Life Cycle Assessment of a seawater reverse osmosis plant powered by a hybrid energy system (fossil fuel and waste to energy)

Abstract

With the rapid increase of the human population and the concomitant increase in freshwater demand, pressure on this natural resource is increasing. One of the approaches used to overcome water scarcity in several parts of the world is desalination of brackish or seawater. Coupling seawater reverse osmosis (SWRO) with renewable energy (RE) is an active research area and understanding the environmental impact of these integrations using Life Cycle Assessment (LCA) is one of the tools available for the selection of sustainable water supply options for remote communities. This study uses LCA to assess the feasibility of integrating a SWRO with a hybrid energy system to meet the water needs in a remote community. The RE is supplied via electricity generated from biogas produced from the anaerobic digestion (AD) of the organic fraction of municipal solid waste. A 4500 m3/day SWRO plant was designed using WAVE software to satisfy the water demand of a small/medium town in a remote area in Lebanon. The biogas plant sizing was performed using HOMER Pro and different renewable percentages were tested. Biogas characteristics were taken from an existing organic waste AD plant in Lebanon. Based on the available mass of solid waste, the maximum achievable renewable fraction required to operate the SWRO was found to be 60%; the remaining electrical demand was supplied from the grid. The LCA was performed using Simapro Ph.D. version 9 to quantify the environmental impacts of this integration. IMPACT2002+ impact assessment method was used. Results show that using AD to power desalination is viable from an environmental perspective and achieves significant reductions in many categories when compared to conventional fossil fuels. Furthermore, increasing the renewable fraction in the hybrid energy system results in further reduction in the environmental impact. In particular, a 60% reduction in global warming potential was observed compared to conventional fossil fuels. However, for some categories, the impact increases upon increasing renewable fraction particularly for categories related to toxicity, eutrophication and acidification and this is mainly attributed to digestate application on land, highlighting the need for digestate enhancement. Accordingly, the system can be further improved by increasing the amount of waste collected and transformed and adopting a more site-specific design.