EVALUATION OF AN EXTENDED AERATION TREATMENT PLANT •by

96 Pages·2014·2.4 MB·English

EVALUATION OF AN EXTENDED AERATION TREATMENT PLANT
• by-
Gary Eugene McCulloch
A Thesis Submitted to the Faculty of the
DEPARTMENT OF CIVIL ENGINEERING
AND ENGINEERING MECHANICS.
In Partial Fulfillment of the .Requirements
For the Degree of
MASTER OF SCIENCE
WITH A MAJOR IN CIVIL ENGINEERING
. In the Graduate College
THE UNIVERSITY OF ARIZONA
1 9 7 0
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfill­
ment of requirements for an advanced degree at The University
of Arizona and is deposited in the University Library to be
made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable
without special permission, provided that accurate acknowl­
edgment of source is made. Requests for permission for ex­
tended quotation from or reproduction of this manuscript in
whole or in part may be granted by the head of the major
department or the Dean of the Graduate College when in his
judgment the proposed use of the material is in the inter­
ests of scholarship. In all other instances, however, per­
mission must be obtained from the author.
SIGNED
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
Associate Professor of Civil Engineering
ACKNOWLEDGMENTS
The author wishes to express his sincere apprecia­
tion to Dr. Robert A. Phillips, Professor Quentin M. Mees
and Dr. Raymond A. Sierka who generously gave of their time
and guidance in the preparation of this thesis. Credit must
be given to the Department of Civil Engineering, University
of Arizona, for providing necessary laboratory facilities.
Gratitude is extended to the Arizona Youth Center
for allowing the use of their facilities for this study.
Appreciation is also extended to Dr. Thomas Carmody and fel­
low students for suggestions and comments during this study.
TABLE OF CONTENTS
' Page
LIST OF TABLES . vi
LIST OF ILLUSTRATIONS . . . . . . . . . . . . vii
ABSTRACT . . .. . . . . . . . . . . . . . . . . viii
I. INTRODUCTION . . . . . . . . . . . . . . . . . 1
II. INSTITUTION SERVED BY TREATMENT PLANT . . . . 4
III. THE EXTENDED AERATION SEWAGE TREATMENT
PROCESS . . . . . . . . . . . . . :. . . . 6
Fundamental Biochemistry . . . . . . . . . 7
Design Criteria . . . . .. . . . . . . . 11
Design of Plant Under Investigation . . . 14
IV. EVALUATION OF PLANT PERFORMANCE . . . . . . . 18
Review of Previous Evaluations . . . . . . 18
Sampling . . . . . . . . . . . . . . . . . 34
Measurement of Flow . . . . . . . . . 34
Evaluation of Plant Performance . . . 34
Laboratory Analyses . . . . . . . . . . . 35
Analytical Results . . . . . . . . . . . . 39
Flow Characteristics . . . . . . . . . 39
Performance Characteristics . . . . . . 43
Discussion of Results . . . . . . . . . . 50
V. EFFECT OF VARIATIONS IN LOADING ON
SETTLEABILITY . . . . . . . . . . . . . . 66
Literature Review . . . . .. . . . . . . . 67
Response of Activated Sludge Systems
to Changes in Influent Substrate
Concentrations . . . . . . . . . . . 67
Settleability of Sludge in Activated
Sludge Systems . . . . . . . . . . 69
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V
TABLE OF CONTENTS, Continued
Page
S clITVp 11 HC|" .7 2
o e o o' ,0 0 . 0 o' o ‘ o o o , o o o o o
Laboratory Analyses ° « <, = . » . . « . . 72
Analytical Results » « « » . = . - . . . . 74
Discussion of Results , . . . . . = « » . 74
VI. CONCLUSIONS . . . . . . . . . . . . . . . . . 81
REFERENCES . . . . . . . . . . . . . . .. . . 85
LIST OF TABLES
Table Page
I. Design Data for Treatment Plant Under
Investigation , „ 16
II. Influent Flow Characteristics Recorded
Between July 10 to September 9, 1969
on Days Sampled „ . . 40
III. Influent and.Effluent Characteristics for
Samples Taken from July 10, 1969 to
September 17, 1969 . 45
IV. Performance Characteristics of Plant on
Sampling Days from July 10 to
September 17, 1969 . . . . . . . . . . . 47
V. Reduction in Total and Fecal Coliform
Bacteria Before Chlorination . . . . . . 47
VI. Characteristics of Sludge in Aeration Tanks
on Sampling Dates from July 10, 1969 to
September 17, 1969 . . . . . . . . . . . 48
VII. Hourly Variations in Influent Loads and
Effect on DO and Settleability . . . . . 75
vi
LIST OF ILLUSTRATIONS
Figure • Page
1. Flow Diagram of Plant . » . . . . . . . . . . 15
2„ Influent Flow for August 26, 1969 . . . „ . .. 41
3. Composite influent Flow for Period from
July 10, 1969 to September 9, 1969 . . . 42
. ABSTRACT
The results of this evaluation of the extended aera­
tion treatment plant at the Arizona Youth Center showed that .
this plant normally produced a highly nitrified and oxidized
effluent and that overall treatment provided at the plant
was normally very good as measured by effluent biochemical
oxygen demand, chemical oxygen demand, and suspended solids.
The major problem encountered at the plant was poor settle-
ability of the sludge.
The evaluation Of the plant further showed that the
poor settleability of the sludge was due to anaerobiosis and
the filamentous nature of the sludge. These conditions were
caused by the low dissolved oxygen concentration in the aer­
ation tanks for long periods each day as a result of periodic
shock loadings on the plant. Extreme variations in hydraulic
and organic loadings on the plant occurred regularly because
of the rigid schedule of activities at the institution served
by the treatment plant.
The long periods of low dissolved oxygen concentra­
tion occurred despite the fact that the amount of aeration
provided at the. installation was increased to a level sub­
stantially above that required under the current design
viii
practices. Also, the daily organic and hydraulic loadings
were ordinarily not too excessive for this type of treat­
ment unit.
It is evident that the aeration equipment for ex­
tended aeration treatment plants should no longer be designed
to satisfy the oxygen demand of the average daily loadings
on the system, as currently practiced, but should be designed
to satisfy the oxygen demand which occurs under peak loading
conditions.
CHAPTER I
INTRODUCTION
This report is an evaluation of the extended aera­
tion sewage treatment plant at the Arizona Youth Center, lo­
cated 20 miles north of Tucson, Arizona. The study was
initiated because there was a serious settleability problem
in the plant and was conducted to determine the cause of this
problem.
Because of an odor problem at the plant, the aera­
tion capacity in the aeration compartments was increased by
the addition of an auxiliary compressor just prior to the
start of this investigation? that is, both of the compressors
provided at the plant were run simultaneously for 24 hours a
day. This immediately resulted in an elimination of the odor
problem and the settleability improved. However, after two
weeks of operation the settleability.showed a sudden deterio­
ration and the final settling tank became completely filled
with non-settling sludge. A preliminary microscopic examina­
tion showed that this sludge contained a large number of fil­
amentous organisms. The contents of the final settling tank
were pumped into a tank truck and transported to the City of
Tucson sewage treatment plant. The extended aeration plant
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