Is Desalination a Solution to Water Shortages?

Only 3% of Earth’s water is viable for human use, and this amount is rapidly diminishing. Global warming, melting ice caps, worldwide droughts, and human population growth are causing this precious resource to evaporate before our very eyes. Action must be taken now to ensure a sustainable water supply, both for irrigation to grow food, and for consumption.

Australia is proposing a desalination plant on the Gold Coast to provide water in emergencies. This area is one of the fastest growing regions in Australia with a population expected to more than double by 2056. Traditional water supply strategies have relied heavily on drawing water from dams. Ongoing dry weather conditions with predicted low rainfall across the region mean that a new emergency water source one that is not dependent on the climate – needs to be investigated.

The project, initially proposed in December 2005, is composed of three phases and is expected to be up and running by December 2007 in Tugun, Australia.

The size of the proposed desalination plant would be 55 million liters per day. The power source options for the plant could involve:

Desalination is the conversion of seawater into drinking water. Of the more than 7,500 desalination plants in operation worldwide, 60% are located in the Middle East. The world’s largest plant is in Saudi Arabia. In contrast, 12% of the world’s desalination capacity is in the Americas, with most of the plants located in the Caribbean and Florida.

A number of technologies have been developed for desalination, including reverse osmosis (RO), distillation (of which Multi Stage Flash is one method), electrodialysis, and vacuum freezing. As of July 2004, the two leading methods were Reverse Osmosis (47.2%) and Multi Stage Flash (36.5%).

The energy used in the desalination process is primarily electricity and heat. Energy requirements for desalination plants depend on the salinity and the temperature of the feedwater, the quality of the water produced, and the desalting technology used.

In RO, feedwater is pumped at high pressure through permeable membranes, separating salts from the water.

In the distillation process, feedwater is heated and then evaporated to separate out dissolved minerals. The most common methods of distillation include multistage flash (MSF), multiple effect distillation (MED), and vapor compression (VC). In MSF, the feedwater is heated and the pressure is lowered, so the water “flashes” into steam. In MED, the feedwater passes through a number of evaporators in series. Vapor from one series is subsequently used to evaporate water in the next series. The VC process involves evaporating the feedwater, compressing the vapor, and then using the heated compressed vapor as a heat source to evaporate additional feedwater.

86% of the Australian population supports the project.

Tugun, the location chosen for the facility, is close to seawater, thereby keeping costs at a minimum.

Tugun is able to deliver emergency bulk water within the timeframes set.

Tugun does not have wetland habitats and protected species in the area to worry about.

Desalinating seawater is more straightforward than desalinating groundwater.

In the Middle East and North Africa, it has become fairly common for dual-purpose facilities to produce both electricity and water, thereby leading to less fuel consumption.

Desalination is already proving effective in many parts of the world.

Fresh water production is becoming a growing necessity as natural resources are disappearing at an alarming rate.

Desalination creates jobs.

Our oceans are a hugely untapped resource; why not use them?

Energy use requirements for desalination plants are high and may cause adverse environmental impacts. However, there has been a 90% reduction in energy use over the past 40 years. This is because of improvements in membrane technology and energy recovery systems. Solar, wind, and waste energy can be used in place of traditional fuel sources to further lessen energy consumption.

The cost to produce water from desalination is high although such costs have been reduced over the years with improved technology.

When seawater is desalinated, the brine is returned to the sea. It is devoid of oxygen and is heavier than saltwater, so it sinks. If it is released into calm water, it can sink to the bottom as a plume of salty water that can kill organisms on the sea bed from a lack of oxygen. It is a lethal byproduct and is a major cause of marine pollution when dumped back into the oceans at high temperatures. However, the brine is usually discharged in a location that allows it to be quickly dispersed, so its effect on the environment can be minimized.

Desalination causes an increase in CO2 emissions, but you can use alternative energy sources like wind to minimize such gasses.

Desalination impracticability and cost of transporting or piping massive amounts of desalinated seawater throughout the interiors of large countries is a problem. Desalinated water isn’t a viable solution for places that are poor, deep in the interior of a continent, or at high elevation. Hence, desalination is most difficult in areas that need it the most.

No solution to water shortages is devoid of problems, and careful thought and decision-making need to partner any option made available. Desalination may not be the complete answer, but it is one that is worth exploring further. Alternative solutions to improve desalination or other creative options need to continue if we are to continue our existence on this planet.

Sherry Obenauer | My Bio & Articles