Technical and Economical Assessment Of Pretreatment Alternative Systems Associated with RO Desalination Plant

Abstract

Water is an integral part of live and has been always mankind’s most precious resource. The total volume of water on Earth is about 1.4 billion km3, 2.5 % only of the total volume is fresh water and 97.5% is salt water. By 2025, 1.8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world’s population could be living under water stressed conditions.A study by Trieb and Muller [18] pointed out that desalination may offer a solution to overcome water shortages in the MENA region [18&19].Reverse osmosis (RO) and Nano- filtration (NF) have long been utilized for desalination, softening and contaminants removal. Both technologies are manufactured, designed and built for ―salt‖ and dissolved ion removal and not particulate matter. Therefore, proper pretreatment plays a critical role in the performance, life expectancy and the overall operating costs of these systems. Consistent high quality pre-treatment of the feed water is one of the most important prerequisites for long-term successful operation of seawater desalination plants. In the present work technical, economic assessment, and comparison of viable alternative pretreatment systems, which may precede RO desalination is conducted with the objective to determine the most appropriate pre-treatment alternative. All alternatives are technically viable and produce adequate water quality for RO process. Pretreatment alternatives included units to prevent the growth of bacteria; fouling caused by suspended solids; disinfection units to disperse calcium carbonate and sulfates precipitates in order to avoid scaling; and de- chlorination units to prevent the presence of residual free chlorine. Every alternative is composed of several components. The capital cost and the operation & maintenance cost (O&M Cost) of each component are determined and compared. The determination of the capital costs as well operation and maintenance costs are adapted from the models given by Qasim [49].The Comparative Life Cycle (CLC) costing method is adopted to compare the total cost for an infinite horizon considering differ life span of the components and an applicable interest rate. The cost of different plant capacities (1,000, 5,000, 10,000 and 50,000) m3/d have been also estimated and compared up to the year 2050 using the CLC method for various alternatives.