Desalination of Seawater by Reverse Osmosis for Drinking

Water scarcity is a growing challenge humanity is facing at the moment. This is either due to drought resulting from global warming or due to our usage habits and unnecessary consumption. There are nearly 25 countries which are facing extremely high water stress level including Saudi Arabia, India, South Africa, Belgium and Greece etc. Desalination of Seawater by Reverse Osmosis for Drinking and household use is being practiced in many countries.

Since 2021, South Africa is facing critical crisis of water shortage in nearly 23 parts of the country where water supply systems are in poor and critical condition. Nearly half of the water supply systems do not comply with microbiological standards. In most of these areas the clean water is contaminated by sewage and bacteria leaving harms to human, animals and plants.

Researchers have addressed a considerable groundwater level decline of more than 0.5 meters (20 inches) per year across the world, including the United States. It has accelerated over the past four decades.

There is an urgent need for more effective steps to address groundwater depletion. Although the situation is alarming but with the right management and sustainable practices, every country can prevent water stress from turning into water crisis.

In some countries, proper measures have already been taken to mitigate the problem but in most cases there are no precautionary measures being taken at private or government levels to address the problem despite alarming situation.

In Unites States, the world's largest wastewater recycling facility of Groundwater Replenishment System is developed in the Orange County Water District in Fountain Valley, California.

This state of the art high-tech water purification project has the capacity to produce up to 130 million gallons of high-quality water every day from waste water specifically, enough to meet the daily needs of nearly one million residents in north and central Orange County, California.

Sea Water Treatment Facilities in the World

United States has similar facilities in Detroit, Chicago, Washington DC and Boston. Detroit Wastewater Treatment Plant is the third largest of its kind in the world which processes up to 6.4 million m3 of water each day.

New Delta Wastewater Treatment Plant in Egypt however is the largest wastewater treatment plant in the world with a capacity of processing 7.5 million cubic meters of water per day.

Water Treatment Methods

Unlike conventional methods of treatment of water through filtration and chemical treatments, sea water treatment is relatively different. It is a combination of sedimentation, filtration and disinfection methods widely used for these purposes.

Sea Water Treatment through Water Filtration

In water filtration process, primarily, concentration of substances, including suspended particles, bacteria, parasites, algae, viruses, and fungi, as well as other unwanted chemicals and biological contaminants from contaminated water are either removed or regulated and then artificially added to produce safe and clean water for drinking and other purposes.

On the other hand, seawater contains extra salt and while our kidneys make urine from water that is less salty than the sea water, through intake of sea water we have to urinate more frequently to remove extra salt resulting in dehydration and ultimately death.

Humans can safely intake and digest only a small amount of salt available in normal drinking water. If humans drink seawater, they are taking extra amount of salt which is much higher than what can be processed by the human body.

Similarly, when we consume salt as part of our daily diets, we are also drinking other liquids and solids, which help to dilute the salt and keep it at a healthy level.

Human cells depend on sodium chloride NaCl (salt) to an extent to maintain the body’s chemical balances and reactions, but, too much sodium intake can be deadly. Some water sources have relatively high levels of natural fluoride, which can lead to enamel fluorosis (mottled teeth), or sometimes even more severe skeletal fluorosis (permanent bending of a person's bones).

Sea water Treatment Through Desalination or Reverse Osmosis

Thermal desalination and reverse osmosis desalination are two most widely used technological approaches for sea water treatment.

Desalination refers to processing sea water by removing all salts and minerals from saline or brackish water to obtain high quality clean water suitable for drinking, irrigation or industrial applications.

In United States, seawater desalination facilities have significantly increased more specifically in coastal areas. This is most likely due to depleting alternative water supply sources and declining freshwater availability.

Sea Water Plants in United States

United States is currently processing 479 million gallons per day of seawater through its 130 desalination facilities in California, Florida, and Texas. The Carlsbad Desalination Plant in California is the largest sea water treatment plant in the USA producing 50 million gallons of freshwater per day serving around 0.4 million people in the area.

Sea Water Treatment Plants in the World

The massive Ras Al-Khair, a hybrid facility of this kind with both thermal multistage flash (MSF) and reverse osmosis (RO) technologies in Saudi Arabia is the largest sea water treatment plant in the world processing 1.036 million m3 (1.036 billion Liters) of water every day. In fact, other three of the world largest desalination facilities are also in Saudi Arabia.

Desalination or Reverse Osmosis Process

Seawater desalination includes removal of salt and impurities from seawater. Most desalination plants use a reverse osmosis process mostly used for drinking water purification.

Initially seawater is pumped into the desalination plant which passes through pre-treatment filtration to remove most particles. The reverse osmosis takes place when the filtered water is passed through special membranes at a specified pressure.

Osmotic pressure is the minimum pressure required to stop solvent flow through the membrane. Therefore, when the solution side (the side where the solute concentration is high) is subjected to a pressure greater than the osmotic pressure, the solvent particles on the solution side move through the membrane to the side where the solute concentration is low. This inverse solvent movement of water through the membrane is called reverse osmosis.

This membrane separates dissolved solutes from water by removing salt, bacteria, viruses and other waste materials. Nearly half of the water that enters the plant from the sea becomes fresh drinking water. The salt and impurities removed from the seawater are returned to the sea via diffusers.

Seawater desalination methods are quite popular in areas where ground water level is low and sea water is quite easily accessible. There are nearly 16,000 operational desalination plants, located across 177 countries capable of generating around 95 million m3 or 95 billion liters of fresh water every day.