Wastewater Treatment Plant and Biological Wastewater Treatment Options
Wastewater treatment plant options for biological wastewater treatment, which conform to the current regulations.
As you can see, there are several different types of wastewater treatment systems - package units, septic tanks and cesspool tanks, where NO biological wastewater treatment takes place.
The cost of running the various domestic systems varies enormously, as can be veiwed when you click the costs hyperlink.
1. Cesspools/Cesspits 
Cesspools and cesspits do not treat sewage. 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.
Cesspool systems must be regarded as a last resort as they are VERY expensive to run. The tankerage charges for a family of four are in excess of £9,000/year and it can be very difficult, if not impossible, to sell a house if it has cesspool drainage.
Typical Cesspool Costs for a single house installation
2. Septic Tanks
Septic Tanks are the traditional method of sewage disposal in rural areas.
They settle and partially digest (anaerobically) the settled sewage. They offer very limited biological sewage treatment system 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 wastewater into a soakaway system of land drains after the tank, which allows the ground to provide further treatment via soil bacteria, although it will kill any soil fauna in the vicinity. Septic tank effluent is extremely polluting.
Details of how the ground may be used for this partial sewage treatment are contained in BS 6297:2007.
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.
A consent to discharge is not required for discharges to ground over 2 cubic metres (10 persons) per day. New installations larger than this do require Consent and this is very difficult to obtain now for most soils and only granted for very small developments. The final effluent CANNOT be discharged to a ditch or watercourse and MUST go for further treatment by the soil to a properly designed soakaway. This is designed after full soil percolation testing results have been obtained and must be constructed in accordance with the regulations. Think carefully before installing a septic tank as a wastewater treatment plant is always the better option.
Typical Septic Tank Costs for a single house
3. Wastewater Treatment Plants
There are three main types
Traditional three stage Wastewater Treatment units. See PRODUCTS
These type of domestic wastewater 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 of unit, e.g. Klargester, Balmoral, Pureflo, etc.
Modern Extended Aeration Wastewater Treatment Plants.
These biological wastewater treatment plant 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)
Filter Wastewater Treatment Plants 
These wastewater 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 from these plants; far better than from electric models.
4. Reed Bed wastewater treatment
Reed Beds achieve very variable results as regards biological 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 reed varieties. 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 Prohibition Notice! You also have to consider your strategy when the reeds are dead during the winter.
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!
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. Consent to Discharge is required from the Environment Agency . Contact us for a correct design according to your site.
Wastewater Treatment Plant and Systems
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