Renewable Energy Driven Small-Scale Sea Water Reverse Osmosis Desalination Systems: A Survey

Abstract

EditorialIn recent years, water and energy constitute two of the most important concerns of the worldwide agenda. These resources comprise essential commodities for the preservation of life on Earth and the human survival. At the dawn of the 21st century, there are more than 2 billion people without access to fresh water [1]. Taking into consideration that 97% of the earth's water comes from the oceans, an attractive solution to the lack of potable water is seawater desalination [2]. The main desalination processes are the thermal and the membranes ones. The membrane processes, such as electrodialysis and primarily reverse osmosis (RO), have been implemented not only on desalination but generally on water treatment and now have more global acceptance than thermal processes [3]. RO is a process where the feed water enters a semi-permeable membrane under pressure, larger than the osmotic pressure, and the membrane produces fresh water and concentrate solution [4].Water separation processes such as desalination require energy to produce fresh water and the minimum theoretical energy for desalination is 1.06 kWh/m 3 [5]. However, desalination plants consume higher amounts of energy per unit volume of fresh water produced. The continuous increase of the fossil fuels prices and their environmental impact as compared to the advantages of renewable energy and corresponding renewable energy systems (RES), makes the combination of RES with desalination units a sustainable and economically viable solution [6]. There are numerous studies for desalination plants powered by renewable energy technologies such as RO desalination units using solar energy, wind energy and thermal energy. Most of them focus on the quantity of the water production from the desalination unit with the aim to minimize the specific energy consumption (kWh/m 3 ) and the total investment cost. Research on Stand-Alone SWRO Desalination PlantsIn the past two decades, various SWRO desalination systems were developed in many areas in the world such as islands and regions, which face significant shortage in drinking water supply. Most of them use energy recovery devices (such as pressure exchangers and turbine systems) in order to reduce the energy requirements of the RO plant since more than 90% of the input energy to a RO desalination system is wasted in the brine line. Excellent results have been attained with regard to the specific energy consumption when small-scale SWRO desalination units are combined with energy recovery devices [7]. Specifically, a small-scale SWRO desalination unit with energy recovery device can present more than 80% reduction in its energy consumption compared to a same conventional desalination system (without energy recovery device) [8]. Historically, SWRO desalination systems were designed and developed for steady power input (nominal load operation). However, various studies have shown that lower specific energy consumption can be reached when a SWRO desalination unit operates at variable load conditions (over a range of input...

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“…RO is a process in which the feed water enters a semipermeable membrane at a pressure greater than the osmotic and the membrane separates the fresh water from the concentrate solution. In addition, sea water reverse osmosis (SWRO) desalination is, by far, the predominant desalination technique today [9]. SWRO desalination is a process of high energy consumption due to the high pressure required to produce fresh water [10].…”

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“…A sustainable solution to potable water shortage is water desalination powered by renewable energy [2]. Reverse osmosis desalination has the widest global acceptance and has been implemented not only for sea or brackish water desalination, but also for waste water treatment [3].…”