewatering properties of the resulting biosolids were studied and the results were compared among different processes. From the study, it was found that An/Aer/An – B (wastage from aerobic reactor) provided better effluent characteristics than An/Aer/An – A (wastage from anaerobic reactor), Ana/Aer or conventional MAD. The study also shows that the Anaerobic/Aerobic/Anaerobic (An/Aer/An, with wastage from the aerobic or anaerobic digester) digestion of the sludge can improve the biosolids quality by improving the dewatering capabilities, with lower optimum polymer dose, reduced CST and increased cake solid concentration, and reduce the odor generation from the biosolids. Both An/Aer/Ana – A and An/Aer/An – B gave 70% VS removal, compared to 50% with single MAD and 62% with only Ana/Aer. COD removal of both An/Aer/An – A and An/Aer/An – B was 70%, while it was 50% and 66% for single MAD and Ana/Aer respectively. In the aerobic reactors of Ana/Aer and An/Aer/An - B, nitrification and denitrification with removal of nitrogen was observed. The An/Aer/An – B system had more ammonia and TKN removal (70%) than Ana/Aer (64%). The effluent from each stage was analyzed for dewatering ability, cake solid concentration and odor production potential. Compared with a single Ana/Aer system, the extra anaerobic step in An/Aer/An – A and – B reduced polysaccharides in the effluent. The Ana/Aer system released less protein than the conventional MAD system and the addition of the second anaerobic step - especially with system An/Aer/An – B (discharge from aerobic reactor) - greatly reduced protein, resulting in improved dewaterability and less polymer demand. An/Aer/An (both of the options: A and B) had lower CST than single MAD (both 15d and 20d SRT) and Ana/Aer. Compared to Ana/Aer, a reduction of 52% for An/Aer/An – A and 20% for An/Aer/An – B in polymer dose requirement was observed, indicating improved dewatering characteristics. The An/Aer/An – B has higher biosolid cake concentration than MAD or Ana/Aer. The results showed that An/Aer/An (both options: A and B) biosolid had lower odor generation potential than single MAD (15d and 20d SRT) or Ana/Aer. Of all the stages,the An/Aer/An – A and – B system, generated odor which peaked at shorter time and lasted for shorter duration of time.
Anaerobic biodegradation of selected organic compounds with and without inhibition of sulfate reducing bacteria
McBrayer, Tinker R. (Virginia Tech, 1989-02-05)
The primary objective of this study was to investigate the use of hydrogen as a structural substitute or as a reducing equivalent in the anaerobic biodegradation of methanol, methyl tert-butyl ether (MTBE), toluene, phenol, and 2,4- dichlorophenol. In addition, biodegradation rates of these compounds at various initial concentrations with and without inhibition of sulfate reducing bacteria were determined along with anaerobic biodegradation rate constants for each of the compounds studied. Rates of methanol biodegradation were only slightly altered in molybdate amended microcosms indicating that methanol is a noncompetitive substrate in Blacksburg soil. MTBE biodegradation was slow and followed first order kinetics with respect to initial concentration. Molybdate had no affect on MTBE biodegradation alone, but increased the biodegradation rate in MTBE microcosms which were amended with ethanol. Toluene, phenol, and 2,4-dichlorophenol biodegradation proceeded at two different rate versus initial concentration relationships for lower and upper concentration ranges. Phenol biodegradation followed first order kinetics. The 2,4-dichlorophenol biodegradation rate order varied from 0.78 to 1.75. Monod kinetics were followed by methanol, toluene, and phenol, but not by MTBE, ethanol amended MTBE, or 2,4-dichlorophenol. Addition of molybdate to inhibit sulfate reduction increased the degradation rates more for compounds which may require hydrogen in a structural position (2,4-dichlorophenol, MTBE) than those which require hydrogen for proton reduction (methanol). Biodegradation or recalcitrant compounds may be stimulated by the addition of organics (such as ethanol) which produce hydrogen upon biodegradation.
Anaerobic Digestion: Factors Effecting Odor Generation
Verma, Nitin (Virginia Tech, 2005-07-19)
Land application of anaerobically stabilized biosolids is a beneficial method of handling the solid residuals from a wastewater treatment plant. One of the main issues that restrict land application of biosolids is nuisance odors associated with biosolids. Despite its importance, few studies have been done to enhance our knowledge of odor causing processes. This study was conducted to evaluate the effects of some factors that have been thought to be linked to odor generation from biosolids. The first part of this study has looked at the role of metals, iron and aluminum in particular, in determining the odor causing processes. The results showed that iron correlated well with headspace organic sulfur odor. In general, as the iron content of sludge increased greater amounts of odorous sulfur gases were produced from dewatered biosolids cakes. Aluminum did not show any relationship with organic sulfur odors. Parameters commonly used for assessing the performance of anaerobic digesters (volatile solids reduction (VSR), residual biological activity (RBA) and effluent volatile fatty acid (VFA) content) also showed no correlation with odors. The second part of the study focused on determining the impact of anaerobic digester solids retention time (SRT) on the odor generation from dewatered biosolids cakes and also on elucidating the nature and impact of the various Extracellular Polymeric Substances (EPS) fractions on odors. The results showed that odors decreased with an increase in the anaerobic digester SRT. VSR and RBA correlated with odors; however, as only one type of sludge was assessed, the conclusions about any relationship may not be universal. The results also showed that sulfur gas generation was a function of EPS material bound to iron, again showing that iron plays an important role in odor generation from dewatered sludge cakes. The third part of the study looked at the effects of advanced digestion processes on odor generation. Digested sludge from acid/gas and temperature phased anaerobic digestion systems were analyzed in the lab. The results show that both acid/gas system and temperature phased digestion had a positive impact on odor generation from dewatered biosolids cake. Comparison of sludge from pancake shaped and egg shaped digesters showed that egg shaped digester was more efficient with regard to odor reduction.
Anaerobic/aerobic pretreatment of blue crab (Callinectes sapidus) cooker wastewater
Diz, Harry Richard (Virginia Tech, 1994-10-05)
Wastewater from the pressure cooking of blue crabs presents a difficult treatment challenge. COD concentrations in the range of 15,000 to 30,000 mg/L are found in this wastewater, with TKN concentrations above 2,000 mg/L. Direct discharge of the wastewater, which is currently allowed, adds nutrients to the Chesapeake Bay, and potentially creates local DO depletion in receiving waters. Anaerobic treatment of this wastewater was studied for the reduction of COD. Nitrification was studied for the conversion of ammonia, present at levels above 1,000 mg/L NH3/NHA4-N, to nitrate for possible denitrification. COD reductions averaging above 11,000 mg/L were found to occur in an upflow anaerobic filter operating with less than a 4 day HRT. Further COD reduction in the aerobic reactor resulted in a final effluent averaging 2,400 to 3,100 mg/L soluble COD with a corresponding BOD₅ of 110 to 340 mg/L. Nitrification proved to be inhibited, perhaps by the high levels of NH₃/NH₄-N in the effluent from the anaerobic stage. Nitrification did occur in a batch study, but only after extended aeration, and depletion of BOD. Non-degradable COD was estimated to be 2,900 mg/L in the anaerobic effluent. Monod model kinetic coefficients for the anaerobic stage were determined on a degradable COD basis to be: k = 0.68 day⁻¹, Ks = 3,500 mg/L (degradable portion), Y = 0.19, and Kd = 0.028 day⁻¹. The effect of the addition of certain trace metals (Fe, Ni, Co, Mo) to the feed was investigated. There was no improvement in COD removal performance, and slight inhibition may have occurred.
Analytical Methods of Testing Solid Waste and Leachate to Determine Landfill Stability and Landfill Biodegradation Enhancement
Bricker, Garrett Demyan (Virginia Tech, 2009-09-10)
This was a study undertaken to investigate municipal solid waste (MSW) landfill stability parameters and landfill leachate properties to determine how solid waste and leachate characteristics can be used to describe stability. The primary objective was to determine if leachate properties could be used to determine stability of the overlying refuse. All landfills studied were engineered landfill bioreactors giving insight to how leachate recirculation affects stability. This study investigated the correlation between cellulose, lignin, volatile solids, and biochemical methane production (BMP). These parameters can been used to characterize landfill stability. The BMP tests indicate that a saturated waste can produce methane. Cellulose is an indicator of landfill stability. Wastes high in cellulose content were found to have high BMP. Paper samples studied indicated gas production from high-cellulose paper was higher compared to low-cellulose samples. Lignin has been found to correlate fairly well with BMP. Increasing cellulose to lignin ratios correlate well with increasing BMP levels, further supporting the use of the BMP test to indicate solid waste stability. In the BMP test for leachate, a mixture of the standard growth medium (less 80% distilled water) and 80% v/v leachate incubated for 15 days produced the most consistent BMP results. Leachate cellulose and BMP correlated well. The chemical oxygen demand (COD) and biochemical oxygen demand (BOD) also had some correlation to BMP tests. Leachate COD was found to decrease over time in landfill bioreactors. The use of leachate rather than MSW to determine stability would be more efficient.
An assessment of factors controlling the biodegradation of benzene in the subsurface environment
Poor, Noreen D. (Virginia Tech, 1996)
The objectives of this research were to correlate benzene biodegradation with soil physical, chemical and biological properties, to determine if biodegradation could be predicted based on measured or observed soil properties, and to investigate the role of nutrients on benzene biodegradation in soil. Benzene disappearance over time was measured in aerobic active and control (autoclaved) microcosms prepared with previously-uncontaminated subsurface soils. Soil microcosm experiments were prepared with initial benzene concentrations of 1, 10 and 50 mg/L. For each soil, logistic, zero-, first-, and 3/2- order kinetic models were fit to benzene disappearance versus time data by regression analysis. The logistic and 3/2-order models fit the data better than zero- and first-order models for experiments prepared with initial benzene concentrations of 1 and 10 mg/L. For an initial benzene concentration of 50 mg/L, experimental data were often better fit by zero- or first-order kinetic models. To obtain predictive equations, logistic kinetic model rate constants were related to soil properties using multiple linear regression (MLR). The “best” MLR models and their regression coefficient estimates were statistically significant at p<0.05. For experiments prepared with an initial benzene concentration of 1 mg/L, the resulting predictive equation contained soil phosphorus concentration and cation exchange capacity (CEC). For experiments prepared with an initial benzene concentration of 10 mg/L, the predictive equation contained soil copper, nitrate-N and phosphorus concentrations, CEC, and % sand. A comparison was made between benzene biodegradation in unamended soil microcosms and soil microcosms amended with ammonium and potassium phosphates (11 mM nitrogen, 6 mM phosphorus and 0.6 mM potassium). Benzene disappearance over time in soil microcosms was stimulated by nutrient addition in one (11%), 6 (50%), and 5 (45%) soils at initial benzene concentrations of 1, 10 and 50 mg/L, respectively. In general, nutrient addition had the greatest affect on benzene biodegradation in low pH soils.
Availability and distribution of heavy metals from sewage sludge in the plant-soil continuum
Rappaport, Bruce D. (Virginia Polytechnic Institute and State University, 1986)
An investigation was conducted using in situ lysimeters (1.5 m x 2.3 m) to determine Cd, Cu, Ni, and Zn availabilities for barley (Hordeum vulgare L.) and corn (Zea mays L.) grown on four sludge-amended soils. These lysimeters were constructed in Acredale silt loam (Typic Ochraqualf), Bojac loamy sand (Typic Hapludult), Davidson clay loam (Rhodie Paleudult), and Groseclose silt loam (Typic Hapludult) soils. An aerobically digested sewage sludge from a sewage system with major industrial inputs was applied at rates of 0, 42, and 84 dry Mg ha-t to the lysimeters in the poorly-drained Acredale soil. Rates of 0, 42, 84, 126, 168, and 210 dry Mg ha-1 were applied to the lysimeters in the well-drained Bojac, Davidson, and Groseclose soils. Tissue metal concentrations were determined in 1984 and 1985 for a three crop rotation, which consisted of corn, barley, and corn on the Acredale soil. Increases in sludge-borne Ni and Zn led to increases in Ni and Zn concentrations in corn earleaf, corn grain, and barley silage. Copper concentration was increased in barley silage but not in corn grain and stover. On this poorly-drained soil, metal movement did not occur below the Ap horizon even when Cu was applied in excess of USEPA guidelines. Although there were increases in metal levels, all four metals were within the range considered normal for corn and barley growth. Soil, corn, and barley plants were sampled in 1984 and 1985 to determine Cd, Cr, Cu, Ni, and Zn availabilities for crops grown on the sludge-amended Bojac, Davidson, and Groseclose soils. Levels of DTPA-extractable Cd, Cu, Ni, and Zn in the Ap horizon of these soils increased linearly with sludge rate. Corn grain and stover yields were not decreased on the Bojac, Davidson, and Groseclose soils when 4.5, 5105, 760, 43.0, 135, and 620 kg ha-1 of Cd, Cr, Cu, Ni, Pb, and Zn were added as a sludge-amendment. Copper and Zn applied in excess of 480 and 60 kg ha- 1 of USEPA guidelines, respectively on the Bojac, Davidson, and Groseclose soils were not phytotoxic to corn plants in 1984. Corn and barley tissue sampled for three consecutive seasons had Cr concentrations <2.8 mg kg-1.
Bacterial extracellular polymers and flocculation of activated sludges
Kajornatiyudh, Sittiporn (Virginia Polytechnic Institute and State University, 1986)
The extracellular polymers produced by bacteria play an important role in bacterial aggregation or bacterial flocculation in secondary waste treatment. The mechanisms responsible for this floc formation are thought to be polymer induced adsorption and interparticle bridging among bacterial cells or between bacterial cells and inorganic colloids. The efficiency of the processes following flocculation in the treatment line such as sedimentation, sludge thickening, and sludge dewatering depends on the extent of this bacterial flocculation. In this research, sludge samples from under various substrate conditions were examined for type, molecular weight, physical characteristics„ and quantity of extracellular polymers so that the general characteristics of the various polymers could be established. An attempt was made to determine if a relationship exists between the state of bacterial aggregation and the polymer characteristics. This research also investigated the sludge physical properties. The effect of various parameters such as pH, divalent cation (mixture and concentration), and mixing (period and intensity) on dewatering properties were studied. A major goal of this study was to develop a flocculation model for activated sludge. This model could be used to determine if plants can increase the efficiency of waste treatment and sludge thickening and sludge dewatering processes.
Biodegradation of organic contaminants in subsurface systems: kinetic and metabolic considerations
Morris, Mark S. (Virginia Polytechnic Institute and State University, 1988)
Groundwater contaminated by organic chemicals from industrial spills, leaking underground gasoline storage tanks and landfills has caused concern about the future of a major source of drinking water. Compounds from industrial sources such as alcohols and phenols are frequently found as groundwater contaminants. These compounds are highly soluble in water and do not adsorb well to aquifer material. They also have the potential to migrate in the subsurface system achieving significant levels in drinking water supplies. In addition, they can serve as carriers for carcinogenic compounds such as benzene, toluene and xylene which are relatively insoluble in water, but are quite soluble in alcohol. A potential alternative to expensive groundwater reclamation projects is the use of the natural soil bacteria to degrade organic contaminants. Very little is known, however, about subsurface soil bacteria to man-made organic chemicals or the degradation rates of these compounds. Such information would be useful in planning cleanup or protection strategies for groundwater systems. This study was designed to measure the kinetic response of tertiary butyl alcohol (TBA), determine the biological degradation rates of methanol, ethanol, propanol, l-butanol, TBA, pentanol, phenol and 2,4-dichlorophenol; describe site specific conditions which enhance or inhibit degradation and compare biodegradation rates with thermodynamic predictions. Laboratory microcosms utilizing soil from two previously uncontaminated sites of widely varying conditions were constructed to simulate the subsurface environment. Nitrate was added to some microcosms to stimulate denitrification and metabolic inhibitors were added to others to define conditions at each site which favor biodegradation. Each of the test compounds except TBA was readily degraded in the Blacksburg soil. Inhibition of sulfate reduction by the addition of molybdate stimulated degradation of all compounds including TBA, whereas, inhibition of methanogenesis with BESA slowed the degradation rates. The addition of nitrate did not affect the biodegradation in Blacksburg soil. In the Newport News soil, all of the test compounds were biodegraded at substantially higher rates than was observed in the Blacksburg soil. The presence of the metabolic inhibitors did not affect degradation, however, the addition of nitrate increased the degradation rates of the alcohols but not the phenols. The degradation rates in each of the soils did not correlate with the bacterial population size or free energies of the reactions.
The biodegradation potential of methanol, benzene, and m-xylene in a saturated subsurface environment
Frago, Cathia H. (Virginia Tech, 1993-03-15)
The increased use of alcohols as gasoline additives, and possible substitutes, has prompted the investigation of the fate of gasoline/alcohol mixtures in the environment. In situ bioremediation is one technique that can successfully be applied to remove ground water contaminants particularly in situations where the adsorptive capacity of the soil plays a major role. Frequently, enhanced in situ bioremediation techniques rely on indigenous microorganisms to degrade ground water contaminants; this technique may sometimes include the addition of acclimated bacteria. In this study, soil microcosms were constructed in order to simulate the conditions found in a saturated aerobic aquifer. The biodegradation potential of methanol, benzene, and m-xylene was investigated. Uncontaminated soil from the surface, 12, 16.5, and 18 foot depths was utilized to observe the differences in microbial responses throughout the soil profile. The biodegradation potential of the indigenous microbiota was determined and compared to that of benzene acclimated bacteria, for all the compounds in the mixture. To observe the impact that chemical and physical soil characteristics may have on microbial responses, soils from each depth were classified on the basis of their particle size, moisture content and pH. Substantial methanol, benzene, and m-xylene biodegradation by the indigenous microorganisms occurred in all subsurface soils. While methanol was readily biodegradable over concentrations ranging from about 80 mg/L to about 200 mg/L, benzene inhibited methanol biodegradation at about 125 mg/L in all soil depths. The addition of benzene acclimated bacteria considerably increased the biodegradation rates of all compounds in the mixture. Such increases in biodegradation rates may be attributed to the activities of both groups, the indigenous microorganisms and the benzene acclimated bacteria. The results obtained by this study suggest that biodegradation of methanol, benzene, and m-xylene can readily occur in a saturated aerobic subsurface environment. The physical and chemical properties of a ground water aquifer seem to have a marked effect on microbial responses, and consequently on the biodegradation potential of water contaminants.
Bioflocculation: Implications for Activated Sludge Properties and Wastewater Treatment
Murthy, Sudhir N. (Virginia Tech, 1998-07-23)
Studies were conducted to determine the role of bioflocculation in the activated sludge unit processes. Laboratory and full-scale studies revealed that bioflocculation is important in determining settling, dewatering, effluent and digested sludge properties (activated sludge properties) and may be vital to the function of all processes related to the above properties. In these studies, it was shown that divalent cations such as calcium and magnesium improved activated sludge properties, whereas monovalent cations such as sodium, potassium and ammonium ions were detrimental to these properties. The divalent cations promoted bioflocculation through charge bridging mechanisms with negatively charged biopolymers (mainly protein and polysaccharide). It was found that oxidized iron plays a major role in bioflocculation and determination of activated sludge properties through surface interactions between iron and biopolymers. Oxidized iron was effective in removing colloidal biopolymers from solution in coagulation and conditioning studies. The research included experiments evaluating effects of potassium and ammonium ions on settling and dewatering properties; effects of magnesium on settling properties; effects of sodium, potassium, calcium and magnesium on effluent quality; effect of solids retention time on effluent quality; and evaluation of floc properties during aerobic and thermophilic digestion. A floc model is proposed in which calcium, magnesium and iron are important to bioflocculation and the functionality of aeration tanks, settling tanks, dewatering equipment and aerobic or anaerobic digesters. It is shown that activated sludge floc properties affect wastewater treatment efficiency.
Biological Treatment of a Synthetic Dye Water and an Industrial Textile Wastewater Containing Azo Dye Compounds
Wallace, Trevor Haig (Virginia Tech, 2001-07-16)
In this research, the ability of anaerobic and aerobic biological sludges to reduce and stabilize azo dye compounds was studied. Synthetic dye solutions and an industrial textile wastewater were both treated using anaerobic and aerobic biomass, separately and in sequential step-treatment processes. The primary objective was to reduce the wastewater color to an intensity that complies with the Virginia Pollutant Discharge Elimination System (VPDES) permit level. This level is set at 300 American Dye Manufactures Institute (ADMI) units. Further objectives were to achieve reductions in the total kjehdal nitrogen (TKN) and total organic carbon (TOC) in the wastewater. Anaerobic and aerobic treatment systems were both effective in reducing the wastewater color; however, anaerobic treatment generally produced the greatest color removal. Anaerobic/aerobic (ANA/AER) sequential step-treatment provided the best reductions in ADMI color, TKN and TOC. Anaerobic/aerobic/anaerobic/aerobic (ANA/AER/ANA/AER) sequential step-treatment did not yield greater reductions in ADMI color, TKN, or TOC as compared to ANA/AER sequential step-treatment.
Biological treatment schemes for preventing oxime inhibition of nitrification
Lubkowitz, Erika M. (Virginia Tech, 1996-05-05)
The purpose of this research was to develop a single sludge multi-environment anoxic/aerobic biological treatment scheme that could achieve oxime degradation and nitrification in the same treatment process. Aerobic and anoxic batch experiments were initially performed to determine degrees of nitrification inhibition caused by three oximes, acetaldehyde oxime (AAO), aldicarb oxime (ADO), and methyl ethyl ketoxime (MEKO), and to investigate the fate of these oximes under anoxic, denitrifying conditions. Results from aerobic batch studies showed that MEKO was the only oxime which caused significant nitrification inhibition at concentrations expected in the industrial client's waste streams. Nitrification rates were reduced by 31% at MEKO concentrations as low as 2 mg/L and were almost completely inhibited above 9 mg/L. Results from anoxic batch studies demonstrated that MEKO was biologically degraded under nitrate limiting conditions, although the microorganism( s) responsible were not explicitly identified. Similar degradation trends were seen for AAO, but at significantly lower rates. ADO, however, appeared to be stable under all anoxic conditions examined. Results from batch studies were utilized to determine operational conditions for a single sludge multi-environment anoxic/anaerobic/aerobic sequencing batch reactor supplied with a synthetic organic wastewater containing up to 40 mgIL MEKO and 56 mgIL AAO. The system was able to achieve complete oxime degradation and nitrification when operated on a one day cycle with a twelve hour anoxic/anaerobic reaction phase and a nitrate:carbon ratio below 0.15 mg N0₃-N/mg TOC.
Biopolymer and Cation Release in Aerobic and Anaerobic Digestion and the Consequent Impact on Sludge Dewatering and Conditioning Properties
Rust, Mary Elizabeth (Virginia Tech, 1998-08-27)
Sludge dewatering and chemical conditioning requirements were examined from the perspective of biopolymer and cation release from activated sludge flocs. Both aerobic and anaerobic digestion processes were considered from two different activated sludge sources at a temperature of 20° C. Polymer demand and specific resistance to filtration increased with an increase in total soluble biopolymer concentration for all temperature ranges. In anaerobic digestion, the protein release was three times greater than the polysaccharide release. Conversely, aerobic digestion of the same sludge resulted in a greater release of polysaccharides than proteins. Polymer conditioning requirements in the anaerobic digestors were an order of magnitude higher than in the aerobic digestors; proteins were considered to be the biopolymer fraction responsible for the high polymer conditioning requirements and poor dewatering properties. Biopolymer is released to the supernatant as colloids bound by divalent cations. Peptidase and glucosidase activity were used to monitor enzymatic activity relative to biopolymer release and degradation. The reasons for the increases and decreases in hydrolase activity are unknown.
Boundary layer transport of small particles
McCready, David (Virginia Polytechnic Institute and State University, 1984)
The transport of small particles across the aerodynamic boundary layer that developed over a smooth, flat, acrylic plate and their subsequent deposition was investigated. The velocity boundary layer over the flat plate was characterized for a wind tunnel mainstream velocity of 2 m/s. Particle deposition was quantified with respect to location on the experimental plate with a microscope. The deposition of 0.8, 0.9, 1.1, and 2.0 micron diameter unit density, polystyrene latex microspheres on to oil-coated, uncoated, upper, and lower surfaces was investigated. Although experimental deposition velocities exhibited run-to-run variation, they were significantly greater than those reported in the literature. A turbulent flow deposition model which included eddy diffusion, Brownian diffusion, inertial, and gravitational deposition mechanisms underestimated the experimental deposition velocities. The experimental plate was nonconductive and could not be electrically grounded. It appears the electrostatic attraction mechanism was responsible for the increased experimental deposition velocities; this mechanism was not included in the deposition model. There was no significant resuspension of 42 micron diameter microspheres deposited to an initially moist experimental plate after 6 hours in the wind tunnel at a mean air velocity of 2 m/s.
A butane freezing process for dewatering sludge
Khan, M. Z. Ali; Randall, Clifford W.; Stephens, N. Thomas (Water Resources Research Center, Virginia Polytechnic Institute and State University, 1976)
Cations and activated sludge floc structure
Park, Chul (Virginia Tech, 2002-07-23)
This research was designed to investigate the effect of cations on activated sludge characteristics and also to determine their influence on digestion performance. For this purpose, cations in solution and in floc were evaluated along with various activated sludge characteristics and the collected waste activated sludge underwent both anaerobic and aerobic digestion. It was found that large amounts of biopolymer (protein + polysaccharide) remained in the effluent of WWTP that received high influent sodium but had low iron and aluminum in floc. However, sludges from plants with high sodium and high iron and aluminum dewatered well and produced high quality effluents, suggesting that iron and aluminum have significant positive effects on floc properties. Following anaerobic digestion, a significant increase in solution protein occurred and correlations between solution protein, ammonium production, percentile volatile solids reduction and iron in floc were obtained. These data indicate that iron-linked protein is released to solution when iron is reduced and its degradation is responsible for volatile solids reduction in anaerobic digestion. In aerobic digestion, polysaccharide in solution increased along with calcium, magnesium and inorganic nitrogen. This implies that divalent cation-bound biopolymer might be the primary organic fraction that is degraded under aerobic digestion. Combined (anaerobic/aerobic) digestion was performed and produced further volatile solids destruction with discrete cation and biopolymer response during each phase of digestion. These results support the theory that two types of organic matter with different cation bindings are present in floc and each type is degraded under different digestion processes.
Changes in Dewatering Properties Between the Thermophilic and Mesophilic Stages in TPAD Systems
Bivins, Jason Lee (Virginia Tech, 2000-11-27)
Temperature-phased anaerobic digestion (TPAD) has become increasingly appealing in recent years due to the pathogen destruction capabilities of the system. However, there has also been concern about the dewatering properties of the sludges created by these systems. A laboratory study was conducted at Virginia Tech to determine the effect of thermophilic solids retention time (SRT) on sludge dewatering properties, to characterize system parameters associated with dewatering, and to understand the mechanisms causing changes in dewatering properties between the thermophilic and mesophilic phases. The study showed that while anaerobic digestion caused dewatering properties to deteriorate, sludges varied little with thermophilic SRT. Acidogenesis was essentially complete after 1.5 days. Subsequent mesophilic digestion resulted in little change to dewatering properties and modest reductions in conditioning doses, but substantial reductions in biopolymer (protein + polysaccharides) occurred. It appears that thermophilic anaerobic digestion creates or releases colloidal materials that cause dewatering to be poor and subsequent mesophilic digestion for 15 days does little to improve sludge properties of TPAD systems.
Characteristics and conditioning of anaerobically digested sludge from a biological phosphorus removal plant
Nash, Jeffrey William (Virginia Tech, 1989-02-05)
A study of the anaerobically digested sludge form a full-scale biological phosphorus removal (BPR) plant (York River Wastewater Treatment Plant, York River, Va.) was conducted to determine the effects of BPR on sludge characteristics and conditioning requirements. Data collected from the plant indicated that both the total and soluble phosphorus (P) concentrations in the anaerobically digested sludge increased dramatically with the initiation of BPR. Accompanying this increase in total P was an increase in the total concentrations of magnesium and potassium content of the sludge, supporting the observations that these ions are co-transported with P during the accumulation and release of P by P accumulating organisms. The majority of the phosphate present in the pre- and post- BPR anaerobically digested sludges was bound by calcium, magnesium, and iron phosphorus precipitates including hydroxyapatite, struvite, and vivianite. Calcium phosphorus precipitates were the most prevalent in both sludges, but the percentage of magnesium phosphorus precipitates increased with the onset of BPR. Cationic organic polymer conditioning dosages needed to achieve acceptable sludge dewatering rates for the post-BPR sludge were similar to those required by the pre-BPR sludge. The cationic organic polymer used to condition these sludges was ineffective in removing excess phosphate; therefore, the addition of either one or both of the inorganic chemicals ferric chloride and calcium hydroxide was required to remove soluble phosphorus. Conditioning with either ferric chloride or calcium hydroxide alone was not effective in achieving acceptable dewatering rates; however, when used together the chemicals produced acceptable dewatering rates and soluble P removal from the post-BPR sludge.
Characteristics and Treatment of Landfill Leachate and Optimization of Leachate Oxidation with Fenton's Reagent
Gulati, Loveenia (Virginia Tech, 2010-05-05)
The purpose of this study was to characterize the leachate from a landfill in Pennsylvania that had been pretreated by activated sludge and propose the most efficient treatment for this effluent. These samples had been pretreated in a sequencing batch reactor that also was operated to remove nitrogen by nitrification/denitrification. The SBR samples were found to have low BOD, high COD, high TOC and a very low BOD/COD ratio. These SBR decant samples have poor UV transmittance and hence quench UV light. Five treatment methods were evaluated, coagulation, ultrafiltration, combined coagulation/ultrafiltration, combined ultrafiltration/oxidation and combined filtration/fentons. These processes were tested for their ability to remove BOD and TOC and also to evaluate the improvement in UV transmittance. It was found that coagulation; Ultrafiltration and Ultrafiltration combined with coagulation do not work in improving the transmittance properties though there is a significant BOD and TOC removal with these processes. Ultrafiltration combined with oxidation was found to work the best in terms of TOC removal. In this study, four oxidants, KMnO?, H?O?, NaOCl and Fenton's reagent were used. It was observed that Fenton's reagent was capable of removing 90% TOC at a dose of 1g/L each of iron salt and hydrogen peroxide at a pH of 4.5. Since Fentons reagent was found to be the most effective method, hence, efforts were made to optimize the oxidation process with Fenton's. The two parameters which were studied were the initial pH and the chemical dosage. The initial pH was varied from a value of 2.5 to 6.5. The range of iron salt and peroxide dose used was from 0.05 to 0.1 g/L. Additional studies were conducted using samples filtered through a 0.45 um filter and oxidized with Fenton's reagent. The Fenton's process for oxidation of filtrates from the 0.45?m filter was also optimized with respect to pH and chemical dosage to determine the most economical operating conditions. The maximum transmittance of 57% was obtained for an iron dose of 0.075 g/L and a peroxide dose of 0.075 g/L at a pH of 4.5. This is in comparison to the transmittance of unoxidized 1K ultrafiltrate which was found to be 21.5%. There was a significant difference in the performance of 1K and 0.45um filtrates in terms of TOC removal and percentage transmittance. The oxidation process for improving the UV transmittance of leachate can therefore be economically optimized depending upon the desired efficiency by varying the operational parameters.

Browsing by Author "Randall, Clifford W."

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