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Water is crucial for living things. Almost two-thirds of the earth’s surface is covered by water. However, a big percentage of human population in various parts of the world has no access to safe drinking water.

If you don’t have a consistent water supply or find yourself in an emergency, seawater desalination seems like a practical solution to this problem.

In this post, we’ll discuss how to desalinate water.

Helpful resources:

  • Emergency Water Survival Kits – link

In an emergency, can you filter ocean water to drink?

Yes, with a DIY desalination unit you can.

The simplest unit you can create at home is a solar-powered thermal system.

To create a thermal desalination unit you’ll need to dig up a hole and cover it with a black plastic polythene sheet. Put a collection container in the middle and fill your hole with contaminated water.

Make sure the water level is beneath your collection container’s tip. You want the container to seize any condensed water instead of filling it with contaminated base water.

Cover the hole with a transparent sheet of polythene and secure it with a small rock.

The rock, in this case, will be a focal point for condensed water. Once water dissolves from sun’s heat it condenses on the upper side of your plastic. It’ll then flow to the rock before dropping in your container.

Keep on refilling your home desalination kit for a constant supply of freshwater.

But, what if you want to make something more longterm?

Let’s look at the options.

What Makes Water Saline?

Water is deemed saline if it contains high concentrations of dissolved salts. The most common salt, in this case, is sodium chloride (NaCI).

Concentration is displayed in PPM (parts per million) Assuming water contains 10,000 parts per million dissolved salts, this means that 1% of the water’s weight consists of dissolved salts.

Saline Water Specifications

Here is how you can classify water depending on the amount of salt in PPM (parts per million)

  • Freshwater contains less than 1,000 ppm of salt
  • Water is said to be slightly saline if the amount of salt ranges between 1,000 ppm to 3,000 ppm
  • Averagely saline water contains between 3,000 ppm and 10,000 ppm of salt
  • Highly saline water contains between 10,000 ppm to 35,000 ppm of salt
  • Ocean water contains around 35,000 ppm of salt

More helpful reading:

What are the 2 main methods of desalination?

Before we can discuss salt water purification methods let’s define desalination.

What’s desalination?

This is the process of removing excess minerals and salts from water to make it suitable for irrigation and human consumption.

Freshwater can also be used for other domestic purposes. Salt water desalination processes can be used for industrial, municipal, or commercial use. When feed water is treated in some of the large-scale desalination processes two products are obtained as seen below.

  • Treated safe to drink water that contains less mineral and salt concentrations. This desalinated water is also known as product water.
  • Brine or concentrate that contains high amounts of minerals and salts than the original salt or feed water. These sources include brackish wells, sea, surfaces such as streams and rivers. They can also include waste, process, and industrial feed water.

As technology for desalinators evolves, desalination of ocean water procedures is becoming more economical. Desalinated water that’s obtained after the desalination process will need demineralization to make it suitable for human consumption. The brine should be disposed of properly.

Types of desalination

The two main desalinator science technologies used to remove salt from water are thermal and membrane desalination. Both of these technologies include various other processes.

There are alternative salt water purifying technologies such as ion exchange and freezing but they aren’t commonly used. All these technologies are often powered by renewable or conventional energy.

Desert Desalination Video

Thermal Desalination Process

Often referred to as distillation, this is the oldest desalination of water processes. This technology is expensive which is why it’s hardly used to remove salt in brackish water.

This salt water distillation technology is based on the science of boiling salt water, evaporating it, and later collecting condensed vapor to get pure water. This process is divided into different types as seen below.

  • Multi-stage flash distillation (MSF)
  • Multi-effect distillation (MED)
  • Vapor compression desalination (VCD)
  • Solar water distillation
  • Cogeneration
Multi-stage flash distillation (MSF)

This is a process of desalting sea water in large quantities through a series of multi-stage chambers. It’s based on the science that boiling temperatures of water drops when air pressure declines.

Once preheated lifestraw ocean water gets in the first stage and part of it boils rapidly to form vapor. This vapor is then condensed to form freshwater in countercurrent heat-exchangers.

Freshwater is accumulated in trays while remaining seawater discharges to the next stage. Multi-stage flash distillation machinery generates approximately 26% of all desalinated ocean water across the world.

Pros of Multi-stage flash distillation

There are various reasons why you may want to use this purifying sea water method as seen below.

  • Multi-stage flash distillation mills are easy to construct and operate
  • Except for the traditional pumps they don’t come with any other moving parts. Further, they only comprise a small percentage of connection tubing
  • The discharged water contains between 2 to 10 ppm of dissolved solids making MSF a high-quality method of desalting water
Cons
  • While the plants run at high temperatures which boost efficiency, this can cause scaling problems. This is because minerals such as calcium sulphate collect along the tube surfaces and cause mechanical and thermal problems such as tube clogging
  • For MSF, the energy required is intensive and requires both mechanical and thermal energy to operate effectively.

More helpful reading:

Multiple effect distillation

This process of removing salt from water has been in existence since the 1950s. While it uses the same approach as multi-stage flash distillation, it takes place in a chain of vessels (effects.) It also uses the principle of condensation and evaporation at low circulating pressure.

In multiple effect distillation, a chain of evaporator vessels generates water at successively reduced pressures. As pressure declines, water boils at decreased temperatures and water vapor in the first vessel becomes a heating medium. Multiple vessels create a high-performance rate.

Water vapor generated during the boiling process is condensed and use of multiple vessels makes this procedure more effective. Multiple effect distillation is popularly known as the oldest large scale method of purifying ocean water.

Pros of multiple effect distillation
  • It operates at low temperatures which reduces scale formation along tube surfaces. This means there’ll be less tube corrosion
  • The energy required is low consumption and high performance. This is why the multiple effect distillation is said to be an efficient and cost-effective portable sea water purifier
  • Pre-treatment and operating costs in this process are minimal
Vapor compression desalination (VCD)

This survival desalination method is also known as vapor-compression evaporation. It can either be operated individually or used together with single-effect vapor compression and multiple effect distillation.

In this process, the heat that evaporates from salt water comes from condensation of vapor. This is different from other methods that rely on direct heat exchange from steam generated in a boiler.

Two gadgets are used in this procedure to compress vapor and produce enough heat to dry up the seawater. Steam jet is the first gadget that’s used for thermal vapor compression. The other gadget is a mechanical compressor. Vapor compression units are made in different layouts.

Understanding a mechanical compressor

A mechanical compressor can be powered by either diesel or generator. It’s used to produce heat for evaporation. This unit forms a vacuum inside an evaporator and condenses vapor acquired from the gadget before compressing it in a tube bundle.

Feed or salt water is sprinkled out of the heated tube bundle where water boils and partially evaporates to produce more vapor. In steam jet vacuum compression distillation, a venture orifice produces and extracts water vapor to create a low atmospheric temperature.

Extracted water vapor is condensed by a steam jet and compressed along the tube walls. This discharged condensation heat evaporates salt water that’s pumped on a different part of the evaporator. These gadgets are usually smaller and commonly used in industries and hotels.

Pros of vapor compression evaporation

  • It’s an easy and reliable science method that can be used as a home desalination kit. They are available in a 3000 m3/day capacity
  • It runs on low temperature making it energy efficient
  • Reduced chances of tube corrosion since the process operates under low temperatures
Solar distillation

This method is ideal for small scale operations. Solar desalination kits come with a different design. However, the basic operating principle is similar to methods we’ve discussed before. In this process, the sun supplies heat energy to remove salt from sea water.

In this process, water vapor produced from the evaporation procedure condenses on clear plastic or glass covering. It’s then collected in a condensate trough as freshwater. The covering is used for transferring radiant energy and enabling water vapor to compress on its inner surface.

Salt and water that remains after this procedure should be disposed of properly. Solar distillation is commonly used in arid areas where there’s lack of fresh and safe water. Solar distillation units generate different amounts of freshwater depending on the geographical location and their design.

More helpful reading:

Cogeneration system for power and water distillation

Electricity in cogeneration mills is produced with high-pressure steam to run turbines. The steam is produced by boilers at extremely high temperatures which can go up to 5,408°C. Once this steam builds up in the turbines its energy levels and temperature decrease.

Distillation plants require steam temperatures operating below 1,208°C. This can be acquired at the end of a turbine after high energy has been used in electric power formation. Steam is utilized for the desalination products process. Condensate from steam is restored to a boiler where it’s reheated and utilized in the turbine.

Pros of the Cogeneration system
  • It uses less fuel compared to other distillation methods
  • It’s as energy efficient
Cons
  • A permanent connection between the desalination mill and power plant may generate water production difficulties. This is a common occurrence when less electricity is required or when your generator or turbine breaks down.

Membrane processes

Membrane applications were originally used in municipal water treatment plants such as desalination and microfiltration. With advancements in science and modern membranes however, this process can be used in other procedures. For instance, chemical separation, beverage purification, and concentration of enzymes.

Membrane procedures use a relatively absorbent sheet. This helps to move salt or water to create two sections of varying concentrations to generate freshwater. These procedures are also essential in municipal water treatment facilities. Reverse osmosis (RO) and electrodialysis (ED) are today replacing other multi-change desalting technologies for providing water to island and coastal communities across the world.

RO is evolving as a cost-effective alternative method to purify salt water. Membrane technology comprises various processes. However, they are different in terms of size of molecules, ions, and hanging particles retained or released through the membranes. The main separation procedures here include microfiltration, ultra-filtration, and nano-filtration. Membrane procedures are further subdivided into,

  • Reverse osmosis
  • Membrane distillation
  • Electrodialysis
Understanding reverse osmosis and nanofiltration

Reverse Osmosis is a new procedure used to purify ocean water. It relies on using pressure to drive salt water through a semi-absorbent membrane into a concentrated brine and product water stream. Nano-filtration is one of the ways to remove salt from water. Reverse osmosis is also used to remove chloride and sodium ions.

About reverse osmosis

This is a natural method where water from low salt solution streams into concentrated solutions through a semi-absorbent membrane. Once pressure is enforced in a high salt concentration solution, the water starts streaming through a semi-absorbent membrane in reverse direction.

Membrane configurations in this method comprise hollow fiber, spiral wound, and a spiraled sheet. The operational pressures for nano-filtration and reverse osmosis range between 50 and 100 pounds per square inch gauge (PSIG.) A reverse osmosis water desalination machine consists of four main systems as seen below.

  • Pre-treatment system
  • Membrane systems
  • High-pressure pumps
  • Post-treatment
Pros of the reverse osmosis process
  • Less metal corrosion problems than is the case with MED and MSF processes as a result of low-temperature conditions
  • It involves the use of polymeric materials to reduce corrosion
Cons

A significant percent (large gallons of water) is wasted during the process.

Electrodialysis (ED)

This process uses electrical power to remove salt from the water. Electrodialysis was originally used as a sea water desalination procedure but today, it’s used to desalinate brackish water.

This process runs through direct current where ions stream through ion-specific membranes to charge the electrodes conversely.

Polarity of the electrodes in these systems is repeated reversely. Dissolved salts in water come in the form of ions. The ions are drawn towards conversely charged electrodes which mean that electrodialysis is reliable towards separating salt from water. This method uses applicable membranes to release specific ions which can be anions or cations.

This technology utilizes the concepts of both membrane and thermal technologies that are membrane and distillation based water desalination processes. Temperature difference in this method is formed amid the;

  • Supply solution that connects with the surface on one section of a micro-absorbent membrane, and
  • The remaining space in an opposite part

This temperature difference causes a variation in vapor pressure. As a result, this triggers transfer of vapor from a membrane to the compression surface.

This entire process relies on the use of hydrophobic membranes. These are only absorbent to the vapor hence eliminating dissolved particles and liquid phase.

Generated vapor then flows over a membrane and gets compressed at the cooling surface to produce fresh water.

Pros of Membrane distillation
  • It’s a simple method that runs at low temperatures and uses less heat. It can be connected with solar energy to make it more energy efficient for the environment.
Cons
  • It needs bigger spaces than other membrane procedures
  • The salt water shouldn’t contain organic pollutants which can limit effectiveness of this process

How long does it take to desalinate water?

Desalination is a complex process. This means it can’t be a quick solution to water problems across the world. Constructing a water desalination plant can take up to two years from. Also, the entire process from conducting environmental impact research and analysis to obtaining legal authorization can take almost three years.

Frequently Asked Questions

Are desalination plants noisy?

Yes. Water desalination plants that operate on reverse osmosis procedures use high-pressure pumps which can be noisy.

How can desalination solve the water crisis?

Desalination may be an effective solution to water problems in different parts of the world – like Saudi Arabia. This can only be possible with use of renewable energy and the lowering of operational costs.

Further, environmental protection regulations should be established to protect marine life. With desalination, some feel water-strapped areas would be able to enjoy a consistent water source.

Why is Desalination Expensive?

Desalination needs a great amount of electricity to drive water through a filter. Treating the water to destroy microbes and replacing filters has a high cost, too. Still, it’s an effective method that guarantees an adequate supply of fresh water. This makes the project a worthwhile investment.

Why is it important to desalinate water?

It provides residents with a reliable source of freshwater for drinking and other domestic purposes.

Get started today

Desalination is a safe water source that doesn’t rely on rain. With the growing popularity of this process, you’re assured of getting medically approved DIY desalination kits.

More helpful reading:

  • Turning salt water into drinking water efficiently – link

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