6.4. Metrics for assessment of water management technologies
Now, as we have a long list and various scales of water treatment technologies, sustainability goals require their careful assessment in terms of environmental, economic, and social effectiveness. LCA analysis is a very common tool to select specific technologies for a particular sustainability system. Note that specific location, hydrological profile, and available infrastructure are pivoting factors in such assessment. LCA cannot be general - it has to be case-specific. Therefore, it would be best for us to consider a specific example that would describe LCA for a particular prospective water treatment technology.
The LCA study referred to below is on a novel membrane-based technology for drinking water treatment. It compares conventional existing practice with a new method using comprehensive lifecycle inventory for both and applying LCA software for data interpretation. This article is a good example to follow when designing an LCA project:
Bonton, A., Bouchard, C., Barbeau, B., Jedrzejak, Comparative life cycle assessment of water treatment plants, Desalination 284, 42-54 (2012). (Full version of this article is accessible via E-Reserves in Canvas.)
This article contains a significant amount of technical details and chemistry data, which some of you may find hard to digest. You do not have to understand it all - your goal will be to follow through the methodology and understand the main steps that lead to authoritative conclusions. While reading, pay attention to the following aspects:
- The goal for this LCA study
- Motivation to consider the new water treatment method. Was there a problem with the existing practice?
- What is "functional unit" and how it is chosen?
- Criteria (metrics) chosen for assessment
- Software used for the analysis
- Results and conclusions: Can you read and explain the diagrams?
This real-life LCA project shows that proper assessment requires a great deal of technical detail and a significant amount of data. As a matter of fact, the authors had to perform an autopsy of system components to enlist all included chemical components with their potential environmental impacts at the stage of system manufacturing. Furthermore, operational data have to be closely tied to the specific demographic and geographic setting and the scale of application.
An additional thought on LCA: The output of LCA is quantified environmental impact, so it is most effectively used to compare alternatives - different products, systems, technologies, or methods. It has much less value when performed for a single product or a single technology since, without a clear reference point (a baseline), it is hard to tell if the impact small, large, or catastrophic, if the alternative brings improvement or makes things worse. Zero impact is probably not a good reference because no such ideal technology possibly exists. LCA also allows identifying the relative magnitude of various impacts. For example, we can determine if there is a particular project has a higher contribution to greenhouse gas emissions or to soil contamination, etc. In turn, this would help direct the mitigation measures - actions to reduce impact by redesigning the system, improving the process, or searching for an alternative.
Here is another example of comparative LCA (in the form of a slide presentation), which is related to three wastewater treatment strategies. This reading is optional, but also provides you with a good illustration of the approach.
Lyons, E et al., Life Cycle Assessment of Three Water Scenarios: Importation, Reclamation, and Desalination (Arizona State University)
Check Your Understanding
Do you remember the main four stages of the technology lifecycle that are typically considered in LCA?
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1. Extraction of raw materials 2. Manufacturing 3. Operation / maintenance 4. Waste management / disposal
Do you remember the main four phases of an LCA project?
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1. Defining goal and scope 2. Life cycle inventory 3. Impact assessment 4. Interpretation of results