A Septic tank conversion not only lowers the cost of replacing a septic tank, but also reduces the carbon footprint of cleaning up our rivers, ditches and streams. I explain everything you need to know about converting a septic tank and why you should consider it as apposed to replacing the tank with a treatment plant.
This is a long article covering everything there is to know. However, the investment in changing your sewage system is often large, and therefore, I hope the information is valuable.
A septic tank conversion is where a traditional septic tank is converted to a sewage treatment system. This can be achieved by:
Either way, you are often significantly improving the treatment which may allow you to discharge to a watercourse, with or without a permit (I will come on to that later).
As from January 2020, any septic tank that discharges into a watercourse must be replaced with a sewage treatment plant.
The purpose of a septic tank is to allow solid matter to be separated from the liquid waste. There is very little biological treatment occurring within the septic itself. Consequently, the liquid produced is high in ammonia which is harmful to plants, fish and the wider environment.
You would be right to therefore wonder what the purpose of a septic tank is. It is merely to retain solids in the tank. To protect the environment, the waste produced is required to have additional treatment in the form of a properly constructed drainage field.
If your tank discharges to a ditch, stream or watercourse, or even if the drainage field wasn’t constructed correctly, you will need to either replace it with a treatment plant or convert it.
The wastewater produced from a treatment plant (or well converted system), will be low in pollution and safe to enter a watercourse.
Many shapes and sizes of septic tank can be converted into a treatment plant provided it is water tight. The following tanks are generally ok to convert:
It is important to note that the tank must be watertight, a tanking slurry can be used to ensure the tank does not leach in groundwater and should be considered when converting older brick built tanks.
Yes, most conversions are successful producing better quality water than the existing tank produced. Some systems are better suited to specific tank sizes than others, and some are more adaptable than others. The after tank units are less dependent on the size of the septic tank, and therefore will be more suited to a larger proportion of septic tanks. However, they will require digging into the ground. "in tank" conversions require no digging but may only be appropriate if the tank is of the right size.
There are a few styles of system that can be considered if you wish to convert your tank. The tanks that are fitted after your septic tank can look promising, however many are what we call “trickle filter” systems (like the Ecoflo), where the water has to travel down through filter material. This is on if you are on a hill, but not if you are on relatively flat ground. Using a tank after your septic tank will also require digging large hoes in the ground. Another option is the marsh Uni:Gem, this is more of a traditional style of treatment system.
That leads me on to the systems that are fitted into the tank, the maintair conversion works very well in onion shaped tanks, the design of this system is essentially taken from ASP treatment plant (active sludge process), examples of these plants are the Premier Tech ASP, WPL diamond, and the Biopure.
These systems aerate continuously to provide oxygen to the water, which enhances the growth of Aerobic bacteria. It is this bacteria that break down contaminants in the water to reduce pollution.
No, unfortunately it is not possible to just add oxygen to the tank using an air blower. This does not work, and I will explain why:
When you oxygenate water, you will get a growth of bacteria, that bacteria will be in the form of activated sludge. Visually, it looks like a brown soup. Without a method to control this, it will quickly grow and fill your tank, then start to be discharged into the environment. Very soon the water coming out will be brown. The bacteria will then die off in the ditch and go black.
The question of whether or not a septic tank conversion meets the general binding rules or not is a question which can only be answered by drilling a little into the detail.
Firstly you must categorise the type of conversion. As I have already stated, there are 2 types:
Conversion units built into the septic tank (type 1) always require a permit. as stated on the government website:
Retrofit systems within an existing septic tank can only be used if they were installed before 2007. If you have a system like this that was installed after that date, or you are planning on installing one of these systems, you must apply for an environmental permit.
www.gov.co.uk
Conversion units that are installed after the tank (type 2) are slightly different, the official term for these is a "secondary treatment unit". The gov.co.uk website states that:
You can only use a reedbed or a secondary treatment unit, installed after a septic tank, to discharge to a watercourse if it meets the relevant British Standard. Otherwise you must either:
www.gov.co.uk
- upgrade to a sewage treatment plant
- apply for a permit so the Environment Agency can assess the risk of using this sort of system in your location
Therefore, if the "secondary treatment unit adheres to British Standards then it complies with this rule. The relevant standard here is EN12566-6. If the unit has been tested to EN12566-6, then no permit is required. It needs to be noted that all the other rules must be adhered to to allow you to discharge without a permit.
Units that have been tested to EN 12566-6 are:
Note to manufacturers, if your system has been tested, please send me the certificate for inclusion
There are many benefits to converting a septic tank. Here are some:
Yes, there are some downsides to consider as follows:
Many installation companies own diggers and want them to be in use as much as possible. So, it is common for an installation company to suggest that conversions don’t work, or your tank is not suitable. Many sewage installers are groundworkers, making money from fitting tanks. If they are reluctant to convert the tank, then it is likely they are nervous of the treatment aspect of this work. Always get a second, or even 3rd opinion. There are a great many “sewage treatment companies” that just want to install tanks.
Tank manufacturers also want to be producing and selling tanks. So, you will rarely hear about converting from an installer or sales rep.
However, some tanks are leaking water, or are not structurally sound, these should be replaced especially if there are serious signs of collapse (large cracks in the brickwork for example).
Typically the cost of converting a septic tank will be in the region of £5000+VAT. As I have already alluded to, it is not just as simple as bubbling air into the water. Often the tank will need to be entered, and the outlet adapted to suit the conversion. A trench will need to be dug to lay air hoses and potentially a cable to the septic tank.
It takes 2-3 days to convert a septic tank. The tank will need to be emptied prior to stating the job, but often can be used again within the first day.
If you have a septic tank and believe it to be structurally sound, then it is cheaper, better for the environment and offers the same results as a package treatment plant. There is no reason not to seriously consider converting the tank over replacing it.