EFFECT OF MEAN CELL RESIDENCE TIME AND
OZONATION ON CARBON ADSORPTION
Ronald E. Buys, Engineer II
Lockwood, Andrews, and Newman, Inc.
Houston, Texas 77056
Tom D. Reynolds, Professor
Civil Engineering Department
Civil Engineering Department
Texas A&M University
College Station, Texas 77840
INTRODUCTION
Petrochemical wastes provide potential pollutants in the form of concentrated oxygen-
demanding organic and inorganic materials, od and oil-like substances, volatile and non-
volatde suspended materials, compounds of tastes and odors, floatables, polymeric products,
and chemical agents that interfere with analytical techniques.
Biological treatment of these wastes usually removes organic matter and other contaminants such as nitrogen and phosphorus. Their uptake, as nutrients essential to microbial
growth, results in partial removal from the wastewater. Depending on the nature of the
wastewater, conversion of organic compounds may be virtually complete. However, the
residuals from this conversion often require further treatment. Two methods of tertiary
treatment for removal of these are ozonation and activated carbon adsorption.
The effect of biological solids retention time on the combined use of biological oxidation, ozone induced oxidation, and granular activated carbon adsorption were examined
in this study. The petrochemical effluent used was obtained from the Bayport Regional
Wastewater Treatment Plant in Bayport, Texas. This plant treats the wastewater from
approximately 28 industrial manufacturing plants, mostly petrochemical and located in
southeast Harris County. The process wastewaters are treated by equalization, biooxidation
by activated sludge, clarification, chlorination and final polishing.
LITERATURE REVIEW
The Activated Sludge Process
Biological treatment with activated sludge requires a controlled environment containing optimum amounts of food, oxygen and living organisms. Control is obtained by varying the contact period between microbial cells and the waste. This is done by design of
hydraulic systems that recirculate some of the activated sludge and waste the rest.
Recirculation of microbial cells can be measured as solids retention time (SRT), sludge
age (SA), or mean cell residence time (MCRT), aU of which define the average length of
time a microorganism stays in the system. Bacteria rather than fungi purify wastewater and
with increased MCRT the microorganisms advance through a succession of species. A MCRT
of 10 days or more is usually necessary for adequate nitrification by the bacterial genera
Nitrosomonas and Nitrobacter. Low MCRT produce effluents with high COD values that
can be reduced by operation of MCRT of up to 40 days. Higher MCRT allow nitrifiers to
mass and degrade the more bioresistant materials in a wastewater.
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