Waste water, or raw sewage, is water that drains from toilets, sinks, showers, baths, dishwashers, washing machines and liquid industrial wastes.
Raw sewage contain chemicals, biological contaminants, suspended solids and gases that must be removed before the water can be re-used or passed to a receiving environment such as the sea, rivers, lakes or canals.
A typical waste water treatment consists of 3 major stages:
- Primary – pre-treatment
- Secondary – sedimentation and aeration
- Tertiary – filtration and disinfection
Of these three stages, secondary treatment is the most crucial part as this is where aerobic bacteria is allowed to consume the organic matter in the sewage through a process called aeration.