27 Jul 2017

A self-builder’s guide to wastewater treatment

A rise in self-build projects in rural parts of the UK has made finding the right wastewater treatment option for individual projects more important than ever before. Here Matthew Rolph, Managing Director at GRAF UK, takes a look at the viable options for homes disconnected from the mains sewage network.

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With urban areas reaching saturation, the number of self-builders choosing to venture further afield and live off-mains is increasing rapidly. This growing trend is forcing us to seek out safe and reliable off-grid methods of managing and treating wastewater – ones that also comply with stringent official regulations on public health and environmental protection.

If you’re building outside the mains sewage network, you can still rest assured: there is an array of different options available that do the job. From simple storage solutions to more modern, super-efficient wastewater treatment systems – what are the key options available, and what guidelines should you be familiar with when embarking on your self-build journey?

Weighing up your options

Historically, septic tanks and cesspools have been the most familiar off-mains drainage solution. Whilst they are both relatively simple solutions, they are not always suitable (or indeed legal) for a given property or its local environment. Septic tanks and cesspools can often be very high maintenance, and require regular servicing to prevent overflowing. What’s more, further treatment is typically needed to ensure waste meets quality requirements. Cesspools do not treat or discharge the sewage at all: they are essentially a holding tank, with no outlet. Septic tanks are similar in construction, but feature compartments that separate solid and liquid waste. The latter is discharged through a soakaway, and cleaned by percolation – but this is only effective in parts of the country with the correct type of soil (i.e. porous).

For an option which actually treats waste, self-builders need to look at package sewage treatment plants. These work by blowing compressed air into the bottom of a tank, which acts as a catalyst for microorganisms to break down the waste. The resulting liquid is relatively clean and can safely be released into the water courses via a soakaway. There are several types of package sewage treatment systems available, but the most popular are:

Moving bed systems, where colonies of bacteria grow on the surface of plastic carriers (known as ‘media’), before mixing with raw sewage by way of aeration.

Activated sludge systems, which continuously blow air into the base of the tank, using air bubbles to enable bacterial growth. Once the bacteria have digested the organic content and pollutants in the waste, what is left is discharged into a clarification chamber, where it settles at the bottom of the tank. The live bacteria then return to the first chamber where the process starts afresh.

Whilst these are two viable options for off-mains projects, they can be difficult and expensive to maintain (e.g. the plastic media need cleaning/replacing regularly). Because waste is being treated continuously, these systems can also struggle to cope effectively when sewage flows through too quickly during peak times – jeopardising the quality of the treated waste.

This is why, more recently, sequenced batched reactor (SBR) systems have gained popularity as a third, more technologically-advanced type of package sewage treatment system for self-build homes. At GRAF UK, we are seeing a particular spike in demand for our Klaro E Professional and One2Clean ranges, which use this technology. SBR systems work in the same way as activated sludge solutions (i.e. by mixing and circulating waste inside a main tank), except they treat sewage in batches instead of continuously. This means the incoming flow rate has no impact on the speed of the treatment process – allowing for more consistent, efficient performance, and resulting in a much higher quality discharge.

All things considered

Whichever wastewater treatment solution you opt for, there are a number of rules and regulations in place to ensure the quality of the treated waste meets public health and environmental standards. Installing the wrong type of system can have unpleasant or even disastrous consequences, such as bad odours and overflowing. It’s worth remembering that in the event of a pollution incident, both the installer and the property owner are at risk of prosecution under Environment Agency regulations – and both can potentially face heavy fines as well as large clean-up bills.

Depending on the size of the project and proposed discharge method, you may also need to apply for permission under the Environmental Permitting Regulations (2014). Not all systems need to obtain consent, but we would always recommend checking. In rare circumstances where treated effluent is extremely pure, it can be released directly into the water courses (subject to prior approval from the Environment Agency). Choosing the right system is absolutely key here though, so ask your manufacturer if in any doubt.

Last but not least, you will also need to think ahead and book in an annual maintenance visit to ensure there is no residual build-up. Some manufacturers offer maintenance contracts as well as installation services – so make sure you enquire to get the best deal possible.

Knowledge is power

If you’re going to be living off the mains sewage network, the question of how to deal with wastewater should be front of mind – and with good reason. However, only an overall understanding of the rules and regulations surrounding wastewater treatment, and a sound knowledge of the different options available, will ensure you are equipped to choose the system that’s right for your self-build project.

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