الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Activated sludge process is considered one of most popular methods used for
treatment of wastewater. Most of the previous works did not focused on the
physical conditioning of the activated sludge, returned to the aeration tank as a
feasible method for the improvement the performance of the activated sludge
process. The present work aimed to study the effect of applying an external
mixing to break up the big clumps and colonies of microorganisms, contained in
activated sludge into infinite number of small floes and active bacterial cells.
These broken floes, when returned to the aeration tank will have a very large
surface area this will lead to minimize diffusion resistance of cells and maximize
the substrate utilization rate and oxygen transfer rate of the floes, and
consequently improve the performance of the activated sludge process.
The experimental work has been carried out on a laboratory bench scale,
continuous flow activated sludge model. A synthetic feed substrate was used, and
activated sludge seed from Zenein treatment plant was utilized. The work was
performed under various intensity of mixing, aeration detention time and organic
loading. The results showed that by increasing the intensity of external mixing of
returned sludge results in increase of DO, OUR, Oxygen transfer rate, substrate
utilization rate, BOD and COD removal efficiencies and in decrease of effluent
VSS and wastage sludge. The optimum energy input corresponding to 92 % and
91 % BOD and COD removal efficiency was 9 Watt. sec applied for one minute
at a minimum aeration time of2 hr. Data obtained demonstrate that the proposed
technique can reduce the capacity of aeration tank to about 25 - 30 % of the
conventional systems.
Key Words:
Biological Treatment, Activated Sludge Modification, Returned Sludge Mixing,
Floc Conditioning, Oxygen Uptake, Substrate Utilization, Mixed Liquor, BOD
Removal.