University of Tehran

Determination of design criteria of an h-ifas reactor in comparison with an extended aeration activated sludge process

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The activated sludge process is a suspended culture system that has been in use since the early 1900s. The process derives its name from the fact that settled sludge containing living, or active, microorganisms is returned to the reactor to increase the available biomass and speed up the reactions. It may be either a completely mixed or plug flow process. The process is aerobic, with oxygen being supplied by dissolution from entrained air Extended Aeration (EA) is one of the modifications of the activated sludge process in which aeration time is increased to about 24 hours. The major advantage of this configuration is that the rate at which waste activated sludge is removed from the process approaches zero. The treatment efficiency decreases, however, and the power costs for aeration are higher (Asano, 1998). Primary treatment is usually eliminated. Some disadvantages of EA activated sludge process can be considered as follows:  Does not remove colour from industrial wastes and may increase the colour through formation of highly coloured intermediates through oxidation  Does not remove nutrients, tertiary treatment is necessary  Problem of getting well settled sludge Recycle biomass keeps high biomass concentration in aeration tanks allowing it to be performed in technologically acceptable detention times Regarding the above problems with activated sludge processes, finding some alternatives which have the advantages of activated sludge process and on the other hand does not include its disadvantages and can improve their efficiencies in a better way, is the first primitive. (Lancaster et al., 1991).

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