05 Apr 2018

An overview of what’s on offer when it comes to off-grid methods

If you’re thinking about embarking on a self-build project outside the limits of the UK’s main urban areas, there’s a good chance you won’t have access to the mains sewage network.

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Matthew Rolph, Managing Director at GRAF UK, provides an overview of what’s on offer when it comes to off-grid methods of managing and treating wastewater.

What is wastewater treatment (WWT)?

WWT is the process of converting wastewater – that is, water that is either no longer needed or no longer suitable for use – into a clean effluent that can be safely discharged back into the environment, without any risk to human health or unacceptable damage to the natural environment.

Why is picking the right WWT solution for my project so crucial?

With built-up areas reaching saturation, there has been a sharp rise in the number of self-builders venturing further afield to more remote parts of the country. This growing trend has reinforced the need for off-mains wastewater treatment systems that are not only highly efficient, but also comply with the ever-tightening health and environmental regulations. Installing an inadequate WWT system could spell disastrous and unpleasant consequences, such as overflowing or bad odours. You could even run the risk of prosecution under Environment Agency regulations in the event of a pollution incident. The result is heavy fines and large clean-up bills – so it pays to get it right from the start. What are my off-mains

WWT options?

When it comes to off-mains WWT, there are three main product groups you should be familiar with:

Septic tanks and cesspools
Although these are the most common solutions for off-mains WWT, they are often extremely high maintenance and need regular servicing to avoid overflowing. What’s more, a second round of treatment is usually required to ensure waste meets quality standards before being released back into the watercourses. This is especially true for cesspools, which collect raw sewage but don’t actually treat the waste. Septic tanks do treat wastewater to some degree, but the resulting effluent is usually still low quality.

Package sewage treatment systems
These work by encouraging bacteria (that break down raw sewage) to form and multiply. In contrast to septic tanks and cesspools, the treated effluent is much higher quality and can safely be discharged into groundwater via soakaways or reedbeds. Two main types of package sewage treatment systems are available: moving bed systems (where colonies of bacteria form on plastic ‘media’ before being mixed in with the raw sewage), and activated sludge systems. The latter encourage bacterial growth by continuously blowing air into the base of the tank.

Whilst both are good options for off-mains projects, each comes with its own limitations: cleaning and replacing the plastic media in a moving bed system can make it expensive to maintain, and activated sludge systems (which treat waste continuously) can struggle to cope effectively when effluent flows through too quickly during peak times – jeopardising the quality of the treated waste.

Sequence batch reactor (SBR) systems
SBR systems are the most technologically-advanced type of package sewage treatment system – and here at Graf UK, we see them as the future of off-mains WWT. They minimise the risk of untreated waste overflowing by treating it in batches using a series of chambers and an additional buffer tank. Whilst SBR systems work in the same way as activated sludge systems by mixing and circulating effluent inside a main tank, the incoming flow rate has no impact on the speed of the treatment process. This allows for an overall more consistent, efficient performance, and a higher discharge quality.

What else should I know?

Depending on the size of your project and the proposed discharge method, bear in mind that you may need to apply for permission under the Environmental Permitting Regulations (2014). Whilst not all systems require prior consent, we would always strongly recommend checking. In some rare circumstances where the quality of the treated effluent is extremely high, it may be possible to release it directly into the watercourses – subject to approval from the Environment Agency. If you’re in any doubt at all at this stage, make sure you ask your manufacturer for advice on the best system for your individual job.

Once you’ve decided on the best WWT option for you, it is also worth factoring in the recommended yearly maintenance visit that will ensure there is no residual build-up. Some manufacturers offer maintenance contracts as well as installation services – so enquire early on to get the best deal.

You will need to do some digging – perhaps literally – to find out what the best WWT option is for your self-build, but rest assured that investing the time and resources now to securing a future-proof, reliable solution to manage wastewater at your off-grid property will save you headaches, money (and possibly visits from the Environment Agency) in the long term.

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