Extended Aeration sewage treatment explained

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 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. Because of this, they can go up to 2 years between emptyings.

Extended aeration process plants cannot deal with long periods of absence and are not a suitable choice for holiday homes. This is because the process is a ‘feast and famine’ principle. There is no primary settlement tank to act as the ‘larder’ and store organic material for later use. If an extended aeration treatment plant is left unfed for more than 2 weeks, you risk serious bacterial death and it takes 8 to 10 weeks to re-establish a working bacterial colony again.

Extended aeration plants do not work well if they are underloaded and should not be chosen if the number of people using them is less than 40% of their design size, eg. a 6 person should have a minimum of 3 people actually using the system. This used to be a fact that was emphasised by the original UK manufacturers, but seems to have been ignored as more and more manufacturers have adopted the design. We service hundreds of extended aeration plants and can verify that underloaded plants have difficulty in meeting their Environment Agency consent standards.

An Extended Aeration Sewage Treatment Plant should be chosen ONLY if the sewage is domestic residential in origin, the property is lived in all the time and the number of people living there is a minimum of 40% of the plant size. If the above criteria are not met, consider 3 stage sewage treatment systems or non-electric sewage plants instead.