Septic Tanks are for domestic sewage disposal where connection to the mains is not possible or practical.
The tanks are designed to meet both the installation requirements and the standard of discharge specified by BS6297:1983
Septic Tank Systems
Septic Tank Sewage Treatment Systems treat sewage at its location, rather than transporting the sewage to a sewer system or larger treatment system nearby. Because many septic tank systems throughout the country are not functioning properly, various laws havw been passed to help prevent the serious enviromental and human health problems that they can cause.
Several regulations have set requirements for minimum treatment standards, new construction and replacement of systems. Therefore if your are not sure your system is or will be in compliance, check with your local building inspector or building control office.
Types of Septic Tank Systems
There are various types of septic tanks systems. The most common type consists of a underground tank of differing sizes, which then connects to a soil treatment system, usually a land drainage system or drainfield, a mound or an at-grade system.
Septic Tanks How Do They Work?
Untreated wastewater from a property flows into the septic tank, where the solids separate from the liquids. Some solids such as soap scum or fat, will float to the top of the tank to form a scum layer. Heavier solids such as human and kitchen waste, settle to the bottom of the tank as sludge. Self forming bacteria in the tank help the system digest these solids and sludge. The remainaing liquids flow out of the tank to a land drainage system or drainfield. Baffles built into the tank hold back the floating scum from moving past the outlet of the tank. Even though the bacteria process will break up alot of the solids, it is recommended that the septic tank tank is pumped out annually, dependant on use, so that solids do not wash out into the soil treatment system. Solids can clog the soil and limit its ability to properly treat the septic tank effluent(What is effluent? - effluent is the liquid that passes through the septic tank).
Many older septic tanks comprise of two rectangular chambers, usually built in brick or stone. The inlet pip into the first chamber ends in a dip pipe which travels down at least 450mm (18 inches) below top water level, whilst the chamber is a minimum of 1500mm (5 feet) deep from the top water level. The dip pipe is usually 110mm (4 inch) minimum and has a vertical pipe for rodding. The outlet pipe from the firt chamber also consists of a dip pipe but the bottom of the pipe is a minimum of 300mm (12 inches) below top water level. The inlet pipe into the second chamber also end in a dip pipe which travels down at least 450mm (18 inches) below top water level, whilst the chamber is a minimum of 1500mm (5 feet) deep from the top water level. The dip pipe is usually 110mm (4 inch) and has a vertical pipe for rodding. The second stage chamber also consists of a dip pipe but the bottom of the pipe is a minimum of 300mm (12 inches) below top water level.
There should also be a vent pipe from the first stage chamber and preferably the second stage as well to vent any gasses that rise from the sludge, to atmosphere. Suitable covers should always be placed completely over a septic tank capable of withstanding an adult’s weight, and to avoid children / animals falling into the tank. (Sometimes it pays to have light duty covers over the tank and to place a lockable strap over the covers.)
Most of Septic Tanks are made in GRP or other suitable stable materials. They are commonly spherical (onion shape) in shape with a narrow shaft at the top to ground level. These tanks have built into them several baffles which will perform the same function as the dip pipes and separate out the heavier solids to the
How it works
A septic tank is the most economical solution where connection to mains drainage is not available. In a septic tank, household wastewater is stored allowing solids to settle to the bottom. Bacteria digest these solids, which reduces their volume. The excess liquid remaining after this process is then discharged to the drain field.
Septic tanks can be used on their own where there is sufficient land available for an adequate drain field. Such tanks partially treat the sewage and rely on the soil in the drain field to continue the treatment process.
A septic tank may not always be suitable for your site. A septic tank may not suit when:
- Soil condition is poor
- There is proximity to watercourses
- There are building regulation factors.
A wastewater treatment system may then be required to provide enhanced treatment performance.