Septic tanks are a crucial part of on-site wastewater and effluent disposal and treatment, and are an important component of public hygiene by keeping the environment free from pathogens in sanitary waste. Their use spans both small residential and commercial installations, although the practicality of single-unit septic tanks is highly skewed in favor of smaller residential dwellings.
Before constructing any structure that will have human occupants, it is necessary to work out the sanitary waste disposal, treatment, and recycling mechanisms as part of the initial structural design. Septic tanks constructed on-site may have a relatively lower initial investment cost compared to other sanitary waste disposal mechanisms. It should however be noted that this cost is wholly dependent on the size and complexity of the said system.
What is a Septic Tank?
A septic tank is a relatively large chamber used to collect, and in some cases, treat and recycle effluent and semi-solid human waste. Septic tanks are constructed with T-type inlets and outlets, with a set of internal separators or baffles and accesses called manholes. For small residential units, a single septic tank can therefore be divided into three separate internal chambers using these baffles. Most septic systems use gravity, although some systems serving larger premises such as commercial properties and gated communities can be emptied using mechanical pumps.
The size of the septic tank will depend on the number of users generating effluent, for example, single residential units with separate tanks and commercial properties will have differently sized tanks. The amount of daily waste generated by each person must be calculated to obtain the size requirements. Septic tank systems must also have a means of waste removal or recycling. For single-unit residential dwellings, the method of treatment may be to pump out the waste using a vacuum pump to another designated area or collector. For larger installations such as gated communities, malls, and industrial facilities, it would be more practical to treat the waste onsite and dispose of the treated waste in a leachate field, or recycle it.
The constituent waste inside a septic tank is separated by baffles into blackwater and solid sludge or scum; the former is transmitted to a leachate field while the solid scum or sludge can be pumped out. This leachate must be treated first before being disposed into the environment, otherwise, it may have a detrimental effect on the groundwater in the area. Other secondary forms of effluent treatment include disposal into wetlands, soak pits, anaerobic filters, etc.
Considerations When Building a Septic Tank
Septic tanks can be cast on-site using concrete, or they may be prefabricated using concrete or plastic and installed once the earthworks excavation is completed. The method chosen wholly depends on the available budget and the builder’s intent. The amount of space available for construction is crucial for the tank design as not all dwelling units have sufficient space to construct a septic tank. An alternative to this would be to build a septic tank below the dwelling as a basement, although this would in effect increase the earthworks costs.
The traditional system of connection for a septic tank is a building sewage pipe outlet, connected through a manhole with the septic tank. The septic tank is then connected to an external disposal system such as a leachate field or a vacuum pump collector. The simplest types of septic tanks usually provide manhole covers that can be removed and a vacuum pump inserted to eject the indigestible waste and black water.
It is important in the plumbing design of the building to separate grey water and black water and to not allow greywater to enter the septic tank. Greywater, simply put, is any water generated that isn’t from toilets. Similar to stormwater, greywater can be disposed of directly into the environment as it doesn’t contain harmful solid waste.
