One of the main disadvantages identified when talking about domestic sewage treatment plants is undoubtedly their power consumption.
It is a reliable, high-performance, compact, silent and odourless device, but all at the cost of up to £50 per year in electricity consumption.
Although this may be seen as a reasonable amount, it is certainly large enough to question whether there is a non-electric domestic sewage treatment plant model on the market today.
Why Does a Domestic Sewage Treatment Plant Need Electricity?
A domestic sewage treatment plant needs electricity for one simple reason: its operation requires the supply of oxygen during wastewater treatment, which takes place in the second compartment.
This oxygen supply to the tank is carried out by means of a compressor, which consumes electricity.
Some domestic sewage treatment plant models using SBR (Sequential Biological Reactor) technology have an electronic system that alternates the treatment and clarification phases in the tank.
Therefore, is it Possible for a Non-Electric Sewage Treatment Plant to Exist?
Yes… and no. The answer to this question is not exactly straightforward.
There is no domestic sewage treatment plant model that operates without electricity.
However, there is one device that has some of the advantages of the domestic sewage treatment plant and does not consume electricity: the compact filter.
What is a Compact Filter?
A compact filter is a compact wastewater treatment system, consisting of a septic tank and a media filter. Its purifying operation consists of two parts:
- The filtering power of the media filter, present inside the sand or fine gravel
- The purifying power of the bacteria that grow around this media filter
The septic tank takes care of the pre-treatment of the water, like the first compartment of the domestic sewage treatment plant. Then, the pre-treated water is discharged into the sand or fine gravel.
It is made of a material called media, chosen based on several criteria, including:
- Its filtering power
- Its resistance to rot
- The possibility of bacterial development
Bacteria develop around this media which purifies the water (similar to a domestic sewage treatment plant but without oxygen supply). The media itself filters the solids in the water, so the compact filter does not require a clarification step.
Here are some types of filter media:
- Coconut fibre
- Bark of a maritime pine (pinus pinaster)
- Hazelnut shells
In recent years, manufacturers have been trying to recover otherwise non-recoverable waste as filter media, e.g. hazelnut shells, coconut fibre or maritime pine bark.
Compact Filter vs Domestic Sewage Treatment Plant
Before detailing the advantages and disadvantages of each device it is important to clarify one thing; a compact filter does not require electricity, but because of its operation which is based on filtration, the water outflow of the filter is lower than the water discharge point.
As a result of this, it could be necessary to invest in a lifting pump to raise the water to its discharge point. This pump, which some manufacturers offer as an option, also consumes electricity, even if it consumes less than a domestic sewage treatment plant.
Here is a table comparing a compact filter vs a domestic sewage treatment plant:
|Compact Filter||Domestic Wastewater Treatment Plant|
|10 m² a 5 people home||5 m² for a 5 people home|
|Lifting pump often required||No need for a lifting pump in most cases|
|No power consumption||Power consumption (£40 per year)|
|Replacement or recharging of the media (once every 10 years or so)||No recharging required|
The main advantage of the compact filter over the domestic sewage treatment plant is undoubtedly the power consumption. However, once every ten years, the filter media of the filter must be recharged or replaced, which can be costly (around £800). This, of course, does not apply to the domestic sewage treatment plant.
Additionally, a compact filter is slightly larger than a domestic sewage treatment plant, but it is better able to withstand long absences and load variations.
If your main concern is power consumption, the compact filter is more appealing than the domestic sewage treatment plant.
If you are looking for compactness or the possibility of above-ground installation if you do not have any land, the domestic sewage treatment plant is the better option.
In any case, the compact filter is a good alternative to the domestic sewage treatment plant for homeowners looking to minimise power consumption.