2. Septic Tanks    

A Septic Tank system settles and partially digests (anerobically) the settled sewage. They provide very limited sewage treatment and the effluent from a correctly sized tank still contains about 70% of the original polluting matter. This pollution can be further reduced by discharging the liquid into a soakaway system of land drains after the tank, which allows the ground to provide partial sewage treatment via soil bacteria, although it will kill any soil fauna in the vicinity.  Details of how the ground may be used for this partial sewage treatment are contained in BS 6297:1983. Percolation tests 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 usully last longer than 10 years as the porous ground becomes blocked with solids and slime. The septic tank should be emptied at least annually. A  consent will be required for a new installation and this is very difficult to obtain now for most soils and only granted for single houses .  The final effluent CANNOT be discharged to a ditch or watercourse and MUST go for further treatment by the soil to a prroperly designed soakaway.  This is designed after full soil percolation testing results have been obtained and must be constructed in accordance with the regulations.  Please see the Environment Agency link on the previous page for more information. 

 These systems provide a very good standard of sewage treatment.

There are two main types

Traditional Packaged Sewage Treatment units  

This type of sewage treatment system 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 liquid 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 sewage treatment unit 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 sewage treatment plants available on the market as these are the oldest and most common types of unit, e.g. Klargester, Titan, Clearwater, Balmoral, Camtech, etc.

Modern Extended Aeration Sewage Treatment Units  

These 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 sewage treatment units 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 Diamond.  (The Balmoral CAP extended aeration sewage treatment unit does not recycle and requires emptying at the same rate as traditional units)  

4. Reed Bed sewage treatment  

Reed Beds achieve very variable results as regards sewage treatment. They usually comprise of a septic tank to remove gross solids, followed by either vertical or  horizontal flow, specially prepared reed beds of specifically reared reeds. They MUST be designed by a specialist, as they are NOT just 'an area of reeds before the ditch', which we have seen on many an occasion, usually as a result of our being called in due to an Environment Agency Phohibition Notice!   In our experience, you should only consider the Vertical flow reed beds when following a septic tank.   We have seen cases where the effluent coming out of a horizontal flow reed bed, (designed by an ‘expert’) following a septic tank was considerably WORSE than the effluent which went in!  The vertical flow beds usually require electric pumps,  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.  Reed Beds are NOT a ‘fit and forget’ item and require considerable maintenance, e.g., harvesting and composting the reeds, re-planting, weeding, etc. and annual emptying of the septic tank.  They can also act as a breeding ground for flies and mosquitoes, so should not be situated close to dwellings.  Consent to Discharge is required from the Environment Agency.  Contact us for a correct design according to your site.