Wastewater Processes

Activated Sludge System

• Complete mix

• Plug flow

• Oxidation ditch

Plug Flow

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

Extended Aeration

Oxidation Ditches

Attached Growth Trickling Filters

Attached Growth Trickling Filters

Attached Growth Trickling Filters

Attached Growth Trickling Filters Example

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