Greywater Recycling in Buildings
By Erwin Nolde, Nolde & Partners
Wastewater is a resource and segregating wastewater into its different streams, e.g. blackwater and greywater, can contribute towards a holistic water management strategy. Greywater recycling is one effective tool to improve the efficiency of water use in buildings and urban environments.
Water and energy are closely linked. Water saving is energy saving. The water sector is considered to be the largest municipal energy consumer. As an example, a city like Berlin with 3.5 million inhabitants requires for its water sector as much electrical energy as the household electrical energy demand for a city with 280,000 inhabitants (http://www.bwb.de/content/language1/html/7198.php).
Today, we find several decentralised greywater recycling systems operating at high-level and providing high-quality service water (non-potable water), which is made available for applications which do not mandatorily require a drinking water quality. Some systems even show a higher level of efficiency than centralised municipal ones. In addition they exhibit lower energy and maintenance expenditure without the use of any chemicals. However, it must be guaranteed that users of greywater recycling systems do not suffer any hygienic risk or loss of comfort. In Germany, the hygienic quality requirements which regulate service water use in buildings are based on the EU Directive for Bathing Water (EU Directive 2006/7/EC) and have proved reliable since over 20 years (http://www.stadtentwicklung.berlin.de/internationales_eu/stadtplanung/download/betriebswasser_englisch_2007.pdf).
In addition to saving energy and water and in turn reducing the water and energy bills, water recycling systems exert less negative impact on the environment. The amortisation period of these systems can be several years dependent on the local water and energy costs.
Low-energy houses and passive buildings are also milestones when it comes down to reducing the indoor heating demand. What remains largely ignored is that most of the thermal energy released today into the environment is via wastewater rather than through the building’s facade. An integrated approach such as combining greywater recycling with heat recovery from greywater would further increase the efficiency of the entire system. The heat energy recovered from greywater can be used to pre-heat drinking water for the generation of hot water in the building, thus saving on energy and improving the overall system’s efficiency.
Well planned greywater recycling systems can contribute considerably to water and energy savings and it is advisable that no new buildings should be planned today without a dual-pipe system for water recycling.
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