Ultrafiltration versus sedimentation-based pretreatment for seawater feed to RO plants: Environmental Impact Study

Abstract

Environmental considerations are the drive behind many recent process changes in desalination plants as different desalination technologies are associated with a number of environmental impacts. Commonly, the main contributors to these environmental impacts are energy consumptions and chemical usage. One tool to assess environmental impacts resulting from shifting from one design choice to another is by conducting Life Cycle Analysis (LCA) of all considered designs/systems. An LCA study considers all the environmental impacts associated with a product or system throughout its life cycle (i.e., from cradle to grave). Fouling is a common problem in Reverse Osmosis plants. This issue is usually addressed by pretreating the feed water. Pretreatment can be achieved using a combination of a number of physical and chemical processes. The choice of these processes depends, amongst other things, on the quality of feed water. The common factor, however, is that each process will still have its own environmental considerations. Traditionally, sedimentation-based pretreatment has been commonly applied. This involves coagulation, sedimentation, dual-media filtration, and microfiltration polishing, in addition to disinfection. Recently, membrane-based pretreatment, using ultrafiltration, has been gaining momentum. This process is marketed as a substitute for all the other stages of the sedimentation-based method, but at a lower environmental footprint. In this work, two alternatives for intake water pretreatment for fouling control were compared: sedimentation based and membrane filtration pretreatment. Standard LCA methodology, using a professional software package (SimaPro), was applied in this iii case study research, based on real data from the Fujairah-1 plant for the sedimentation based system and full design data for the alternative UF system, provided by XFlow®. By use of LCA, a comprehensive environmental modeling of the considered options for the above study was conducted. The pretreatment systems, including their components (e.g., equipment) and material and energy flows throughout their lifetime, were modeled. Environmental impacts of these systems, using alternative energy mixes, were also modeled. The findings of this work indicate that a membrane based pretreatment has a lower environmental impact, throughout the system’s life cycle, than the existing sedimentation based pretreatment in the Fujairah-1 desalination plant. This result holds under all alternative energy mix assumptions; including renewable, natural gas, oil, and nuclear energy. Our findings also show that the most significant contributor to the overall environmental impacts of both pretreatment systems is energy consumption.

Date of Award	Jun 2013
Original language	American English
Supervisor	Hassan Arafat (Supervisor)