• Better water management
• Reduce GHG emissions
• Reduce energy needs
• Promote the materials cycle
• Better waste management

Direct connection to technical solutions:

• Greywater and rainwater reuse at building level
• Waste to energy (co-digestion) at buiding level
• Multi-level green walls/ green façades 
• Constructed wetlands

Technical aspects / infrastructure:

The efficient treatment of un-segregated water in buildings is implemented through a complex serial stages and with several technical requirements:

• Separation of liquid/solid fraction of wastewater: equipment for the separation of wastewater (for example, a chamber tank). Dimensioning and depth according to legal requirements based on the inflow volume of person equivalent (PE).
• Treatment of liquid fraction with NBS (constructed wetlands and multi-level green walls/ green façades): NBS to be built on the appropriate facing wall orientation (southern). A compost heater can be implemented to optimize the biological activity, together with temperature control, humidification through automatically controlled systems or plant-based air-filter for air purification.
• Post-treatment using commercial O3/UV hygienisation.
• On the other hand, the space requirement for the water pipes and green walls/façades or the land availability for the wetlands needs to be considered. Safety measures to prevent leakages in all the installations, especially the ones which carry wastewater in any form (chamber tank, pressure pipes, sewer pipes, etc.)

Project governance and implementation modalities:

A common governance challenge is the lack of a clear construction and maintenance responsibility, as a multi-stakeholder participation and agreement is typically needed. This also has implications for the financing of the project (real estate, capital and maintenance expenditures). The multi-disciplinary nature of these schemes (ecology, hydrology, engineering), as well as the limited availability of monitoring data from case studies, make design and implementation more challenging - thus considered riskier compared to traditional engineering approaches.

Social context:

For renovation projects, it is necessary to find consensus in multi-owner buildings.

Technical:

Maintenance over long term, continuous, periodic sampling and analytics (physico-chemical and microbial parameters).

Policy and regulatory/legal framework:

Compliance with current regulations regarding wastewater discharge, water reuse, management of wastes or sanitary requirements:

The EU Water Reuse Regulation. The requirement of periodic sampling is a barrier (logistically, financially, etc.) for using on-site or decentralised water treatment systems.

EU wastewater discharge regulation. Obligation for sewage disposal and connection to the municipal sewage treatment plant.

Taxes and charges for building permits can be a barrier for further implementation.

Social:

Need of end-user engagement (tenants and residents) in renovation projects and their concern about noise or odour generation or the potential increases of the renovation costs, and thus, rents.

Wetlands are typically associated with the emission of GHG, particularly methane. A comparative life-cycle assessment should be carried out with alternative traditional engineering measures to assess contributions to net-zero [1].

• HOUSEFUL Project: https://houseful.eu/solutions/efficient-treatment-and-reuse-of-un-segregated-water/
• http://en.puxintech.com/domesticbiogasplant
• https://sites.google.com/a/alamsantidesign.com/alamsantidesign---copy/permaculture-developments/wastewater-management

Air quality: The plants are able to absorb polluting substances.

Green space management: NBS increase the green areas and create new little ecosystems.

Potential of economic opportunities and green jobs: This NBS creates new value chains including implementation and maintenance jobs.

Indicative KPIs: Water reuse: 95%. For other KPIS, see:

• Green walls and green façades: https://netzerocities.app/resource-174
• Constructed wetlands: https://netzerocities.app/resource-1378

Climate change mitigation:

Multi-level green walls/ green façades increase thermal insulation in the building and therefore reduce the use of energy in air conditioning and heating.

Constructed wetlands: GHG emissions, particularly methane (eq tons CO2);

Circular economy:

Reclaimed water reuse can be a major benefit for garden or agricultural irrigation, toilet flushing, street cleaning, etc.

• One-stop-shop for building renovation https://netzerocities.app/resource-1913
• Instruments for incorporating innovative solutions in public procurement: EU Briefing on Innovation Partnerships:
• https://ec.europa.eu/docsroom/documents/47178

HOUSEFUL Project demo-sites:

Residential building El mestres (Sabadell, Spain): The building consists of eight residential floors with two flats per floor. It is adjacent to an educational centre and was initially intended as a teachers’ residence. The building has become increasingly disused over recent years and all 16 flats need deep refurbishment. The refurbishment project foresees the implementation of the multilayer façades.

Residential building Ronda Arraona, 30 (Sant Quirze del Vallès Spain): It was constructed in 2002 and it consists of 30 residential units of rental social houses distributed in 3 blocks. The refurbishment project foresees the implementation of green façades.

Cambium Community Center Kasernstrasse 2, (Fehring, Austria). A former military barrack built in 1960. The refurbishment project foresees the implementation of the water purification system.

Houseful project. Green façades (left) and water purification system (right).

[1] D. de la Varga, I. Ruiz, J.A. Álvarez, M. Soto, Methane and carbon dioxide emissions from constructed wetlands receiving anaerobically pretreated sewage, Science of The Total Environment, Volume 538, 2015, Pages 824-833, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2015.08.090.