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Daily maintenance precautions for nanofiltration

Daily maintenance precautions for nanofiltration

08

2022

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08

Common faults and solutions of Roots blowers

Common faults and solutions of Roots blowers

03

2022

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08

Have you ever wondered why reverse osmosis cleaning often places alkaline cleaning after acid cleaning?

Have you ever wondered why reverse osmosis cleaning often places alkaline cleaning after acid cleaning?

01

2022

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08

What is severe fouling of reverse osmosis membranes?

What is severe fouling of reverse osmosis membranes?

Reverse osmosis membrane elements, as a deep filtration method, inevitably have colloids, microorganisms, impurity particles, and the precipitation of sparingly soluble salts remaining on their surface. Therefore, reverse osmosis devices used in various fields ultimately require cleaning once put into use, only the cleaning cycle length varies. However, online cleaning, as a means of cleaning and maintenance, shock sterilization, and regular protection of reverse osmosis systems, is powerless when faced with severe pollution of reverse osmosis membrane elements. At this time, offline cleaning of the reverse osmosis membrane elements is required. Although the design of reverse osmosis systems will have a certain degree of surplus to ensure that in emergencies, the water production or desalination rate of the reverse osmosis system will not decrease, and the pressure difference of the reverse osmosis system will not increase, so as not to cause insufficient water supply and threaten safe production, in fact, it is precisely because of the existence of these surplus amounts that sometimes hidden faults cannot be manifested in time, which may eventually lead to severe pollution of the reverse osmosis membrane elements. Concept of Severe Pollution of Reverse Osmosis Membrane Elements This refers to the surface adhesion and deposition pollution caused by suspended solids, colloids, organic matter, microorganisms, and other particles contained in the reverse osmosis system feed water to the RO membrane, or the generation of chemical scales caused by the accumulation of chemical ions in the water on the membrane surface due to factors such as concentration polarization exceeding the solubility product. Severe pollution refers to the situation where the single-stage pressure difference after pollution is more than twice the single-stage pressure difference value at the initial operation of the system, the water production of the reverse osmosis system decreases by more than 30%, or the weight of a single reverse osmosis membrane element exceeds the normal value by more than 3 kg. Severe pollution is often the superposition of severe physical and severe chemical pollution. In some cases, the two coexist. Causes and Characteristics of Severe Pollution of Reverse Osmosis Membrane Elements Due to the different water quality of water sources in different regions and the different treatment methods adopted, the causes of RO membrane element pollution are also different. Common causes and characteristics of pollution include the following: 01 Design and Manufacturing Defects of Water Treatment Process System ① For reverse osmosis pretreatment filters, when the source water is not well water, the equipment filtration rate is greater than 8.5 meters/hour, while the equipment filtration rate in surface water design is greater than 8 meters/hour, resulting in the reverse osmosis feed water SDI exceeding the standard; ② The source water contains colloids, suspended solids and other impurities, but there are no removal measures in the design; ③ COD in the source water >3 and there are no removal measures; ④ The reverse osmosis membrane element design has an over-standard throughput, and the two-stage scaling and pressure difference increase rapidly in the reverse osmosis device, and the water production and desalination rate decrease rapidly. The above design defects ①②③ may lead to an increase in the first-stage pressure difference of the reverse osmosis system; ③ may also lead to an increase in the second-stage pressure difference, and all the above design defects may lead to a decrease in the system water production. 02 Improper Selection of Reverse Osmosis Additives and Other Consumables ① Improper selection of the type or dosage of reverse osmosis antiscalants, such as: the type of reverse osmosis antiscalant is incompatible with the source water, for example, the source water contains aluminum ions, iron ions, or iron and aluminum flocculants are used in pretreatment medication, it is best to choose organic phosphorus-based reverse osmosis antiscalants, and try to avoid using polycarboxylic acid type; the dosage of reverse osmosis antiscalants is generally between 2-4ppm (calculated according to the water intake), and the maximum cannot exceed 6ppm, etc. Improper selection of the type and dosage of antiscalants will lead to a rapid decrease in system water production and a significant increase in system pressure difference; ② When selecting reverse osmosis security filter cartridges, it is necessary to ensure reliable quality. Cartridges that are claimed to be 5 microns but do not actually reach the accuracy are very unfavorable to the safe operation of reverse osmosis membrane elements; ③ Improper selection of flocculants and coagulants in the reverse osmosis pretreatment system will cause serious pollution of the membrane elements, while improper selection of bactericides will cause serious damage to the desalination rate of the reverse osmosis system (containing Cl--). 03 System Abnormalities Caused by Sudden Changes in Water Treatment Operating Conditions Generally, it is due to climate change leading to an increase in the content of suspended solids in the source water, or a change in the type of source water (such as changing from groundwater to tap water, leading to an increase in the residual chlorine content in the reverse osmosis feed water), resulting in deterioration of the operating condition of the reverse osmosis device and forming severe pollution. 04 System Operation and Management Problems ① Failure to operate according to operating procedures; ② Failure to adjust equipment status parameters in time; ③ Improper adjustment of operating parameters; ④ The metering of added chemicals has not been optimized; ⑤ Failure to clean the system in time when the system reaches the cleaning conditions; ⑥ Failure to calibrate the system on time; ⑦ Lack of operational management summary. 05 Water Treatment System Water Supply Shortage In addition to the above situations, in many enterprises, due to the tight water supply of the water treatment system, even if the reverse osmosis device has deteriorated operating parameters and the system is polluted, it cannot be cleaned in time due to the tight water supply, resulting in gradual and severe system pollution, forming severe pollution.

28

2022

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07

A quick and easy method for identifying the types of membrane fouling in reverse osmosis operation

A quick and easy method for identifying the types of membrane fouling in reverse osmosis operation

27

2022

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07

The reuse rate of water in the steel industry needs to reach 97%, but don't blindly launch zero wastewater discharge projects.

The reuse rate of water in the steel industry needs to reach 97%, but don't blindly launch zero wastewater discharge projects.

27

2022

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07

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