About Septic Tanks

There are several different types of septic tank systems, and they all work on the same basic principle: to separate the solids from the liquids and allow the liquid to flow out into a soakaway. The soakaway allows the bulk of the waste, which is mainly water, to 'soak away' into the surrounding ground, through an arrangement of pipe work and drainage stone.

Traditional septic tank

The first job of a septic tank is to allow the solids to settle. A proportion of solids float and a proportion sink. The liquid in the middle then flows through the chambers via dip pipes and out into the soakaway.

Just like everything else, septic tanks need to be serviced from time to time. This involves regular de-sludging in order to remove the build-up of solids. If this is not carried out the solids can build-up in both tanks and then overflow into the soakaway. This will block the soakaway pipe work and drainage stone, possibly resulting in expensive and messy remedial work. The condition of the dip pipes should also be checked from time to time.

Bottle septic tank

Bottle type septic tanks work using the same principle but have two chambers that are stacked one on top of the other, instead of side by side.

Sewage treatment plant

There are many different types of sewage treatment plant and they work using the same basic principle: settlement, biological treatment then further settlement.

The biological treatment zone comprises a large surface area on which bacteria may grow where air and food (i.e. sewage) are present. The air can be introduced in different ways through SAF (submerged aerated filter) or RBC (rotating biological contactor) technology.

The aim of the sewage treatment plant is to produce a final effluent of sufficient clarity to meet the standards set by the Environment Agency via a "Consent to Discharge" to enable the final effluent to discharge into a water course or soakaway. The obvious benefit of this is in areas where the ground porosity is poor and the effluent can be discharged into a water course.

Cesspools

In some cases, if there is nowhere in the surrounding area to site a soakaway, it may not be possible to have a septic tank or a sewage treatment plant. In this case it may be necessary to have a cesspool. This is a giant holding tank for waste with no outlet. Large volumes then need to be emptied from these at regular intervals. This can work out as an expensive option.