Water is the basic need of every human being. 71% of earth’s surface is water but this water is not readily drinkable. Freshwater sources are just 3% of total water on the earth and they are scanty to provide each individual on earth with drinking water. Some areas such as the Gulf and Middle East are completely devoid of fresh water sources and most of their region is covered with dry deserts. In such areas, sea water is usually used as a main source of water supply. Wait! Is sea water readily able to drink? No, not at all; it is highly saltfish and brackish. It must be desalinated to be used as an alternative of freshwater. Desalination is the technique through which dissolved salts and minerals in seawater are separated and water is made available to the general public for drinking. Desalination plant in Jebel Ali Dubai is converting 182 million liters of sea water into fresh water on a daily basis through reverse osmosis.
RO systems are commonly used nowadays to purify sea and saltwater into freshwater. In regions where fresh water is very scarce sea water is converted into desalinated fresh water for the purpose of drinking. In the water filtration industry, use of RO systems is highly recommended for such conversion due to being less expensive and efficient. Reverse osmosis filters operate on the idea of osmosis where water flows from an area of lower solute concentration to an area of higher solute concentration when separated by a semipermeable membrane till a state of equilibrium is attained. RO systems work oppositely to this osmosis phenomenon where through electricity salt water is pushed by pumps through a semipermeable membrane and it moves from an area of high impurities concentration to an area of low impurities low salt concentration. These filters usually work by letting water pass through a semipermeable membrane which removes the majority of the impurities by keeping impurities on one side and clean water moves to the other side. This membrane is known commonly as reverse osmosis membrane. It acts as one stage in RO water filtration systems.
How RO systems work to convert salt water into fresh water?
For converting brackish/salty water through reverse osmosis systems commercial large scale setup is used. Each RO system usually comprises 6 stages depending on the filtration needs. RO systems have different filtration levels that make the water pure, clean and healthy.
Salt water is introduced into the RO systems via pumps to desalinate it.
Pre Filtration stage
Before the sea water is allowed to pass through this reverse osmosis membrane water usually gets through first from the pre-filters.
These pre-filters are namely
- polypropylene filter cartridge
- granular activated carbon filter (GAC) and
- carbon block filter
The saltwater initially in the first step passes through the polypropylene filter. This pre-filter has been designed to remove all types of suspended particles from the water such as sand, clay and silt. If these suspended particles are not removed initially they can block the reverse osmosis membrane as well as the whole RO system itself. This PP membrane has a filtration capacity to remove sediments from the water up to 5µ.
GAC and carbon block filters as the name suggests are used to remove any bad taste and odor in the salt water. GAC is made up of acid washed coconut shells and coal with carbon in higher concentration.
CTO is able to absorb more impurities as carbon is compressed to increase its strength and performance. Due to removal of harmful substances from the water it tends to be free of any kind of odor and taste change caused by their presence.
Reverse Osmosis Membrane
Pre-filtered water is when passed through this membrane on the principle where a solvent (salt water) is passed from an area of higher concentration to an area of low concentration. This removes all remaining impurities and harmful salts from the water. The salt water gets converted into potable water. RO membrane filters the water upto 0.0001micron.
Post Filtration Treatment
The water is passed through certain post filtration methods such as it is sterilized through
chlorination (adding chlorine in the water to kill germs and bacteria.
Water is stored in storage tanks at last from where it is supplied to the main pipelines for use by the general public.
Pros and Cons
Right now on a large scale globally seawater is being converted into fresh water to fulfill the demand of water. The problem of water scarcity has given rise to desalination which is currently being considered a problem solver by supplying masses with the freshwater supply but it is not free of detrimental effects as well. The major drawback is that it makes water expensive as water is produced after certain treatments and it takes time and money to produce freshwater from seawater. Secondly, waste produced as a result known as brine is added back to sea that disturbs the natural aquifers and marine ecosystem. Research is ongoing to reduce these problems in order to make desalination of saltwater through reverse osmosis by attaining the cost reduction as well.