The eco-efficiency assessment of wastewater treatment plants in the city of Mashhad using emergy and life cycle analyses

The aim of this study is to evaluate the sustainability of two actual wastewater treatment plants using the eco-efficiency index based on emergy and life cycle analysis. The life cycle analysis is used for environmental investigation to estimate the eco-efficiency index. Moreover, the emergy theory indicating the input and output flows of the ecosystem are applied to assess the sustainability considering ecosystem services. Two treatment plants are studied in the city of Mashhad in Iran. The potential for sustainability improvement of plants is analyzed in some scenarios including the production of agricultural compost from sludge, 10% reduction of energy consumption, and 10% reduction of chlorine consumption. The eco-efficiency index based on life cycle analysis determines KhinArab plant with 10% reduction of energy consumption as sustainable alternative. While the eco-efficiency index based on emergy analysis as well as emergy sustainability index introduce Al-Teymour treatment plant with installation of a composting unit as the most sustainable option. The no-action costs play a major role in the interpretation of results. The methodology and the results of this study will be of great interest for wastewater treatment plant managers and water authorities as well as citizens to increase the sustainability of water cycle in the city. (C) 2019 Elsevier Ltd. All rights reserved.