The object of this investigation was to determine, by the concept of specific resistance, the effect of certain variables on the filterability of calcium sulfate sludge resulting from lime neutralization of synthetic, return sludge seeded, sulfuric acid samples, The variables investigated were rate of mixing, rate of lime addition, degree of neutralization, return sludge loadings and acid concentration. Mixing rate and lime addition rate are factors effecting the characteristics and filterability of calcium sulfate sludge. Slow lime addition provided a more effective return sludge than did rapid lime addition. Slow sample mixing produced a more filterable sludge than did rapid mixing for a given lime addition rate. The degree of sample neutralization appeared to have only a minor effect on the filterability of the sludge, with the filter ability improving as the final pH of the sample decreased. The sample return sludge dosage appeared to have only a minor effect on the filterability of the resulting sludge with filterability decreasing as return sludge loadings increased. A complete evaluation of the effect of return sludge loading cannot be made, however, until these studies are expanded to include the optimum return sludge loading for the given acid-lime system. The values of specific resistance obtained were influenced by the resistance of the filter paper. For samples with similar dry solids concentration the effect is approximately the same; however, the amount of filter paper interference decrease with increased sample dry solids concentration. For varying acid concentrations there was a minor decrease in specific resistance as the acid concentration, and dry solids concentration, of the samples increased. This decrease was thought to be due to decreasing amounts of filter paper interference rather than improved sludge filterability. / Master of Science

The objective of this study was to examine excess biological phosphorus removing bacterial populations and their substrate utilization mechanisms. This study was a smaller part of a overall study of temperature effects upon excess biological phosphorus removal. Bacterial populations in both a continuous flow UCT (University of Cape Town) system and batch reactors were examined by direct counting using a well known staining procedure (Neisser staining), and a microscopic counting method developed by Cech and Hartman (1993). Substrate utilization was examined using PHB (Poly-β -Hydroxybutyrate - an internal substrate storage product) analysis by gas chromatography to supplement COD and acetate measurements. The results showed that Poly-P bacterial counts were significantly greater at a 5 day sludge age compared to a 10 day sludge age. It was noted from microscopic observations that the size of the poly-phosphate granules in the bacteria seemed to be a better indicator of system performance than the actual counts. It also was observed that the 'G' bacteria first described by Cech and Hartman (1993) were abundant at the 10 day sludge age but completely absent at the 5 day sludge age. PHB storage occurred in both the anaerobic zone and the first aerobic tank, and PHB utilization was seen in the subsequent aerobic tanks of the UCT system. The formation of PHB in the first aerobic reactor when no substrate was available supports the Mino (1987) model for excess biological phosphorus removal. In batch studies, substrate storage release were demonstrated in the aerobic zone. This explained why when acetate was present in the aerobic zone net phosphorus uptake didn't occur until all the acetate was utilized. When the temperature was lowered in the UCT system nitrification ceased. This resulted in soluble COD breakthrough into the aerobic zone, which stimulated filamentous growth, and eventually caused a lack of PHB formation. All of these factors contributed to a loss of excess biological phosphorus removal at the low temperature. / Master of Science

A full-scale rotating biological contactor treatment system primarily used for treatment of wastes from single-family dwellings was studied at the Blacksburg-Virginia Tech wastewater treatment plant. Municipal primary clarifier effluent was pumped into the 600 gpd rated RBC unit at the rate of 480 gpd for a period of 4 1/2 months. The RBC unit contained a primary clarifier, four stages of discs, and a secondary clarifier. A thorough sampling and analysis program was performed to determine start-up characteristics and resistance to controlled shock loadings. Samples from seven locations, ranging from the influent through each stage of the RBC into the effluent, were collected and analyzed in order to monitor treatment performance. Samples were analyzed for COD, TKN, NH₃-N, Org-N, NO⁻₃-N, SS, DO and total alkalinity. Based on an analysis of the results obtained it was determined that a start-up period of approximately 30 days was required to develop a sufficient growth of biofilm mass to reach"steady state" conditions, i.e., maximum consistent organic removal and nitrification efficiency. Shock loading investigations included step increases in hydraulic and organic loads as well as controlled diurnal flow patterns. From these studies it was determined that the RBC was resistant to changes in effluent organic concentration, but that nitrification efficiency could be notably suppressed. The attached biofilm was not adversely affected by the shock loads. Throughout the manuscript diagrams and tables are provided to clarify procedures and materials used. Analytical results are presented in three-dimensional plots to illustrate patterns revealed by the data. / Master of Science

No description available.

No description available.

Ph. D. / incomplete_metadata

The effect that the COD:TKN ratio had on total nitrogen removal efficiency. as well as, the effect on COD removal efficiency, nitrogen distribution in the effluent streams, and total system mixed liquor suspended solids concentrations in the activated sludge process as a function of the mean cell residence time (θ_c) were examined in this investigation. A definite relationship was shown to exist between the influent COD:TKN ratio, mean cell residence time, and nitrogen removal efficiency by operating two bench scale activated sludge reactors under continuous feeding. Theoretical data, which were generated by applying biokinetic equations and stoichiometric relationships, were compared to laboratory obtained data to evaluate the validity of using stoichiometric relationships to establish design and operational criteria. The mean cell residence time was used as the control parameter in this investigation. It was demonstrated that nitrogen removal efficiency increased via waste sludge incorporation as θ_c was decreased. It was also shown that nitrogen removal efficiency increased with an increase in the influent COD:TKN ratio by both experimental results and theoretical data. Optimum nitrogen removal efficiencies were found to occur at decreasing mean cell residence times and increasing COD:TKN ratios. / M.S.

The effect of phosphorus limiting conditions on process performance was investigated using laboratory scale activated sludge units. Data were collected for COD:P ratios of 287:1, 212:1, 87:1 and 56:1 at several mean cell residence times. Data collected at COD:P ratios of 287:1 and 212:1 produced sludge with extremely poor settling characteristics and data were collected for only one mean cell residence time at each ratio; Data for COD:P ratios of 87:1 and 56:1 were used to estimate kinetic coefficients. These kinetic coefficients were used to develop predicted values of process performance subject to phosphorus limiting conditions utilizing mathematical and stoichiometric relationships. Predicted values were compared to laboratory data. For both predicted values and laboratory data, a phosphorus limitation resulted in decreased COD removal efficiency, nearly 100 percent phosphorus removal efficiency, decreased reactor solids concentrations, solids with poor settling characteristics, decreased sludge production and artificially high F/M ratios. / M.S.

In the recent past more and more attention has been given by sanitary engineers to the problem of nitrogen removal in sewage treatment. This attention is brought about by several problems associated with nitrogen. First, in some locations, such as our southwest United States, there is both an essentially constant supply of water and an increasing demand for water. This calls for water recycling. or reuse, as a means of meeting the demand for potable water. An accumulation of impurities, such as compounds of nitrogen, can limit the recycling of water. One such substance is nitrate nitrogen, which when in excess of ten parts per million can cause the disease methemo-globinemia in bottle-fed infants. / Master of Science

The performance of fibrous biomass support media (Ringlace) and porous spongelike biomass support media (Captor) was evaluated for enhanced nitrification and denitrification in a pilot-scale Virginia Initiative Project (VIP) biological nutrient removal (BNR) process. Four separate pilot-scale treatment trains were constructed and operated during this research. Three of the four treatment trains were operated with fixed film media (Ringlace/Captor) incorporated in the aerobic zone of the system and are referred to as the Integrated Fixed Film Activated Sludge (IFAS) systems. A fourth treatment train (Control train) was operated without any fixed film media. All experiments in this research were performed using domestic wastewater from Blacksburg, Virginia, and the Virginia Tech campus. Enhanced nitrification was observed in the IFAS system containing porous biomass support media (Captor) that was freely suspended in the mixed liquor of the aerobic zone. Near-complete nitrification was observed in the IFAS system containing Captor media even at total suspended growth MCRTs as low as 5.6 days and a 12°C liquid temperature. Significantly higher nitrification rates were observed in the IFAS system containing Captor media compared to both the IFAS system containing Ringlace media and the control train. However, there was less denitrification in the aerobic zone of the IFAS systems containing Captor media compared to the Ringlace media systems. Enhanced nitrification could not be statistically shown in the IFAS system containing Ringlace media. The overall nitrification rates in the Ringlace media system were about the same as the control train for the MCRTs and temperatures used during this research. However, a significantly greater amount of denitrification was observed in the aerobic zone of the IFAS system containing Ringlace media compared to both the IFAS system containing Captor media and the control system. Microscopic examination of the growth on the fixed film media (Ringlace and Captor) showed that red worms always grew on the Ringlace media, and were detrimental to performance on at least one occasion. Methods for controlling the worms were developed and applied successfully. During certain operating phases, lower sludge productions and observed sludge yields were measured in the IFAS system containing Ringlace media. However, a Statistical difference could not be calculated between the sludge production in the Ringlace media system and the control system. Lower sludge production and observed sludge yield were also observed in the IFAS system containing Captor media, but only two data points were available and a Statistical t-test analysis was not possible. / Master of Science