Introduction

Groundwater depletion is a challenging issue that has garnered heightened attention from geologists, environmental scientists, and politicians in the past few decades. Although this problem is quite prevalent throughout most of the world, it is especially impactful in regions defined by excessive water usage. By harnessing the power of agricultural and chemical technologies, however, this loss of subterranean liquid can be addressed through a variety of means. Specifically, one of the most effective techniques in meeting public demand for water as supplies decline is desalination. In this process, originally saline fluids are stripped of their salts and minerals and turned into consumable sources of water.

Desalination Methods

As 97% of the world's water is too salty to drink, there are quite a number of ways to desalinate brine. Typically, these methods fit into one of two categories based on their system structure. The first class of desalination, currently the most commonly implemented form worldwide, utilizes a technology known as reverse osmosis (RO). Plants that use RO purify water by passing a solvent through a semipermeable membrane under high pressure. As the liquid is passed through the porous material, solid substances such as salt are retained on one side of the membrane, while the water flows freely through the holes. Depending on flow rates and pore size, the speed and purity of the solution can be modified according to different needs.

Alternatively, desalination can be performed by manipulating temperature gradients to evaporate water in a process known as thermal distillation. Unlike RO, distillation requires a change in state of the saline solution from a liquid to a gas to isolate unwanted products from the resulting steam. Afterwards, the vapor is collected and cooled through coils in order to condense the evaporated water into its liquid form again. A major disadvantage of distillation is that the technique requires a large amount of energy to complete the phase change of the vapor. Accordingly, RO is often preferred because of the financial drawbacks that come with the greater energy needs of distillation.

Advantages and Disadvantages

While desalination has the potential to satisfy some of the growing demand for water supply, its widespread use comes with a number of pitfalls that discourage many organizations from supporting its development. Initially, it is very expensive to build operating plants, with average construction costs ranging anywhere from $300 million to $2.9 billion USD. Moreover, the large energy quantities required to maintain the performance and functionality of distillation plants only further increase their costs. To make up for steep prices, the purified water that plants produce is markedly more expensive than traditional water sources, costing consumers twice as much as recycled wastewater plants do. Additionally, disposal of resulting waste from plants is an area of concern for many environmental groups. Once released, the resulting brine from the manufacturing process can modify salinity of water at disposal sites and consequently kill off animals. The carbon emissions produced from desalination plants also reduce its attractiveness as an environmentally friendly solution to groundwater depletion.

Nonetheless, desalination still retains numerous benefits that do substantiate its implementation as a major water source. By and large, its primary redeeming factor is that desalination can provide access to drinking water where no other supplies exist. In arid regions where few natural sources of water exist, there are few options besides desalination to obtain potable water for both municipal or rural consumption. In Saudi Arabia, for example, 70% of freshwater is procured using desalination plants. Moreover, desalination often produces water that not only meets but exceeds local standards for water quality. Especially after incidents such as the Flint water crisis, this makes desalination an appealing way to more effectively ensure clean drinking water.

Conclusion

In the future, technologies such as desalination will have to be exploited further to meet the demands of our growing population while still complying with environmental standards. Like any system, this technique comes with both positive and negative effects that must be weighed before utilizing it on a larger scale. However, new forms of desalination that rely on solar-power and other renewable energy forms are being explored continually in order to fully maximize its potential. Once its pitfalls have been overcome, desalination will likely serve as an integral part of providing clean water to the world in an ever-increasingly drought-ridden and resource dependent society.

References

Science Magazine

US Geological Survey

MIT Technology Review

IDE Technologies

The New Yorker

View of the Carlsbad Desalination Plant in San Diego (Credit: Creative Commons)