CONVENTIONAL PRETREATMENT SYSTEM FOR THE DOHA REVERSE-OSMOSIS PLANT - TECHNICAL AND ECONOMIC-ASSESSMENT

The conventional pretreatment method is widely used to treat surface seawater feed for the seawater reverse osmosis (SWRO) process; however, this method is cumbersome and costly and has many drawbacks that lead to higher product water cost by RO desalination technology. This paper outlines the experience gained from 65 months of operation of a surface seawater conventional pretreatment system at the Doha Reverse Osmosis Plant (DROP) in Kuwait. The paper describes the pretreatment system used, problems and drawbacks encountered during the course of operation, namely: instability of Silt Density Index (SDI) value, high rate of chemical consumption, high rate of water consumption for backwashing and high energy consumption, and gives an economic assessment for the pretreatment system. The economic analysis shows that the cost for the conventional pretreatment system accounts for 26.7% of the total capital investment cost for a 4,546 m(3)/d two-stage spiral-wound (SW) RO system, similar to the one used at DROP. A 30% saving in unit product water cost could be achieved if a beachwell intake pretreatment system is used instead of the conventional pretreatment system.