Document Type


Date of Award


Degree Name

Master of Science in Environmental Engineering - (M.S.)


Civil and Environmental Engineering

First Advisor

Yeun C. Wu

Second Advisor

Paul N. Cheremisinoff


The activated sludge was cultivated in two pilot-scale activated sludge systems under three ratios of BOD to N, equal to 20:1, 70:1 and 300:1 in the influent wastewater. The aeration tank of the activated sludge system was constructed in two different configurations: one without compartments in the tank, the other consisting of six compartments. The activated sludge withdrawn from the last compartment of each system was tested in a one-liter graduate cylinder to measure its zone settling velocity. The solids-flux method was employed to analyze the sludge settling characteristic as a function of solids concentration. The results show that the activated sludge grown under the nitrogen-sufficient condition and cultivated in a compartmentalized aeration tank under the nitrogen-deficient condition were excellent in settleability. In contrast, the poor settling sludge was found in the severely limited nitrogen system and in the nitrogen-deficient system without compartments in the aeration tank. This study indicates that sufficient nitrogen in the wastewater is necessary for successful treatment of wastewater, and the compartmentalization of the aeration tank could improve the efficiency of the secondary sedimentation tank.



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