Most of us flush the toilet without a second thought, but what happens to the wastewater if the property’s not connected to mains drainage?
There are several options available to homeowners:
Cesspits and cesspools
A cesspit or cesspool is simply a holding tank for receiving and storing wastewater from a property. The wastewater enters the cesspit where it remains until it is emptied by a vacuum tanker. As the cesspit merely holds the wastewater rather than treating it, the tanks tend to fill quite quickly resulting in the need for frequent emptying which can be costly.
Cesspits are usually only used as a temporary measure until the property is connected to mains drainage or because the Environment Agency doesn’t allow the property to discharge. Cesspits are typically viewed as the least desirable wastewater treatment system due to a number of unfavourable factors. As the cesspit receives all the waste from a property they have to be large enough to cope with this; the sizing criteria is based on a loading of 180 litres per person per day and must have the capacity to hold 45 days’ worth of effluent which inevitably leads to a large tank.
Septic Tanks
Septic tank systems store and minimally treat sewage and usually consist of a storage tank with two or three chambers to separate the solid and liquid waste. The chambers within the septic tank hold the sewage solids long enough to allow the solids to form sludge at the bottom of the tank and are designed to retain any floating matter.
The sludge is partially broken down through anaerobic digestion and the remaining liquid passes through the outlet to a soakaway drainage system. A soakaway system disperses this partially treated liquid (known as effluent) into a drainage trench where the pathogens, nutrients and organic material are dispersed into the gravel and are removed or neutralized as the liquid moves through into the soil.
The remaining sludge in the septic tank needs to be emptied regularly; the frequency of septic tank pumping depends on the amount of waste entering the septic tank and its size.
Sewage Treatment Plants
A sewage treatment plant is by far the best method of wastewater treatment. In a sewage treatment system, the wastewater enters the plant where it is treated, producing final effluent that is of a high enough standard, as set by the Royal Commission, to be discharged to a watercourse or groundwater.
Most home sewage treatment systems comprise a primary settlement chamber, biological zone and final clarification. Depending on which make and model you choose, these components could be in separate units, or enclosed in one.
Some systems have a primary settlement chamber where the raw solids separate from the liquor; the solids need to be periodically taken away by a tanker (tankered) and the liquor is then biologically treated. Other systems don’t have a separate treatment chamber, and the solids are continuously mixed in an aeration chamber with bacteria and oxygen to allow aerobic organisms to degrade the wastewater contaminants. This type of water sewage treatment also requires tankering, although to a lesser extent than one with a primary treatment chamber. Typically, a sewage water treatment system that has a separate primary treatment chamber has to be emptied of sludge (desludged) every nine to twelve months, whereas other systems that do not rely on primary tanks can have desludge intervals of between three and five years.
It’s clear to see why single unit wastewater sewage treatment plants are often viewed as beneficial over other methods of sewage treatment, which is why many residential sewage treatment plants are installed to replace septic tanks or are specified when a new property which is not connected to mains drainage is being built.