Water purification by distillation is a highly effective method that relies on evaporation to purify water, separating clean water from impurities based on their different boiling points. This process mimics the natural hydrological cycle, producing exceptionally pure water.
Understanding the Distillation Process
Distillation is a physical separation process that leverages the principle that water boils at a lower temperature than most contaminants. It's a time-tested technique for removing a wide range of impurities, making water safe for various uses.
Step-by-Step Distillation
The purification process through distillation involves several key stages:
- Heating Contaminated Water: The impure water, often referred to as "feed water," is placed in a distillation unit and heated to its boiling point (100°C or 212°F at standard atmospheric pressure).
- Evaporation to Form Steam: As the water reaches its boiling point, it turns into steam (water vapor). Crucially, inorganic compounds and large non-volatile organic molecules do not evaporate with the water and are left behind in the boiling chamber. This includes minerals, heavy metals, salts, and many non-volatile chemical contaminants.
- Cooling and Condensation: The steam, now separated from the contaminants, rises and is directed into a cooling chamber or condenser. Here, it encounters a cooler surface (often cooled by circulating water or air), which causes the steam to lose heat.
- Formation of Purified Water: As the steam cools, it then cools and condenses to form purified water. This distilled water is collected in a separate, clean container, leaving the concentrated impurities in the original boiling chamber.
What Distillation Removes
Distillation is highly effective at removing:
- Inorganic Compounds: Such as salts (e.g., sodium chloride), nitrates, nitrites, sulfates, and heavy metals (e.g., lead, mercury, arsenic). These contaminants have much higher boiling points than water and remain behind.
- Large Non-Volatile Organic Molecules: This includes many pesticides, herbicides, and other industrial chemicals that do not easily vaporize with water.
- Microorganisms: Bacteria, viruses, and other pathogens are also effectively eliminated as they cannot vaporize and are destroyed by the high temperatures.
- Sediments and Particulates: Any suspended solids are naturally left behind.
It's important to note that very volatile organic compounds (VOCs) with boiling points lower than or similar to water might co-distill. For ultimate purity in specific applications, a distiller might be combined with activated carbon filtration to address such VOCs.
Key Stages of Water Distillation
The following table summarizes the fundamental stages of the distillation process:
| Stage | Description | Outcome |
|---|---|---|
| Heating | Contaminated water is brought to a boil. | Water converts to steam. |
| Evaporation | Pure water vaporizes, leaving non-volatile impurities behind. | Separation of water from contaminants begins. |
| Condensation | Steam is cooled, causing it to revert to liquid form. | Purified water droplets form. |
| Collection | The condensed, purified water is collected in a clean vessel. | Production of highly pure, distilled water. |
Benefits of Distilled Water
The resulting distilled water is exceptionally pure, free from minerals, salts, and many organic and inorganic contaminants. This makes it ideal for applications where mineral-free water is crucial, such as:
- Laboratory use: For accurate chemical experiments and solution preparation.
- Medical and pharmaceutical applications: For sterilization and manufacturing.
- Automotive use: In car batteries and cooling systems to prevent mineral buildup.
- Household appliances: In irons, humidifiers, and CPAP machines to prevent scale and extend appliance life.
- Sensitive electronics: For cleaning and rinsing.
Practical Applications
Distillation systems range from small, countertop units for home use to large industrial distillers for commercial and scientific applications. Home distillers can provide a reliable source of pure drinking water, especially in areas where tap water quality is a concern or alternative purification methods are insufficient.
