Mittuniversitetet

Emergy analysis and socio-ecological principles were used for sustainability assessment in a wastewater treatment case study. A constructed model of a microalgae wastewater treatment plant (ALGA), assumed located in Sweden at latitude 60°N, was tested by comparing it to a conventional three-step treatment plant (WWTP), and a mechanical and chemical treatment plant complemented with a constructed wetland (TP+CW). Based on the results from the two assessment methods the ALGA model were considered having a better position for sustainable development, than the other two. In emergy terms the ALGA model had about half the resource use of the other two alternatives, the highest relative use of local free environmental resources, and the best emergy sustainability index (ESI). The violation against the 2nd and 3rd socio-ecological principles were considered equal for the three alternatives. The 4th was estimated to be in favour of the ALGA model, and the 1st principle was calculated to be in favour of the ALGA model with about 8 times lower indicator value. This paper focus on the methods used in the case study. The performance of the methods is compared, including a discussion on how they relate to the concept of sustainability. The two methods were developed from very different starting points, and use different assessment parameters. Regardless of this, the ranking of different options comes out identically, indicating that both methods are equally useful for assessments of sustainability in the studied system.