Selection of pretreatment technologies for seawater reverse osmosis plants: A review

Seawater desalination using reverse osmosis (RO) process has increased substantially in the recent past and is expected to grow at an increasingly rapid pace in the future. Successful operation of a seawater reverse osmosis (SWRO) plant depends on the ability of the pretreatment system to consistently produce adequately treated filtered water for the subsequent RO process. Both conventional (e.g., conventional/lamella sedimentation, dissolved air flotation, granular media gravity/pressure filtration) and membrane-based pretreatment processes (e.g., microfiltration, ultrafiltration) have found practical application worldwide. Although most of the currently operational pretreatment systems are conventional, low-pressure membrane based pretreatment systems are increasingly being considered for future plants. Thus, selection of conventional versus membrane based pretreatment is increasingly becoming difficult. Both water quality perspectives and non-water quality based criteria (ease of operation, facility footprint, construction costs, operating costs, economy of scale, design specifications, contractual agreements, etc.) need to be critically reviewed to make a prudent decision. This paper provides a critical review of both conventional and membrane-based pretreatment technologies by presenting water quality issues impacting their performances, critical design characteristics and their impacts on pretreatment selection, non-water quality based selection criteria, and a conceptual decision matrix for selection of pretreatment technologies for site specific conditions.