When we covered how sewage treatment works recently, we didn’t define the differences between the two main domestic systems. Septic tanks and sewage treatment plants are solutions to the same problem, but which one you use depends on several factors.
Here are the main features of both – and what they mean for you and your property.
What is a septic tank?
A septic tank is a traditional wastewater solution, typically buried underground, serving properties unconnected to the mains sewers. Wastewater flows into the tank, solids settle and form sludge, then the liquid effluent flows to a drainage field or soakaway. This further treatment stage enables discharge to be filtered by bacteria before slowly soaking into the surrounding soil.
Septic tank pros and cons
- Pros
- Aside from regular (typically annual) emptying and maintenance/inspection, septic tanks are relatively low maintenance
- They contain no moving parts or complex machinery and should operate for decades if properly maintained
- Cons
- Effluent leaving a septic tank must percolate through a soakaway drainage field to avoid polluting nearby watercourses
- Not all properties have sufficient land available for a compliant drainage field
- Older septic tanks may need upgrading to comply with General Binding Rules (2020)
What is a sewage treatment plant?
Small sewage treatment plants use mechanical and biological processes to treat effluent waste. Oxygen is introduced to the system to help bacteria break down waste more thoroughly and efficiently than a septic tank. This higher treatment standard means liquid can pass into a natural watercourse without the need for a soakaway.
Sewage treatment plants pros and cons
- Pros
- Cleaner effluent can be legally discharged directly to a watercourse (subject to permits and required standards)
- Suitable for smaller sites as no larger drainage field required
- Better for sensitive sites near watercourses or high groundwater
- Cons
- Usually requires electricity as a power source for pumps
- Higher maintenance – more moving parts and machinery means potentially more maintenance costs
Which is right for me?
Often, whether you use a septic tank or sewage treatment plant will depend on the relevant environmental regulations. Since January 2020, all septic tanks in England haven’t been permitted to discharge directly into watercourses. This was further amended in 2023, to place even stricter stipulations on how and where each type of system can discharge wastewater. These General Binding Rules should be referred to if there is any doubt – or you should seek professional support to make doubly sure.
As a rule, if you’re in a newbuild property or an area close to watercourses, it’s likely that you’ll need a sewage treatment plant. And if you have ample land for a larger drainage field and you’re not near environmentally sensitive sites, a septic tank may be suitable.
More questions on septic tank vs sewage treatment plant?
Ultimately, the most straightforward way to determine which system is better for you is to ask an expert. If you’d like to speak to an experienced professional, please contact us.