Specifying off-mains drainage solution

There are an estimated one million properties in the UK that cannot readily connect to the mains sewer to support the sanitary facilities within the building. Each property will present engineers with a unique set of challenges pertinent to the demands of the specific site, building use, and facilities, all of which must be addressed within legal frameworks.

The Challenge – Ensuring Off-mains Drainage Solutions are safe and legal

Before drainage is installed, the site should be subject to an inspection in accordance with both 2010 Building Regs and the DETR report 3/99.
The inspector must address a number of issues including:
• Managing all effluent safely, legally
• Connecting to the mains if at all possible
• Sizing/specifying the solutions correctly
A sewer connection for the building requires sufficient gravitational forces to move the waste to the sewer; if gravity is insufficient then waste will need to be pumped to the sewer using a suitably sized pump station in accordance with Building Regs.
Only if any connection is deemed to be impractical will the next best option, a private drainage solution, be explored.
Whichever route is finally decided upon, the solution must be correctly specified to suit the application in order to avoid the unappetizing prospect of overflowing toilets and drains – either of which could lead to the property owner and the builder being prosecuted under The Public Health Act 1936.
Waste from commercial applications will vary in strength, dilution and quantity, all of which will need to be taken into account.

The Solution – Correctly Sizing and Specifying Off-mains Products

Pump Stations
Commercial pump stations such as the Kingspan Klargester Pumpstor, offer the option of a connection to the sewer for properties where gravity cannot be relied on.

There are two principle regulations dictating design and use of pump stations – Building Regulations H1 and British Standard EN 752-6. Section H1 of Building Regulations for Foul Drainage details the need for 24 hours of foul storage within the pump station in case power supplies fail. BS EN 752-6 gives general design guidance for package pump stations.
Klargester also offer the adoptable and high specification pumping stations designed to meet the requirements of ‘Sewers for Adoption 7th Edition’: On the 1st of October 2016, all pumping stations serving two or more domestic properties in England and Wales will become the responsibility of the Water Companies. Klargester pumping stations are completely prefabricated.

Private Drainage Options

If pumping effluent to the main sewer proves too difficult because it is too far away then sewage will need to be dealt with inside the boundaries of the property.
Sewage treatment plants (STPs) such as the Kingspan Klargester Envirosafe should be considered as the preferred, default solution; they provide an environment where aerobic bacteria can break down sewage and are highly efficient, treating more than 90% of the pollutants.
Gortnahown Housing, Envirosafe 005NOLOGO
Packaged sewage treatment systems with tertiary treatment such as packaged reed beds are the current ‘gold standard’, bringing the efficiency rating up to 98%. They produce a clear overflow that is environmentally friendly and suitable for discharging even on sensitive sites.
Effluent from an STP is allowed to discharge into a watercourse, but this is regulated and may require registration with the Environment Agency/Environmental Protection Agency.

Sizing a Sewage Treatment Plant

Commercial waste can vary from one site to the next in terms of flows, loading, and concentration of solids, ammonia and biological oxygen demand (BOD).
The British Water’s established Flows and Loads code of practice is invaluable reading for system designers, providing help in calculating daily sewage loading, plus advice on the nature of the sewage to be treated, and anything which may affect treatability and system performance.
If we consider a campsite scenario, then there are static as well as touring caravans, tents, as well as full and part time staff to consider.
Consideration should be given to systems such as Kingspan Klargester Envirosafe that can cope with low loadings and shock loadings as well as prolonged periods of shut-down.
pumpstor commercial horizontal
The sewage strength from the cocktail of detergents and chemicals in commercial applications demands a greater treatment capacity than a purely residential application. In such instances the Kingspan Klargester team can offer a free site visit to advise on the best possible treatment to meet your requirements efficiently and cost-effectively.
Leading specialists in the design and manufacture of complete off-mains solutions for 60 years, Kingspan Klargster not only manufacture the products but also work closely with regulatory authorities and industry bodies to ensure total compliance in every component design and installation practice. Highly qualified professional advisors provide free on-site assessment as well as advice on product selection and specification.

To book our CIBSE accredited CPD seminar ‘Guide to Sewage Treatment Plants’ go to www.kingspanenviro.com/CPD.

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