Application of reverse osmosis in wastewater advanced treatment

The main process flow is as follows

Wastewater pretreatment →Raw water tank→Multi-media filter→Activated carbon filter→Security filter→RO→Desalination water tank→Water point

Fault cause analysis

1. When the influent water quality changes greatly, if PAC is not adjusted in time, it will be yellow and viscous in the security filter cartridge due to excessive addition, and black when the addition is insufficient.

2. Excessive addition of reducing agent will cause membrane fouling and reduce water production.

3. Large-dose addition of membrane scale inhibitors will increase the operating pressure drop of RO, which is unfavorable to operation.

4. Insufficient addition of hydrochloric acid cannot reduce PH in time, and pretreatment chemicals may indirectly affect the security filter cartridge and RO membrane, causing filter clogging and membrane fouling.

Solution

Reagent adjustment:

1. Adjust the type of reagent to reduce the turbidity of the effluent from the pretreatment system. After the beaker experiment, PAC is changed to PAFC to effectively ensure that the effluent turbidity is below 2NTU.

2. Adjust the addition process to ensure appropriate addition, providing a guarantee for the stable operation of pretreatment.

3. Through chemical testing and tracking operation, the dosage of PAM is adjusted to the optimal dosage. To ensure the addition in the optimal state, the maturation time of the coagulant aid is required.

4. Through the chemical analysis of membrane pollutants and the operation parameters of the membrane system, the dosage of reducing agent is adjusted to the optimal ratio, the scale inhibitor is replaced with Jiach-MSIT-401, and the optimal dosage of chemicals is calculated.

5. Add a hydrochloric acid injection point at the inlet of the multimedia filter.

Operation control of reverse osmosis system in chemical operation management

1. Pressure difference

The pressure difference monitoring of the reverse osmosis system should be controlled according to the constant flow rate. After the chemical cleaning, the first stage pressure difference should return to about 0.15MPa. During normal operation, the value of the first stage pressure difference should be ensured to be below 0.01MPa. If it increases to more than 0.01MPa, the cause of the problem should be checked in time, and short-term chemical cleaning should be carried out to ensure that the pressure difference returns to the normal value; the pressure difference of the security filter should be controlled within the range of 0.1MPa. Generally, the increase of its pressure difference will be very insignificant, but when the pressure difference increases too fast, it is usually necessary to replace the filter cartridge of the security filter; the screen pressure difference is usually maintained at 0.03MPa. If the pressure difference rises abnormally, it indicates that the screen is blocked. At this time, the screen should be disassembled and cleaned and checked, and the blockage should be analyzed;

2. Residual chlorine

The level of residual chlorine usually changes greatly with the change of organic components, influent COD value and water temperature, etc. To ensure that the residual chlorine at the inlet of the reverse osmosis system is below 0.05mg/L, to ensure that the water passing through the reverse osmosis membrane does not contain other chlorinated substances, when its value is higher than the normal value, the input of reducing agent should be increased on the basis of controlling the quality and concentration of reducing agent.

3. PH value

When at the inlet of the security filter PH value detection, it should be ensured that it is within the range of 8.0～8.4. If the PH value is too low, it may cause microbial pollution, so the change of the first stage pressure difference and the pressure difference of the security filter should be observed. If the PH value is too high, the specific change of the second stage pressure difference should be noted. If the aluminum and iron content increases at the same time, it may be that the subsequent group reduces the dispersion degree of aluminum and iron, which may cause alternating pollution of the first stage, so the control of PH value should be strengthened.