(177a) Strategies for Reducing the Cost of RO Water Desalination

Desalination of both seawater and inland brackish water is currently being considered in various locations around the world, with a growing number of large-scale desalination plants in the planning and/or construction stages. In addition, desalination is being increasingly implemented in water reuse application, and RO desalting of agricultural drainage (AD) water is also being evaluated for reclamation and reuse of irrigation water. In order to reduce RO process energy consumption and decrease the volume of generated concentrate stream, product water recovery must be optimized while keeping the overall water production cost at a reasonable level. Accordingly, a multi-pronged approach to improving the efficiency of reverse osmosis desalination must be undertaken. In order to systematically assess the options for reducing the energy required for membrane desalination, a formalized theoretical framework was developed to evaluate options for minimization of energy consumption with and without energy recovery devices (ERDs), considering the impact of membrane cost and the cost of brine management. Such an approach is the basis for comparison of single versus multi-stage and two-pass membrane desalting including considerations of stream mixing and recycling. In addition to optimizing process operation and configuration, significant efforts have been devoted in recent years to improving RO membrane performance to attain additional reduction in water production cost. Examples of recent developments of advanced RO membranes will be discussed with a focus on the implications for improving the efficiency of membrane desalination and assessment of future membrane development needs. Additional reduction in the efficiency of RO desalination can also achieved via various improvements in process operability, including advanced control and real-time process optimization, in addition to the use of accelerated chemical demineralization for high recovery desalination. The above will be discussed and illustrated based on laboratory, pilot plant studies, as well as in a new advanced "smart" RO pilot system, with a focus on directions that could potentially lead to lowering the cost of RO water desalination.