An Experimental Study of Dewatering of Alum Sludge

Date of Award

Spring 1989

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil & Environmental Engineering

Program/Concentration

Civil Engineering

Committee Director

William A. Drewry

Committee Member

Gary C. Schafran

Committee Member

A. Osman Akan

Call Number for Print

Special Collections LD4331.E54K45

Abstract

The use of aluminum sulfate (Alum) as a coagulant for treating surface water was introduced in 1884. When this salt is added to water, the aluminum Ion hydrolyzes by reaction that consumes alkalinity in water. The gelatinous hydroxide thus formed in the reaction, carries suspended material with it as it settles. In addition, however, it is likely that positively charged hydroxyl-bridge dimmers and higher polymers are formed which interact specifically with the colloidal particles, bringing about coagulation. These gelatinous floes settle by gravity, called sludge, consists of relatively large quantities of suspended and colloidal inorganic and organic materials.

The disposal of these wastes from water treatment plants is not a new problem. These sludges are highly variable in composition containing the concentrated materials removed from raw water and the chemicals added in the treatment processes.

This sludge dewatering remains perhaps the most difficult and elusive of the environmental engineering challenges. One of sludge dewatering' s most bothersome aspect is that there seems to be no accepted means to evaluate the case with which a sludge will release it's water.

The purpose of this study was to investigate the effect of hydrogen peroxide addition on sludge dewaterability utilizing sludge macro-properties such as pH, capillary suction time (CST), viscosity, and specific resistance. Hydrogen Peroxide resembles Ozone in its strong oxidizing qualities. Dilute solutions of hydrogen peroxide when reacted with the Al(OH) 3 floe appears to liberate oxygen and water. Specific dewatering processes investigated include sand beds, centrifugation, vacuum filtration, and pressure filtration. Water treatment plant sludges generated at the four major treatment plants in the South Eastern Virginia were examined.

Experimental results indicated that: hydrogen peroxide generally aids in sludge dewatering, providing higher cake solids concentrations. A laboratory (and possible Pilot) investigation is required in order to determine the optimum hydrogen peroxide dosage and the appropriate dewatering process for any particular sludge.

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DOI

10.25777/nbkt-m546

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