Temperature and
Retention Time Relationships in the
Activated Sludge Process
JOSEPH V. HUNTER, Associate Professor
EMIL J. GENETELLI, Assistant Professor
Department of Environmental Sciences
Rutgers -- The State University
New Brunswick, New Jersey
M. E. GILWOOD, Consultant
M. E. Gilwood Associates
New Brunswick, New Jersey
INTRODUCTION
In future domestic and industrial waste water treatment, methods for increasing the efficiency of treatment processes which are not considered economically
justifiable today may eventually become acceptable. As today's treatment is
primarily through biological processes, one method for increasing process efficiency would be to operate at higher temperatures. Although domestic waste water
volumes and temperatures would mitigate against such a process change, there
are instances where waste volumes may not be too large and where there may be
sufficient waste heat to render such a process change feasible. Examples of such
instances would be the chemical industry, steamships, etc. For this reason, the
study described here was made on the effect of temperature and retention time on
an activated sludge system.
Ludzak, et al (1) indicated that increasing the temperature from five to 30 C
increased process efficiency and decreased sludge accumulation. Using a waste
somewhat similar to one studied by these investigators, the temperature range
from four C to 55 C was investigated to observe the effect of temperature on the
behavior of the system in greater detail, and if possible, establish how high the
temperature could be raised before process efficiency deteriorated and sludge
accumulation increased. In addition, what effect temperature would have on the
solids characteristics of the system. The study was made using a batch operated
activated sludge system with a 16 hr retention time. The temperatures studied
were 4,20,28,35,45 and 55 degrees centigrade. The synthetic waste was designed
to have a high suspended matter and BOD concentration, and its preparation and
and formula is given in the appendix.
Once the highest temperature giving acceptable BOD and suspended matter
removals was determined, a retention time study was made to determine how
short a retention time could be employed to give acceptable removals and whether
an extended retention time would give sufficiently low solids accumulation to warrant its use.
PROCEDURES
The Temperature Study
One liter volumes were aerated in three liter flasks at temperatures of 4,20,
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