Introduction to Impurities in Water

H₂O=H⁺+OH^-

Water is both a primary component of life and a crucial element of social production. Pure water, composed solely of H₂O molecules, does not exist in nature. Water typically contains the following impurities:

1. Particulate matter: Insoluble inorganic and organic impurities larger than 10 μm (some larger than 40 μm are visible to the naked eye), such as sediment, metal oxides, or hydroxides commonly found in tap water.

2. Ionic matter: Substances that dissociate into anions and cations upon dissolving in water. The sum of anions and cations in water is called the salinity (mg/L).

3. Colloids: Colloids are substances between ions and particulate matter, with a size of approximately 0.1 μm.

4. Organic matter: Matter can be divided into two main categories: organic and inorganic. Hydrocarbons belong to organic matter, while non-hydrocarbons belong to inorganic matter. Organic matter is generally combustible and is a major component of life. Natural organic matter is mainly found in surface water. In recent years, industrial wastewater, fertilizers, pesticides, and other synthetic organic matter have caused significant pollution to the aquatic environment.

5. Gases: Some gases, such as CO2, NH3, and NO2, are soluble in water and react with it to form certain acid radicals, affecting the quality of the finished water. Ultrapure water will rapidly deteriorate in quality if left exposed to air.

6. Microorganisms: Bacteria, viruses, spores, etc., are on the micrometer scale.

7. Pyrogens: Pure water is a very low-nutrient environment, but a small number of bacteria—Gram-negative bacteria—can still survive. If their cell membranes enter the human bloodstream, it can cause fever, high fever, or even death; hence, they are called pyrogens (also known as endotoxins). Pyrogens must be removed from water for injection and water used in biological cell experiments.

8. Disinfectants: After the raw water is treated by the water company, disinfectants such as sodium hypochlorite will remain in the water. Cl- can cause considerable damage to the RO membrane, so activated carbon unit is needed to filter out CL-.