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

No description available.

The flow parameters involved in the transportation of sludge from the place of origin to the place of disposal has long been a problem to the sanitary engineer. To obtain the greatest efficiency in the design of pumps and pipelines the properties of sludge need to be thoroughly understood. This investigation examined the flow characteristic of raw and digested sludge from the Blacksburg Treatment Plant using a rheological approach. A Brookfield viscosimeter was used in the investigation and formulas developed by Krieger and Maron (1) were used to determine the shear stress and velocity gradient. A series of graphs involving shear stress vs velocity gradient were plotted. These graphs were compared to the Standard Newtonian and Non-Newtonian curves, in order to determine the flow behavior of the sludges. The results showed the method of analysis was satisfactory for determining the flow behavior of sewage sludges. The curves obtained showed that the raw and digested sludge examined was pseudoplastic in behavior and shear stress values for the domestic sludge showed it to be more viscous than the raw sludge. / M.S.