Blog Post

Black water and grey water treatment plants explained

Need of the hour- black water treatment plants and grey water treatment plants

There are millions of people who don’t benefit of the advantages of clean water. Meanwhile, about 90% of the waste water is produced globally remains untreated and eventually ends up in polluting the global waters. Therefore, it’s highly important to recover water. The best way to do that is through treatment plants.

Waste water is divided in two main domestic categories:

  • Black water
  • Grey water

Grey water

The waste water also called “grey water” is linked to washing and cleaning as it comes from baths, bathroom sinks, laundry or showers. It contains dirt, cleaning products and other pollutants. It has a low organic composition and an increased content of salt.

Black water

The sewage known as “black water” comes mostly from toilets, so it refers to water that was polluted with human or animal excrement or urine.

Black water contains extremely harmful materials, therefore it has to be treated before being released or reused, otherwise it could be a terrible source of diseases for humans and animals. Most of the time, black water reaches a municipal sewer systems and then ends up at a black water treatment plant where it can be treated and safely disposed of. If the systems are advanced enough, black water can even be recycled and used for agricultural crops.

Black water and grey water are usually treated separately through black water treatment plants and grey water treatment plants. The waste water treatment companies should build plants according to the type of waste water that needs to be treated.

Through black water treatment plants and grey water treatment plants, the waste water treatment companies aim to mimic the processes that normally occur in nature on an accelerated rate. So, the water that results from a treatment plant and that is poured into a river is safe enough to be released there. It will be very diluted of all its former constituents and the river itself could actually be considered a fourth stage of dilution.

Waste water treatment companies have to ensure that both black water treatment plants and grey water treatment plants are built to the highest standards and that they can be maintained easily.

If the black water treatment plants or the grey water treatment plants also disinfect the waste water, it can be recovered and even be used for irrigation.

The basic components of waste water management are the sewage system (represented by the municipal sewer system) and the actual treatment of the waste water.

Waste water treatment companies usually use the same steps to recover water using both black water treatment plants and grey water treatment plants:

  • After travelling through the sewage system, the waste water reaches the treatment plant.
  • An initial selection keeps big materials such as diapers or plastic from entering the treatment area.
  • The holding tanks for the waste water permit particles to settle to the bottom.
  • The floating materials at the top of the water such as oil, trash, grit or fat are skimmed.
  • In the second phase, oxigen is pumped in the waste water to separate sludge from water.
  • The water and sludge are treated separately.
  • The clean water can be released into rivers.
  • The adequate sludge, which only contains organic compounds, can be used as fertilizer.

Black water treatment plants recover water and reuse it for activities such as toilet flushing, irrigation, industrial purposes, washdown.

Grey water treatment plants recover water and use it again for activities like garden watering.

Treatment plants are highly important to recover water. The black water treatment plants and the grey water treatment plants allow water to be reused efficiently. Waste water treatment companies have to develop more and more plants to ensure the safety of the environment and the health of the communities.


Wettech Africa is a proudly African company specializing in all aspects of waste water treatment and management providing following main services : – Consulting – Design & Implementation – Operational Maintenance.

Visit our official website here:

You may also like
Sludge Treatment – An Achilles’ heel of the wastewater treatment plants
Wettech Africa – Expert Waste water treatment plant designers

Leave a Reply