The different types of aerobic and anaerobic treatment are as follows:

• Activate sludge process

• Trickling filter

• Rotating Biological Contactor (RBC)

• Anaerobic digester

• Sludge drying bed

• Oxidation ditch

• Oxidation pond

• Aerated lagoons

Aerated lagoons:

• An aerated lagoon is an earthen basin about 2.5-4m deep in which sludge sewage is filled and aerated by means of diffused air or mechanical aeration. Commonly mechanical aerators can be used.

• They are firmly fixed on permanent foundation. Sewage is sent in these lagoons after passing the grit chamber into giving any primary treatment.

• The detention period of 3-5 days is provided.

• It is ideally suited for middle size towns. The waste water of industries such as paper standard and food industries can also be easily treated by aerated lagoon.

• Due to increased depth they require shorter detention time i.e. 1/8-1/10 of these required for stabilization pond.

• The oxygen capacity varies from 1.5-2.5 kg of O2/lit/hr at 20 degree Celsius.

• The values vary depending on the characteristics of the sewage.

Anaerobic treatment:

• It produces biogas. This energy source is used by industries for heat and power generation or stream production.

• It produces less waste sludge (biomass) than aerobic systems, less to dispose off.

• Used as an alternative to or in conjunction with aerobic treatment systems-depending on the fate of the treated effluent.

• Used to remove COD/BOD prior to discharge to a municipal sewer.

• Used with aerobic plant-first stage anaerobic followed by aerobic treatment to discharge standard.

• Anaerobic digestion is increasingly applied because high rate rector designs overcame some problems.