Carbon Transformation in Activated Sludge
Wastewater Treatment Processes
A. YOUSEF, Associate Professor
WALDRON M. McLELLON, Chairman
Department of Civil Engineering and Environmental Sciences
Florida Technological University
Orlando, Florida 32816
INTRODUCTION
Knowledge of the levels of organic and inorganic carbon in wastewater has become
increasingly important because of its relationship to all problems of sewage treatment and
disposal. The organic carbonaceous matter is a major oxygen demanding pollutant which is
often estimated through oxygen consumption by biological, chemical, and physical
systems. These systems include tests for biochemical oxygen demand (BOD), chemical
oxygen demand (COD), and total oxygen demand (TOD). Reliable tools are now available
to measure the inorganic carbon (IC) and total organic carbon (TOC). TOC measurements
are gaining greater acceptance because the method is rapid and results are precise and can
be duplicated (1).
Several investigators have recently indicated the importance of carbon in regulating
algal growth (2). Others have suggested that carbon is really the most important limiting
nutrient in natural water (3,4). The effect of carbon on algal growth and its relationship to
eutrophication has been reviewed (5) and it is concluded that carbon could possibly be
growth rate limiting and possibly controlling the algal mass in systems where other
nutrients are considerably in excess. These systems include sewage lagoons, lakes which are
already eutrophic, and laboratory flask studies with artificial media. The role of various
nutrients has also been reviewed (6,7). It is stated that C, N, and P are the elements that can
be controlled. However, as CO2 is always present in the atmosphere and N can be fixed by
blue-green algae, P is the likely nutrient to be removed. The controversy over the limiting
nutrient and the suggestion that carbon is probably the most important nutrient in natural
water would stress a need for careful consideration of the amount and type of carbon in
wastewater effluents released to the natural environment. The effectiveness of activated
sludge wastewater treatment plants in carbon removal and transformation during
treatment processes is of particular interest.
OBJECTIVE
The broad objective of these research studies is to investigate the fate of inorganic,
organic, and refractory carbon during various processes in activated sludge plants and
attached lagoon systems. These studies include: 1) Determination of the efficiency of
carbon removal during various treatment processes; 2) The feasibility of using total organic
carbon for treatment evaluation if automatic control of plants is to be required; 3) The role
of polishing ponds as a carbon source or sink; and 4) Changes in carbon species between the
plant influent and the effluent of the attached lagoon system.
EXPERIMENTAL METHODS
Florida Technological University owns and operates a modified activated sludge
wastewater treatment plant. The plant was built by Walker Process in 1968 and has a design
capacity of 500,000 gallons per day. A layout of the plant, Figure 1, shows the various tanks,
their capacities and the flow pattern. The influent from the wet well is pumped to the contact
tank where it is mixed with the return sludge. The activated sludge flows by gravity to the
clarifier where separation between solids and water carrier will occur. The supernatant goes
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