Browsing by Author "Pramanik, Amit"

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    Characterization of water distribution in sludges
    Pramanik, 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.
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    Evaluation of organic and hydraulic loading on the performance of a roughing trickling filter tower using sessil media to treat a high strength industrial wastewater
    Pramanik, Amit (Virginia Tech, 1991)
    This pilot plant study evaluated the pretreatment capabilities of a “Sessil” media for an undiluted high strength industrial wastewater (from a cellulose acetate manufacturing plant) over a ten-month period from May 1989. The Sessil media used consisted of 20 feet long 1.15 inch wide polyethylene strips hanging from wooden slats at the top of a 26 feet tall tower. The effects of organic and hydraulic loadings on the performance of the tower were examined. The characteristics of the influent wastewater on treatment performance were also determined. The wastewater, comprised mainly of waste acetic acid, some acetone, other organic solvents such as isopropyl alcohol, and some cellulose acetate fibers, had an average COD of 2300 mg/l, BOD of 1600 mg/l, influent suspended solids of 200 mg/l, SO₄ of 3000 mg/l, and an influent pH of 4.5, at an influent temperature of 40 C. The tower was found to consistently reduce the chemical oxygen demand (COD) of the wastewater even under adverse conditions as experienced during the shock loading phase when glacial acetic acid was added to the influent stream. During steady-state conditions, net total COD (TCOD) removals ranged from 28 to 52%, with an overall mean of 39%. For organic loads ranging from 164 to 374 lb TCOD/1000ft³day, the net removals (i.e. TCODinfluent-TCODeffluent) were between 81 to 104 lb TCOD, while biological removals (TCODinfluent-Soluble CODeffluent) ranged between 113 to 184 lb. COD removal was found to be an exponential function of the organic loading rate. The COD removals were not directly dependent on the hydraulic loadings, which ranged from 673 to 1738 gallons/day/ft². However, high hydraulic loading rates increased the rates of biomass sloughing and the variability of the tower effluent suspended solids (SS). The hydraulic retention time in the tower averaged 31 minutes and appeared insensitive to the hydraulic loading rates over the range studied. Volatile organic compounds did not appear to be a significant problem and there was insignificant volatilization of the compounds during its passage through the tower. Reductions in COD during volatilization tests were a result of biological stabilization. Tower influent organic constituents (viz. acids and alcohols) were reduced during passage through the tower. Acetic acid and acetone (the major components of the wastewater) were significantly reduced but incompletely removed. The other constituents (e.g. isopropyl and other alcohols) were more completely removed. Most of the removals appeared to have occurred in the upper one-third portion of the tower.