Weighted score ratios (WRS) give transparent weighting in multicriteria sustainability assessments - A case study on removal of pharmaceutical residues from wastewater.

Sustainability assessment using multicriteria analysis (MCA) is a structured way of including criteria from the three sustainability dimensions (environmental, economic, and social) when comparing different alternatives. A problem with the conventional MCA methods is that the consequences of the weights given to different criteria are not transparent. Here, we amend the simple additive weighting MCA method with weighted score ratios (WSRs), which are used during the sustainability assessment to show how the weights affect the valuation of the criteria (e.g., cost per kg CO2e). This enables comparisons to other sustainability assessments and reference values from society, which increases the transparency and can make weighting more objective. We applied the method to a comparison of technologies for removal of pharmaceutical residues from wastewater. Due to growing concern about the effects that pharmaceutical residues can have on our environment, implementations of advanced technologies are increasing. However, they entail high requirements of energy and resources. Therefore, many aspects must be considered to make a sustainable choice of technology. In this study, a sustainability assessment was performed of ozonation, powdered activated carbon and granular activated carbon for removal of pharmaceutical residues at a large wastewater treatment plant (WWTP) in Sweden. The outcome showed that powdered activated carbon is the least sustainable choice for the studied WWTP. Whether ozonation or granular activated carbon is most sustainable depends on how climate impact and energy use are valued. The total sustainability of ozonation is affected by how the electricity is assumed to be produced, whereas for granular activated carbon it depends on whether the carbon source is of renewable or fossil origin. Using WSRs allowed the participants in the assessment to make conscious choices on how they weighted different criteria in relation to how these criteria are valued in society at large.

A collaborative planning process to develop future scenarios for wastewater systems.

Wastewater infrastructure has a long lifetime and is subject to changing conditions and demands. When plans are made to upgrade or build new infrastructure, transdisciplinary planning processes and a robust analysis of future conditions are needed to make sustainable choices. Here, we provide a stepwise collaborative planning process in which future scenarios are developed together with local stakeholders and expert groups. The process was implemented at one of the largest wastewater treatment plants (WWTPs) in Scandinavia. With a combination of workshops and the use of a web-based digital tool, future scenarios including flows, pollutant loads, and treatment requirements could be created. Furthermore, sustainability prioritizations affecting the WWTP, were identified. The future scenarios developed for the WWTP in the case study, predict stricter and new regulations, constant or lower future loads and ambiguous future flows. The highest ranked sustainability priority was low resource and energy consumption together with low CO2 footprint. The quantified future scenarios developed in the planning process were used as input to a process model to show the consequences they would have on the WWTP in the case study. Applying this collaborative process revealed future scenarios with many, sometimes conflicting, expectations on future WWTPs. It also highlighted needs for improvements of both the collection system and the WWTP.