Besides Pure Laboratory Water, What Other Common Water Treatment Indicators Are There?

In laboratory pure water treatment, we commonly see indicators such as resistivity, conductivity, and desalination rate. Besides these, what other indicators are used in water treatment?

1. Turbidity: This refers to the degree of cloudiness in water. It is an optical effect caused by the presence of suspended solids (including colloidal substances). The unit is NTU. Turbidity is one of the main visual characteristics used to determine whether water is polluted. The standard unit for turbidity is defined as 1 degree of turbidity caused by 1 mg of SiO2.

2. Flocculant: An agent that can cause colloidal particles to coagulate and bridge, thus causing flocculation.

3. Total Alkalinity: This refers to the total amount of substances in water that can neutralize strong acids.

4. Acidity: This refers to the total amount of substances in water that can neutralize strong alkalis.

5. Hardness: This refers to the content of certain metal ions in water that easily form precipitates, usually calcium and magnesium ions.

6. Conductivity: The electrical conductivity of a solution between two parallel electrodes with a cross-sectional area of 1 square centimeter and a distance of 1 centimeter at a given temperature. It can indirectly indicate the dissolved salt content in water.

7. Resistivity: An indicator of water's ability to conduct electricity. The higher the resistivity of water, the lower its conductivity and the fewer ions it contains. Its common unit is MΩ·cm. It has a reciprocal relationship with conductivity. For example, if the conductivity of water is 0.2 μS/cm, then its resistivity is 1/0.2 = 5 (MΩ·cm).

8. TDS (Total Dissolved Solids): The inorganic matter remaining after filtering out suspended solids (SS) and colloids and evaporating all water. The unit is ppm or mg/L, and it can be measured using a TDS meter. It also reflects the ion content in water. A rough correspondence between it and conductivity is: for a sodium chloride reference solution, 1 ppm of TDS corresponds to a conductivity of 2 μS/cm. 9. pH Value: The relative content of acids and bases in a solution. pH value is a measure of the negative logarithm (log) of the hydrogen ion concentration in water. pH values range from 0 to 14. A pH value of 7.0 indicates neutral water; a pH value less than 7.0 indicates acidic water; and a pH value greater than 7.0 indicates alkaline water.

10. Alkalinity: Alkalinity refers to the content of substances in water that can accept [H+] ions and neutralize strong acids. The main substances that produce alkalinity in water are carbonate alkalinity (from carbonates), bicarbonate alkalinity (from bicarbonates), and hydroxide alkalinity (from the presence of hydroxides).

11. SDI: Sludge Index—used to measure the amount of suspended solids in the raw water used in reverse osmosis systems.

12. Recovery Rate: The ratio of the output product water flow rate to the influent flow rate.

13. Desalination Rate: A parameter reflecting membrane performance; typically, a single-stage RO membrane system achieves a desalination rate of over 97%. A simple calculation is possible: (Raw water conductivity - Product water conductivity) / Raw water conductivity.

14. Salt Content: The salt content of water, also known as mineralization, indicates the amount of salts contained in the water. Since various salts in water generally exist in ionic form, salt content can also be expressed as the sum of the amounts of various cations and anions in the water.

15. Pure Water: Pure water refers to water in which easily removable strong electrolytes and difficult-to-remove weak electrolytes such as silica and carbon dioxide have been removed to a certain extent. Pure water has a salt content below 1.0 mg/L and a conductivity less than 3 μS/cm.

16. Suspended Solids (SS): Refers to solid substances suspended in water, including insoluble inorganic and organic matter, as well as mud, clay, microorganisms, etc. The suspended solids content in water is one of the indicators for measuring the degree of water pollution. It is the amount of solids obtained by drying the residue on filter paper after filtering the water sample at a temperature of 103-105 degrees Celsius. Unit: mg/L.

17. Ultrapure Water: Ultrapure water, also known as high-purity water, refers to water in which almost all conductive media have been removed, and non-dissociated colloidal substances, gases, and organic matter have been removed to very low levels. Ultrapure water has a salt content below 0.1 mg/L and a conductivity less than 0.1 μS/cm. Besides strict requirements on salt content and conductivity, pure water and ultrapure water also have strict limits on the content of various metal ions, organic matter, particle size and quantity, and the number of microorganisms.

18. Distilled Water: Distilled water is produced by heating raw water to vaporize it and then condensing the steam. Generally, distilled water has a conductivity of around 10 μS/cm. Double distillation of once-distilled water yields double-distilled water, and multiple distillations yield multi-distilled water, with conductivity reduced to a very low level of around 1.0 μS/cm.

19. Scale Inhibitor: Scale inhibitors are agents that can disperse sparingly soluble inorganic salts in water, prevent or interfere with the precipitation and scaling of sparingly soluble inorganic salts on metal surfaces, and maintain good heat transfer performance in metal equipment.

20. EDI: Continuous Electrodialysis, a novel ultrapure water preparation technology that gradually developed in the 1990s. It cleverly combines electrodialysis and ion exchange technologies. Through the selective permeation of anions and cations by cation and anion exchange membranes and the ion exchange effect of ion exchange resins, ions migrate directionally to the concentrate chamber under the action of a DC electric field, thus achieving deep desalination of water to obtain ultrapure water. Simultaneously, water molecules are electrolyzed into hydrogen ions and hydroxide ions, regenerating the resin and eliminating the need for traditional acid-base chemical regeneration.