See the UK regulations your Biodigester must comply with below
When building or renovating a home that has no connection to mains drainage for the disposal of sewage then alternative options have to be considered.
The UK currently has four different Environmental Regulators for surface and groundwater pollution control:
England – The Environmental Agency (EA). Tel: 03708 506 506
Wales – Natural Resources Wales / Cyfoeth Naturiol Cymru. Tel: 0300 065 3000
Scotland – SEPA (Scottish Environment Protection Agency) Tel: 0300 099 66 99
Northern Ireland – Northern Ireland Environmental Agency (NIEA) Tel: 0845 302 0008
These regulators operate in different ways and consequently generalisations have to be made.
Starting off specifically with the EA in England a document produced by DEFRA (Department of the Environment, Fisheries and Rural Affairs) entitled General Binding Rules for Small Sewage Discharges (SSDs) with effect from January 2015 is the yardstick. Refer to www.gov.uk
For the other regulators go to their websites or ask for assistance.
The standard checking procedure starts off with the question ‘How far is the site from the nearest public foul sewer?’ If more than 30m then alternative options can be considered in most cases.
If considering pumping to a public foul sewer there need to be checks regarding the legal rights of access, connection fees, obligations in perpetuity and the technical aspects of pumping and storage.
If a property’s wastewater cannot be connected into a sewer there are three alternative options, a Cesspool, a Septic Tank or a Package Treatment Plant. Package Pumping Stations are available constructed in glassfibre (GRP) or other materials with pumps of different types.
Under current naming conventions a Cesspool is a holding tank that has no overflow and from which all the effluent must be taken away by a licensed tanker firm. Compliance with Building Regulations requires a large capacity tank of several thousand gallons.
Even with extreme water saving measures the cost of emptying a cesspool is likely to be several thousand pounds in a single year. The use of cesspools is therefore best avoided.
Septic Tanks are much smaller tanks than cesspools with two or more chambers that settle out some of the solids that come into them.
However the liquid part remains a strong polluting liquid that may only be dispersed into a system of soakaway trenches, sometimes also called sub irrigation systems. Soil porosity tests have to be carried out in accordance with BS6297:1983 and the Amendments of 2007 & 2008 and the soakaway system sized and designed accordingly.
The trenches need to be constructed with 25mm-40mm clean stone to a depth of 400mm around a rigid 100mm diameter pipe with slots or holes at the bottom. The width of each trench is normally 600mm or 900mm and there needs to be a suitable covering sheet.
Traditional herringbone soakaways are best avoided as if the main artery blocks the whole system may block. A rectangular grid allows alternative pathways. On sloping ground soakaway trenches should be constructed at a constant depth along one or more contours.
BS6297:1983 requires that septic tank soakaway trenches should only be constructed where there is at least 1 metre of soil between the soakaway and the water table at all times.
This rules out the use of septic tanks in many areas where there is low lying flat ground with clay soil and a high water table.
For septic tanks there may be a restriction on their use due to underground sources used for extraction of drinking water. In England check the Environment Agency’s Protection Zones at www.gov.uk or ask a specialist to check this for you. There may also be restrictions with respect to Sites of Special Scientific Interest (SSSI) or similar sites where installation is within and also near to such a site.
The discharge of septic tank effluent into a watercourse, including ditches has been illegal since the 1960’s. DEFRA now requires that any existing discharges are stopped by 2020.
Septic tanks should be emptied once per year to avoid failure of the soakaway system.
Package treatment plants
Package treatment plants are the modern alternative to septic tanks that produce a clear effluent suitable for discharge into a watercourse if one is available. The effluent is typically 20 times cleaner than that from a septic tank. Most new properties built in the countryside nowadays use treatment plants as they represent the environmentally friendly option.
If no watercourse is available the treated effluent still needs to be discharged into a system of soakaway trenches. The use of a treatment plant may overcome the difficulties of a high water table, underground water supply areas or sites of special scientific sensitivity.
To overcome a high water table or discharge into a watercourse that may flood it can also be necessary to use an automatic effluent pumping system that manufacturers supply with their treatment plants, normally as an option. These systems have a non-return valve that prevents any back flow.
A number of different types of package treatment plant are available. The ones with complicated mechanical and electrical components are becoming less popular and aeration of the sewage with a small air blower is now commonplace. Some of the aerated systems still have a septic settlement stage with the risk of odours and the need for emptying once or more times per year. The better systems aerate all the sewage that comes into them including all solid matter. The best systems will go for several years before they need to be emptied. The use of Linear Air Blowers provides operation that is efficient and economical with little maintenance required for the best systems. Package treatment plants should be located no nearer to inhabited dwellings than 7M.
In selecting your wastewater solution for Off Mains Drainage it is important to cover the requirements of the appropriate Environmental Regulator, BS6297:1983 as amended and local Building Regulations.
Consent to Discharge has been replaced by Environmental Permitting Programme – Second Phase (EPP2).
As of 6th April 2010, you may apply for exemption from a Permit to Discharge if the following criteria are met:
Discharge is to ground and is of 2m³ per day or less via a septic tank and infiltration system (soakaway) and is outside a source protection zone 1 (approximately 9 people occupying a single property)
Discharge is to surface water (ditch, stream, river) and is of 5m³ per day or less via a package sewage treatment plant (approximately 31 people occupying a single property)
Sewage is only domestic
Sewage system is maintained in accordance with the manufacturer’s instructions (if not, British Water codes of practice and technical guides) and you keep a record of all maintenance
Discharge does not cause pollution of surface water or ground water
For more information on Exemption from EPP2 or the check if you are in a Groundwater Protection Zone, see the Environment Agency web site.
The Building Regulations 2000 Drainage and Waste Disposal 2002 edition Part H-H2
The main provisions of these regulations are:
The Sewage Treatment Plant must be sited more than 7m from habitable property.
The discharge point shall be more than 10m from habitable property.
If the discharge is to a soak away a sampling point must be provided before the soak away. These are available from us.
Clause H2 0.1/ 1.16 “Septic tanks should be sited at least 7m from any habitable parts of buildings, and preferably down slope”
As Clause 0.1 links septic tanks with wastewater treatment systems, then you should assume that this clause related to a BIODIGESTER.
Clause 1.54 “The discharge from the wastewater treatment plant should be sited at least 10m away from watercourses and any other buildings.” Subject to consent from the Environment Agency, the treated effluent can be discharged directly to a watercourse or a ditch.
You will need to decide where the effluent is going, in most cases it is either to a soak away or a ditch/ stream. If it is to a soak away, you will have to carry out a percolation test. You will also need enough space to install a soakaway on the land available.
Note the actual length of the pipe will depend upon the size of the plant and the porosity of the soil. The example shown is for a T6 Biodigester.
If you are discharging to a soak away you should install a sampling point before the soak away. These are available from Burnham Environmental Services Ltd.
You will need to ensure that a road tanker for emptying will be able to get within 30m of the plant. If the access is higher than the unit the differential should be within 5m.
The unit is not designed to be installed in a driveway, unless you ensure that the loading of traffic is carried by some form of support to take the load away from the structure of the BIODIGESTER.
If the unit is installed in a field with livestock, protect the access lid with a stock fence.
If you are to install in an area of a high water table, you may need to use a BIODIGESTER with an integral pump. This allows the effluent to be discharged near the surface and has a non return valve to ensure that it will not flood.
If the installation is in an area of flooding, we can provide a neck extension to raise the access lid above the flood level. Many people build a flower bed around it.
If any of these criteria cannot be met, contact us. There are always ways around the problem.