Last edited 08 Jul 2020

Black water recycling

Water.jpg

Water is an increasingly scarce resource. As the population increases, and climate change makes rainwater patterns less predictable, it is becoming more important that we reduce the amount of water we consume and discharge into the sewerage infrastructure. In addition, the treatment of water to make it suitable for drinking and other uses consumes a considerable amount of energy. Treating water to make it suitable for ‘drinking’ just to use it for purposes that do not require this level of treatment, such as watering gardens, washing cars or flushing toilets, is extremely wasteful.

Environmental concerns, utilities bills and the imposition of restrictions such as requirements for sustainable urban drainage systems and hosepipe bans mean that people are increasingly looking to re-use or re-cycle water.

Typically, water is categorised within one of three broad groups, with the degree of contamination increasing, and so the number of suitable uses decreasing and the treatment requirement increasing:

Despite this contamination, black water can be recycled and re-used. Typically this re-use is for applications such as watering landscape (although generally not crops) or for flushing toilets (Ref Thames Water, Recycled Londoners’ sewage keeping Olympic Park green). It is also possible, although expensive, to make black water suitable for drinking.

Recycling black water can:

However, it can be:

  • Expensive.
  • Difficult to manage and maintain.
  • There can be perception and stigma issues.
  • It requires a separate, clearly identified pipe network.
  • Long payback times combined with small storage volumes mean it can be less effective than other water-conservation measures.

It is possible to recycle black water at a domestic scale, but this is not common due to the expense involved, despite the fact that many remote domestic properties already have septic tanks to deal with sewerage locally. Generally, the process is only adopted on larger sites, or for multi-home developments.

Treatment is generally by a process of settlement, bacterial break down, filtration, aeration, and chemical treatment. This can include the use of reed beds. For more information see The Green Age, Recycling Domestic Sewage.

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