BIOLOGICAL TREATMENT OF SOY SAUCE FERMENTATION WASTE
—COMPUTER SIMULATION OF FILL-AND-DRAW
ACTIVATED SLUDGE SYSTEM
Chi-Jen Liu, Engineer
Bureau of Environmental Protection
Taichung Taiwan
Republic of China
INTRODUCTION
The fill-and-draw activated sludge system is operated in such a mode that both the biological
conversion of organic substances into biological mass and the separation of the resulting biomass by
sedimentation can be carried out in one reactor. The operation cycle of the system is started by filling
the reactor with raw wastewater (Filling Period), the content is then mixed and aerated allowing
microorganisms to grow and organic substances to be converted (Reaction Period). Afterwards, the
biological solids are allowed to settle under quiescent conditions in the same reactor and the clear
supernatant is then decanted (Settling Period). After the completion of the first cycle, raw wastewater
is again pumped into the reactor to start another cycle of operation. If denitrification is desired, the
mixture is agitated under anaerobic conditions between the aeration period and the sedimentation
period. This will help the growth of denitrifying microorganisms to convert nitrogeneous compounds
into nitrogen gas thus achieving removal of nitrogen. Microbial reactions to convert organic car-
boneceous substrance occur mainly during the filling period and the reaction period.
In the past, when applied to a full scale operation such as a municipal wastewater treatment plant,
the fill-and-draw procedures were considered tedious and required too much labor to perform manually. In contrast, in a continuous activated sludge system, the aeration reactor is continuously fed
with raw wastewater and the aerated liquid is continuously discharged into a separate clarifier where
the sedimentation of biomass is performed. The separated biomass is then partially returned to the
aeration reactor, and the remaining portion is wasted. All the operations can be automated and easily
controlled with pumps, valves, and control panels. Thus, the continuous-flow activated sludge has
been extensively employed for treating municipal and industrial wastewaters.
With the advent of the microprocessor and microcomputer, the steps for operating a fill-and-
draw activated sludge system could be performed easily. Thus, this process has been revived for
treating industrial wastewaters that are of relatively small volume and exhibit large variations in both
flow rate and concentrations. These may include seafood processing wastewaters and food processing
wastewaters such as soy sauce fermentation wastewater. The main advantage of a fill-and-draw activated sludge system is its flexibility. The operation of this system needs not approach a so-called
steady-state, thereby eliminating the step of equalizing the influent wastewater. Besides, since one
reactor is used as an aeration reactor and a clarifier, savings in construction and materials for reactors, pipes, valves, and pumping can be achieved. Another consideration in using the fill-and-draw
system for treating some industrial wastewater is the possibility of achieving denitrification by simply
holding the liquid under anaerobic conditions after the aeration period. Successful application of the
fill-and-draw activated sludge in treating a number of industrial wastewaters has been reported by many
researchers [1,2,3].
The objective of this paper is to use a mathematical model which has been calibrated with the
results of treatability studies performed on soy sauce fermentation wastewater to simulate the fill-
and-draw activated sludge operation. The purpose is to study the influence of the filling time on
effluent quality. Results of treatability studies conducted on soy sauce fermentation wastewater published by Li and Liu ]1] are utilized but the techniques and results are applicable to other types of
wastewaters.
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