With energy costs rising year on year, more and more consumers are looking at the energy costs of their appliances within the home. Many people that need to upgrade their sewage treatment facilities are turning their attention to the energy cost of treating their wastewater. Therefore, it is clear that non-electric sewage treatment plants are on the rise.
In this ultimate buyers guide to Energy free sewage treatment plants you will learn:
This article may seem long, however, if you are planning to buy a non electric treatment plant then the considerations and points raise will prove very useful to you.
A non electric sewage treatment plant, is a biological treatment system for the treatment of sewage waste. Unlike most systems available, These sewage treatment plants require no power to perform the treatment necessary to clean and discharge waste into the environment. Sounds great, and yes it is great, however, like all things, there are pro’s and con’s. In this article, you will learn how one works. We will also look at cost comparisons and why one might, or might not be suitable for you.
Like all biological sewage treatment plants, non electric systems grow bacteria to feed upon the contaminants in your wastewater. Understanding how a normal sewage treatment plant works is a good first step to understanding this fully.
If you already have a good idea of how a normal system works then you will understand the need for the growth of aerobic bacteria in a treatment plant. Energy free sewage treatment systems are no different, they are what we might call “trickle filter” systems. This Style of treatment plant has been round for a long time.
There are a couple of key points here which we will discuss later. Firstly the bacteria need oxygen and secondly; the water comes out at the bottom of the tank. We will discuss these points later in the article.
Note: These systems do the same job as a correctly constructed drainage field (in the sense that the gravel in a drainage field acts as a biological filter). Therefore, there is little to no point using one of these if you are planning to construct a drainage field.
Firstly we should look at the cost of an electric sewage treatment plant. Most small 6 person sewage treatment plant will use an 80L/minute air blower to add oxygen to the water. These use between 50-70 watts (the HiBlow XP80 for example uses 58watts). Here is an example of a normal system which will have to run for 24 hours a day (keep in mind certain systems like the solido smart don’t have to run all the time). A system using a less efficient blower can use up to 75watts, so keep that in mind.
| Blower Watts | 58w |
| Energy Price | £0.34 per Kwh (October 2022 price cap) |
| Running time | 24 hrs Per day |
| Power consumed | 1.392kwh/day |
| Cost per day | 47pence. |
| Cost per year | £171.55 |
So, on paper you will save £171.55 per year in electricity using a non electric treatment plant.
To buy a non electric sewage treatment plant, you will be looking at £3500-£5000 for a 6 person system. This is vs £2000-£3000 for an electric powered sewage treatment plant. As you may already see, energy free treatment plants are more expensive and often require a larger hole to be dug to install.
In short, 15 years. The justification of that is a little more detailed as follows:
If we take the product alone, and disregard the installation costs for a moment. And if we say that there is £2000 difference in price (roughly), then given the example of the system with a hiblow XP 80. Then the payback period would be 10 years.
However, there is more to it than just that. We must factor in replacement air blowers and maintenance for an electric system.
It’s not easy to find out what maintenance is required for a non electric treatment plant (Because the manufacturers don't like to say, the suppliers tend to lie or don't actually understand what they are selling).
I would say it is a good idea to rake the top of the filter material, to avoid water only channelling through a certain pathway. Therefore:
| Non Electric | Electric | |
| Power Consumption | N/A | £172 |
| Service Engineer | £150 | £150 |
| Replacement Parts | N/A | £26 |
| Total: | £150 | £348 |
| Yearly Cost Difference | +£198. |
We can now be fairly sure that the cost difference is £198 per year (including maintenance and parts). Therefore Given £2000 difference in upfront costs, the payback would be 10 years.
This doesn’t factor in any difference in cost of installation which could be more for the non electric system given the hole is bigger.
We spoke earlier about the need for the bacteria within the system requiring oxygen. To achieve good treatment quality, we must give the bacteria 3 things:
Without oxygen, bacteria won’t survive and your nice non-electric treatment plant wont work. Therefore you must ensure the system is well ventilated. I have an article on this venting a treatment plant, which is worth a read. At the bare minimum you will require a normal soil stack (not an air admittance valve) and a low-level vent at the treatment plant (for air to come in), this should be 4 inch with a mushroom cowl on the top . With this air flow coming through the system, you will give the bacteria the oxygen it needs. But keep in mind, some systems actually require a high-level stack immediately before the treatment plant. Which could look ugly in your garden. Check this with your supplier.
Top tip: If you are discharging to a water course and have an open, unrestricted pipe, with the opening not too far away from the system, that could be considered the low level ‘inlet’ air vent.
If you’ve got this far, well done! We are nearly there. As I stated at the beginning of the article, the wastewater must pass through the filter material and come out at the bottom. Why is this relevant?
Most waste pipes are approximately 600mm below ground. Once you pass water through 1.5m of filter material, the outlet will be 2.1m below ground. This is fine if your garden slopes down and away, but if the ground is flat, and you are trying to discharge to a watercourse, you may have to install a pump to lift the cleaned water up to the level of the ditch. Your non electric sewage treatment plant now requires a power supply, and electric (all be it a lot less electricity than a normal electric system).
In this scenario, I would only promote the use of a non-electric treatment plant if the system is going to be used infrequently like a holiday home.
So from the above, it looks like there are more cons than pros. However, I really like all the non electric treatment plants on the market. There is a place for them, just not a big place. Here are some situations where you might consider a non electric system over a conventional one:
The short answer to this is the Premier Tech Ecoflo. This is 100% non-electric and specifically is the shallowest system on the market. Therefore, the outlet remains shallow in the ground and allows more scenarios where you can discharge to a ditch without the need for installing a pump.
It might feel like a bit of a minefield, however I hope this hasn’t put you off the idea of a non-electric treatment plant. Just be sure you don’t dismiss normal treatment plants, or low energy ones like the Solido smart. Whilst I generalised a little with the costs, I hope this article has armed you with some more knowledge to aid your decision.
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