A quick scan tool for the evaluation of the environmental impacts of wastewater treatment plants

Abstract

Sustainable development is gaining importance in the water sector. The evaluation of environmental impacts in the water sector asks for a holistic approach, in which all relevant factors are taken into account. Drinking water company Oasen is developing such a holistic model, named the Water Sustainability Diagram (WSD). This model evaluates the environmental impacts resulting from activities of Oasen. In order to evaluate all environmental impacts in the water cycle, wastewater treatment plants (WWTPs) should be included. For that reason, the aim of this research is to develop a quick scan tool that is able to evaluate the environmental impacts of WWTPs while meeting Oasen’s preconditions: (I) the quick scan tool is made in Microsoft Excel, (II) gathering of data and setting the input of the quick scan tool can be done in one day and (III) the quick scan tool should score the impacts based on indices from zero to five. Consulting review papers and life cycle assessment (LCA) studies are the starting point for identifying relevant environmental impacts and corresponding indicators. Complementary expert consultancy was conducted. The identified environmental impacts that the quick scan tool evaluates are: (I) climate change, (II) receiving water quality, (III) local nuisance and (IV) various impacts based on life cycle assessment (LCA) methodology. The corresponding indicators are (I) CO2-eq. emission, (II) Water Pollution Index (WPL), (III) local nuisance and (IV) ReCipe scores based on chemical use. To assess whether the quick scan tool can produce truthful results while meeting all of Oasen’s preconditions, four case studies are modelled: WWTPs Kralingseveer, Ammerstol, Soest and Amersfoort. Only WWTPs Kralingseveer and Ammerstol could be fully evaluated, but only some minor adjustments in evaluating the environmental impacts in sludge treatment are required to ensure all existing WWTPs could be evaluated. The quick scan tool largely meets Oasen’s preconditions, yet a definitive scoring system has not been developed for the CO2-eq. and ReCipe scores. Although a full validation of the results was not possible, due to the structure and calculations in the quick scan tool it is expected that the environmental impacts are evaluated truthfully when the input data is reliable. However, in the evaluation of direct N2O emission, which can be a considerable part of the total CO2-eq. emission, uncertainty remains. No scientifically sound method for evaluating N2O emission has been identified, therefore it is recommended to further research for this. The quick scan tool’s value is questionable for non-existing WWTPs, because estimation of input parameters will most likely cost a considerable amount of time and decrease its reliability compared with actual data. This applies especially because the parameters in the quick scan tool are modelled as if being independent from each other, while in reality they are at least partly (co)dependent. The emergence of new technologies or future changes in WWTPs will therefore be difficult to evaluate with the quick scan tool. Two other drawbacks are, firstly, the lack of expertise Oasen has on WWTPs, which makes them fully dependent on collaboration with others (e.g. water boards) and, secondly, the arbitrariness of the local nuisance and half of its magnitude is most likely not distinguishable between case studies. In conclusion, although that the quick scan tool is in itself not (completely) new for science, especially in the evaluation of impacts on climate change and ReCipe scores, it is a tailor-made quick scan tool that evaluates the most important environmental impacts of WWTPs in a quick manner. It can be fully integrated into the WSD with only few adjustments, yet Oasen should be aware of the quick scan tool’s limitations.