The energy demand associated with provision of sufficient and safe water is a real issue for water managers. Water and wastewater treatment and transport can account for up to 44% of a city’s municipal energy cost. Some have also reported that with population growth, urbanization, and stricter water quality standards, the energy associated with water and wastewater management may increase by an additional 20% by 2023.
The estimated carbon footprint associated with RO desalination ranges from 0.4 to 6.7 kg CO2eq/m3 (of water produced), whereas water reuse systems range from 0.1 to 2.4 kg CO2eq/m3. Ranges are primarily because of several study differences: geographical location, technology, life cycle stages considered, and estimation methodologies. For example, location not only impacts the quality of a source but also the distance to transport reclaimed water. Furthermore, regional energy grids differ in their carbon intensity.
RO technologies have lower CO2 emissions than thermal desalination technologies and the carbon footprint of seawater RO desalination (0.4–6.7 kg CO2eq/m3) was generally greater than brackish water RO desalination (0.4–2.5 kg CO2eq/m3) and water reuse systems (0.1–2.4 kg CO2eq/m3). Brackish water desalination also yielded a lower carbon footprint (0.4-2.5 kg CO2eq/m3) compared to seawater desalination (0.4-6.7 kg CO2eq/m3). Furthermore, the carbon footprint of RO systems with membrane pretreatment (e.g. ultrafiltration) (0.4-4.0 kg CO2eq/m3) is generally higher than RO systems with conventional pretreatment (e.g. granular media filtration) (2.3-2.5 kg CO2eq/m3) for seawater desalination.
Our study identified and critically reviewed 16 tools that can estimate carbon emissions from water reuse and desalination facilities. We compared the simplest tool that requires minimal data inputs (e.g. electricity consumption, electricity mix) to a more sophisticated tool that had greater input requirements (e.g. material production, chemical usage, fuel usage, electricity consumption, electricity mix). We then applied both tools to estimating the carbon footprint of a 26.1 MGD facility used for: 1) seawater desalination, 2) brackish groundwater desalination, and 3) water reuse. Results showed the estimated carbon footprint from the simpler tool accounted for 55–58% of the more data-intensive estimation tool. This difference demonstrates the simpler tool underestimates life cycle impacts that are included in the more comprehensive tool.
The paper is available here:
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This blog post was originally published on IWA Water Wiki on May 15, 2015.