Frequently asked questions about sewage treatment plants and ‘off-mains’ drainage systems

Whether you’re ready for a new sewage treatment plant installation or just wondering how often to service your current model, the topic of ‘off-mains’ drainage can be confusing.

 Here at Marsh Industries we are always happy to answer any questions you may have regarding sewage treatment plants and off-mains drainage. So if there is anything you would like to ask us, please do not hesitate to get in touch. However for your convenience and peace of mind Marsh Sales Director, Nigel Swallow, answers a list of frequently asked questions that should allay any concerns you may have.

What is sewage treatment?

Sewage treatment is the physical, chemical or biological process of removing contaminants from wastewater or sewage from domestic, commercial or agricultural properties. Its objective is to produce an environmentally safe fluid waste stream (or treated effluent) and a solid waste (or treated sludge) suitable for disposal or reuse.

The majority of urban houses in the UK are linked to the public sewerage system: you pull the plug, flush the toilet, pay the monthly bill and have little more to worry about. This is known as ‘mains’ drainage.

In rural areas many homes and villages as well as caravan parks, lodges and holiday homes are self-contained – the sewage flows to a treatment plant, septic tank or cesspool. This has no connection to the public sewerage system and is known as ‘off-mains’ drainage.

What are the UK and European standards for sewage treatment plants?

BS EN 12566:3 is the highest testing standard for sewage treatment plants.

The Marsh Ensign:Ultra and Ensign:Standard range of sewage treatment plants is tested and certified to BS EN 12566:3. Published test results of 11.5:19.2:8.4mg/ltr (BOD:suspended solids:ammonia), with influent concentrations on test higher than those chosen by most competitor plants, effectively equates to 97% pollutant removal. These successful test results mean the Ensign range is well within national consent requirements and can discharge directly to a drainage field or surface water.

Are sewage treatment plants expensive to run? …Should I look at a non-electric bio-system?

Not really. The power of a Marsh Ensign six-person plant is 60W. This means the running cost is approximately £52 per annum.

Bio-systems are normally designed with a very deep outlet, which means a pump must be fitted. This has a higher running cost than that of a sewage treatment plant compressor.

Some bio-systems require a large/separate primary chamber. They also need full concrete surrounds, which bulks up the installation costs. The layers of media in a bio-system also need cleaning more regularly.

Why should I buy a sewage treatment plant? …Does it smell and is it noisy?

The Marsh Ensign range of sewage treatment plants is one of the most economic, efficient and environmentally friendly systems on the market.

As long as the plant is installed correctly, the system is virtually odourless and operates near-silently.

Backed by a 25-year structural guarantee, Ensign sewage treatment plants are extremely energy efficient and normally only require 30 minutes of annual maintenance. Our six-person Ensign sewage treatment plants are extremely robust and are only 1.95m in depth with an inlet invert of 500mm, reducing both the time and cost of installation. In normal ground conditions the unit simply requires a pea-shingle surround.

Will an unsightly lump or cover be showing in my garden where my domestic sewage treatment plant will be installed?

Provided that your sewage treatment plant has been specified and installed correctly, there should be no unsightly lump in the ground.

Compressor housings and lids can be visible, however they are usually green, brown or black to blend with the surrounding environment. Acoustic housings are available to further reduce noise generated by compressors. These can be positioned up to 10m away from the sewage treatment plant.

Where should a sewage treatment plant be installed?

For guidance, ideally a sewage treatment plant should be positioned 7m from a dwelling or 10m from a stream.

Can I install a sewage treatment plant into my driveway?

Yes. The Marsh Ensign sewage treatment plant can be adapted so that it can be installed under a vehicle driveway.

What is a pumped outlet?

A pumped outlet is required where there is no natural fall of gravity from the outlet pipe. The pump allows the effluent to be directed to a higher level.

The Marsh Ensign design allows easy access for pump fitting, meaning a separate pump chamber may not need to be installed, saving both money and installation time.

My drain is deep. Can I still connect up to a sewage treatment plant?

Yes. Invert risers which cater for deeper inlet connections up to a further 1 metre can be fitted to a Marsh ensign sewage treatment plant.

What is desludging?

Desludging is the process of removing sediments by draining and cleaning a tank.

Sewage treatment is an on going process and microorganisms within the chambers must stay healthy for the system to work. Systems should be desludged regularly (usually annually or in line with manufacturer instructions) to prevent the build-up of sludge and solids and to ensure sewage flows freely through the unit. It is recommended that not all sludge is removed as it can also act as an anaerobic seed.

Is there a sewage treatment plant suitable for multiple dwellings or industrial sites?

Yes. Marsh Ensign sewage treatment plants are designed for both domestic and commercial properties, which are off-mains with no access to the main sewer network. Marsh Industries manufactures sewage treatment plants up to 500+ persons. These can be in single or multiple tank configurations.

Are Marsh sewage treatment plants structurally sound and fire safe?

Structural integrity tests, performed in accordance with EN ISO 179-1/1eA: 2010-11 have been undertaken to evaluate the strength of Marsh Industries’ GRP materials against similar GRP materials used by other manufacturers. Results proved Marsh GRP material to be 40% stronger than the other materials tested.

Fire resistance testing has been performed to assess ignitability of products subjected to direct impingement of flame. Marsh Industries’ GRP material passed all practical testing to achieve EN ISO 11925-2:2010 standard.

Check out the performance specifications and read what the installers and merchants say about Marsh sewage treatment plants at www.marshindustries.co.uk/unrivalled

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