Al Dur SWRO plant: a double challenge for pre- and post-treatments

Abstract

The Al Dur Power & Water Company is a 2.1 billion USD gas-fired greenfield power generation and seawater reverse osmosis desalination plant that is located on the southeast coast of Bahrain. The company Degremont has been selected to design and build the Reverse Osmosis (RO) desalination plant, for a drinking water production capacity of 218,000 m 3 /day. The plant design had to answer to particularly challenging requirements, both for the pre-treatment and for the post-treatment steps. The pre-treatment step is one of the key factors for the success of desalination using the reverse osmosis process. Its purpose is to remove the major foulants, which can be found in the seawater to allow for a reliable operation of the reverse osmosis units. It is even more essential within the Gulf area, where the seawater contains high concentrations of organics and is subject to algal blooms. Al Dur RO plant was thus designed with an efficient two-step pretreatment process: a flotation step, including an enhanced coagulation stage, and a filtration step. In parallel, to assess the seawater variability and demonstrate the performances of the selected pre-treatment line, a pilot study was carried out on-site during one year. Al Dur drinking water objectives were particularly challenging and the design had to incorporate unusual guarantees such as a Silt Density Index below 3.0%/min, a turbidity below 0.2 NTU and a Langelier Saturation Index between 0.1 and 0.3. As a consequence, to comply with both the Bahraini drinking water standards and the tender specifications, the Al Dur mineralization unit design included a high velocity lime water saturator and a lime water filtration unit. The present paper describes the pre- and post-treatment performances based on the initial project design, the pilot study and the on-site results during the commissioning and the first few months of operation.