Two main categories of wastewater sources are generally noted, namely:
- Domestic - Wastewater from domestic households include that originating from the use of the toilet and from baths, showers, sinks, dishwashers, washing machines, etc.
- Industrial - Many industries are reliant on the use of water for operations (cooling systems, etc). Industrial wastewater (or effluent) is often a by-product of these operations and must be handled and treated accordingly. Some industries discharge these wastewaters directly to municipal sewer systems, whilst other industries treat their wastewaters on-site for discharge/disposal or reuse. Industries that may impact on wastewater quality thereby increasing the challenge to treat wastewaters include: power generation, mines, metal production, oil refining, abattoirs, breweries, soft drinks, wine making, laundry, textile, tanning and leather finishing, sugar, paper and pulp.
In addition to the above two general types, infiltration/inflow and stormwater may contribute to wastewater flows.
Wastewater is normally characterized in terms of its physical, chemical and biological composition. Contaminants of concern in wastewater treatment include:
- Suspended Solids - Can lead to sludge deposits and anaerobic conditions.
- Biodegradable Organics - Can lead to depletion of oxygen leading to septic conditions.
- Pathogens - Cause disease.
- Nutrients (Nitrogen/Phosphorous/Carbon) - Can lead to growth of undesirable aquatic life.
- Priority Pollutants - Inorganic and organic compounds which are carcinogenic, mutagenic, etc at very low concentrations.
- Refractory Organics - Include surfactants, phenols, pesticides, etc and are generally not removed via conventional wastewater treatment methods.
- Heavy Metals - Are toxic at low levels and are undesirable in treated sludge to be reused for beneficial purposes.
- Dissolved Inorganics - May need removal if wastewater is to be reused (e.g. irrigation - salinity)