Extended Aeration Sewage Treatment Explained

Extended Aeration Sewage Treatment - the modern way to digest raw sewage.

Septic Tanks

These are not extended aeration sewage systems, in fact, no air is introduced into the sewage at all. The digestion is anaerobic and the resulting septic effluent is exactly that - SEPTIC. See septic tank systems.

Septic tank effluent has a very high Biological Oxygen Demand (BOD) and strips oxygen out of anything it touches, be that in watercourses or the soil, leaving an environment which cannot sustain animal life. Even worms breathe oxygen through their skins, so installing a septic tank soakaway system under your lawn ensures a sterile, dead garden with resulting drainage problems.

Septic tanks also produce Methane as a by product of the digestion by anerobic bacteria. Methane gas, which is generally vented to the atmosphere form the tank, is a 21 times worse pollutant than carbon dioxide and are a significant contributor to greenhouse gas emissions.

Septic tanks must be emptied annually.

Traditional aerated sewage treatment plants

These are 3 stage units. They are not extended aeration sewage plants. The first stage is a Primary Settlement Tank which works in the same way as a septic tank - it settles out all the large solids for regular removal by tanker and produces a septic, methane producing effluent which has to be oxygenised in the second stage or biozone. These plants aerate the sewage for around 6 hours, during which time the aerobic bacteria digest the remaining solids in the effluent.

The emptying of the tank is the most expensive running cost of a sewage treatment system.

Primary Settlement Tanks are not odourless.

A correctly operating Primary Settlement Tank in a three stage sewage treatment plant

Primary Settlement Tanks are NOT odourless

Extended Aeration sewage treatment plants

These don't need a Primary Settlement Tank. The raw sewage flows directly into the aerobic digestion chamber where all the solids are digested by the aerobic bacteria. This is possible because the sewage is aerated for a minimum of 24 hours, giving vastly increased time for almost complete digestion of all the solids, not just those in suspension.

No Methane is produced.

The benefits of the Crystal sewage treatment plant are enormous.

An Extended Aeration Sewage Treatment Plant is odourless throughout the system.