Life Cycle Assessment for Tertiary Wastewater Treatment and Reuse versus Seawater Desalination

Abstract

Wastewater reuse is now indispensable for meeting the increasing water demand, particularly under conditions of alarming water scarcity, which is now already affecting every continent. The objective of this study is to apply life cycle assessment (LCA) to evaluate the environmental impact and missed opportunity of treating municipal wastewater to tertiary quality and compare it to conventional seawater desalination in the Gulf Corporation Council (GCC) countries, namely: Multistage flash distillation (MSF), multi-effect distillation (MED) and seawater reverse osmosis (SWRO). The study follows the ISO 14040/44 standards and uses a functional unit of 1 Mm3 of tertiary treated effluent (TTE). The modeling concept adopts the cradle-to-gate consequential paradigm. The life cycle inventory is based on fielded data collection, reports, literature and Ecoinvent database processes. The scope includes: infrastructure, grid, materials, energy requirements, chemical additives and sludge disposal; for primary, secondary and tertiary treatment. The life cycle impact assessment is applied on both the characterized and normalized levels using the ReCiPe method. Compared to distillation, TTE exhibits an average reduction of 94% in fossil depletion. For climate change and particulate matter, an average reduction of 79% and 73% can be realized respectively. The large difference is due to energy consumption in desalination, despite that fact that the energy considered is only the allocated portion to distillation in the cogeneration total, using exergy specific power consumption.