What Are They and How Do They Work?
Septic tank – A septic tank is a sealed underground tank that treats wastewater by separating solids from liquids. The solids settle (forming sludge), lighter materials float (forming scum), and the partially clarified liquid (effluent) exits via drain pipes or soakaway. It requires periodic emptying.
Sewage treatment plant – A treatment plant adds further processes beyond simple separation. It often uses aerobic treatment (oxygen-based), filtration, or biological media to reduce contaminants, odours and pathogens. The effluent is cleaned more thoroughly and can often meet stricter discharge standards.
Key Differences
1) Level of treatment
- Septic tank: provides only basic treatment by separating solids from liquids and allowing some breakdown by bacteria.
- Sewage treatment plant: uses biological and sometimes mechanical processes to achieve a much higher level of treatment.
2) Discharge quality
- Septic tank: effluent is of lower quality, usually only suitable for soakaways in suitable ground.
- Sewage treatment plant: produces cleaner effluent that can often be discharged into watercourses if regulations permit.
3) Maintenance needs
- Septic tank: requires desludging every 1–5 years depending on usage.
- Sewage treatment plant: needs more frequent servicing, including care for mechanical and electrical components.
4) Regulatory requirements
- Septic tank: simpler rules but with increasing restrictions in sensitive areas.
- Sewage treatment plant: must meet stricter standards and often needs permits.
5) Cost
- Septic tank: usually cheaper to install with lower initial outlay.
- Sewage treatment plant: higher installation and running costs due to added components and energy use.
6) Space and footprint
- Septic tank: requires space for the tank and a suitable soakaway with the right soil conditions.
- Sewage treatment plant: may need more room for chambers or filters, and a careful site assessment.
Get expert guidance with Proseptic
We can help you understand your options, compare costs, and choose the right system. If you’d like, we can arrange a free site visit or quote to see whether a septic tank or sewage treatment plant suits your property best.
