• Reduce GHG emissions
• Reduce energy needs
• Increase access to clean, affordable, and secure energy
• Proximity economy
• Increase technological readiness
• Better waste management
• Promote the materials cycle
• Better water quality
• Better water  management
• Improvement in soil health

Direct connection to technical solutions:

• Greywater and rainwater reuse at building level
• Efficient treatment and reuse of un-segregated water at building level

Technical aspects / infrastructure:

Waste to energy in buildings is implemented through different stages and with several (complex) technical requirements:

• Pre-treatment stage: (1) greywater/blackwater separation in place, (2) grinding equipment for bio-waste treatment in place, (3) homogenization system, (4) odour treatment and (5) space requirement for the waste pipes.
• Anaerobic Membrane Bio-Reactor (AnMBR) treatment: (1) Due to the weight of the AnMBR system the surface must be solid, flatten and levelled.
• Post-treatment stage: (1) Availability of a biogas storage system and a fuel cell for biogas valorisation as energy, (2) gas piping has to be installed underground and (3) Stabilisation of digestate for final use as fertilizer in local gardening.

Security:

Regarding security aspects, it is necessary to use ATEX electrical installations as the system contains gas storage with biogas (flammable gas).

Economic and social context:

The economic feasibility of this solution is strongly linked to the scale of the anaerobic digestion process, which will depend on the number of residents/tenants and the waste production. For renovation projects, it is necessary to find consensus in multi-owner buildings.

Regulatory framework:

The permit from local building authorities need to include a comprehensive safety and explosion prevention concept.

Technical:

Maintenance over long term, continuous monitoring (sensors, flowmeters and flow regulators, manometers, pressure sensors), periodic sampling and analytics.

Policy and regulatory/legal framework:

Compliance with current regulations regarding wastewater discharge, water reuse, management of wastes, sanitary requirements, and biogas security aspects:

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. In places where there is no possibility to connection to a sewage system, it is suggested to have two independent systems for food waste and blackwater.

EU Urban Waste Water Directive

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.

Waste to energy recovery is often done on a case-by-case basis, there is no standard solution due to very individual and site-specific boundary conditions, as well as the limited number of real-life case studies. This results in high efforts to plan, design and operate systems. Consequently, the engineering and instrumentation efforts and connected costs are relatively high compared to other energy sources.

Noise or odour generation due to the AnMBR treatment can also be considered as adverse impacts of the solution.

• HOUSEFUL Project: https://houseful.eu/solutions/blackwater-and-bw-treatment-for-biogas-production/
• Mengjiao, Gao, et al. (2020) High-loading food waste and blackwater anaerobic co-digestion: Maximizing bioenergy recovery. Chemical Engineering Journal, 394, 124911. https://doi.org/10.1016/j.cej.2020.124911

Indicators [1], [2]

• Removal of Chemical Oxygen Demand (COD): ≥ 90%
• Organic Loading Rate: 10 to 15 kg COD/m3d
• Biogas production 0.06 to 0.382 L CH4 / g COD
• Energy production from potential methane production ≤ 0.246 kWh/m3 CH4

Climate change mitigation:

Waste to energy solution leads to a significant greenhouse gas emissions on a lifecycle basis.

Circular economy:

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

• Local energy communities can implement this technology. https://netzerocities.app/resource-618
• Capacity building and training is required for manpower https://netzerocities.app/resource-1578
• 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

LEITAT building (HOUSEFUL Project). Waste to energy is implemented by a two-stage AnMBR to treat kitchen wastes from the catering and the blackwater generated in the office building.

Energy consumption: 800-900 kWh/m3 treated

[1] Kanafin YN, Kanafina D, Malamis S, Katsou E, Inglezakis VJ, Poulopoulos SG, Arkhangelsky E. Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review. Membranes (Basel). 2021 Dec 8;11(12):967. doi: 10.3390/membranes11120967. PMID: 34940468; PMCID: PMC8703433.

[2] Yisong Hu, Xuli Cai, Runda Du, Yuan Yang, Chao Rong, Yu Qin, Yu-You Li, A review on anaerobic membrane bioreactors for enhanced valorization of urban organic wastes: Achievements, limitations, energy balance and future perspectives, Science of The Total Environment, Volume 820, 2022, 153284, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2022.153284.