• Sewage Treatment FAQs

We spend a lot of time answering a wide range of questions. We hope by posting some of the most commonly asked questions and answers we can help you be more informed about your system. If you have a question that doesn’t appear below, please contact us on 01984 623404 and we’ll be happy to assist.

Q. What is EN12566-3 2005? What should I know?

EN12566-3 2005 is the new standard for small package sewage treatment plants under 50pe. It is a requirement for the CE mark which became mandatory in the UK in 2013. The British Standards Institute has advised that, in their opinion, ONLY package plants which have the EN12566-3 2005 certification are legal in the UK. WCI will only specify systems that have been designed and tested in accordance with BS EN 12566-3:2005 and can produce an effluent standard better than 20mg/l BOD; 30mg/l SS and 20mg/l NH3.

Q. What is the difference between a septic tank and a cesspool/pit?

A cesspool is a sealed underground tank where all the sewage and water from a property is stored. A septic tank differs insofar as only the solids are retained within the tank and the septic water is passed into a soakaway where treatment and dispersal occurs. A cesspool will need emptying by a tanker every 4-6 weeks as no water leaves the cesspool, whereas a septic tank will require emptying once a year. As a result of this, a cesspool is only installed when all other system possibilities have been explored and rejected.

Q. I heard the Environment Agency has changed the consenting (permitting) process. How does this affect me?

The general binding rules on small sewage discharges in England were published and came into effect from 1 January 2015. These rules outline the new requirements for small sewage discharges and, if the new discharge meets all the rules, no permit is required from the Environment Agency. If you don’t meet these rules, then a permit MUST still be applied for. If you require help with the new GBR, please contact WCI on 01984 623404 or take a look at the rules on the Environment Agency’s website (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/397173/ssd-general-binding-rules.pdf).

Q. Can I reduce my installation costs by asking WCI to supervise other contractors’ work?

Yes. We will supervise another competent contractor’s work. This often helps homeowners keep costs low, for example where other contractors are already present on site.

Q. What is the cost for running my electrical package new sewage treatment plant?

Costs vary, but an example cost is £120 per year for a 6 population gravity system served by a continuously running 90W air blower.

Q. How long will I be without drainage when you’re installing a new system?

The turnkey installation of a new sewage treatment plant usually takes between 2-5 days (depending on the site). However, it is very rare that a site is without drainage for more than a couple of hours. Even during these couple of hours, toilets and hand basins can be used – just not emptied please.

Q. How often should I empty my septic tank?

Most modern septic tanks (fibreglass onions) are designed for complete emptying/desludging every 12 months. The rate of desludging depends on the number of people using the system and the working capacity of the tank.

Q. What can I put down my drains when I am served by a private sewage treatment system?

WCI can provide you with a list of do’s and don’ts on request. However, normal domestic use should cause no problems. Too many disinfectants or antiseptics will kill off the bacteria necessary for the breakdown of sewage.

Q. Can I fix my soakaway by jetting it?

Probably not. The jetting may dislodge a blockage but, if your soakaway has failed, jetting is only likely to move the issue deeper into the soakaway and alleviate the problem in the short term. The sign of a failing or failed soakaway includes ponding of water or nettles in the area of the soakaway or issues such as backing up of water with the drains.

Q. Can my rainwater and septic tank discharge into the same soakaway?

No. Building regulations require separate soakaways for foul water and rainwater.

Q. My septic tank discharges directly into a ditch/watercourse. Is this illegal? What can I do about it?

If your septic tank system discharges effluent (no matter how clean) to a watercourse or ditch you are committing an offence under Section 85 of the Water Resources Act 1991, rendering you liable to conviction and a fine. If your septic tank is fit-for-purpose you may be able to add on a secondary form of treatment such as a sewage treatment plant, reed bed or soakaway. Give us a call to arrange for a site inspection to discuss your treatment options.

Q. What is the grey cotton wool-like material in the ditch where my system discharges?

This is sewage fungus, which is a pollution indicator. It is often used as a visual sign that there is a lack of secondary treatment, that a septic tank discharges straight into a watercourse or ditch, or that a sewage treatment system is failing or not performing correctly.


Pollution occurring from a falling sewage treatment plant


Q. Do I still need a septic tank when I install a reed bed?

Yes, a septic tank is used to settle out the solids from the incoming wastewater before the septic tank effluent discharges to the reed bed. If the solids are not captured in a septic tank, they will block the gravels within the bed and reduce treatment efficiency and the bed’s longevity.

Q. I have a manhole preceding my brick-built septic tank which always blocks. It appears to have a higher level pipe above the inlet pipe which is at the bottom of the manhole. What is this and how do I solve the blockages occurring?

What you are probably describing is an interceptor trap, disconnecting chamber or a version of a Buchan trap. Such a device uses a water seal (u-bend) to prevent sewer gases and vermin travelling back up the pipe work. The trap will collect solids, sludge and waste over time in the u-bend and can block causing wastewater to back up. It was devised in the 19th century when it was believed that cholera was an airborne infection and often denotes the end point of the domestic property’s sewer before it joins the main public sewer. They can, however, be found on private sewage treatment systems often preceding septic tanks in clay drain runs. Today, pea traps and u-bends on sinks, baths, showers and toilets prevent smelly gases entering the property and, therefore, the chamber is without a use. The best thing is to replace the whole chamber with a new manhole.


Q. Will the brine from my water softener damage my septic tank?

There are two schools of thought on this subject and a fair amount of research has been undertaken in the US. Researchers have found that brine wastes have no negative effects on the bacterial population living in the aerobic treatment tank, even when the system was loaded with twice the normal amount of brine. The additional amount of water discharged to a treatment tank during the regeneration process has no negative impact. It was also found that the water softener regeneration brine did not reduce the percolation rate of water in the absorption field of a normally operating septic system.

Some experts don’t agree with the findings above and would like to see more research done. Senior engineering scientists believe the sodium in the ‘plug flow’ of brine might cause metabolic shock to the bacteria in the septic tank. This shock could cause the bacteria to be less able to digest the cellulose fibres, which then might be carried over into a septic system’s drainfield. Other engineers have also stated that there are noticeable differences between septic tanks with and without water softener brine discharges in septic tank systems including a reduced scum layer development and a less distinguishable ‘clear zone’ that might mean solids remain suspended instead of settling in the tank.

Q. Why do I need a submersible pump in my system?

If the topology at your property does not allow for a gravity system, then a submersible pump will be used to pump septic tank effluent to the secondary treatment system (soakaway or reed bed). The pump could also be used to pump treated effluent from a sewage treatment plant to the discharge location (watercourse, ditch or soakaway).

Q. I have a ‘sewage’ smell in my bathroom. How can I get rid of it?

There could be a number of causes and an easy way to detect smell is for a smoke test to be conducted. The smoke bomb is usually placed in the manhole preceding the septic tank or sewage treatment plant. The smoke will vent as the smell would, but is traceable. One possible cause is that water in the u-bend or P-trap has evaporated due to infrequent use and is therefore not stopping smells travelling into the room. Just flush the toilet or run water to fill the traps. Another cause can be water in the traps removed by siphoning caused by inadequate venting which allows a vacuum to form when a large quantity of water is discharged into the drain e.g. a dishwater emptying. Check your pipe work for hairline cracks and make sure your soil vent stack is not too close to a window or door.

Q. There is a sewage smell around my system. What can I do?

There are many reasons why a system is smelly and usually it is a process of elimination to find the culprit. Such reasons include lack of soil vent stack, blocked vents, submerged pipe runs due to damage, kinks in a flexible vent pipe work in roof spaces, poor positioning of vents, dual soil vent pipes, roof water entering the system and wind direction. Contact WCI now for a survey to eliminate the problem.

Q. Does a reed bed smell?

The simple answer is no. The main reason any system smells is due to an inadequate soil venting system. The soil vent system allows warm, smelly air to vent to atmosphere via the soil stack at the head of the drain run. A poorly designed or maintained horizontal flow reed bed however can mean effluent pools on the surface of the gravels which could cause smell. This can often be easily rectified. Contact WCI now on 01984 623404 to discuss your options.

Q. Does a reed bed attract mosquitoes?

No. Mosquitoes are attracted to stagnant water which they use as a breeding site. All water within a horizontal flow bed is below the gravels and does not stagnate. Although a vertical flow bed’s surface is periodically flooded, the water soaks away through the bed and the water does not stagnate.


Q. My reeds look dead what should I do?

Reeds die back in the winter months and appear to be dead. Once spring has sprung, new green growth will push through the old. If by late April you have seen no improvement, contact WCI on 01984 623404 to arrange a site visit.


Q. I wish to discharge into a winterbourne watercourse. Could I use a reed bed for this?

A horizontal flow reed bed would be ideal as the discharge from a horizontal bed in the summer months is little or none. This coincides with when the watercourse flow is at its lowest, therefore reducing the environmental impact. WCI can undertake the Environment Agency discharge consent application. Contact us now on 01984 623404 to arrange a site visit.

Q. How much space do I need for a secondary treatment foul water horizontal flow reed bed system?

A typical 4 bedroom property would need a footprint of 4m x 16m. There would also need to be room for a preceding septic tank. A lesser footprint is needed when using a vertical flow reed bed which is often better suited to a steeper site. Both beds have different functions and applications which can be discussed with WCI.

Q. What maintenance is involved with a reed bed?

Maintenance is basic and involves weeding the bed within the first 6 months to ensure the reeds become established. Once established, they will outcompete weeds. A strip around the bed should be kept mown to ensure the carryover of weed seeds is minimal. The septic tank should be emptied as advised by WCI.

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