The differences between Cesspools, Septic Tanks and Sewage Treatment Plants

If a property has no connection to mains drainage, there have been 3 options – a cesspool (cesspit), a septic system or a package sewage treatment plant. The differences are briefly described below.

Cesspool (Cesspit)

A cesspool is effectively a sealed tank, normally underground, in which the effluent is stored. There is no treatment of the contents of the tank. Emptying is required frequently, generally monthly.

Cesspools are uncommon nowadays as they tend to be expensive to maintain due to the frequency of emptying. Cesspools are installed only where there is no other feasible alternative. 

Septic Tanks

A septic tank is also an underground tank that uses a simple process to crudely treat the waste and then will discharge the settled liquids into a drainage field or soakaway.

As waste enters the tank, solids will either settle to the bottom of the primary chamber or form a crust on the surface. Settled liquors will pass through to a secondary chamber where further settlement will occur. Eventually the settled liquids will discharge under gravity to the soakaway.

The sludge that settles to the bottom of the tank will need to be removed regularly, generally every 6-12 months.

Care should be taken when using a septic system. Excessive use of cleaning products or discharging fats, oils and grease (FOG) can affect the bacteria contained in the system. Bacteria is vital to the biological processes that break down the waste.

Sewage Treatment Plants

A sewage treatment plant acts similarly to a septic tank, using the first two chambers to settle out the solid matter. Settled liquids will then discharge into the’ biozone’ chamber where the liquids are mechanically aerated and is further broken down by aerobic digestion. Fine solids will settle out in a final settlement chamber before discharge. Generally, a high -quality final effluent is achieved in accordance with EA regulations.

Desludging and routine maintenance of the plant is essential to ensure the system meets it consent to discharge and the frequency is generally determined by the manufacturer (please refer to your operating 7 maintenance manual). As a rule, this is normally every 6-12 months.

To check if your treatment plant is meeting the required standard – call The Tank Sampling Company for a free quotation.

The 2020 guidelines

Under the new guidelines, effective from 1 January 2020, septic tanks will be prohibited from discharging directly to a watercourse (a river, stream, ditch, canal, or surface water drain).

If this is the case with your septic tank, there are really only 2 options available to you.

  1. Reroute your discharge away from the watercourse and to a soakaway facility
  2. Replace the septic tank with a small package sewage treatment plant so the final effluent meets the required standard to enter a watercourse.

Urgent action is needed to meet the deadline.