There are many application fields of water treatment. Some of them have high requirements for water quality, while others are not so strict. More and more people enter the water treatment industry. Let's share some water treatment related knowledge and learn and discuss with you.

PART 1——Noun explanation

1、Raw water: refers to untreated natural water or city tap water, also known as raw water

2、Clarified water: water with suspended impurities removed from raw water

3、Desalted water: refers to the water whose cation and anion are basically removed or reduced to a certain extent, which is called desalted water. The desalting methods include distillation, electrodialysis, reverse osmosis and ion exchange

4、Turbidity: refers to the degree of water turbidity, it is due to the water contains a certain amount of suspended solids (including colloidal substances) produced by the optical effect. The unit is NTU. Turbidity is one of the main characteristics to judge whether water is polluted in appearance. The standard unit of turbidity is 1 mg SiO2, and the turbidity is 1 degree

5、Flocculant: the agent that can cause colloidal particles to coagulate and bridge to flocculate

6、Total alkalinity: refers to the total amount of substances that can neutralize strong acids in water

7、Acidity: refers to the total amount of substances in water that can neutralize with strong alkali

8、Hardness: refers to some metal ions in water that are easy to form sediment, usually refers to the content of calcium and magnesium ions

9、Conductivity: refers to the conductivity of solution between two parallel electrodes with a cross-sectional area of 1 square centimeter and a distance of 1 centimeter at a certain temperature. It can indirectly express the content of dissolved salt in water

10、Resistivity: it is also an index reflecting the conductivity of water. The higher the resistivity of water, the worse the conductivity of water, and the less ions it contains. Its common unit is m Ω. CM。 The relationship between it and conductivity is reciprocal. For example, the conductivity of water is 0.2 μ S / cm, then its resistivity is 1 / 0.2 = 5 (m) Ω. CM)

11、TDS (total dissolved solids): it is the residual inorganic matter after removing SS and colloid and evaporating all water. The unit is ppm or mg / L, which can be measured by TDS instrument. It also reflects the ion content in the water. There is a rough correspondence between it and conductivity: for sodium chloride reference solution, the TDS value of 1ppm corresponds to 2 μS/cm

12、PH value: the relative content of acid and alkali in solution. PH is a measure of the negative logarithm (log) of hydrogen ion concentration in water. When pH value is 7.0, water is neutral; When pH value is less than 7.0, the water is acidic; The pH value is more than 7.0. The water is alkaline

13、Alkalinity: alkalinity refers to the content of substances in water that can accept the neutralization reaction between [H +] ions and strong acids. The alkalinity in water is mainly caused by carbonate alkalinity, bicarbonate alkalinity and hydroxide alkalinity

14、SDI: pollution index - used to measure the amount of suspended solids in raw water used in reverse osmosis system

15、Ozone: an unstable and highly active form of oxygen. It is produced by natural lightning or high-voltage charge through the air. It is an excellent oxidant and disinfectant

16、Residual chlorine: the residual effective chlorine in water after chlorination and contact for a certain period of time

17、Total Escherichia coli: total coliform refers to a group of aerobic and facultative anaerobic gram-negative non bacillus which can ferment lactose at 37 ℃ and produce acid and gas within 24 hours. Total coliform group refers to the number of total coliform groups contained in each liter of water

18、Recovery rate: it refers to the ratio of the flow rate of product water produced by the system to the inflow flow rate

19、Desalination rate: a parameter reflecting the performance of the membrane. Generally, the desalination rate of the primary RO membrane system is more than 97%. It can be simply calculated as follows: (conductivity of raw water conductivity of product water) / conductivity of raw water

20、Salt content: the salt content of water, also known as salinity, is the amount of salt in water. Since all kinds of salts in water generally exist in the form of ions, the salt content can also be expressed as the sum of the amount of cations and anions in water

21、Sedimentation: one of the technical methods of wastewater treatment. It can be divided into physical precipitation and chemical precipitation. Precipitation is usually referred to as physical precipitation, that is, gravity separation method

22、Reclaimed water: there are many explanations, such as reclaimed water in sewage engineering and reclaimed water in factories, which are generally distinguished by water quality. It mainly refers to the non drinking water that can be reused in a certain range after the treatment of urban sewage or domestic sewage reaches a certain water quality standard

The quality of reclaimed water is between the upper water (drinking water) and the lower water (domestic sewage), which is the origin of the name of reclaimed water. People also call the system of supplying reclaimed water as reclaimed water system

23、Organic pollution: refers to natural organic matter and other biodegradable synthetic organic matter in the form of carbohydrate, protein, amino acid and fat. It mainly comes from domestic sewage and industrial wastewater

24、Concentration polarization: under the operation condition of reverse osmosis, the salt on the membrane surface is concentrated, and there is a concentration difference with the salt in the water. If the flow rate of concentrated water is small and the flow rate is low, the water with high content of salt can not be taken away in time, and a high concentration difference will be formed on the membrane surface, which hinders the diffusion of salt. This phenomenon is called concentration polarization

25、Suspended solids (SS): refers to the solid matter suspended in water, including inorganic matter, organic matter, sand, clay, microorganism, etc. The content of suspended solids in water is one of the indicators to measure the degree of water pollution. It is the amount of solid obtained by drying the residue on the filter paper at 103-105 ℃ after the water sample is filtered. Unit: mg / L

26、Aeration: the process of transferring O2 in the air to the mixture and being used by microorganisms. The purpose is to provide the dissolved oxygen needed by microorganisms such as activated sludge and ensure the oxygen demand of microbial metabolism process

27、Biochemical oxygen demand (BOD): refers to the dissolved oxygen consumed by microorganisms in the process of decomposition and oxidation of organic matter in water at specified time, temperature and conditions. It usually takes 5 days, temperature is 20 ℃, abbreviated as BOD5, unit: mg/L

28、Chemical oxygen demand (COD): refers to the amount of oxygen consumed by oxidizing organic substances in wastewater with strong oxidants under certain conditions. Potassium dichromate is generally used as oxidant in wastewater inspection standard, unit: mg/L

29、Water hammer: also known as water hammer. In the process of water (or other liquid) transportation, due to the sudden opening or closing of the valve, the sudden stop of the pump, the sudden opening and closing of the guide vane and other reasons, the flow rate changes suddenly, and the pressure fluctuates greatly

30、Adsorption: refers to the use of porous solid adsorption of some or several pollutants in wastewater to recover or remove some pollutants, so that the wastewater can be purified

31、Enzyme: it is a kind of catalyst (biocatalyst) made in biological cells. Its basic component is protein, which promotes the speed of biochemical reaction

32、Sewage: sewage refers to the water discharged in production and living activities. In human life and production activities, a lot of water is used, which is often polluted to varying degrees. The polluted water is called sewage

33、Sewage treatment: it is to use various technologies and means to separate and remove the pollutants contained in the sewage, recycle or transform them into harmless substances to purify the water

34、Wastewater reuse: the reuse of wastewater or wastewater after secondary treatment and advanced treatment for production system or domestic miscellaneous use is called wastewater reuse. When the treated water meets the specific reuse requirements, it can also be called reclaimed water

35、Scale: that is, due to the poor quality of boiler water, after a period of operation, the solid attachment formed on the pipe wall of the heating surface in contact with water

36、Water slag: refers to the solid substance suspended in the boiler water and the sediment deposited at the bottom of drum and lower header where the water flow is slow. Difference from scale: water slag is loose, suspended or sediment state, and part of it is easy to be discharged with boiler blowdown; The scale can be firmly adhered to the pipe wall and is not easy to be discharged

37、Iron, manganese, aluminum: trace amounts of iron and manganese will cause problems such as dyeing, scaling and taste. Iron exists in the form of water-soluble Fe2 + in the reduced state. When it comes into contact with air, it will gradually oxidize into yellow brown colloidal Fe3 + and finally precipitate into brown ferric hydroxide. The characteristic of manganese is similar to that of iron. Because the oxide of iron, manganese and aluminum is one of the reasons of RO membrane fouling, it is necessary to analyze its content

38、Pure water: refers to the water that can remove the strong electric medium that is easy to remove, and the weak electrolytes such as silicic acid and carbon dioxide that are difficult to remove to a certain extent. The salt content of pure water is less than 1.0mg/l, and the conductivity is less than 3.0mg/l μ s/cm

39、Ultrapure water: also known as high-purity water, refers to the water that almost completely removes the conductive medium in the water, and also removes the colloidal substances, gases and organic substances in the water to a very low level,. The salt content of ultrapure water is less than 0.1mg/l, and the conductivity is less than 0.1mg/l μ s/cm

In addition to strict requirements on salt content or conductivity, pure water and ultra pure water also have strict limits on the contents of various metal ions, organic matter, particle size and quantity, and microbial quantity.

40、Distilled water: the raw water is heated and vaporized, and then condensed into steam, which is called distilled water. Generally, the conductivity of distilled water is 10 μ The conductivity can be reduced to as low as 1.0 s/cm μS/cm

41、Scale inhibitor: it can disperse insoluble inorganic salt in water, prevent or interfere with the precipitation and scaling of insoluble inorganic salt on metal surface, and maintain good heat transfer effect of metal equipment.

42、Ion exchange resin: it is a high molecular compound with functional group (active group with exchange ion), network structure and insoluble. Usually spherical particles

43、Ion: refers to the stable structure in which an atom loses or gains one or more electrons due to its own or external effects, so that it reaches the outermost layer with 8 or 2 electrons (helium atom) or no electrons (four neutrons). This process is called ionization.

44、Water yield (water flux): refers to the capacity of the reverse osmosis system, that is, the amount of water passing through the membrane per unit time, usually expressed in tons per hour (T / h) or gallons per day (g / D)

45、EDI: continuous electro desalting for short, is a new ultra pure water preparation technology. It skillfully combines electrodialysis technology and ion exchange technology.

PART 2——Explanation of basic process of pure water treatment

1、Coarse filtration: refers to mechanical filtration to remove suspended solids, colloid, turbidity, chroma, odor, etc. The main filtration methods are clarifier, fast filter, sand filter, sand filter, multi-media filter, activated carbon filter, disc filter, high efficiency fiber filter, etc.

2、Fine filtration: the filtration membrane made of special materials has high filtration precision. The common ones are microfiltration membrane and filter element.

3、Ultrafiltration: it is a kind of membrane filtration to remove macromolecules, colloids, bacteria, etc. Ultrafiltration membrane is a common one with high filtration precision.

4、Reverse osmosis: RO for short, its principle is that the raw water passes through the reverse osmosis membrane under the action of high pressure, and the solvent in the water diffuses from high concentration to low concentration, so as to achieve the purpose of separation, purification and concentration, because it is opposite to the permeation direction of nature.

5、Ion exchange: various inorganic salts in water are ionized to form cation and anion. When passing through the hydrogen ion exchanger layer, the cation in water is replaced by hydrogen ion, which is the desalination principle of cation bed; When passing through the OH - type ion exchanger layer, the anions in water are replaced by OH - ions, which is the desalination principle of anion bed.

The mixed bed is an ion exchange device in which cation and anion exchange resins are mixed and loaded in the same exchange column according to a certain proportion.

6、EDI: is a new desalination process combining electrodialysis and ion exchange. It takes the advantages of electrodialysis and mixed bed ion exchange, uses ion exchange for advanced treatment, does not need reagent regeneration, but uses ionization to produce H + and oh -, so as to achieve the purpose of resin regeneration.

PART 3 —— Common water treatment processes

1、The raw water is groundwater: sand filter + precision filter + reverse osmosis + mixed bed or EDI

2、The raw water is tap water: sand filter + activated carbon filter + precision filter + ro + mixed bed or EDI

3、Surface water：

① Multi media filter + activated carbon filter + precision filter + ro + mixed bed or EDI

② Multi media filter (or other filter) + ultrafiltration + precision filter + ro + mixed bed or EDI

③ Disc filter + ultrafiltration + precision filter + ro + mixed bed or EDI

PART 4 —— Pipe materials commonly used in water treatment engineering

1、Carbon steel pipe: used for raw water inlet pipeline.

2、UPVC pipe: it is better to be used when the pipe diameter is less than DN 150, and the installation is convenient.

3、Stainless steel pipe: used for special occasions, mostly for small medical systems.

4、Steel lined rubber or plastic pipe: used in large projects, reliable use, construction more trouble.

PART 5 —— Various uses of pure water

Pure water and ultra pure water are widely used in power plant, electronics, medicine and chemical industry. Harmful ions in water can be removed by various membrane filtration or ion exchange.

1、Power plant: multi purpose desalted water. The main indexes of desalted water quality are hardness equal to zero and conductivity ≤ 0.2 μ s.cm，SiO2≤20ppb

2、Chemical plant: there are many kinds of chemical water, usually the water quality is not higher than that of power plant, but it may have requirements for some ions, so the primary or secondary reverse osmosis process is commonly used. The conductance of effluent quality is 5 ~ 10 μ s. It is more than 10 cm. If there are higher requirements, mixed bed or EDI will be added at the back.

3、Medicine: medical water mostly requires conductivity and bacteria, and has requirements for materials used in the system. Stainless steel products are mostly used. Usually pure water after adding sterilization device.

4、Electronic industry: the electronic industry has the highest requirement for water, most of which require 18 megabytes of water. The requirement of resistivity is only a small part of electronic water, it has higher requirements for many ions, so it has special requirements for installation materials and pipes. The selection process is also the most complex. Usually, polishing mixed bed, ultrafiltration, sterilization, nitrogen sealing water tank and other devices are added after EDI, and the cost is also very high.

PART 6 —— According to the requirements of water quality, the process is usually adopted

1、The conductivity of produced water is required to be 10~20μS/cm: RO pretreatment + primary reverse osmosis (chemical)

2、The conductivity of produced water is 2 ~ 9 μ S / cm: RO pretreatment + secondary reverse osmosis (medicine and chemical industry) or ro pretreatment + softening + primary reverse osmosis + EDI (medicine and chemical industry)

3、The conductivity of produced water is less than 0.2~2μS/cm: RO pretreatment + primary reverse osmosis + mixed bed

4、Water resistance 5 ~ 13m Ω. Cm: R0 pretreatment + softening + primary reverse osmosis + EDI or ro pretreatment + secondary reverse osmosis + EDI (medicine, chemical industry, electronics, power generation)

5、Water resistance 13 ~ 17m Ω. Cm: R0 pretreatment + softening + primary reverse osmosis + EDI + mixed bed or ro pretreatment + secondary reverse osmosis + EDI + mixed bed (medicine, chemical industry, electronics, power generation)

6、Water producing resistance 18m Ω. Cm: RO pretreatment + secondary reverse osmosis + EDI + mixed bed + sterilization + nitrogen sealing.

PART 7 —— Questions and answers on key and difficult points of pure water treatment

1、What are the main measures to reduce acid and alkali consumption?

(1) Ensure the quality of the influent water;

(2) Ensure the regeneration quality and extend the cycle of water production;

(3) Ensure the quality and purity of the regeneration liquid, and strictly control the regeneration operation procedures;

(4) Ensure the safe, reliable and normal operation of the equipment.

2、What are the reasons for the stability of colloids in water?

(1) The colloid surface is charged;

(2) There is water level layer on the surface of colloid;

(3) The colloid surface adsorbs some substances that promote colloid stability.

3、What is the purpose of using coagulant aids?

1) Improve the structure of flocs to make them grow, strong and heavy;

2) Adjust the pH value and alkalinity of the treated water to achieve the best coagulation conditions and improve the coagulation effect; The coagulant aid itself does not play the role of coagulation, but can promote the coagulation process of impurities in water.

4、The basic concept of coagulation?

Because the colloidal particles in the water are negatively charged, they repel each other in the same sex, and at the same time, they constantly do "Brownian motion" in the water, which is extremely stable and not easy to sink. When an appropriate amount of coagulant is added, the micro colloidal particles in the water can destabilize, produce adsorption bridging effect, flocculate into flocs, and sink rapidly. This process is called coagulation.

5、What are the main factors affecting the coagulation effect?

1) PH value of water: if PAC is added to hydrolyze Al (OH) 3 colloid, when pH value is 6.5-7.5, the dissolution is minimum, and the coagulation effect is good;

2) Alkalinity of water: when the alkalinity is insufficient, the coagulant will produce H + continuously in the hydrolysis process, which will reduce the pH value and the coagulation effect;

3) Water temperature: when the temperature is low, the viscosity of water is high, the hydrolysis speed is slow, the floc formation is slow, and the structure is loose, the particles are small and not easy to precipitate;

4) The composition and concentration of impurities in water have great influence on the coagulation effect.

6、What is the relationship between the form of carbonates in water and pH value?

1) When pH ≤ 4.3, there is only CO2 (free) in water;

2) When pH value is 8.3-3.4, more than 98% of HCO3 -;

3) When pH > 8.4, there is no CO2 in the water

7、Purpose of water treatment in boiler?

1) To prevent water and steam from accumulating deposits and corrosion in boiler body and auxiliary system during operation. Improve the heat transfer efficiency of boiler.

2) Ensure the quality of steam, prevent the scaling and corrosion of steam turbine components, reduce the loss of boiler blowdown under the condition of ensuring water quality, and improve economic benefits.

8、How does a centrifugal pump work?

Centrifugal pump uses the impeller rotation to make water produce centrifugal force to work. Before starting the pump, the pump shell and suction pipe must be filled with water, and then start the motor to make the pump shaft drive the impeller and water to rotate at high speed. Under the action of centrifugal force, the water is thrown to the outer edge of the impeller and collected into the pump shell, and flows into the pressure water pipeline of the pump through the passage of the scroll pump shell.

At the same time, the center of the pump impeller is thrown out to form a vacuum, and the water in the suction tank is sucked into the impeller through the suction pipe under the action of atmospheric pressure. The impeller keeps rotating, and the water is constantly thrown out and replenished. This forms the continuous water delivery of centrifugal pump.

9、What is resin regeneration?

After a period of softening or desalting operation, the resin lost the ability of ion exchange; At this time, acid, alkali or salt can be used to reduce and regenerate the resin to restore its exchange capacity. This process of restoring resin capacity is called resin regeneration.

10、What are the main factors that affect the resin working exchange capacity?

(1) The quality of the water in the influent;

(2) The control index of exchange terminal;

(3) Height of resin layer;

(4) Water temperature and flow velocity;

(5) The regeneration effect of exchanger depends on the performance of resin itself.

11、What are the chemical properties of the resin?

1) Reversibility of ion exchange reaction, such as:

RH+Na+RNa+H+

2) Acidity and alkalinity:

ROHR+OH-;RHR+H+

3) Selectivity: the adsorption of different ions on ion exchange resin is different.

4) Resin exchange capacity

Cation exchange resin:

Fe3+>Al3+>Ca2+>Mg2+>K+≈NH4+>Na+

Anion resin:

SO42->NO3->Cl->HCO3->HSi

12、What is the pollution of mixed bed resin?

1) Suspended pollution: mostly in the form of cation resin. Strengthen the pretreatment of raw water.

2) Organic pollution: mainly occurred in strong alkali cation resin. Main resuscitation method: soak the resin in the mixed solution of NaOH (1-4%) and NaCl (5-12%) for 24 hours.

3) Heavy metal ion iron pollution: mostly formed in anion resin, strengthen the corrosion of pipes and equipment, reduce the Fe content of influent water, and increase iron removal measures.

13、What are the main reasons for the performance degradation of RO membrane?

1) Chemical changes of membrane itself: hydrolysis of membrane, oxidation interference of free chlorine and active chlorine

2) The physical changes of membrane itself: the compaction of membrane makes the permeability rate decrease and the desalination rate increase; Fouling of membrane: fouling, microorganism and solid particles on the surface or inside of membrane.

14、Process principle of security filter?

It is the mechanical filtration with 5um porous PP filter element, so that the residual micro suspended particles and colloidal microorganisms in the water are intercepted or adsorbed on the surface and voids of the filter element. With the increase of water making time, the resistance of the filter element increases due to the solids. When the pressure difference between the inlet and outlet increases to 0.1MPa, the filter element should be replaced; The filter element of the filter is a replaceable cartridge filter rod.

15、How to prevent the scaling of RO membrane?

1) Do a good job in the pretreatment of raw water, ensure the SOI < 4, and add bactericide to prevent the growth of microorganisms；

2) In RO operation, the appropriate working pressure should be maintained. Generally, with the increase of working pressure, the water yield will increase, but if the working pressure is too large, the membrane will be compacted;

3) During ro operation, the flocculent state of concentrated water should be maintained to reduce the concentration polarization of the solution on the membrane surface and avoid the precipitation of insoluble salts on the membrane surface;

4) When the RO is out of service, it is necessary to add chemicals for flushing in the short term and CH2O protection solution for protection in the long term;

5) Chemical cleaning should be carried out when the RO produced water is obviously reduced or the salt content is increased, and the surface is scaling or polluted.

16、The role of NaHCO3 in the desalination process of RO unit?

Eliminate or reduce the residual chlorine content in water to ensure the stability of RO components. The residual chlorine of our company is less than 0.1mg/l.

17、Function of setting electric slow opening automatic valve in front of RO membrane module?

To prevent the sudden start-up and shut-down of high-pressure pump during ro operation, resulting in high-pressure impact on RO membrane components, forming water hammer and damaging RO membrane.

18、What is filtration cycle? How many links are involved? What is the role of each link?

Filtration cycle is the actual running time between two backwashing, including three links: filtration, backwashing and forward washing；

The purpose of backwashing is to remove the dirt accumulated in the filtration process and restore the interception capacity of the filtration medium；

Is washing to ensure filtration operation? It is a necessary link for water to be qualified. Only after the washing is qualified, can it enter the periodic operation of water production.

19、Principle of chlorine removal by activated carbon

The removal of residual chlorine by activated carbon is not physical adsorption, but chemical reaction. When the free residual chlorine passes through the activated carbon, it will produce catalytic effect on its surface. The free residual chlorine will hydrolyze oxygen atoms quickly and react with carbon atoms to generate carbon dioxide. At the same time, the HClO in raw water is also rapidly converted into CO2 gas.

Comprehensive response: 1

C+2Cl2+2H2O→4HCl+CO2↑

According to the above, the activated carbon in the reaction vessel will be gradually reduced according to the residual chlorine content in the raw water, and it should be supplemented appropriately every year.

20、Principle of reverse osmosis process

Ro is the use of semi permeable membrane water impermeable characteristics, remove most of the salt in water. Pressurize the raw water side of RO to make a part of pure water pass through the membrane along the direction perpendicular to the membrane. The salt and colloidal substances in the water are concentrated on the membrane surface, and the rest of raw water is taken away along the direction parallel to the membrane. There is only a small amount of salt in the permeated water. The purpose of desalination is achieved by collecting the permeated water.

Source: Miaozhi Hydrosphere

Original title: 7000 words summary! Basic knowledge of environmental water treatment, all here!