Nature-based solutions - Sustainable water management

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Grey water reuse

Greywater (i.e. all produced household wastewater expect those from WC) are easily treatable with nature-based solutions, providing a big source of "new water" within a sustainable water management approach, also in line with the circular economy and the resource-oriented new paradigms.

Since the beginning of its activity, IRIDRA has proposed the separation fof blackwater and greywater, and the treatment of the latter with nature-based solution (constructed wetlands, roof wetlands, green walls), aiming both an outside (irrigation, pavement cleaning) and inside (WC flush tank filling) reuse of treated greywater.

Advantages grigie riuso pune web

  • water saving
  • reduction of wastewater to be treated by treatment plants
  • discharge of less dilluted wastewater, increasing the efficiencies of biological wastewater treatment plants

More information

Probably, the most relevant difference between grey and black water is the different degradation velocity of the pollutants. Black water, in fact, contains organic substances that have had one of the most degradation processes present in nature: the process of human gastro-intestine. Therefore it is easy to understand that residues of that process can't be rapidly decomposed in water, that is an inadequate environment for the microbial populations present in the residues. For example, in 5 days of biological degradation process, only 40% of organic matter has complete mineralization, while for grey water in the same period a removal of 90% is obtained. This rapid loss of organic matter in grey water can be explained with the abundance of sugars, proteins and lipids, easily available for bacteria.

Grey water compared with black water contains only 1/10 of total nitrogen and less than half of organic load.

After natural depuration treatment with constructed wetland, the treated grey water easily reaches quality standards that make it employable for toilet flushing or for other less noble uses (washing of squares, irrigation, etc). Moreover, black water separated from grey water are treated with more efficiency and fewer costs and can be reused for irrigation of garden or cultivated areas. In case of further separation of faeces from urines – by special urinators with low consume – urine can be directly used as fertilizer.


black grey water composition it

Source: SWAMP Project -

IRIDRA's experience

IRIDRA has several experiences in the design of nature-based solutions for greywater treatment and reuse. One relevant example is the constructed wetland for greywater treatment and reuse of the residential area in Preganziol (TV - Italy): the greywater reuse was only one of the intervention within a system of solutions for sustainable water management, including the installation of water saving devices and rainwater harvesting.

grigie riuso palestina oxfam  web

Separation, treatment with a constructed wetland, and reuse of greywater  from a Beduin village in Palestine. The treated greywater is reused for irrigation of olive trees and fodder. The nature-based solution was designed by IRIDRA, commissioned by the NGO OXFAM Italy, and funded by EU ECHO, FAO, and Sardinia Region

grigie riuso pareganziol  web

Horizontal flow constructed wetland designed by IRIDRA for the treatment and reuse of greywater produced by a residential area in Preganzionl (TV, Italy). Thre treated greywater is reused for toilet flushing.


IRIDRA's authors are highlighted in bold.

Conte G., "Nuvole e Sciacquoni", Edizioni Ambiente, ISBN 978-88-89014-76-9. 2008. Free e-book link.

Lindstrom Greywater: what it is…how to treat it…how to use it , disponibile su

Masi, F., Bresciani, R., Rizzo, A., Edathoot, A., Patwardhan, N., Panse, D. and Langergraber, G. Green walls for greywater treatment and recycling in dense urban areas: a case-study in Pune. Journal of Water Sanitation and Hygiene for Development, 6 (2) 342-347, 2016.

Masi F., El Hamouri B., Abdel Shafi H., Baban A., Ghrabi A., Regelsberger M. “Segregated black/grey domestic wastewater treatment by Constructed Wetlands in the Mediterranean basin: the Zer0-m experience”, Water Science & Technology, 61, 1, 97-105, 2010. doi:10.2166/wst.2010.780.

Scheumann R., Masi F., El Hamouri B., Kraume M., “Greywater treatment as an option for effective wastewater management in small communities”, Desalination and Water Treatment, 4, 33–39, 2009.