A septic tank is designed to provide what is known as primary biological treatment to crude sewage produced in a normal domestic environment. It retains solids and allows them to settle out, where they can be partially broken by biological action so that only the remaining liquor is left to flow down the outlet drain. This liquor (normally called effluent) is then sufficiently treated to soak into the ground in an underground distribution system.
A Continuous Aeration Plant (CAP), is desigfned to provide full tratment to crude sewage in a normal domestic enviroment. The CAP teats sewage to a higher standard than a septic tank, but does no offer the same degree of control available from a Sequential Batch Reactor (SBR) The standard of effluent discharged from a CAP is such that it does not need to be passed through a soakaway and can be discharged directly to a watercourse.
The Sequential Batch Reactor is designed to provide full biological treament to crude sewage prodeuced in a nomal domestic enviroment. These units are normally installed in sutuations where there is no public sewer and where a septic tank or CAP is not enviromentally acceptable. The SBR treats the effluents to a very high standard (normally to 15mg/litre suspended soilds and 10mg.litre BOD) which is suitable for discharging directly into a watercourse.