Sewage Treatment Plants

What is a sewage treatment plant?

A sewage treatment plant is the modern way to treat wastewater and sewage.

Sewage treatment plants produce a liquid that is non-polluting and which resembles clear water. They can discharge directly to a ditch, stream or river without harming fish and other wildlife.

They achieve this by utilising millions of friendly aerobic (oxygen breathing) bacteria which digest the organic pollutants in the sewage and wastewater.

More Facts

In the old days, the usual method of dealing with household sewage in rural areas was to install a septic tank (often called a 'cesspit') and soakaway.  The problem is that we use far more water now than we used to and the septic tank effluent does not always soak away fast enough, especially in heavy soils. The system then backs-up and fails.

Septic tank effluent is also very polluting and can affect groundwater used in public drinking water supplies, contaminating it with bacteria and viruses.

The Environment Agency prefer the use of sewage treatment plants (with a servicing contract) over septic tanks nowadays.

Which sewage treatment plant is the best?

There is no such thing as the 'Best' sewage plant. It depends how it is going to be used. Some plants do not work well if they are very underloaded, some do. Some plants die if they are left for any length of time without use, others continue to survive for weeks. There are many different types of sewage treatment plants and many manufacturers are economical with the truth about their plants' capabilities.

There are 6 basic important things to consider when buying a sewage treatment plant.

1. The tank warranty period. A minimum 5 year free tank warranty is essential. Some have only 12 months, which is not enough to protect you, as tanks rarely fail in the first 12 months. They fail after 2 to 3 years when the ground has settled fully. Some companies even CHARGE you for an extended warranty beyond 12 months! Up to 5 years should be FREE!
2. Internal moving parts. Sewage is corrosive, so a sewage plant with no internal moving parts or metal components has an advantage.
3. Electricity consumption. The most efficient 6 person sewage plant uses only 34 watts/hour, whilst the least efficient ones use 135 watts/hour.
4. The blower should be housed outside the tank, never inside it. Inside the tank, the humidity is 100%. In cold weather, water condenses on the cold lid and drips down onto the blower. Water and electricity are not a good combination.
5. Service and emptying intervals. These vary from 3 monthly to annual. A plant which needs and annual service will save you around £130 per service and £150 per emptying, or up to £840/year when compared to a 3 monthly one.
6. A tank which has a one-piece construction. Avoid tanks that are made in two halves and joined together. Even the best seals will fail eventually and the plant is then in serious trouble, as are you with the Environment Agency.

You have some work to do as well. See steps to take for a successful sewage installation

What To Look For

Look around the internet for details of the important points of the plant to consider, listed opposite.

Many sewage treatment plant manufacturers only list the good aspects of their systems and leave out the bits that are not so good. Don't be satisfied with this - if the tank warranty period is not stated, ring them and find out and don't pay extra for any warranty up to 5 years. Likewise, if it is not clear if the tank is made in 2 halves, or the electricity consumption is not obvious, ring and ask the questions.

It does not matter if you have the best sewage treatment process in the world - if the tank splits, cracks or if the seals perish, then the system is ruined.

This is the type of effluent you want - clean, odourless and cheap to produce!