Renewable energy powered reverse osmosis system for seawater desalination.

Abstract

Desalination is one of the most successful procedures for freshwater supply from seawater in the world. Reverse osmosis (RO) is a major technology in the business of seawater desalination because of its ability to produce excellent potable water of highest quality from the seawater source with low energy consumption compared to other technologies. Freshwater is a prerequisite for life and procreation. Water as an essential commodity is used in every phase of human life, ranging from domestic activities such as drinking, cooking, washing, etc., to innumerable industrial and agricultural purposes such as power generation. Today's increasing demands for freshwater by the world population cannot be met by the available fresh water in our ecosystem. This is why numerous technologies for seawater desalination have been established and advanced over the years to augment/satisfy the ever-increasing global demand for freshwater. One such technological development is the use of computer-based modeling for the design and system analysis of the RO treatment process for optimum performance. The hands-on modeling of an efficient full-scale reverse osmosis (RO) system may be daunting work due to the RO systems’ operating conditions which continually fluctuate due to cyclical variations in seasons and progressive fouling of the membrane during long-term filtration. The RO plants design, the cost of capital estimation (CAPEX), and operation expenses (OPEX) for large projects have become important factors for potential investors and consulting engineers to bear in mind for pre-construction planning and proper evaluation. This study reviews existing seawater reverse osmosis (RO) desalination protocols, covering key areas such as pretreatment, RO treatment, and post-treatment of seawater desalination for best performance, with emphasis on solar energy powered RO systems for seawater desalination. This study also models an RO desalination plant using ultrafiltration and IX polishing for feed water pretreatment and post-treatment respectively using the W.A.V.E. software program for design efficiency. The success of seawater desalination using RO technology is predicated upon an efficient feed water pretreatment and post-treatment regime. The use of an ultrafiltration system in combination with filtration has been tested and adjudged to generate excellent quality feed water for the RO system, notwithstanding the quality of the raw seawater. The model framework depicted in this study can serve as a guide for design engineers in providing effective tools for the design of an efficient RO system while maintaining an acceptable balanced hydraulic performance with considerable cost savings. For the experimental study, the physical experiment was conducted at the Victoria and Alfred (V & A) Waterfront Desalination Plant in Cape Town, South Africa. The experiment was aimed to investigate and quantify the effects of feed water temperature, pressure, salinity, and pH parameters on RO membrane elements. The raw data collected were processed and analyzed to establish the working principle of SWRO, and at the same time develop a relationship model based on the identified system parameters for a better understanding of SWRO operation. The modeling results are validated against the experimental result to evaluate RO system performance. This financial analysis covering capital expenditures CAPEX and operational expenditure (OPEX) of a traditional seawater reverse osmosis (SWRO) desalination plant was conducted. The key parameters involved in the determination of life cycle costs of seawater desalination were listed and analyzed. The parameters include water quality characteristics, production or plant capacity, location, energy consumption, materials, maintenance, operation, RO module costs, chemicals, and award year. For clarity, a 2 MGD SWRO plant was designed using WAVE software, and the design result was used to calculate the lifecycle cost of producing a unit (m3/d) of potable water in Lagos, Nigeria, deploying a curve fit approach and pertinent water economic analysis tools to develop a reliable life cycle cost for RO systems with acceptable levels of accuracy, based on verifiable and practical parameters