Introduction
Water is a tasteless, odourless and colourless chemical, which is composed of two molecules of hydrogen and a molecule of oxygen. There are different types of water like deionised water, filtered water and distilled water. Deionised water is a water in which all the charged ions are removed. It is prepared by taking conventional water and exposing to electrically charged resins that will hold together and attract salts then it is removed from water.
Purified water is that which has been mechanically filtered or processed to remove impurities and make it suitable for use. Water which has been boiled to vapour and then condensed to liquid is called distilled water. Impurities which are present in the normal groundwater do not boil at the temperature near or below the boiling point of water. So, the impurities present in the water settle in the container.
Distilled water is one of the types of purified water. Distilled water has wide applications in laboratories (chemical and biological), surgical purpose, batteries, food processing and so on. In this article, we will give an idea about how distilled water is produced and its application in various sectors.
Process flowchart of distilled water
Distilled water needs and applications
Drinking-Water – It provides purified water free of contamination, chemicals and bacteria having less salt content for a healthy life.
Ships - Used in ships to attain desalinated water in the ocean. It is used as a coolant especially in nuclear vessel ships causing less error.
Lead Acid Batteries – It acts as a coolant to cool down batteries, hence it increases the life of batteries and vehicles also.
Aquariums – Freshwater fish lives in freshwater only which is available by process of distillation and improves the life of fish and aquarium tanks.
Surgical Purposes – Hospitals have no microbes for patient safety, hence use distilled water. It is also used for instruments cleaning.
Food preparations and cooking - Use of distilled water in preparations of food provides safety to the food and also increases the taste, nutrition and its appearance. Distilled water is used for washing of fruits and vegetables based on its ability to be a good solvent. Following are some of the applications of distilled water in food processing sector:
a. Ice Cubes – Distilled water lacks impurities, hence can be used for making clear and shiny ice cubes in less time than normal tap water ice.
b. Fruits and Vegetable Juice – Distilled water improves the taste of concentrated fresh juice of orange, grapes and tomato resembles much like actual fruits and it improves the volume of fresh juices.
c. Tea and Coffee – Distilled water improves the taste of tea and coffee at less quantity than tap water and does not produce any ugly film over the product surface.
d. Cooking Vegetables – Cooking of fresh vegetables in distilled water induces no discolouration and contamination. Soups are safer and pure. Distilled water helps in sprouting for vegetables and beans.
e. Baking Process – Quantity of distilled water needed by flour for absorption is less than tap water quantity and it also saves the texture of the product and hence provides smoothness.
f. Pasta Products – Pasta, noodles, and macaroni absorb more distilled water than tap water which improves their flavour and maintains a texture that improves quality of the cooked product.
g. Reconstitution of Dehydrated Foods – Process of dehydration removes only pure water hence in rehydration process pure distilled water is used to maintain the quality of food product.
Equipment used for distilled water production
Distillation replicates the process of nature’s hydrological cycle for producing pure water i.e., water free from impurities and salts. Distiller works on the principle of evaporation and condensation; it is an electric appliance that is used to distil water, the basic elements in any type of distiller consists of a heating element which boils the incoming water in a container, the resulting steam leaves the container and heads towards a cooling coil where the steam condenses to form distilled water. Steam raised due to evaporation is cooled either by means of air or due to counter flow of the incoming water. Provision for float switch is provided to cut off the power supply of the heating element, the concentrated mineral solution left in the tank is drained off and then the chamber is refilled manually or automatically.
Countertop water distiller is used for batch distillation process, producing 3-4 litre of water and mainly used for residential purpose, for laboratory use, pyrogen-free distilled water is required for various analytical procedures, in lab-scale distilled water is produced using various types distiller namely single/double staged quartz distillation unit, glass distiller, Barnstead type (tabletop) water distiller.
On a commercial scale, distilled water is produced by eliminating the impurities from various sources of water. This is achieved by vapour compression distiller, where the evaporation of fresh water is obtained by the application of heat which is delivered by compressed vapour. The multiple-effect distiller is also used for the production of distilled water which consists of multiple stages.
Membrane distillation and solar water distillation are also employed for distilled water production from various sources of water on a large-scale basis. Successive evaporation/condensation process of volatile components through a porous membrane results in the production of distilled water. Solar water distillation utilises solar energy for desalination, this particular method can be employed in the water-stressed area to obtain freshwater free from salts and ions. This technique imparts potential benefits since a natural source of heat is employed thereby it is energy-efficient.
Conclusion
Distillation is a purification process; it is a manmade replica of the hydrological cycle for the production of pure water. Distilled water is of prime importance in conducting any analytical experiments in the laboratory, it is used for various applications in processing sector i.e., in confectionery and juice preparation, commercial ice production. Almost all distillation equipment follow a common working principle that involves heating of the incoming water by a heating source and condensation of steam by a cooling unit. On a commercial scale, distilled water is produced by removal of impurities and salts from various sources of water, for achieving this various equipment such as vapour compression distiller, multistage distiller, membrane distillation and solar distillation units are employed.
(Dr Venkatachalapathy is professor and head of department of food engineering, Thangaraju, Yashaswini and Sharma are research scholars at Indian Institute of Food Processing Technology, Thanjavur, Tamil Nadu. They can be contacted at venkat@iifpt.edu.in)