Challenges in capital and operation cost reduction of reverse osmosis desalination process

During the last three decades, there has been consistent developments in seawater reverse osmosis (SWRO) desalination process. The energy consumption of seawater reverse osmosis (SWRO) desalination process has been successfully brought down by more than 50% since then. However, its energy consumption is still considered high and further investigations on energy intensive areas of SWRO plant are being carried out to make potable water production from seawater more affordable. Although some of the innovative technologies such as forward osmosis, membrane distillation, electrochemical desalination etc. have been tested successfully which may address the longstanding operational issues with conventional SWRO desalination process, these technologies have their own deficiencies and need further development for their use on a large production scale. On the other hand, the new improvements in the RO membrane, high pressure pumps and energy recovery devices have resulted in a steady reduction of energy consumption and other operating costs of the SWRO system. This trend of decline in operating cost of SWRO plants due to recent developments and an increase in cost of water produced by conventional processes due to stringent global regulatory requirements, are expected to keep a continued reliance of the potable water production on SWRO desalination plants. This paper presents various ways to improve key components of the SWRO system aimed at reducing energy consumption and capital cost. Major factors affecting specific energy consumption (SEC) in SWRO systems have been analysed, and possible strategies of energy optimization such as use of hybrid membranes, a three-centre design, high efficiency energy recovery devices (ERDs) etc. have been investigated along with an overall capital and energy cost investigation. For a 200 MLD SWRO desalination system, the capital and operating energy costs between a conventional SWRO system and a proposed energy efficient SWRO system have been calculated and compared in this paper.