February 28, 2023     Posted by :

1 What are the pretreatment plant you know?

A: Pretreatment plant are: sand filter,, activated carbon filter, precision filter, ultrafiltration, microfiltration, sodium ion softener, iron and manganese removal filter, dosing device, raw water tank, aeration tank.

2 What are the desalination system that you know?

A: Desalination system has reverse osmosis unit

3 What are the deep desalination system you know?

A: Deep desalination system are anion exchanger, cation exchanger, mixed ion exchanger, distillation system, EDI system

4 How is the mechanical filter selected? What is its working principle?

A: The selection of mechanical filter is based on the total water intake of the system to select the size of the filter and the combination (one mechanical filter is not enough to select multiple parallel use and the number of backup), such as the size of the water recovery rate of the reverse osmosis system and the ratio of system water production to the total water intake of the system. The filler in the mechanical filter is made of many refined quartz sand of different particle sizes in strict order from large to small, thus forming a good quartz sand gradation.

When the filter is first put into use, the filtration effect is often not very good because at the beginning, the filter does not form a “bridge”, the so-called “bridge” refers to the formation of an interceptor net by the suspended matter in the water, the interceptor net intercepts the suspended matter with its particle size, and then intercepts the suspended matter with smaller particle size.

The interception network intercepts the suspended matter of comparable particle size, and then intercepts the suspended matter of smaller particle size, forming an anti-grain size filtration process of intercepting large particles first, and then intercepting small particles. Once the filter forms a “bridge”, the filtration effect is very good.

As the filter is put into operation for a longer period of time, the filtration precision becomes higher and higher, the interception net becomes thicker and thicker, and the pressure difference between the import and export becomes larger and larger, and when the pressure difference reaches 1 kg/cm2, the filter should be backwashed, and it is better to have compressed air to scrub the quartz sand during the backwashing process.

The general engineering experience is that mechanical filters with diameter less than 2500mm do not need to use compressed air; while mechanical filters with diameter greater than 2500mm must be scrubbed with compressed air to achieve a satisfactory cleaning effect; backwashing flow is generally 3-4 times the design capacity of the filter.

Most of the old mechanical filters use large pebbles as the basic bedding layer, and the bottom is evenly perforated with convex steel plates, which makes the water distribution uneven and easily produces a large filtration rate in the center and a small filtration rate at the edges; when the filter is backwashed, the phenomenon of mixed layers of quartz sand will occur, which will inevitably lead to the leakage of filter material into the lower pipeline and precision filter, forming a serious threat to the precision filter and reverse osmosis device.

This is a serious threat to the precision filter and reverse osmosis device. After continuous practice and experiment, many manufacturers have improved the mechanical filter, and the water distribution device adopts a porous plate with a special form of ABS water cap, which has the function of two-way force, i.e., the force is smaller when running, and the force can be increased several times when backwashing, so that the water distribution of the filter is more uniform when washing, and more thorough when backwashing, and the water quality is greatly improved. In order to prevent fine sand from penetrating the filter during operation or backwashing, the permeation gap of this ABS water cap is very small, generally around 0.1-0.2mm. It is worth noting that in the process of filling the filter, a certain amount of water must be injected into the filter to prevent large quartz sand from breaking the ABS water cap; in the process of installing the water cap, hard shoes should not be worn to prevent stepping on the ABS water cap.

Mechanical filter is equipped with backwash water inlet limit butterfly valve to control and adjust the flow of backwash water, backwash intensity should make the filter layer expand 15-25%, backwash compressed air intensity is generally 10-18L/S.m2. If there is no compressed air, consider using Roots fan.

5 How is the precision filter selected? How many ways are there for cartridges?

A: The selection of precision filter is matched with the total water intake, and the diameter of precision filter is selected according to the total water intake. For 40″5um filter cartridge, the single water output is about 2m3/h. The types of cartridge are polypropylene cartridge, honeycomb cartridge, spray fusion cartridge, folding cartridge, etc.

6 How to remove iron in water?

A: The iron in groundwater is generally divalent ferrous iron, so the divalent ferrous iron must be oxidized to trivalent iron, the oxidation process is completed by aeration, aeration device to bring the water into full contact with oxygen and produce natural oxidation; aeration of the water through the iron and manganese removal filter for iron removal process. If most of the iron in the water is trivalent iron, it does not need to be aerated and directly enters the iron and manganese removal filter for removal.

7 How many ways of anti-corrosion?

A: There are several ways of anti-corrosion such as rubber lining, epoxy, plastic lining and enamel.

8 Reverse osmosis plant is mainly composed of that equipment?

A: Reverse osmosis plant mainly consists of high pressure pump, high pressure pump outlet gate valve (manual or electric), high and low pressure protection switch, inlet water flow meter (also can not be added), production water flow meter, concentrated water flow meter, production water conductivity meter, membrane components (pressure vessel, reverse osmosis membrane element), concentrated water electric valve, concentrated water shut-off valve, inlet water pressure gauge, inter-segment pressure gauge, concentrated water pressure gauge, production water pressure gauge, reverse osmosis bracket, reverse osmosis control panel, reverse osmosis sampling panel, bursting membrane and corresponding pipes, clamps, elbows, etc. control panel, reverse osmosis sampling panel, bursting membrane, and corresponding pipes, clamps, elbows, etc.

9 How is the frequent automatic reversal system of concentrated water circulation realized? What is its significance?

A: In the current water treatment industry, the concentrated water cycle frequent automatic reversal system is based on the programmable controller as the control core, with the system water production process running time as the control function, the use of electric or pneumatic straight-through valve, three-way valve to switch the direction of water flow of concentrated fresh water at regular intervals, so that fresh water always flows into the water production tank, while the concentrated water is discharged into the concentrated water cycle tank fixed.

In today’s increasingly scarce water resources, concentrated water circulation frequent automatic inversion system has far-reaching significance,

first the system’s high water recovery rate can reach 80% (depending on the quality of the incoming water), in some large water treatment system in the effect of water saving is very obvious.

Secondly, the cost of the system is relatively low, the requirements of the system water quality is relatively low, easy to promote (in some high recovery rate requirements and not able to invest more money in the water treatment projects of enterprises or mines are more competitive).


10 What kinds of pumps are needed in water treatment system projects? How to select the pumps of different manufacturers?

A: The water treatment system project needs ordinary pump, booster pump and anti-corrosion pump. Ordinary pumps generally use IS type cast iron pumps; booster pumps generally use stainless steel pumps such as New Territories high pressure pumps (depending on the specific situation); anti-corrosion pumps generally use IH type chemical pumps or engineering soluble pumps.

The pump models of different manufacturers are different. Firstly, choose the flow rate of the pump according to the process requirements of the system; secondly, choose the head of the pump according to the process requirements (1kg is about 10m head, 1MPa is about 10kg); again, choose the material of the pump according to the process requirements (mainly refers to the material of the pump head); finally, choose the pump according to the power consumption of various pumps that can meet the process requirements and save the energy consumption of the system.

Finally, according to the power consumption of various pumps, choose the pump that can meet the process requirements and save the energy consumption of the system.

11 Several basic concepts in water treatment systems: TDS, SDI, LSI, KSP


TDS : total dissolved solids (generally and mineralization approximation)

SDI: pollution index is a measure of the system pretreatment effect, SDI <6.7, for deep well water (well water), reverse osmosis system on the feed water SDI requirements for SDI <5.

LSI: Langelier Saturation Index, Langelier index is to measure the tendency of scaling in reverse osmosis system, LSI=0, the system has no scaling and no corrosion tendency; LSI>0, the system has scaling tendency; LSI<0, the system has corrosion tendency. For reverse osmosis system, the LSI value should not be greater than 0. The LSI value of the system can be reduced by adding acid, or by reducing the system water recovery rate.

Ksp: solubility equilibrium constant, the reverse osmosis system to the raw water solvent, solute selective permeation, in the concentrated water side due to the reduction of solvent and concentration, when the concentration of dissolved solids on the concentrated water side appears because the concentration product is greater than the solubility equilibrium constant, it will crystallize and precipitate, which brings harm to the reverse osmosis system. Increasing the solubility equilibrium constant of the system can be done by adding scale inhibitor, which can increase the solubility of dissolved solids.

12 What kinds of instrumentation are necessary in reverse osmosis systems?

A: Several instruments are necessary in reverse osmosis system.

1 Pollution index meter: used to measure the SDI index of the system pretreatment.

2 Concentrated water flow meter: used to measure the flow rate of concentrated water in the system, and used in conjunction with the production water flow meter to determine the system recovery rate.

3 produced water flow meter: used to measure the flow rate of the system produced water. Produced water conductivity meter: used to measure the system produced water quality (conductivity)

4 Pressure gauge: to measure the system inlet pressure, inter-segment pressure, concentrated water pressure, produced water pressure

5 Intake water flow meter: used to measure the total intake water flow of the system

6 Thermometer: used to measure the temperature of the system operation.

7 Inlet water PH meter: used to measure the changes in the system inlet water PH value.

8 Feed water conductivity meter: used to measure the system feed water conductivity, and produce water conductivity used in conjunction to determine the system desalination rate.

9 Redox meter: used to measure the amount of oxidizing substances in the system feed water to determine the degree of threat to system safety.

10 High and low pressure protection switch: Used to protect the system from operating at low pressure (insufficient water supply) and high pressure.

A reverse osmosis system is complex and the instrumentation used is determined by the process requirements and the user’s investment. A normal reverse osmosis system only needs a flow meter for produced water, a flow meter for concentrated water, a conductivity meter for produced water, a pressure gauge, and high and low pressure protection is sufficient.

13 What is the water hammer phenomenon? How to solve this problem?

A: “Water hammer” is due to the pressure vessel mixed with air, in the start-up device does not use the necessary means to remove the air in the vessel, so that the high pressure water mixed with air to the vessel when the movement of violent vibration, serious will be the membrane element smashed, bringing unrecoverable losses.

“Prevention in the first, prevention is the main”, how to prevent the phenomenon of “water hammer” is quite important.

The following measures are generally taken.

1 high pressure pump using soft start to avoid, such as buck start, frequency conversion speed start, with automatic controller string resistance start.

2 in the operation mode to avoid, such as in the start of the inlet valve closed or closed small, and then slowly open the valve until it reaches the system working pressure.

3 Use control to prevent avoid, such as using PLC to control an electric slow door to open the valve in a few tens of seconds.

4 Use the installation process to prevent, such as setting up a return pipe at the discharge of concentrated water, so that the highest point of the pipe exceeds the highest pressure vessel in the reverse osmosis unit,

so that the pressure vessel will be full of water when the unit stops running. The above points are often used in the application of engineering measures, can be adopted or according to the actual situation using a few points, it is worth noting that no matter which project point 4 is necessary.

14 Why must the reverse osmosis concentrated water discharge pipe be a little higher than the device?

A: The concentrated water discharge valve is always open when the reverse osmosis system is running, so that when the reverse osmosis system stops running, if the highest point of the discharge pipe is lower than the highest point of the pressure vessel, the phenomenon of “siphoning” will occur, and the water in the pressure vessel will flow out of the reverse osmosis system through the concentrated water discharge pipe due to its own weight, and air will be mixed in the pressure vessel.

First, it is easy to cause water hammer phenomenon, and second, the oxygen in the air will have more or less oxidation effect on the reverse osmosis membrane element when it is shut down, which will affect the service life of the membrane element.

15 Reverse osmosis feed water indicators?

The feed water indicators of reverse osmosis are: Iron content: Fe ≤ 1mg/l Free chlorine: CL ≤ 0.1mg

SDI: less than 4 Temperature range: 5-45 ℃ Turbidity: less than 1NTU

16 Mechanical filter, iron and manganese removal filter, carbon dioxide removal device inlet and outlet water indicators?

A: The inlet water suspended matter of mechanical filter is ≤20mg/l, and the outlet water suspended matter is ≤5mg/l. The inlet water iron content of iron removal and manganese removal filter is ≤30mg/l, and the outlet water iron content is ≤0.3mg/l. The inlet water carbon dioxide content of carbon dioxide removal device is ≤330mg/l, and the outlet water carbon dioxide content is ≤5mg/l.


17 What are the characteristics of the UV sterilizer?

A: The characteristics of the UV sterilizer are as follows.

1 UV sterilization speed, high efficiency, good results.

2 UV irradiation will not change the physical and chemical properties of water, the pure water will not bring such as the pollution introduced by additional substances.

3 can be applied to a variety of water flow under the use of simple operation, easy to use, only need to regularly clean the quartz glass tube set.

4 small size, lightweight, low power consumption, long life.

18 What are the factors that affect the effect of UV sterilizers and the matters to be noted?

A: The factors that affect the effect of germicidal UV are the intensity of UV, the wavelength of the UV spectrum and the irradiation time. Matters that should be noted when using the UV sterilizer are

Installation location: The closer the location of the UV installation to the point of use, the better, but also should be left from one end of the quartz tube set into or out and replace the lamp operation space.

Flow: In the same sterilizer, when the radiation energy of the UV is certain, the bacterial content of the water does not change much through the sterilizer water flow size has a significant impact on the sterilization effect.

Water physicochemical properties: water chromaticity, turbidity, total iron content of the UV have different degrees of absorption, the result of the germicidal effect is reduced.

Lamp power: The ignition power of the lamp has a great impact on the germicidal efficiency.

The temperature of the medium around the lamp: UV lamp radiation spectrum energy and the temperature of the lamp wall.

Quartz tube sleeve: Adapt to the quality and wall thickness of the tube sleeve and the transmission rate of ultraviolet light, quartz tube sleeve of high purity, good efficiency.

Water layer thickness: the thickness of the water layer has a great relationship with the sterilization effect.

19 What are the characteristics of water ozone generator?

A: Ozone is one of the most effective germicidal agents in water treatment, and only free chlorine can be compared to the germicidal power of ozone. The advantage of disinfection with ozone is its high bactericidal efficiency, even for resistant microorganisms such as viruses and cysts, it is by far the most effective disinfectant.

It reduces the odor, taste and color of the feed water, and the only remaining substance in its decomposition is dissolved oxygen. In addition, ozone’s disinfection ability is unaffected by changes in pH and ammonia.

There is a downside to ozone disinfection because ozone must be generated electrically and cannot be stockpiled, making it difficult to adjust ozone requirements in time for changes in water quality and quantity.

Experience has shown that ozone is most suitable for water plants with low and stable water consumption; in addition, although ozone is a strong oxidizer, its oxidizing ability is selective and not universally oxidizing, like ethanol, which is easily oxidized, but not easily and ozone.

20  water quality analysis in the water sample collection should pay attention to what issues?

A: Water quality analysis in the water sample collection should pay attention to the following issues.

Sampling should be representative, that is, the water samples taken can represent the water quality of the entire water body.

Water quality samples should be used and analysis between the water quality should be stable and unchanged or no significant changes. Sampling volume should be 4-5 times the amount of samples required for testing projects to ensure repeat analysis and retesting of water samples, the minimum sampling volume should be to ensure the accuracy and precision of the analysis requirements.

Try to shorten the contact time of water samples and sampling equipment, water samples flowing through the pipeline should take a high linear flow rate, if the adoption of the need to connect the pipeline and valves and other intermediate flow path, special attention should be paid to the pollution of this intermediate link, the material and cleaning requirements should be consistent with the use of containers.

Field test items, such as PH value, dissolved oxygen, alkalinity, CO2, ferrous iron, ammonia nitrogen, residual chlorine and other content, should try to shorten the sampling to the analysis of hunger time interval, and should try to use online analysis and detection.

Records should be available and labeled on the sampling container, indicating the name of the adoption, time, location, temperature, sampling volume, the adoption of the container and the sampler.

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