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Extended Aeration• Extended aeration, is more common with oxidation
ditch systems. • Extended aeration in complete mix reactors is only
used for small plants due to the increased size of aeration basin.
• Primary clarification is omitted as the key objective is to minimize the amount of sludge generated.
• Ideally, all substrate removal is converted to energy and then oxidized so that no excess biomass is generated
Nitrification
• Nitrification or ammonia oxidation depends on the population of nitrifying bacteria, which depend on:– temperature, – ammonia concentration, – organic substrate, – pH, – DO concentration, – residence time
• From AWWA(1992), for each kg of ammonia oxidized to nitrate the following OOOJ[S:– 4.18kg of O2 are consumed– 14.1kg of alkalinity as CaC03 are destroyed . – 0.15kg of new cells are produced (extra sludge) . – 0.09 kg of inorganic carbon are consumed
Denitrification• Denitrification follows on completion of nitrification. • It is achieved biologically under anoxic conditions, i.e. in the
absence of oxygen. • The energy required for denitrification comes from the organic
content of the wastewater.• The overall d..enNitOrif)ic-a-tiNon--p+roNces2s is from
AWWA (1992) as: – NO3 N2– Oxygen recovery is 2.86 kg O2 / kg NO3-N reduced– Alkalinity recovery is 3.0 kg CaCO3 / kg NO3-N – Biomass production is 0.4 kg VSS / kg COD removed