The Pros and Cons of Reverse Osmosis Desalination

A new generation of large scale desalination plants are beginning, or about to begin, full scale operations, prompting another round of discussion about the pros and cons of desalination as a water management strategy.

Additional Resources Dead Zones Toxic Algae Blooms Beach Water Quality

In the United States, two plants that use reverse osmosis membrane technology (RO), are record setters, with stated production goals of around twenty five million gallons of drinking water per day.

RO technology is pretty easy to understand. Desalination plant designs basically consist of a pipeline and filtration section. Water having some degree of salinity is drawn from a local source from a pipeline connected to a filtration plant. The plant consists of a series of smaller pipes filled with RO membranes. As the water moves through the RO membranes, they catch salt and other organic and inorganic materials considered unhealthy in drinking water. The waste product, a concentrated saline solution, moves through a series of pipes for discharge. The final drinking water product is piped to the local distribution system.

Scheduled for operation in August 2007, The El Paso/Fort Bliss Desalination Plant will be the largest inland desalination plant in the world. Most people associate desalination plants with coastal locations because of the proximity of the water source. Inland desalination plants operate on similar technological principles, however they draw their source water from inland sources such as local aquifers. Waste disposal also differs because of the absence of an ocean. The El Paso plant plans to inject the waste into underground wells apart from the fresh and brackish water sections of the aquifer.

The Tampa Bay Seawater Desalination Plant, which restarted operations in April 2007, after a three year delay, is the largest seawater desalination plant in the United States. The plant is well known to water policy planners because of the difficulties trying to get it operational. In round numbers the plant's original cost estimates were in the one hundred million dollar range.

Lack of adequate planning for dealing with the stock water and/or unanticipated problems with an invasive species, the Asian green mussels, paved the way for a series of setbacks that increased the plant's cost to around the one hundred and fifty million dollar level.

The pros and cons of the latest round of RO desalination plants are straight forward. Desalination plants offer a partial solution to fresh drinking water problems for millions of people around the world.

Closer to home, water managers from all geographical regions of the United States consider a variety of factors, including climate induced changes in water supply, when deciding future water policy. The Canadian Centre for Climate Modeling and Analysis, for example, published an animated map version of Projected change in 5-year mean precipitation - 1990-2100. The yellow, orange and red marks that show up around the desert southwest of the United States indicate decreasing average rainfall amounts as the century progresses. If the model predictions hold up, local population will have less fresh water to draw from their rivers and aquifers than previously considered. Inland desalination might help mitigate some of the potential problems that arise under low water conditions.

Critics of large scale desalination projects commonly point to cost and energy intensity as their two biggest drawbacks.

Research into membrane production and manufacturing offers promise for more reliable and longer lasting filters, which reduces long term plant operating costs. Since larger scale RO plant construction is at the beginning of its technological cycle, there is little factual knowledge about the real economic costs of the plants. Tampa Bay residents are currently paying three times more for their desalinated water than the price stated on the original agreement.

Desalination plants are also energy intensive operations. The Tampa Bay plant, for example, is situated next to, and consumes electricity from the area's coal fired power plant. Critics argue the inappropriateness of using fossil fuel electricity sources for desalination plants because they contribute to climate change. A pilot program at Tularosa Basin National Desalination Research Facility in Alamogordo, NM, is studying ways to use renewable energy to reduce plant operating costs. Some projects, such as the desalination project in Sydney, Australia incorporated renewable energy use into their design plans.

© 2007 Patricia A. Michaels