Wastewater is used water from any combination of domestic, industrial, commercial or agricultural activities and any sewer inflow or sewer infiltration. It can contain physical, chemical and biological pollutants. Wastewater can be discharged through the sewerage system or be treated on-site. The main types of wastewater are:
- greywater – from showers, baths, hand basins, washing machines, laundry troughs and kitchens
- blackwater – for example, toilet waste
- sewage – a combination of greywater, blackwater and trade waste
- industrial wastewater – includes all waterborne waste except sewage. Industrial wastewater’s quality and quantity may vary significantly depending on the specific industry process and business size.
How wastewater can impact human health and the environment
Wastewater can contain microorganisms, bacteria and viruses that can cause disease. Contact with dangerous bacteria can cause skin, eye and nose infections or gastroenteritis (gastro or upset stomach).
Wastewater can also contain pollutants, including:
- suspended solids or sediment – soil, sand and other particles that can build up in waterways.
- microorganisms – organisms we can’t see that can spread disease (for example, harmful bacteria, virus, protozoa and helminth).
- chemicals and heavy metals – including industrial waste elements, or elements naturally present in the environment that can be harmful in large amounts.
- nutrients (Nitrogen and Phosphorus) – excessive nutrients in wastewater that enter a water body may lead to harmful algal blooms which impacts the water quality and releases toxins, resulting in fish kills. This limits the beneficial use of the water.
- water with too high or too low pH also presents a risk to the environment (biota) and human health when there is close human contact.
All these can impact water quality, harm plants and animals that depend on water and present risks to human health.
How to control risks from wastewater
The risks from wastewater should be properly controlled from the wastewater catchment, through to treatment, disposal and reuse.
Depending on the quality and quantity of the wastewater, site conditions and other considerations, wastewater may be collected in the following ways:
- By the sewerage system, with flow into a wastewater treatment facility, or
- Kept within the premises and then treated on-site, or
- temporarily stored and then transferred to a licenced facility for treatment.
After the wastewater is collected, it will be treated by different technologies depending on the quality and quantity of wastewater, site condition and the uses of the treated wastewater. Wastewater may be treated in the following ways:
- For domestic wastewater in an unsewered area, an on-site wastewater management system is used. This is regulated by local government according to the Code of practice – on-site wastewater management (publication 891).
- For a large-scale wastewater catchment, the duty holder should select the appropriate treatment technologies for the quality and quantity generated to achieve the required quality target for disposal and reuse.
Disposal and reuse
Wastewater treated to the required quality can be disposed to land, discharged to a waterway or coastal/ocean outfall, or reused on-site or offsite: