Post-treatment design of seawater reverse osmosis plants: boron removal technology selection for potable water production and environmental control

A decision support model for the selection of treatment preferences for permeate polishing is presented. The model is based on the analytical hierarchical process that integrates multi-criteria issues into the selection of post- treatment technology for a specific seawater reverse osmosis (SWRO) plant. The objectives in using this decision-supporting tool are several, including the poor experience of the decision-maker with respect to the technology to be purchased, the high number &both qualitative and quantitative attributes that have to be considered in the selection process, and the number and variety of the alternative technologies available on the market. This paper introduces methodologies that rank the design options, provide recommendations based on permeate quality and process design, and improve the quality of information for the selection of boron removal treatment. The tool provides appropriate design guidelines for the impact of post-treatment on design and operation of SWRO plants prior to pilot and economic studies. The advantages of this approach are discussed in general terms while a specific example is presented for the Mediterranean Sea basin (Israel).

The production of cost-effective permeates in SWRO desalination is becoming more common as a way of achieving sustainable water usage. The design of a cost-effective boron reduction unit to achieve a desired permeate quality can be very difficult, as a large number of treatment options is available. This process is further compounded by the many criteria that need to be considered in the selection of a course of action. This study demonstrates the possibilities and appropriateness of using AHP for selection of an optimal post-treatment method and provides a systematical decision making framework with several characteristics: (1) the importance of different performances of treatment systems can be evaluated using multiple criteria--both quantitative and qualitative -- rather than profitability alone, (2) the use of ratings makes it possible to evaluate the applicability of different alternatives for the end-user, (3) the use of the AHP method provides an effective way of documenting the management process, and (4) the proposed approach forms the basis for a continuous process of planning and managing technology selection so that the priorities of the treatment processes can easily be modified and updated. The work demonstrates that the AHP method can be useful in the field of adequate post-treatment process selection. The work presents the variability effects of process variables and shows how the AHP technique points out the importance of one criterion: waste disposal. This characteristic is of direct scientific and engineering concern and provides useful explanations for analysis of post-treatment performance and selection.