Environmental assessment of municipal wastewater discharges: a comparative study of evaluation methods

Abstract

Wastewater treatment plants produce high environmental impacts on receiving water bodies and pose economic burdens on municipalities or industrial facilities. Their overall operational costs and achieved effluent quality depend very much on the influent type, presence of priority pollutants, treatment technology and required effluent quality (for discharge or for recycle/reuse). Life cycle assessment (LCA), environmental impact quantification (EIQ) and water footprint (WF) are important instruments for sustainability assessments applied for products, production and consumption evaluations in connection with natural resources depletion and pollution threats. This study focuses on the environmental assessment of a municipal wastewater treatment plant (MWWTP) discharges by means of these three evaluation methods with the purpose to understand their (methodological) weak and strong points in capturing the impacts. Such a comparative analysis is necessary to understand how the (individual) advantages provided by each of these instruments can be complimentarily used to improve an assessment framework for various stakeholders concerned with water use cycle management (regional water operators, water management authority, public authorities, research entities, societal organizations, etc.). The three assessment methodologies (LCA, EIQ, WF) are presented, implemented and critically analysed based on a unitary set of data concerning the MWWTP of Iasi city (a municipality of approx. 300,000 inhabitants situated in the North Eastern region of Romania), the wastewater and river water quality indicators as well as all the other relevant data being collected for the year 2012. Although the three methodologies have different principles for environmental impact quantification, the results have shown that most impacts induced to surface waters due to Iasi MWWTP effluents are given by the nutrients (nitrogen and phosphorous compounds), which could induce an eutrophication impact, and to a lesser extent by pollutants responsible for toxicity impacts (such as heavy metals). Based on the results of this comparative study, a critical analysis of these three methods was realized by considering the data requirements, their development and integration status. Furthermore, the strong and weak points that are relevant for each method implementation and their subsequent use by decision-makers and Water Authorities are discussed, in the context of legislative requirements (including the Water Framework Directive), actual development of regional water operators and stakeholders' interests.