Desalination: A Solution to the Global Water Crisis

Desalination is a water clarification process in which excess salt, minerals, and other impurities are removed from seawater. This results in fresh water which is potable and can be utilised for human consumption, manufacturing, and irrigation.

Desalination is primarily conducted to provide water in areas where water supply is scarce or in time of natural disasters like drought.

In the past desalination was written off as an energy-intensive way to remove salt from water and used as a source of fresh water supply for marine vehicles. But with the coming of new technology that has allowed reduction in energy requirements as well as environmental dependence, this method of cleaning seawater to produce freshwater has come into the spotlight.

Desalination has become a necessity and a viable source of freshwater in the distressing climate of increasing global temperature, burgeoning populations, and unsustainable groundwater. With groundwater supplies diminishing, desalination is gaining popularity.

Seawater can be desalinated using a number of methods. These include distillation, ion exchange, membrane processes, reverse osmosis, nanofiltration, and membrane distillation, freezing, solar humidification, and high-grade water recycling.

The following are the two most commonly used methods of desalination:

Reverse Osmosis Filtration

Desalination can be conducted through reverse osmosis filtration by forcing water through a membrane that has microscopic pores. The size of these pores is only large enough to allow water molecules to pass, salt particles are too large to pass through these pores. The following stages are involved in the filtration process.

1. Pre-treatment: Methods such as sedimentation and coagulation are used to eliminate contaminants such as suspended solids and bacteria, that could clog the filtration membrane.

2. High-pressure pumps then force the water through the membrane that is made of composite polymers. This water is allowed to flow into a central collecting tube.

3. The last step of this process is post-treatment which may involve moderating adjust pH levels of water to disinfect it before it is released to the municipal water supply.

This desalination process is highly effective. It removes almost 100% of salt from seawater. However, it also removes other healthy minerals from the water.

A drawback of this filtration process is that pesticides, herbicides, and other toxic chemicals also pass through the membrane. An additional treatment process is required to be employed to remove these harmful chemicals from water.  

Multi-Stage Flash Distillation

Flash distillation involves heating salt water to a point where it vaporises into steam. The salt particles are left behind, leaving pure, potable water. The steam is allowed to cool and condense back into a liquid state. Multi-stage flash distillation is a technology that will enable efficient distillation of saltwater on a large scale.

The steps involved in multi-stage flash distillation are as follows:

1. Water is heated under high pressure and released to a chamber where the pressure dissipates, causing the water to boil instantly.

2. A heat exchanger condenses the evaporated steam converting it back to liquid form.

3. The process is repeated a number of times with the remaining water to recover as much water possible.

To get high-grade freshwater from the desalination process, it is crucial to find an experienced manufacturer who provides top of the line equipment to carry out this process. Thermax is a leading supplier of seawater desalination plants and are reputed for their numerous water treatment plant offerings including sewage treatment plants.