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Thesis (M.S.)—University of Nebraska—Lincoln, 1967. Department of Civil Engineering.


Copyright 1967, the author. Used by permission.


The purpose of this research is to study the microbial oxygen utilization in a full-scale proprietary high rate activated sludge system.Emphasis is placed on determining the relationship between the ultimate B.O.D satisfied by the system and the oxygen utilization.A second objective is to study the effects of the dissolved oxygen concentration and the B.O.D. loading rate on the oxygen utilization rate.

This study was performed at the municipal sewage treatment plant for the City of Lincoln, Nebraska.The municipal sewage treatment plant is located at the northern edge of Lincoln. The plant is designed for primary and secondary treatment.The effluent is discharged into the Salt Creek.Salt Creek is a perennial stream that flows into the Platte River.

The raw sewage entering the treatment plant passes through a bar screen before entering the wet well.The sewage is pumped from the wet well to a distribution box. A venturi tube placed in the pipe between the wet well and distribution box measures the influent flow.From the distribution box the sewage flows into aerated grit chambers which remove grit and provide pre-aeration.Following pre-aeration, the sewage flows to primary sedimentation tanks and then into the secondary treatment systems.Sludge disposal is by anaerobic digestion and vacuum filtration.

Performance tests consist of dissolved oxygen measurements and determinations of the oxygen utilization rate at design loadings. The tests are conducted between 12:00 noon and 5:00 p.m. on three consecutive days between Monday and Friday. At the time of the lowest dissolved oxygen concentration for each day, a sample of mixed liquor is tested to determine the oxygen utilization rate in the aeration tank.The mixed liquor suspended solids concentration should be between 4000 and 5000 milligrams per liter.

Based on the author’s interpretation of the performance requirements, the data indicates that the activated sludge system tested does not meet the manufacturers specifications.

Advisor: Mark J. Hammer