David Stagg, technical manager for Graf UK, says that ‘commissioning’ of domestic wastewater treatment plants is as vital as getting gas and electricity services signed off by specialists, and wonders why it’s not happening 

Wastewater treatment plants became established in the UK in the late 1990s when specifiers and homeowners finally woke up to the limitations of septic tanks. As a result, you would think it was safe to assume that the need to commission these plants, or to set them up properly, was also recognised.

However, some manufacturers are finding that only 25% to 50% of their systems, at best, are being commissioned. The reason they are not cannot be the cost – it is only between £150 and £300 – nor the time – the 15 to 20-point checklist only takes less than an hour for a trained specialist service provider. So, what is the reason?

It is most likely that a large percentage of specifiers and end users simply are not aware that commissioning is available and/or how important it is to the long-term wellbeing of their wastewater management system. 

While registration systems do not guarantee the quality of long-term service and maintenance and the protection of groundwater from potential pollution, such systems exist in Wales and Scotland, but not currently in England.

Historically, there were some agencies which registered and tracked treatment plants, but when the General Binding Rules (a set of rules-based regulations intended to simplify the regulation of small sewage discharges) were introduced by the Environment Agency in 2015, all this, ironically, seemed to cease.

While more and more people are now doing their research and due diligence before purchasing a wastewater treatment plant, some manufacturers are bridging the gap and putting their money where their mouth is, by offering free commissioning.

These watchdogs for their own systems would rather help specifiers and end users avoid any potential emotional, economic and environmental impact that may be caused without such measures in place.

Issues with non-commissioned wastewater treatment plants are generally due to poor installation and system set-up rather than the systems themselves as they are typically relatively simple to operate. 

The first symptom is likely to be a bad smell. Contrary to popular opinion, this is not what end users should expect from a wastewater treatment plant!

It is likely something has stopped working. Perhaps a compressor error. Perhaps the air diffusers that blow oxygen into the water in the tank have got blocked or damaged in some way. Maybe a power cut caused an issue with the timings and workings of the system. 

Perhaps the waste content is not suitable for the system to work at its optimal rate. For want of a better way of describing this, is the tank being filled with too much liquid and not enough solids? That can affect how the treatment process works. 

The same goes if the system takes in more grey water from sinks, washing machines and showers, than it does black water from toilets. It’s called a sewage treatment plant for a reason – it needs sewage! Too much soap and not enough sewage might mean the treatment quality drops. 

The number one reason for issues with wastewater treatment plants is poor aeration caused by air hoses and diffusers (that sit in the bottom of the tank and release small air bubbles into the effluent) which have not been connected properly, or air hoses that kink. This affects the most important part of the treatment process – the quality and quantity of aeration. If the dissolved oxygen levels in the treated effluent are low, this will result in odours. 

If the diffusers are not located in the tank correctly, such as lying on their side or one on top of the other, some of the air holes may seal up over time as air will always take the path of least resistance which is from the highest point. This again reduces the quality of aeration into the treatment zone and creates more back pressure on the compressor, forcing it to work harder and resulting in a shorter design life.

Tanks can even be installed the wrong way round, with the inflow going into the outlet which will obviously cause issues from the moment go, and if tanks aren’t level, gravity flow into or out of the tank will be affected. And if the wrong backfill material is used, even the most robust tank may be damaged by sharp stones or bricks.

Some systems have not even been switched on! If this was discovered say six months after the system should have been commissioned, the plant would only have been acting as a septic tank, a storage vessel with no capacity to treat its contents, for all that time.

Contemporary wastewater treatment plants run on two 12-hour or four six-hour cycles so even if something as basic as checking the date and time are correct is not done, this will affect its ability to function properly.

And let us not even talk about drainage fields! Even though these are invisible once installed, if they have not been sized and designed correctly, any issues will soon become extremely visible…as well as extremely smelly.

David Stagg is technical manager for Graf UK