Seawater Desalination Technology Trends
Extracted from Desalination Technology Trends
As the Earth’s population continues to grow and develop, are limited fresh water resources become increasingly scarce, fortunately that the oceans offer an alternative and can provide a sustainable supply of potable water.The most significant trend in seawater desalination technology is the increased growth of the reverse osmosis, Nowadays membranes are more efficient, more durable, and much less expensive, Improvements in membrane technology are complimented by improvement in pre-treatment technology, which allow RO membrane to be considered on a much wider range of applications.
RO system uses a semipermeable membrane, by pressurizing the feed water, the high pressure would be able to force water separate into two streams; a high-quality product stream, and a highly concentrated “reject” stream. By using modern membranes and pressures as high as 1000 psi, it is possible to produce potable water from seawater in a single pass.
Not only have membranes become more efficient at rejecting salts and other particles, improvements in manufacturing techniques have reduced production costs and resulted in higher quality membranes with improved durability. It has been estimated that for the same capital investment spent on seawater desalination in 1980, 27 times more water can be produced by today’s systems.
Seawater desalination energy costs are directly related to feed water salinity and can represent more than one third of a seawater desalination system’s operating cost. There are a number of design considerations that can significantly reduce a system’s specific energy consumption?
Nowadays energy recovery devices can recover increasing amounts of energy from the concentrated, and reuse the pressure to new feed water. it can reduce energy requirements by 10-50%. Further energy cost reductions may also be available by negotiating favorable off-peak or “interruptable” power rates with a local electrical provider.[/vc_toggle]
The design complexity and operation of a large-scale RO plant is not significantly different than that of a smaller plant, and economies-of-scale can contribute to a considerable reduction in the cost of water production. Development and permitting costs are much more dependent on siting-related issues than they are to a plant’s production capacity.
The inherent modularity of RO systems is an important consideration when planning very large desalination plants and there is no theoretical or design size limit for RO systems. Larger systems are able to use larger, more efficient pumps and energy recovery devices contributing to the lower energy/operating costs of the systems.
Prior to 1998, most SWRO plants ranged in size from 0.2 to 4 million gallons per day (mgd). Most of the SWRO projects announced in the past several years range in size from 14 to 72 mgd. Individual RO train sizes in many new systems frequently exceed 2.6 mgd.
The following chart4 was adapted from the US Bureau of Reclamation Desalting Handbook for Planners and illustrates the relationship between production capacity and water cost.
Inland Brackish Water Desalination
It has already been noted that the cost of desalination is directly proportional to feed water salt concentration, thus BWRO is inherently less expensive than SWRO. Brackish water aquifers are often located closer to the consumers than a seawater source, dramatically reducing treated water distribution costs. In addition, many brackish groundwater sources have a low level of suspended solids and require far less pretreatment than seawater sources.
RO concentrate disposal remains the biggest obstacle in the development of more BWRO installations. Disposal options at many inland locations are limited and may be environmentally and/or cost prohibitive. As technology further addresses this issue, the number of BWRO installations will increase at an even faster rate.
Nanofiltration (NF) membranes are very similar to RO membranes and account for approximately 6% of membrane production capacity. NF operates at a lower pressure than RO and is used in membrane softening applications to remove the ions that cause hardness in water, or to remove soluble organics from groundwater. They may also be used in sulfate removal to further improve performance of RO or thermal seawater desalination systems.
The benefits of research and development are apparent in the growth of desalination’s installed capacity, and new research and development initiatives have been announced that should continue this trend.
The US Bureau of Reclamation has recently developed a Desalination and Water Purification Technology Roadmap to serve as a strategic research pathway for desalination technologies.
Advances in desalination membrane technologies, pretreatment technology, energy recovery, improved integration of facilities, and more environmentally-conscious intake and outfall designs have resulted in better performance, lower capital & operating costs, and increased application of membranes in a variety of desalination applications. In the face of increased water shortages and growing costs of “conventional treatment,” this trend is expected to continue.