This paper describes seawater reverse osmosis processes, reviews the technologies used to minimize energy consumption and contrasts their efficacy. It also examines the role of energy recovery devices in improving the energy efficiency of high pressure water application beyond desalination.

Keywords: desalination, seawater, energy, ERD, ERI

1 INTRODUCTION
Water scarcity is recognized as a significant problem throughout the world. Yet the demand for fresh water continues to grow, driven by the need for drinking water to satisfy the world’s growing population, changing weather patterns, an increasing need for water for agriculture and industry and the concentration of populations in urban areas that lack sufficient fresh water resources. Humanity now uses more than half of the available surface fresh water on earth. In 2003, the United Nations Population Fund predicted that global consumption will increase by 40% by 2025. A study conducted by the International Water Management Institute projects that by 2025, 33% of the population of the developing world will face severe water shortages. The uneven geographic distribution of fresh water supplies compounds this problem; at least 300 million people live in regions that already have severe water shortages. By 2025, the number could be 3 billion.

Existing water resource infrastructures are being strained in many regions, in part because of changing weather patterns and surface water availability.