Browsing by Author "Knocke, William R."
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- Adsorption kinetics for the removal of soluble manganese by oxide- coated filter mediaHungate, Robert W. (Virginia Tech, 1988-12-05)This study was conducted to examine the kinetics of manganese sorption on oxide-coated filter media. Initial experimentation confirmed the findings of other investigators, the Mn²⁺ sorption capacity of oxide-coated media increases as solution pH increases. Further study revealed that uptake rate kinetics could be described by first order kinetics and also increased with increasing solution pH. The addition of free chlorine (HOCl) to solution greatly enhanced Mn²⁺ uptake rate kinetics. Later studies indicated that the oxide coating had very little impact on the physical properties of the media tested. Actual data from a water treatment plant filter confirmed laboratory experimental results by showing that sorption of soluble manganese does indeed occur on oxide-coated filters. The water treatment plant data also suggested that the sorption kinetics were relatively rapid, again upholding laboratory findings. Results from the manganese kinetics and sorption experiments were combined to formulate a theoretical model which would predict manganese breakthrough in a filter, given a known set of loading parameters. Preliminary use of the model indicated that oxide-coated filters could sorb significant quantities of soluble manganese before detectible levels of manganese appear in the effluent.
- Analysis and Prevention of Usable Fiber Loss from a Fine Paper MillBarber, Steven Donald (Virginia Tech, 1998-09-17)Reducing losses of usable waste fiber from paper mills conserves valuable resources and has the capacity to produce considerable economic returns to the manufacturer. The purpose of this research effort was to evaluate the potential for the prevention of loss and/or recovery of usable waste fiber from paper machines within a fine paper mill. Further, a preliminary evaluation of fiber loss prevention strategies and fiber recovery technologies was conducted. The paper mill in question experienced losses of usable waste fiber to the sewer in amounts approaching, and sometimes exceeding 40 tons/day. An existing database of usable fiber test results was analyzed to determine patterns of fiber loss. Further testing showed that the most significant fiber losses resulted from centrifugal cleaner cones. These cones, designed to remove foreign material from stock, are one step in a series of mechanical cleaning devices in the stock preparation area of the paper mill. Cleaner cone systems on two of the paper machines were found to contribute most significantly to total fiber loss. Contrary to cleaner cone design, the dirt content of fiber rejects from cones experiencing excessive loss was very low. Cleaner cones on other machines operated normally. These rejects were extremely dirty and quantities of fiber were low. These results indicate poor operating efficiency of two of the cleaner cone systems in question. By adding cones where space is available, system capacity and efficiency will increase, fiber losses will decrease, and the dirt content of rejects will increase. This will result in substantial resource and financial savings to the paper mill. Technologies have been developed to recover usable fiber from paper mill sludge. However, prior to further investigation of the use of such innovations at this paper mill, efforts should focus on the reduction of fiber loss from point sources.
- Aqueous Silica in the Environment: Effects on Iron Hydroxide Surface Chemistry and Implications for Natural and Engineered SystemsDavis, Christina Clarkson (Virginia Tech, 2000-05-09)Aqueous silica is present in all natural waters and exhibits a high affinity for the surfaces of iron oxides. Therefore, it is expected to play an important role in environmental systems. Experiments were conducted to investigate the fundamentals of silica sorption onto pre-formed ferric hydroxide at pH 5.0-9.5 and silica concentrations of 0-200 mg/L as SiO₂. Over the entire pH range studied, sorption densities exceeding monolayer sorption were observed at silica levels typical of natural waters. Under some circumstances, sorption exceeded a monolayer while the particle zeta potential remained positive, a phenomenon which is inconsistent with available models. To address this deficiency, an extended surface complexation model was formulated in which soluble dimeric silica sorbs directly to iron surface sites. This model fits sorption density data up to 0.40 mol SiO₂/mol Fe, and it accurately predicts trends in zeta potential and the observed H⁺ release during silica sorption to ferric hydroxide at pH 5.0 and 6.0. A second phase of research was aimed at identifying the practical implications of silica sorption to iron hydroxide in natural and engineered systems. Two types of surfaces were prepared by exposing pre-formed Fe(OH)₃ to aqueous silica (0-200 mg/L as SiO₂) for periods of 1.5 hours or 50 days. The concentration of pre-formed iron passing through a 0.45 micron pore size filter at pH 6.0-9.5 increased as the solids aged in the presence of silica. Consistent with formation of small, stable colloids, "soluble" iron concentrations exceeded 0.2 mg/L only at zeta potentials < -15 mV. When arsenate was added to iron hydroxide particles equilibrated with silica for 1.5 hours, percentage arsenate removals were high. In contrast, arsenate removals decreased markedly as pH and silica concentrations increased if silica was pre-equilibrated with the iron for 50 days. Trends in percentage removal of humic substances were similar. Competition for sorption sites was the main cause of hindered anionic contaminant removal. However, interference with hydrolysis and precipitation are expected to be important under some circumstances, particularly during water treatment.
- Assessment of a Fixed Media Partial Denitrification/Anammox Process Startup in a Full-Scale Treatment TrainWieczorek, Nathan Vincent (Virginia Tech, 2024-04-18)Partial denitrification anammox (PdNA) is an emerging wastewater treatment technology with the potential to increase process capacity and save on energy and carbon. PdNA circumvents potential issues with stability of the more familiar mainstream partial nitritation anammox (PNA) process. The PdNA process can be used to effectively remove ammonia, nitrate, and nitrite from mainstream municipal waste streams. To retain slow growing anammox, some sort of retention system is needed with media being a common solution to this problem. PdNA has been successfully implemented in mainstream full-scale systems in sand filters and with moving media. The goal of this study was to assess the denitrifying capabilities, anammox treatment capacity, and effective surface area to volume of two types of fixed media. A nitrifying pilot was set up to assess the effective surface area to volume. To assess the nitrifying and anammox ammonia removal capabilities of the fixed media, a fixed media PdNA system was installed in the second anoxic zone of a full-scale municipal wastewater treatment plant. The fixed media system consisted of three modules of sheets modified to mimic a plug flow system. After accounting for the estimated nitrate removal from mixed liquor, denitrification rates normalized to media surface area were 0.52 +/- 1.9 g/m2-day in the first module, 0.62 +/- 0.91 g/m2-day for the second module, and 0.56 +/- 0.90 g/m2-day for the third module. In ex situ batch testing it was found that maximum ex-situ anammox ammonia removal rates for the
- An assessment of household hazardous waste collectionScott, Denise Whittington (Virginia Tech, 1987-03-15)Many civic groups and local governments are involved in campaigns to safely collect and dispose of "household hazardous waste." Although it is difficult to define, household hazardous waste is generally considered to be any chemical waste generated in a family dwelling which, if disposed of improperly, may be harmful to human health or the environment. Growing concerns are centered around the disposal of these potentially toxic wastes by burying them in landfills or pouring them down drains or storm sewers. The most popular method of addressing the problem of household hazardous waste is that of holding "collection days," at which householders are encouraged to bring their hazardous waste to some central location for proper handling by responsible authorities. Although the availability of information about the total costs of holding these collections days is presently limited, it is apparent that the expense per household served is quite high. Some people have questioned whether the expense is justified, since there has been little documentation of the risks associated with the handling of household hazardous waste in the municipal waste stream. This thesis presents the findings to date of a study examining the quantities of household hazardous waste present in the municipal waste stream (in order to assess the risks associated with their disposal) and the costs associated with collection days. A telephone survey was used to develop a preliminary estimate of the nature and quantity of hazardous waste generated by households in a Virginia city. Cost data from collection days held in Virginia and elsewhere in the United States are documented and discussed.
- Assessment of the fate of manganese in oxide-coated filtration systemsCrowe, Andrea L. (Virginia Tech, 1997-01-24)"This study examined the fate of manganese in manganese oxide (MnOx(s)) coated filter media. Specific objectives of the project included the following: 1. Determination of the effect of influent pH upon Mn(II) sorption and oxidation and upon the physical characteristics of the coating on the media. 2. Determination of the effect of backwash rate upon MnOx(s) coatings. 3. Examination of the effect of air scour upon MnOx(s) coatings. 4. Observation of the effect of an increasing MnOx(s) coating on the physical characteristics of anthracite coal filter media. 5. Development of an overall mass balance on manganese loading and accumulation on the filter media. Resolution of the stated objectives involved construction, optimization, and continuous operation of a pilot-scale filtration system for the purpose of removing manganese from filter-applied water. The pilot-scale filter system functioned like a typical water treatment plant filtration system with similar hydraulic loading rates, influent manganese concentrations, free chlorine dosage, filter media bed depths, filter run times, and backwash rates. With regard to the fate of manganese in MnOx(s)-coated filter media, it was determined that as long as free chlorine was present to oxidize sorbed manganese, manganese continued to accumulate and remained on the media in sufficient concentrations to promote continual removal of soluble Mn(II). While oxide coating that was susceptible to breakage was removed in backwash, some portion of coating remained on the media. The combination of MnOx(s) accumulation during filtration and its partial removal during backwash maintained a net amount of MnOx(s) coating optimal for catalyzing further manganese removal and, yet, did not hinder filtration for turbidity by significantly altering the size of the media. The results of the pilot-scale study also indicated the following pertinent conclusions: 1. Neutral or slightly acidic pH conditions (7 ≥ pH ≥ 6) inhibited Mn(11) oxidation before filtration and, instead, promoted sorption and oxidation of Mn(II) on MnOx(s)-coated media. Alkaline filter influent pH (pH > 7) allowed some Mn(II) oxidation before filtration, resulting in significant manganese removal by MnOx(s) particle filtration. 2. Although the intent of MnOx(s)-coating on the filter media was to remove influent Mn(II) from filter-applied water, MnOx(s) that was removed by particle filtration also provided MnOx(s) surface area within the filter and, thus, additional sorption sites for Mn(II) removal. 3. Increases in fluid backwashing rate tended to produce greater amounts of MnOx(s) release from filter media for the duration of these backwash operations. However, backwashing did not result in complete MnOx(s) release from the media surface; rather, there was always sufficient Mn0Ox(s) retained to permit efficient soluble Mn(II) removal after the filtration operations were restarted. Removal of soluble Mn(II) by sorption and oxidation proved to be a dependable, low-maintenance Mn(II) removal technique that worked well within a wide range of raw water influent conditions. Because the process is cost-effective and easily integrated into new or existing water treatment facilities, it is an economical and competitive alternative for removal of soluble Mn(II)."
- Bacterial extracellular polymers and flocculation of activated sludgesKajornatiyudh, 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.
- Bioflocculation: Implications for Activated Sludge Properties and Wastewater TreatmentMurthy, 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.
- Characteristics and conditioning of anaerobically digested sludge from a biological phosphorus removal plantNash, 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.
- Characterization and modeling of soluble manganese removal from drinking water by oxide-coated filter mediaMerkle, Peter B. (Virginia Tech, 1995)Where Mn²⁺ (aq) is found in water supplies, filter media may naturally develop surface coatings bearing MnOx(s). These may absorb Mn²⁺ (aq), and in the presence of oxidant, sorbed Mn²⁺* is oxidized to MnOx(s), regenerating sorption capacity. The filter accomplishes Mn²⁺ (aq) removal, a process called the "natural greensand effect". Characterization of naturally coated media showed variation in coating composition and structure. With thicknesses from 1 - 125 μm, primary coating constituents were Al and Mn, with incorporation of minor amounts of Fe, Cu, and Si and trace elements. "Growth ring" features in coating cross-section corresponding to compositional variation were characterized by SEM, electron microprobe, and energy-dispersive x-ray analysis (EDS). Media surface areas of 2 - 135 m² g⁻¹ land microporosity of 15 - 533 cm³ kg⁻¹ were linearly related to extractable Mn content. Diatom remains found in coatings suggest a key role for coating deposition in filtration phenomena. Atomic force microscopy found surface self-similarity over 10 nm - 10 μm. X-ray photoelectron spectroscopy (XPS) confirmed heterogeneous surface composition including C, Al, Si, and Fe. A method to rapidly deposit up to 4 mg g⁻¹ Mn on media was developed, employing sequential batch and recycle reactors. Mn(IV) was the surface species found by XPS analysis. The Freundlich isotherm described Mn²⁺ sorption on this and the naturally coated media; sorption capacity increased between pH 6.0 and 7.5, and was reduced by [Ca²⁺] = 60 mg L⁻¹. The global Mn²⁺ oxidation rates for all coated media at pH 7.5 were 0.008 - 0.11 mg Mn²⁺ g⁻¹ hr⁻¹: rates increased with flow and decreased with pH. A numerical process model for sorption and oxidation of Mn²⁺ (aq) was calibrated with short bed absorber and differential reactor columns. The Freundlich isotherm, film transport, internal diffusion, and hydrodynamic dispersion were included, with sorption capacity apportioned into kinetically available and unavailable sites. The model performed well in calibration, predicting dynamic system response across a range of flow, pH, [Ca²⁺], and reactant levels. Model performance in validation was less satisfactory, probably due to experimental difficulties and the sensitivity of process performance on recent coating history and media regeneration status.
- Characterization of water distribution in sludgesPramanik, Amit (Virginia Tech, 1994)Knowledge of water distribution in sludges is important in developing a better understanding of the mechanisms by which various fractions of water are bound to the sludge matrix as well as the extent to which sludges may be dewatered in an economic manner. Various models have been proposed in the literature to describe the types or fractions of water present in sludges, both before and after dewatering. Likewise, there exist a variety of measurement techniques to quantify the fractions of water believed to be present in sludges. The major objective of the research reported herein was an attempt to develop a more rational basis for defining the various fractions of water present in sludges, as well as to apply and develop feasible analytical techniques to characterize moisture distribution in sludges and determine if there was any correlation between these techniques. Secondary objectives included investigation of polymer addition, mechanical dewatering, and the effect of freeze-thaw cycles to different water fractions in sludge samples, and measuring or estimating various densities (bulk, floc, dry) and specific surface areas of sludge particles in an attempt to predict the dewatering performance of various sludge samples. The matrix of sludges included various water treatment plant/inorganic chemical sludges and biosolids. The sludge moisture characterization techniques used or developed in this study were the thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dilatometric methods. The TGA method developed used the drying curve rate technique whereby changes in the drying (water removal) rates would provide information on moisture distribution in sludges. The DSC and dilatometric methods used the property of the free water fraction to freeze by -20° C, as compared to the bound water fraction that is thought not to freeze until well below -20°C. It was found that there were uncertainties in the determination of different sub-fractions of sludge water. In an effort to better rationalize these various subfractions, it has been proposed in this study that water in sludges be considered to be in two major fractions: bound and unbound. For the TGA, the demarcation point between these two fractions was indicated by the onset of the first critical/inflection point on the drying rate curve. The DSC and dilatometric methods determined the amount of bound water by first measuring the amount of unbound water that froze by -20°C, and subtracting this value from the total water present in the dry solids analysis. While the DSC measured the calorimetric (enthalpic) changes, the dilatometer measured the expansion of the unbound water. The three DSC instruments evaluated in this study were not able to measure the rapid exothermic change of the freezing of unbound water, but was able to measure the amount of unbound water that melted. Freezing point depression (supercooling) phenomena was also observed for various samples using this technique. Due to these effects, the sludge moisture characterization method developed for the DSC measured the amount of unbound water from the endothermic changes upon melting. The three different analytical techniques used to determine moisture in sludges were found to provide different quantities of the bound water fraction. Other sludge characteristics evaluated included the bulk, floc, and dry density values, as well as the specific surface area of dry sludge particles. Correlations were attempted to determine if there were any meaningful relationships in the results obtained.
- Chemical and Biological Treatment of Acid Mine Drainage for the Removal of Heavy Metals and AcidityDiz, Harry Richard (Virginia Tech, 1997-08-11)This dissertation reports the design of a process (patent pending) to remove iron from acid mine drainage (AMD) without the formation of metal hydroxide sludge. The system includes the oxidation of ferrous iron in a packed bed bioreactor, the precipitation of iron within a fluidized bed, the removal of manganese and heavy metals (Cu, Ni, Zn) in a trickling filter at high (>9) pH, with final neutralization in a carbonate bed. The technique avoided the generation of iron oxyhydroxide sludge. In the packed bed bioreactor, maximum substrate oxidation rate (R,max) was 1500 mg L⁻¹ h⁻¹ at dilution rates of 2 h⁻¹, with oxidation efficiency at 98%. The half-saturation constant (similar to a Ks) was 6 mg L⁻¹. The oxidation rate was affected by dissolved oxygen below 2 mg L⁻¹, with a Monod-type Ko for DO of 0.33 mg L⁻¹. Temperature had a significant effect on oxidation rate, but pH (2.0 to 3.25) and supplemental CO₂ did not affect oxidation rates. Iron hydroxide precipitation was not instantaneous when base was added at a OH/Fe ratio of less than 3. Induction time was found to be a function of pH, sulfate concentration and iron concentration, with a multiple R² of 0.84. Aqueous [Al (III)] and [Mn (II)] did not significantly (α = 0.05) affect induction time over the range of concentrations investigated. When specific loading to the fluidized bed reactor exceeded 0.20 mg Fe m⁻² h⁻¹, dispersed iron particulates formed leading to a turbid effluent. Reactor pH determined the minimum iron concentration in the effluent, with an optimal at pH 3.5. Total iron removals of 98% were achieved in the fluidized bed with effluent [Fe] below 10 mg L⁻¹. Further iron removal occurred within the calcium carbonate bed. Heavy metals were removed both in the fluidized bed reactor as well as in the trickling filter. Oxidation at pH >9 caused manganese to precipitate (96% removal); removals of copper, nickel, and zinc were due primarily to sorption onto oxide surfaces. Removals averaged 97% for copper, 70% for nickel and 94% for zinc. The treatment strategy produced an effluent relatively free of iron (< 3 mg/L), without the formation of iron sludge and may be suitable for AMD seeps, drainage from acidic tailings ponds, active mine effluent, and acidic iron-rich industrial wastewater.
- Colloid Formation for the Removal of Natural Organic Matter during Iron Sulfate CoagulationMasters, Erika N. (Virginia Tech, 2003-05-29)Removal of organic matter is increasingly important to drinking water utilities and consumers. Organic matter is a significant precursor in the formation of disinfection by-products (DBPs). The maximum contaminant levels for (DBPs) are decreasing and more DBPs are believed carcinogenic. Traditional coagulation focuses on the removal of particulate matter and in the last decade soluble species have also been targeted with high coagulant doses. However, colloidal matter is smaller than particulate matter and therefore not easily removed by conventional drinking water treatment. This research focused on the conversion of soluble organic matter to colloids using relatively low doses of ferric sulfate coagulant and the subsequent removal of the colloids by filtration during drinking water treatment. The goal is to achieve enhanced removal of soluble organic matter with minimal chemical costs and residual formation. This study investigated the effects of pH, iron coagulant dose, turbidity, organic matter concentration, and temperature on colloid formation. Characterization of the colloidal organic matter was attempted using zeta potential and sizing analyses. Cationic low molecular weight, nonionic high molecular weight, and cationic medium molecular weight polymers were evaluated on their removal of colloidal organic matter. Colloidal organic matter formation was affected by changes in coagulation pH, coagulant dose, and organic matter concentration, whereas turbidity and temperature did not significantly impact colloid formation. Decreased coagulation pH caused increased organic carbon removal. As coagulant dose was increased, colloid formation initially increased to maximum and subsequently rapidly decreased. Colloid formation was increased as the organic matter concentration increased. Due to low sample signal, the colloids could not be characterized using zeta potential and sizing analyses. In addition, polymers were ineffective for aggregating colloidal organic matter when used as flocculant aids.
- Colloid Formation Resulting from Alum Coagulation of Organic-Laden SourcewatersHardin, William Michael (Virginia Tech, 2003-09-10)This research evaluated natural organic matter (NOM) dissolved-solid phase separation resulting from alum coagulation under the following sourcewater conditions: pH, initial NOM concentration, initial turbidity, and temperature. The solid phase was partitioned into two operationally defined size fractions; colloidal matter was defined as organic carbon (OC) retained by a 30 kilodalton ultrafiltration membrane, and particulate matter was defined as OC retained by a 1μm glass-fiber filter. Coagulation pH had a considerable impact on residual OC colloid formation, signified by more colloids formed as a function of alum dose at pH 6.8 as compared to pH 5.8. Initial NOM concentration strongly influenced the alum dose range over which OC colloid formation occurred and was found to be a proportional relationship. The presence of bentonite clay (used as the initial turbidity source) somewhat affected OC colloid formation by exerting some amount of coagulant demand, signified by decreasing OC colloid formation with increasing initial turbidity. Coagulation temperature had a considerable impact on particulate matter formation, as there was an increase in the dose at which particle formation first occurred at 4 ºC when compared to 25 ºC. Phase separation of OC from dissolved to colloidal matter was very similar at both 4 ºC and 25 ºC. The ability for low doses of polymers to replace a large portion of alum in order to further aggregate colloids during flocculation was unsuccessfully investigated. OC phase separation resulting from alum and iron sulfate coagulation was compared on a molar coagulant metal basis. The amount of residual OC associated with colloidal matter was similar, while the critical coagulant dose at which particulate matter formed was shifted to a much higher dose for iron.
- Color removal from pulp and paper wastes by coagulationBhinge, Deepak (Virginia Tech, 1986-05-27)Coagulation studies were conducted to determine an appropriate treatment approach to remove color and organic carbon from the pulp and paper wastes from the Union Camp Corporation, Franklin, Va. Based on a preliminary analysis of the data collected during this research, either alum or ferric chloride may be used to remove color from pulp and paper wastes. An effluent with final residual color less than 5 color units can be generated using PAC treatment after flocculating certain waste streams with alum or ferric chloride. Higher molecular weight organics (above 5K mass units) showed a near complete removal by coagulation. It is expected that alum coagulation would involve a lesser cost in pH adjustment as compared to ferric chloride coagulation. Alum sludge dewatered and thickened more rapidly than the iron sludge; however, after mechanical dewatering, the alum cake had a slightly greater moisture content than the sludge produced after ferric chloride coagulation.
- A comparative study of freeze-thaw processes for conditioning wastewater and water treatment sludgesTrahern, Patti Gremillion (Virginia Polytechnic Institute and State University, 1989)This research effort involved the application of indirect- and direct-contact, freeze-thaw conditioning techniques for improving the dewatering characteristics of both wastewater and water treatment sludges. Sludges tested included waste activated sludge, primary sewage sludge, waste activated/primary sewage sludge mixtures and alum sludge. The direct-freeze methods examined were the use of a secondary refrigerant (butane) evaporated in the sludge and the use of gas hydrate or clathrate formation by addition of Freon 12 under appropriate temperature and pressure conditions. Sludges were also frozen solid using indirect freezing methods, thawed and tested for comparative purposes. Particle size distribution and floc density measurements were used to determine changes in particle characteristics; specific resistance values and dewatered dry solids concentration were used to assess dewatering characteristics. Results of direct- and indirect-contact, freeze-thaw conditioning were compared to the effects of polymer conditioning. The results indicated that direct-freeze methods do not appear technically or economically competitive with currently accepted conditioning methods. The superior results obtained with the indirect-contact, freeze-thaw process when compared to the direct-contact processes suggested that the extent and rate of freezing may greatly influence the particle characteristics of the conditioned sludge, and thus its dewatering characteristics.
- Conditioning for shear in sludge dewateringBuckley, Margaret M. (Virginia Tech, 1994-04-10)The purpose of this study was to determine how chemical conditioning agents and mechanical dewatering devices affect sludge dewatering with respect to shear. Bench scale experiments were performed to determine the effect of shear and mole charge on polymer dose requirements using anaerobically digested sludge. Lime, ferric chloride, and polymer were used to condition anaerobically digested sludge to evaluate the influence of these conditioning agents, separately and in combination, on shear resistance. Dewatering studies were performed using a plate and frame press, a centrifuge, and a screw press to determine the amount of shear within each device and to develop a means of estimating polymer dose for each device. It was determined that increased molecular charge of polymer decreased chemical dose requirements and improved shear resistance. Both lime and ferric chloride improved sludge dewatering rates but only ferric chloride conditioned against shear. Ferric chloride addition prior to polymer conditioning improved sludge shear resistance, improved the dewatering rate (CST), and decreased the required polymer dose. The dewatering study using the plate and frame press verified that polymer dose could be estimated using CST values and a Gt value of approximately 30,000. Also, ferric chloride in combination with polymer improved filtrate quality, increased the cake solids concentration, and increased the filtrate volume throughput of sludge conditioned with lower polymer doses than if polymer alone was used. The dewatering study using a high speed centrifuge found that polymer dose could be estimated using CST values at a Gt between 10,000 and 20,000 or by use of the wedge zone simulator. The dewatering study of the screw press found that CST values and the wedge zone simulator under predicted polymer dose. This was thought to be the result of shear in the feed system prior to dewatering.
- Development of Soluble Manganese Sorptive Contactors for Enhancing Potable Water Treatment PracticesZuravnsky, Lauren (Virginia Tech, 2006-09-11)Without proper removal at a water treatment facility, the soluble manganese (Mn) concentration can reach and exceed the Secondary Maximum Contaminant Level (SMCL) of 0.05 mg/L in the water distribution system. At this level, soluble Mn can be oxidized to solid Mn-oxide particulates, leading to water discoloration events and resulting in numerous consumer complaints. Manganese-laden water can severely stain fixtures and laundry as well as increase turbidity and foul tastes. A major discoloration event can cause a decrease in consumer confidence in the quality of water provided to their taps. Currently, there is no other treatment alternative available that can remove soluble Mn with the high efficiency of the "natural greensand effect. Therefore, researchers are developing ways to effectively create the natural greensand effect in a post-filtration sorptive contactor for application at water treatment facilities. The process of adsorption and oxidation of Mn onto oxide-coated media grains in the contactor will be used for the removal of soluble Mn. However, small media grains, such as sand or anthracite, could produce prohibitive head loss in a sorptive contactor. The focus of this research project was to show that Mn could be effectively removed via adsorption onto larger media (2.0-6.4mm) at hydraulic loading rates of 16-24 gpm/ft², thus producing less head loss and furthering the development of soluble Mn sorptive contactors to be implemented in water treatment facilities. Research was conducted by executing laboratory- and pilot-scale experiments using columns packed with oxide-coated media. Three types of media were used: large grain "torpedo sand," pyrolucite granules, and small gravel. Before being packed into the columns, the torpedo sand and gravel media was coated with an oxide coating using a technique previously developed by Merkle (1995). Manganese uptake capacity was determined for each media type prior to use and after a number of contactor column experiments were completed. Water samples were collected during the experiments and analyzed for soluble Mn concentration. The Mn removal profile was determined by taking water samples at a certain time and at various depths in the media bed. Experiments were conducted to determine the removal profile of the media types under different operating conditions. Hydraulic loading rate, influent Mn concentration, influent free chlorine concentration, and pH were the operational parameters varied. The effect of these parameters of the Mn removal profile was evaluated. Although each media type was able to remove some percentage of soluble manganese from the applied water, pyrolucite media was the most effective media, often providing approximately 80-90% removal of initial manganese concentration. The removal performance of the large-sized media beds was affected by operational parameters as expected from knowledge of prior research. The contactor media beds also provided adequate soluble manganese removal under conditions available at the water treatment facility as determined from the pilot-scale experiments conducted at the Blacksburg-Christiansburg-VPI Water Authority Another important and complementing facet of this research was the development of a proven model that would predict soluble Mn removal performance of various oxide-coated media types and the development of recommendations that could be used for implementing and operating such post-filtration sorptive contactors. A model was developed from first principles for the prediction of soluble Mn removal and fitted to the experimental data. The predictive model showed that removal performance depended on the specific surface area of the contactor media, HLR, and the mass transfer coefficient. Recommendations for the operation of a sorptive contactor containing large oxide-coated media include an applied hydraulic loading rate of 16-24 gpm/ft² with an initial free chlorine concentration of 1.0-2.0 mg/L and a slightly alkaline pH of 7.0-8.0. Greater hydraulic loading rates are recommended to provide capital cost savings due to the decreased contactor footprint required. Alkaline pH is recommended for improved Mn removal. Facilities with a slightly acidic pH due to enhanced coagulation practices should consider adjusting the pH of the finished water for corrosion control prior to the Mn removal contactor for improved Mn adsorption performance.
- Effect of conditioning on the performance of a plate and frame filter pressZoccola, Gregg (Virginia Tech, 1988-03-15)Experiments were performed on samples of alum, anaerobically digested, and aerobically digested sludges to determine optimum polymer dosages for various mixing intensities produced during conditioning by a high-stress mixing unit. Mean velocity gradient (G) values were established for each of the mixing speeds used ranging from 250 sec-1 to 4,000 sec-1. Using the optimum conditioning dosages determined each mixing speed, batches of optimally, conditioned sludge were introduced into a pilot scale plate and frame filter press. Filtrate volume per unit time and final cake solids were used to characterize the press performance. Results indicated that filter press, performance can be optimized by selecting mixing. speeds during conditioning that simulate the shear conditions produced in the filter press during operation. It was shown that press performance was substantially reduced using sludge conditioned at a mixing speed of 200 rpm, corresponding to a Gt equal to 17,000. Tests using mixing speeds of 400 rpm and 1800 rpm corresponding to Gt values of 32,000 and 230,000, respectively indicated better performance and, thus, the filter press is thought to generate Gt values within this range. A substantial increase in polymer requirements is shown for sludge conditioned at a mixing speed of 1800 rpm, and therefore, it was concluded that sludge conditioned at mixing speed of 400 rpm best characterized the filter press producing optimum operational conditions. It was also postulated that the filter press may not be characterized by a single Gt value, but, by a range of values dependent on press run time.
- Effect of mixing intensity on polymer conditioning of sludgesBandak, Nazih (Virginia Tech, 1986-07-05)Conditioning studies were conducted on several water and wastewater sludges using polymers to determine the effect of high-intensity mixing on floc formation and breakup. Mechanisms acting in particle coagulation were also investigated. A rapid mixing apparatus was used in conditioning the sludge to simulate the high velocity gradients encountered in most dewatering equipment. Anionic and cationic polymers of varying molecular weights and an inorganic coagulant were chosen as the conditioning agents. Dewatering rates were measured by the capillary suction time (CST) apparatus. The effect of rapid mixing on the polymer efficiency was evaluated by premixing the polymer, using the same mixing apparatus, prior to applying it to condition the sludge. Data analyses revealed the great impact the primary floc breakup has on the sludge dewatering rate, although this was shown to be dependent on the nature of the sludge particles. Some minor changes were imparted to the polymer chains by intense mixing but there was no evidence that particle polymer bonds were fractured. The mechanisms of coagulation were observed to be related to sludge type. Overall, successful conditioning of sludges by polymers requires a proper determination of the sludge characteristics, a correct choice of polymer type and dose, and a knowledge of the mixing intensities.