Review of the Biodisc
The Biodisc is arguably the most well known treatment plant in the country.
However, is it a good choice for homeowners? To learn more about this treatment plant, read my review below.
The Biodisc® is a sewage treatment plant made by the UK manufacturer Klargester (pronounced "klar-jester"). Klargester are owned by the Kingspan group. A Sewage treatment plant is designed to treat wastewater enabling the water to be discharged into the environment.
The Biodisc® has a series of discs that rotate slowly within the tank. The discs are semi submersed in the wastewater. As the discs turn, bacteria that naturally develops on the discs come in contact with the wastewater (to feed). Contact happens when the portion of the disc enters the wastewater. The top of the disc is exposed to air inside the tank, this allows the bacteria to receive oxygen.
If you’ve read any of my other posts you may be aware that bacteria need 3 things:
Biodisc® treatment plants are classed as RBC (rotating biological contractor) style treatment plants.
A motor within the chamber turns the discs slowly, there is normally a belt or chain the connects the motor from the discs.
It is very hard to hear the Biodisc® in operation. Since it does not rely on an air blower to inject oxygen to the water, noise is a lot less than most air blower powered systems. You may hear the noise of the flow balancing cup (I’ll come on to that later), but this will be difficult to detect unless you really pay attention.
The downside to this treatment plant is its visual appearance. It has a large dome lid. So if you are planning to install one it is best hidden by a bush, or tucked away somewhere. Klargester have done their best to make the cover a natural green colour.
The Biodisc uses 1.3kWh/day, at £0.34 per kilowatt, this equates to £160 per year for the smallest model. This isn’t too bad, and if the system is used for 4 people it equates to £40 per person. Most systems running 24 hours a day will be around this cost.
Like any treatment plant, regular servicing of the Biodisc® is highly recommended. The shaft that holds the discs has 2 bearings to make it rotate smoothly, these bearings wear out and require regular replacement. This is not something a consumer should attempt to do themselves as it requires lifting the shaft and discs. A good analogy that I think you will understand is not replacing the bearings is akin to not replacing brake pads in a car.
Loss of rotation can be problem for the Biodisc®, which is why klargester include a loss of rotation alarm. If the discs stop rotating, a biomass will quickly build up on the portion of the discs that are in the water, causing the whole disc unit to become heavy on one side. If you catch it in time and repair the fault, then there really isn't a problem. left unchecked and the repair bill will be higher.
Don’t be put off by these potential problems, all treatment plants have potential problems, just make sure you have a good service professional in your phone book in the event the loss of rotation alarm sounds. Acting quickly will save you money.
One under reported feature of the Biodisc® is its natural flow balancing. Why is flow balancing beneficial I hear you ask? because bacteria like a steady food source, rather than lots of food (waste) and then none.
The Biodisc® balances the flow of waste coming into the system by means of a small cup that is attached to the discs. It’s a clever and simple function; as the discs rotate, the cup dips into the water. As the cup comes out of the water it empties its contents into a second chamber slowly moving the waste through the treatment zone. Therefore, if you empty a bath and 80 litres enters the treatment plant, the cup slowly adds that, litre by litre from the first treatment zone to the second. For the bacteria in the treatment plant, this means more regular food rather than all at once then nothing.
The Biodisc achieved the following results during its 37 week testing:
BOD5: 10mg/l
NH4-N: 3.8mg/l
SS (suspended solids): 15mg/l
Whilst the test results aren’t amazing, one could argue that the flow balancing mentioned previously provides good stability.
The Biodisc® has been a mainstay for years. Those in favour of it say it is “the best” those selling alternative treatment plants will say that you don’t want moving parts in the tank. My personal opinion is that moving parts are fine if the system is looked after. If you neglect the Biodisc® it will bite you back in costly repairs, this is true of all treatment plants.
I really like the flow balancing and being a fixed biology treatment plant, one could argue that the bacteria on the discs can service a little longer in the event of no usage than treatment plants using activated sludge, however I would impress on anyone that under normal household circumstances, this isn't really an issue for any system (we don't normally leave our homes long enough to cause bacterial die off problems), and bacteria will regrow in the event that we have left for a long period.
What I try and impress to people I speak to is there is no “best” treatment plant. They all have pros and cons and some systems suit some sites better than others.
The Biodisc is extremely quiet, offers stabilised treatment, and given the sheer numbers in the ground, there is likely someone in your area that can maintain it well. Furthermore, maintenance of a biodisc is largely a mechanical job, which incidentally, is why we have seen a rise of motor mechanics moving into the treatment plant industry.
The difficulty a consumer has is finding someone that is independent to supply or install their treatment plant.
Many (not all) online shops don’t actually understand their products, as most sales people have not had to repair a broken one. Many “professional installers” are groundworkers and struggle with the finer points of sewage treatment (note: there are obviously some fantastic installers out there) Which ever system you buy, be sure there is someone local to help look after it, and note, you do not have to have the person that installed it, look after it.
“Klargester” are a sewage treatment plant manufacturer. It is common for people to use their name in the same way people use “hoover’s” name. Referring to “a Klargester” can often just mean “ a Sewage treatment plant”
At the time of writing the smallest Biodisc is around £4800 inc VAT.
The Biodisc is one of the least noisy treatment plants in the market.
No. Whilst the water can be cleaned very well from a Biodisc, the water will contain some bacteria and therefore should under no circumstances be consumed.
Building Regs part H suggests the treatment plant should be at least 7 metres from a habitable building. Building control should be consulted if this is unachievable.
Providing all of the other rules are adhered to, yes.
Regular maintenance contracts are available from £120 for a yearly visit and check over
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