The effects of coagulation pH and influent turbidity on aluminum and ferric hydroxide sludge macro-and micro-properties were investigated. To reduce the number of variables, sludges were produced under specific operating conditions in a 400 L/day continuous-flow pilot-plant. The effluent turbidity was monitored to evaluate process modifications. Sludge thickening and dewatering characteristics improved with reductions in the coagulation pH, increases in the influent turbidity levels, and/or reductions in the coagulant dose/influent turbidity ratio. Sludge floc/ aggregate density was the dominant sludge micro-property; sludges with superior thickening and dewatering characteristics were composed of higher density flocs/aggregates. A trade-off appeared to exist between improved sludge characteristics and effluent quality; however, verification will require additional research. / M.S.

The objective of this research was to determine whether or not variations in dissolved oxygen concentration above the critical dissolved oxygen concentration affect the kinetic coefficient and settleability of activated sludge. Synthetic substrate loadings of 0.25, 0.50, 0.75 were applied to bench scale activated sludge reactors with average mixed liquor volatile suspended solids concentrations of 2000 mg/1. The substrate removal rate coefficient, oxygen uptake coefficients, yield coefficients, and sludge settling properties were evaluated at dissolved oxygen concentrations of 2, 4, 8, and 10 mg/l. The kinetic coefficients were different at each dissolved oxygen concentration investigated but the differences could not be correlated with dissolved oxygen concentration variations. Instead, the variations in the coefficients appeared to be distributed in a random manner due to inaccurate test methods and fluctuating environmental conditions. Sludge settling properties as measured by the sludge volume index and the initial settling velocity were independent of dissolved oxygen concentration. The results of the study indicated dissolved oxygen concentration has no noticeable effect upon the kinetic coefficients and sludge settleability in activated sludge systems operated at loading levels and solids concentrations similar to the ones employed in this study. / Master of Science

The problems of sludge handling and disposal have significantly increased in the past decade because of more stringent discharge limits which create more disposable sludges and because regulations have been enacted which control the ultimate disposal of sludge residues. These problems have resulted in a need for producing sludges with both good dewatering characteristics and low water content so as to minimize the ultimate volume of disposal solids. Because of the need for more information concerning sludge dewatering this project was undertaken. The objectives of this study were to quantify the physical properties of sludges following chemical conditioning by a variety of conditioning chemicals. Water and wastewater sludge samples from full-scale Blacksburg water and wastewater treatment plants were used. The iron sludge was made in the laboratory. Each one of these samples was subjected to dewatering studies using laboratory-scale vacuum filtration equipment and sand drying beds. This study indicated that the best conditioner for activated sludge is ferric chloride. Addition of ten percent ferric chloride (on dry solids basis) enhanced the dewatering process and slightly increased the shear strength. Polymer was also an excellent conditioner for activated sludge. A polymer dose of 0.6 percent on a dry solids basis increased the shear strength slightly and increased the dewatering rate of activated sludge. The increase in solids concentration of activated sludge conditioned with polymer was smaller than that by conditioning with ferric chloride. Since the volume of sludge to be disposed has an impact on economics, polymer conditioning might be preferred over ferric chloride conditioning. Lime conditioning of activated sludge appeared to be useless. Conditioning with a mixture of 15 percent lime and 5 percent ferric chloride on dry solids basis did not improve the dewatering rate of activated sludge but conditioning with 20 and 25 percent lime and 5 percent ferric chloride for each mixture appeared to modestly improve the dewatering rate and greatly increase the shear strength of activated sludge. However, conditioning with mixture of lime and ferric chloride appears to be unreasonable when ten percent ferric chloride alone can produce a better-conditioned sludge. Polymer appeared to be an excellent conditioner for alum and iron sludges. / Master of Science

The technical and economical problems associated with sludge handling and disposal have significantly increased in the past years due to: (1) the introduction of more stringent water and air pollution regulations, often requiring the use of processes that produce large quantities of sludge as by-products; and (2) the development of regulations stipulating the means of ultimate disposal of sludge residues. These problems have resulted in a need for producing sludges with both good dewatering characteristics and low water content so as to minimize the ultimate volume of solids which must be disposed of. Recognizing the need for further work in this area of research, the objectives of this study were to examine the fundamental parameters which affect sludge dewatering characteristics. Included in this investigation were an analysis of both sludge dewatering and sludge handling characteristics. Parameters of interest were floe size, shape, and density, sludge viscosity and shear strength, and floc compressibility. The experimental investigation involved the collection of both water and wastewater sludge samples from full-scale treatment plants in the Commonwealth of Virginia. These samples were analyzed for each of the parameters previously mentioned; in addition, each was subjected to dewatering studies using laboratory-scale vacuum filtration, sanbed, and filter press equipment. The experimental results showed clearly that particle size distribution was a key parameter for describing the response of sludges to each of the dewatering methods utilized. For biological sludges, other factors such as biopolymer content were felt to have a major effect on dewatering characteristics. Sludge floc density was shown to have a direct correlation to the ultimate solids concentration obtained by vacuum filtration. Sludge handleability was conveniently evaluated through the use of the standard Atterburg liquid limit test procedure. Finally, the use of high-pressure filtration was found to provide much more appropriate information regarding water content than the centrifugation method proposed by Vesilind (1979). / Master of Science

Bench scale activated sludge reactors were acclimated to dextrose and then to low levels of pentachlorophenol. The metabolic activity of activated sludge was evaluated by its specific rate of dextrose uptake, Δs/Δt/X (measured by COD removal). Depression of the specific uptake rate, resulting from batch experiments in which the activated sludges were spiked with priority pollutants, indicated the relative inhibition caused by that toxin dosage. This study intended to determine if: (1) acclimation to low levels of PCP would provide any protection to the biomass against detrimental effects of higher shock loads of pentachlorophenol; (2) PCP-acclimation would decrease the inhibitory effect of related priority pollutants; (3) PCP would be consistently and efficiently degraded in the reactors. The practicality of this study was twofold. First, to determine the feasibility of introducing small concentrations of a toxin to the biological system of a treatment facility in order to gain protection against shock loads of that and related toxic chemicals. Secondly, to develop a rapid and easy method for evaluating the effects of a chemical load on activated sludge. The procedure was found to be applicable and it showed that acclimation of activated sludge to PCP provided protection against shock loads of pentachlorophenol as well as phenol, 4-nitrophenol, 2-chlorophenol, and 2,4,6-trichlorophenol. Gas chromatography analysis showed very little disappearance of PCP in the 1 mg PCP/L reactor; however, in the 15 mg PCP/L reactor, the penta concentration decreased to virtually zero for about a week and then it began to gradually increase. / Master of Science

Dialysed activated sludge was used as a substrate to test for enzymes which can hydrolyse activated sludge floc. Two hundred and fifty aerobic and anaerobic microorganisms were tested against activated sludge for the presence of hydrolytic enzymes. These included known genera and organisms obtained by various enrichment procedures. Anaerobic digester mixed liquor was contacted with activated sludge agar under anaerobic conditions. None of the microorganisms present in the digester liquor hydrolysed the floc. The following commercial enzymes were contacted with activated sludge singly, in combination, and sequentially under various physical and chemical conditions: protease, lipase, cellulose, pectinase, phospholipase C, trypsin, and glucuronidase. Although commercial enzymes and various microorganisms reacted with known substrate controls neither the enzymes nor microorganisms employed affected the activated sludge floc. Treatment of activated sludge floc with ethylenediaminetetraacetic acid resulted in gross deflocculation and release of humic substances. The floc particle, probably a combination of polymers bound in a complex manner, is resistant to enzymatic degradation. Several workers have reported on the enzymatic hydrolysis of polymers produced by axenic cultures isolated from activated sludge floc. It is unlikely that the results of their work can be extrapolated to the complex structure of activated sludge floc particles.

The purposes of this study were to develop a reliable bench-scale testing procedure to adequately predict polymer conditioning requirements for full-scale belt filter presses, and to determine the additional polymer demand exerted by applied pressure during the expression stage of a dewatering process. Bench-scale experiments performed with anaerobically digested, alum, and secondary sludges used a high-speed mixer to gauge mixing intensity effects, and a wedge zone tester to gauge applied pressure effects on conditioning requirements. Full-scale experiments varied Sludge throughput, belt speed, and polymer dose to evaluate polymer performance. The polymer requirements to optimize performance of a full-scale belt filter press can be predicted with a bench-scale mixing device, where the shear (Gt) of the mixer matches that of the full-scale press. An estimate of the Gt value of the full-scale belt filter presses used in this study was 10,000. Alternatively, a bench-scale wedge zone tester, operated in an applied pressure range between 5 psi and 20 psi, can predict polymer doses for optimum belt filter press performance. The range of applied pressures used to simulate the expression phase of a dewatering process did not exert a Significant additional polymer demand for optimum conditioning. The shear (Gt) associated with mixing sludge and polymer during conditioning can exert a greater polymer demand than the expression phase of the wedge zone tester. / Master of Science

Dewatered sludges and biosolids generated from wastewater treatment facilities are known to emit malodorous odors causing public inconvenience. The odors typically comprise of reduced organo sulfur based compounds and nitrogen containing compounds. Lime stabilization is a technique which is commonly used in the wastewater industry to produce biosolids having reduced odors that can be safely land disposed. In this research, odors produced from dewatered sludges and lime stabilized biosolids were investigated. Lime dosing and incorporation in sludge play an important role in generation of reduced sulfur and trimethylamine (TMA) odor compounds. Results revealed that poor lime dosing can lead to an increase in odors due to biological generation of volatile sulfur compounds (VSCs) during storage. In this study, a belt filter press gave a higher production of sulfur and TMA odors compared to a vacuum filter for the same sludge, which is attributed to the shear imparted to sludge during the dewatering process. Preliming studies suggested incomplete mixing of lime with sludge led to biological activity. The achievement of the correct pH and its maintenance during storage is considered critical for effective odor management from lime stabilized biosolids. A positive linear relation was obtained between sulfur based odor production and labile protein content in sludge. Furthermore, as the Al/Fe ratio increased, the labile proteins was observed to decrease. Trivalent metals are found to play an important role in binding of labile proteins thus effecting odor potential contained in sludge/biosolids. This was found true for most sludge irrespective of their liming status and independent of upstream process conditions. Further work in this area is needed to be able to provide a better understanding of odor production to aid in development of odor control techniques. Trimethylamine odors, having a characteristic fishy odor, are commonly found in lime stabilized biosolids. Cationic polymers used as dewatering aids are the primary precursors for TMA production. Proteins present in sludge are also associated with odor forming compounds but they produce much lower levels than polymers. These two components under the action of shear present in dewatering devices such as centrifuge are more likely to cause an increase in odor production from lime stabilized biosolids. It was also determined that abiotic polymer degradation to produce TMA either does not occur, or the rate is so slow that TMA production in this way is insignificant for actual field situations. / Master of Science

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. / Ph. D.

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. / Ph. D.