Black water recycling
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:
- Fresh, potable water or ‘drinking water’ is sometimes referred to as ‘white water’.
- Wastewater from showers, baths, washbasins and washing machines that is not considered to be potentially dangerous is referred to as ‘grey water’.
- Water from toilets that may be contaminated with hazardous material is referred to as ‘black water’ (or sometimes brown water, foul water, or sewage). Some definitions of black water also include water from kitchen sinks, dishwashers and waste disposal units which may contain food particles.
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:
- Reduce water use.
- Conserve energy and reduce utilities bills.
- Reduce loads on local sewerage systems.
- Contribute to sustainability standards such as LEED.
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.
[edit] Related articles on Designing Buildings
- Filtration.
- Flood and Water Management Act.
- Green roof.
- Greywater.
- Greywater recycling at the Millennium Dome.
- Hosepipe ban.
- Marine energy and hydropower.
- Passive water efficiency measures.
- Planning for floods.
- Rainwater harvesting.
- SuDS - is there light at the end of the tunnel?
- Sustainable urban drainage systems.
- Types of water.
- Waste water.
- Water consumption.
- Water engineering.
- Water quality.
[edit] External references
Featured articles and news
Ministers to unleash biggest building boom in half a century
50 major infrastructure projects, 5 billion for housing and 1.5 million homes.
RIBA Principal Designer Practice Note published
With key descriptions, best practice examples and FAQs, with supporting template resources.
Electrical businesses brace for project delays in 2025
BEB survey reveals over half worried about impact of delays.
Accelerating the remediation of buildings with unsafe cladding in England
The government publishes its Remediation Acceleration Plan.
Airtightness in raised access plenum floors
New testing guidance from BSRIA out now.
Picking up the hard hat on site or not
Common factors preventing workers using head protection and how to solve them.
Building trust with customers through endorsed trades
Commitment to quality demonstrated through government endorsed scheme.
New guidance for preparing structural submissions for Gateways 2 and 3
Published by the The Institution of Structural Engineers.
CIOB launches global mental health survey
To address the silent mental health crisis in construction.
New categories in sustainability, health and safety, and emerging talent.
Key takeaways from the BSRIA Briefing 2024
Not just waiting for Net Zero, but driving it.
The ISO answer to what is a digital twin
Talking about digital twins in a more consistent manner.
Top tips and risks to look out for.
New Code of Practice for fire and escape door hardware
Published by GAI and DHF.
Retrofit of Buildings, a CIOB Technical Publication
Pertinent technical issues, retrofit measures and the roles involved.
New alliance will tackle skills shortage in greater Manchester
The pioneering Electrotechnical Training and Careers Alliance.