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Basic Knowledge of Water Treatment

Views:5     Author:Robin     Publish Time: 2020-11-10      Origin:Site

I. Types of water

(1) Raw water: Raw water refers to water that has not been treated.In a broad sense, the water before entering the water treatment process is also called the raw water of the water treatment process.

Softened water: Softened water is water to which hardness (mainly calcium and magnesium ions) is removed or reduced to a certain degree.In the process of water softening, only the hardness decreases, but the total salt content remains the same.

(2) Desalted water: Desalted water refers to water in which salts (mainly strong electrolytes dissolved in water) are removed or reduced to a certain extent.Its electrical conductivity (25) is generally 1.00-10.0 S/cm, and its salt content is 1-5mg/ L.

Pure water: Pure water refers to water in which strong and weak electrolytes (such as SiO2, CO2, etc.) are removed or reduced to a certain extent.Its conductivity is generally 1.0-0.1 S/cm salt content <1mg/ L.

(3) Ultra-pure water: Ultra-pure water means that the conductive medium in the water is almost completely removed, and the gas, colloid and organic substances (including bacteria, etc.) are also removed to a very low degree.The conductivity is generally <0.1 S/cm and the salt content <0.1mg/ L.

In addition, there are: boiler water, circulating cooling water, etc.

water treatment system

Ⅱ. The main index of water

(1) Suspended matter: particles with large diameter, mainly composed of sediment, clay, protozoa, algae, bacteria, viruses and macromolecular organic matter, are often suspended in the water flow, resulting in turbidity of water.These particles are unstable and can be removed by precipitation and filtration.Heavy particles (mainly inorganic materials such as sand and clay) settle when water is left standing.Light particles (mainly organic compounds of plants and animals and their remains) float to the surface and can be removed by filtration.Suspended matter is the main source of turbidity, chroma and odor.

(2) Turbidity: The degree of obstruction caused by a suspended 

body of water to the passage of light;Impurities that cause turbidity include microorganisms, silicic acid, iron, manganese and other compounds, and clay.

Generally, the turbidity of 1L distilled water containing 1mg silica is defined as 1 degree (NTU).

The water turbidity of soft drinks should not exceed 2 degrees.The turbidity of RO inlet water is less than 0.5NTU

(3) Stink and smell

The causes of odors and odors in water are complex and may be inorganic (sulfur, chlorine, etc.), organic (fishy, putrid, hydrocarbon odor), and gas.

Harm: influence beverage aroma and taste, and sometimes cause precipitation.

Deodorization or deodorization: If the odor is caused by gas, degassing can be used;Odors caused by reducing substances can be oxidized by chlorine or ozone;Activated carbon filtration and adsorption is an effective method.

(4) Electrical conductivity: Because the water contains a variety of dissolved salts, and exist in the form of ions.The conductivity reflects the amount of salt in water and is an important index of water purity.

The international unit is si ·m-1 (S·m-1), usually S/cm;The reciprocal of resistivity is the electrical conductivity, commonly used units are M 

Ω · cm.

It is generally considered that secondary RO is used for raw water conductivity >300 S/cm in the production of pure water, and primary RO is used if the conductivity of raw water is <300 S/cm.

(5) Hardness: Some metal cations and anions in water are combined together. In the process of water heating, due to evaporation and concentration, scale is easy to form, which is attached to the heating surface and affects the heat conduction. We call the total concentration of these metal ions in water as the hardness of water.

The most common metal ions in natural water are calcium ions (Ca 2+) and magnesium ions (Mg 2+).Iron, manganese, zinc and other metal ions will also form a small amount of hardness, generally ignored.

The units of hardness commonly used are mmol/L or mg/L and are usually expressed in terms of CaO or the mass concentration of CaCO 3.

The hardness produced by calcium and magnesium carbonate and bicarbonate is called temporary hardness, while the hardness produced by calcium and magnesium sulfate, chloride and nitrate is permanent hardness.Most natural water has both temporary hardness and permanent hardness, and the hardness of water generally refers to the total hardness of water.

Total hardness of soft drink water <100mg/L(CaCO 3);One German degree is equal to 10mg/L CaO;

1mmol/L=5.6 German degree = 100mg/L (CaCO 3)

water treatment system

(6) PH: The PH value of water is the negative logarithm of hydrogen ion concentration in water, which is expressed as: PH= -lg[H+]

Neutral aqueous solution, PH=-[lg[H+]=-lg10-7=7;

Acid aqueous solution, PH<7, the lower the PH value, the more acidic;

Alkaline aqueous solution, PH>7, the higher the PH value, the stronger the alkalinity;

(7) Total dissolved solids: All impurities in water except dissolved gases are called solids.The sum of the dissolved and suspended solids 

is called the total solid of water.

Total dissolved solids (TDS) are all kinds of inorganic salts, organics, etc. that still dissolve in water after water filtration.The reference value of primary RO and secondary RO is 250mg/L.

Suspended solids are those that can be filtered out, insoluble in water sediment, clay, organic matter and other suspended matter.

The measurement of total solids is obtained by evaporating water and then weighing it.

(8) Salinity: The salinity of water (also known as salinity) is the amount of salts in the water.Since all kinds of salts in water generally exist in the form of ions, salt content can also be expressed as the sum of all kinds of cations and anions in water.

The salt content of water differs from that of dissolved solids in that dissolved solids contain not only dissolved salts but also organic matter.

Alkalinity: Alkalinity is produced mainly by the presence of carbonate, bicarbonate, and hydroxide.The sum of the three anions in natural water constitutes the total alkalinity.

Beverage water was calculated as CaCO 3 with alkalinity <50mg/L

(9) Total organic carbon: The content of organic matter in water, expressed by the amount of the main element in organic matter - carbon, is called total organic carbon.

Soluble organic carbon (DOC), TOC and DOC are commonly used water quality indexes.

(10) Oxygen demand

Chemical oxygen Demand (COD) and biological oxygen demand (BOD)

Chemical oxygen demand is an indicator of how much of a reducing substance is in water.

Chemical oxygen demand is an indicator of how much of a reducing substance is in water.

A measure of the amount of organic matter in water.

(11) Water pollution Index SDI

Daily monitoring of the pollution index SDI(also known as deposition index) of the pre-treated water

Make sure SDI 15 5

SDI 15 =[1-t 0/ T 15] ×100/15





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