4.1.1 Liquid wastes from residential areas

  • List three liquid wastes from your daily life.

  • I’m sure you thought of several. Examples include the wastewaters from washing your face in the morning, from washing clothes, from taking a shower and from washing dishes. You may also have mentioned human bodily waste, which is also classified as liquid waste.

In urban areas, the liquid wastes from residential areas are often referred to as domestic wastewaters. These wastewaters come from our day-to-day living and include those from food preparation, washing, bathing and toilet usage. As you read in Study Session 1, different terms are used to describe wastewater from these various domestic sources.

  • What is the difference between blackwater, greywater and sullage?

  • Blackwater is wastewater that contains human excreta (faeces and/or urine). Greywater is wastewater from activities such as washing and food preparation and does not contain excreta. Sullage is another name for greywater.

Blackwater and greywater are produced from domestic dwellings with access to a piped water supply and also from business premises and the various institutions, such as schools and health centres, found in residential areas. The term sewage is used to describe a combination of all these types of liquid waste, frequently also with surface run-off.

In many towns and cities in the world, sewage is collected in underground sewers that carry the effluents to a sewage treatment works (Figure 4.1). (Effluent is another term for wastewater that flows out from a source.) At the treatment works, the sewage is cleaned by various physical and biological processes before being discharged into a river or lake. It may be possible to reuse the treated water, typically for irrigation. (Sewage treatment is described in Study Session 6.)

Figure 4.1 Sewage entering a sewage treatment works.

The quantity and type of liquid waste generated in a residential area depends on several factors, such as population size, standard of living, rate of water consumption, habits of the people and the climate. It also depends on the number and type of institutions such as schools and health centres in the area.

4.1 Sources of liquid waste

4.1.2 Liquid wastes from commercial areas