Needed seawater reverse osmosis pilot plant in Qatar

Abstract

Seawater reverse osmosis (SWRO) is the most cost-effective, practical, and widely used desalting system. Its energy consumption, for Arabian Gulf seawater conditions is in the range of 5–6 kWh/m3. These are less than 1/3 of the equivalent mechanical energy of the thermal desalination systems presently used in Qatar. Besides, these thermal systems consume 2–4 kWh/m3 for pumping. Therefore, using SWRO system in Qatar can save up to 75% of the desalination energy cost. For Qatar, current desalting water production using thermal methods is 480 Mm3/year at $0.1–1.2/kWh energy price; the energy cost is at least one Billion US dollars per annum. A SWRO pilot plant is to be built in Qatar prior to building a full size desalting plant (DP) in order to determine site-specific treatment guidelines and to provide a full range of performance information to be used in the design of a full-scale plant. The pilot plant will be tested when the feedwater quality is good, and when there are major storm events or algae blooms exist. Red tide events in 2008–2009 forced many DPs in Gulf Co-operation Countries area to shut down. This paper reviews the SWRO pretreatment process, which depends on local conditions and is the main factor affecting the SWRO reliability. These include the extensively used conventional pretreatment of coagulation–flocculation and granular media filtration (GMF). This is almost necessary for open sea intake. Sever red tide blooms, when occur, cause clogging of GMF, resulted in biological and organic foulants on SWRO membranes, and even DP shut down. So, low-pressure membranes such as ultrafiltration (UF) or microfiltration (MF) can replace or integrated with GMF. Since flotation is more robust than sedimentation (used in GMF) in dealing with high concentration of suspended matter, dissolved air flotation is started to be used as pretreatment. Since it is a new method that met success in several plants, it thoroughly reviewed in this paper when integrated with GMF or membrane treatment. Additionally, the expensive pretreatment with UF and MF is discussed with given examples. Preliminary experimentation with SWRO pretreatment in Qatar was presented. Moreover, energy recovery devices to be used with the pilot SWRO are discussed. Membranes configuration and the equipment to be included are also outlined.