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Sewage Treatment Options
Sewage treatment - options for rural properties which conform to the current UK regulations
As you can see, there are several different types of sewage treatment systems - package units, septic tanks and cesspool tanks, where NO biological wastewater treatment takes place.
Cesspools and cesspits provide no sewage treatment. NO biological treatment occurs and the tank has no outlet. They are simply huge sealed underground tanks where all the wastewater from a property is stored until it is emptied by a tanker.
The MINIMUM size allowed for a one bedroom house is 18,000 litres.
Cesspools need emptying by a licenced waste disposal tanker contractor, and must have adequate capacity to store a minimum of 45 days sewage production. Approval to install a cesspool is required from the Local Authority under the Building Regulations. They will generally only allow one as a temporary measure, i.e. if mains drainage is planned for your village fairly soon. They are NOT allowed in Scotland or France.
Septic Tanks
A Percolation test will be required to determine whether or not the ground will absorb the liquid efficiently and remove the pollutants. If the ground cannot accept the liquids properly (i.e. CLAY ground is NOT suitable) then it is probable that the soakaway will become blocked very quickly and the system will fail. In any case, septic tank soakaways do not usually last longer than 10 years as the porous ground becomes blocked with slimy black biomatt and made waterproof by sodium binding. The septic tank should be emptied at least annually.
These type of domestic sewage treatment systems comprise of a small electrically driven packaged plant, usually all contained in a single tank. The sewage is first settled to remove the gross solids (which are not aerobically digested),and then the liquid effluent is biologically treated in a filter bed, or by rotating disc media, or by air injection, with a final settlement stage to remove the fine solids. The treated wastewater effluent can be discharged to a land drainage system or watercourse, (subject to Local Authority and Environment Agency Consents). Maintenance, (which can be expensive) and emptying of the plant to remove the settled gross solids, will be required at regular intervals. This is usually annually for a single dwelling domestic sewage treatment plant and 2 to 6 monthly for a multiple dwelling unit, as the settlement tank is comparatively smaller in multiple house units.
There are numerous variants of packaged wastewater treatment plant available on the market as these are the oldest and most common types
Modern Extended Aeration Wastewater Treatment Plants.
These biological sewage treatment plants digest the gross solids and liquids together in the first compartment via air injection. There are no gross solids to remove, as the units recycle them back to the digestion chamber via gravity, so the units achieve about 97% reduction in pollutants and up to 90% reduction of viruses The effluent can be discharged into a land drainage system or a watercourse, subject to the necessary consents.
Maintenance of these treatment plants is cheap and the plants only require emptying about every 3 to 5 years ( even for 5 house units) to remove surplus micro-organisms and inorganic solids such as soil and grit.
The tanks include Crystal, DM series and Condor. (The Balmoral CAP extended aeration wastewater treatment unit does not recycle and requires emptying at the same rate as traditional units)
These new generation sewage treatment systems have the cheapest running costs as they use no electricity for the process and only require an annual service. They are the most sustainable plants in the UK.
The liquid is split from the solid waste in the pre-filter tank (or existing traditional septic tank if one is available) and the wastewater is biologically filtered using natural stone fibre material and natural air draft in the BIOROCK plant.
The effluent quality is superb; far better than from electric treatment plants.
Reed Bed Sewage treatment
In our experience, you should only consider the Vertical flow reed beds when following a septic tank. We have seen many cases where the effluent coming out of a horizontal flow reed bed, (designed by a firm of ‘expert reed bed designers’) following a septic tank was considerably WORSE than the effluent which went in! As our local Environment Agency officer told me - a reed bed was his first successful pollution prosecution!
Reed Beds
The vertical flow beds nearly always require electric pumps which are expensive to run, although the system can be operated without power, if an adequate fall is available across the site.
Horizontal flow reeds beds can successfully follow sewage treatment units as a tertiary treatment but should never be considered as an answer to cleaning septic tank effluent.
Reed Beds are NOT a ‘fit and forget’ item and the wastewater treatment system requires considerable maintenance, e.g. harvesting and composting the reeds in the Autumn, re-planting, weeding, etc. and annual emptying of the septic tank. They can also smell and act as a breeding ground for flies and mosquitoes, so should not be situated close to dwellings. Children and pets must be kept away from reed beds as they will be paddling in dangerous sewage effluent. All reed beds should be fenced. Consent to Discharge is required from the Environment Agency. Contact us for a correct sewage treatment design according to your site.
