septic tank upgrade

Difference between a Septic Tank and Sewage Treatment Plant

In this blog, we discuss the difference between a septic tank and sewage treatment plant and explain which is better at treating wastewater and why.

In a nutshell, there really is no contest between the two. A sewage treatment plant does much more than a septic tank, but the terms are often confused and used interchangeably. Strictly speaking, a septic tank is not a sewage treatment plant but it can be used as part of a sewage treatment plant or system.

The primary reason you purchase a sewage treatment plant or septic tank is to receive and treat the sewage and wastewater from your dwelling. A septic tank is basically just an empty tank to store sludge. The only form of treatment that occurs is basic settlement of large solids.

Why is a sewage treatment plant better than a septic tank?

A sewage treatment plant is better than a septic tank because it actively treats the incoming sewage by aerating [adding oxygen to] the wastewater, either by a small air blower, or naturally via ventilation. The extra oxygen accelerates the natural biological process of breaking down the waste in the sewage.

Inside a septic tank, heavy solids settle at the bottom to form sludge. The rest of the sewage discharges into to the environment. So a septic tank has a treatment efficiency of approx 25%. In contrast, our best selling sewage treatment plant, the Biocell Quickone+, has a treatment efficiency of almost 99%. Big difference. Low quality septic tank effluent means pollution of groundwater, pollution of streams and clogging of soakaways with effluent with very high amounts of suspended solids.

So to protect the environment, to protect your drinking water and to keep your soakaway working well – a sewage treatment plant is a must have. If you have a septic tank and need to change it into a sewage treatment plant, have a look at our blog post on septic tank conversion and upgrade.

Can a septic tank be turned into a sewage treatment plant?

A septic tank can form the basis of a sewage treatment plant by acting as the chamber which facilitates primary treatment [settlement of solids]. After primary treatment, the effluent must flow to a second chamber for aeration, also known as secondary treatment [or biological treatment] to be considered a sewage treatment plant. The aeration process is what makes a sewage treatment plant different from a septic tank.

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