Reticulated sewerage systems (network of pipes) carry sewage from homes to modern sewage treatment plants. Treated water from these plants is either reused or released into the environment.
The pipes in your home are generally made of UPVC plastic or iron and the underground drains would probably be made of clay or UPVC plastic. These underground drains would lead to a reticulation sewer that carries the sewage to the nearest sewage treatment plant.
Treatment processes for sewage can be grouped under four headings:
- Physical processes relying on gravity or mechanical assistance to separate solids and gases from water.
- Chemical processes relying on chemical reactions to convert dissolved or tiny particles of suspended solids to solids that can be physically separated; or to oxidise or reduce impurities.
- Biological processes relying on bacteria which can convert dissolved and very fine solid impurities to more bacteria and gas.
- Land Treatment processes relying on components of each of the previous three groups.
All of these processes remove solids from the sewage in the form of sludge. The more efficient a sewage treatment process is, the greater the amount of sludge it will produce.
Most, if not all, the previously noted treatment processes only remove some of the disease-causing pathogens from the sewage. Final disinfection is needed prior to disposal to kill any remaining pathogens.
Although not all the processes described here are carried out by us, they have been included as they are used in many large sewage treatment plants.