Sewage treatment plants and septic tanks serve the same purpose to an extent - they both provide buildings, without access to mains sewers, with a way to process their wastewater. Despite their similarities, they do have important differences.
What is a septic tank?
A septic tank is a large chamber where the sewage from your house is treated. The sewage enters the tank with gravity before being separated into solids (sludge) and oils (scum). The separated wastewater (effluent) then leaves the septic tank via an outlet and goes into a drainage field. Once the water leaves the outlet pipe and has gone into the drainage field, the effluent is percolated through the ground to remove bacteria, before being dispersed and rejoining watercourses.
What is a sewage treatment plant?
As with the septic tank, the sewage enters the unit via gravity and the sludge settles to the bottom where the plant treats the effluent. Sewage treatment plants are an eco-friendly solution as they use naturally occuring bacteria to treat and digest organic matter. This means the liquid from the tank is non-polluting and can be discharged straight into a stream or drainage field.
What are the main differences?
Sewage treatment plants have mechanical components which means they need a constant electrical supply to operate. Septic tanks have no such components so can operate with no power supply.
A sewage treatment plant provides treatment to the waste whereas a septic tank simply separates it. Therefore, the wastewater that leaves a sewage treatment plant is cleaner than the wastewater that leaves a septic tank, so it is a lot more environmentally friendly.
Septic tanks have to be emptied to remove the sludge depending on usage, sewage treatment plants do not.
Due to a sewage treatment plant having cleaner wastewater, it can be discharged straight into a local watercourse whereas a septic tank cannot as it is very polluting.
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