Application of reverse osmosis in advanced wastewater treatment

Author: Hongjie Water

The main process flow is as follows

Wastewater pretreatment → Raw water tank → Multi medium filter → Activated carbon filter → Security filter → RO → Demineralized water tank → Water consumption point

Fault Cause Analysis

1. If PAC is not adjusted in a timely manner when the incoming water quality changes greatly, it will become yellow viscous substance due to excessive addition to the security filter element, and black when the amount is insufficient.

2. Excessive addition of reducing agents can cause membrane fouling and reduce water production.

3. The large dosage of membrane scale inhibitor will increase the operating pressure drop of RO, which will bring adverse effects to the operation.

4. If the dosage of hydrochloric acid is insufficient and the pH cannot be reduced in a timely manner, the pre-treatment agent may indirectly affect the cartridge and RO membrane of the security filter, resulting in cartridge fouling and membrane fouling.

Solution

Medication adjustment:

1. Adjust the types of reagents and reduce the turbidity of the pre-treatment system effluent. After the beaker experiment, change PAC to PAFC, effectively ensuring that the effluent turbidity is below 2NTU.

2. Adjust the dosing process to ensure an appropriate amount of dosing, providing guarantee for the stable operation of pre-treatment

3. Through testing and tracking operation, adjust the dosage of PAM to the optimal dosage. To ensure optimal dosing, it is required to ensure the curing time of the coagulant aid.

4. Through the analysis of membrane pollutants and the operating parameters of the membrane system, the dosage of reducing agent was adjusted to a better ratio, and the scale inhibitor was replaced with Jiach MSIT-401, and the optimal dosage was calculated.

5. Add a hydrochloric acid dosing point at the inlet of the multi-media 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 based on a constant flow rate. After chemical cleaning is completed, the pressure difference in one section should return to around 0.15MPa. During normal operation, the value of the pressure difference in one section should be ensured to be below 0.01MPa. If it increases to above 0.01MPa, the cause of the problem should be checked in a timely manner and short-term chemical cleaning should be carried out to ensure that the pressure difference returns to normal values; The pressure difference of the security filter should be controlled within the range of 0.1MPa. Generally, the increase in pressure difference is not significant, and when the pressure difference increases too fast, it is usually necessary to replace the filter element of the security filter; The pressure difference of the partition network is usually maintained at 0.03MPa. If the pressure difference rises abnormally, it indicates that the partition network is blocked. At this time, the partition network should be cleaned and inspected, and the blockage should be analyzed;

2. Residual chlorine content

The level of residual chlorine usually changes significantly with changes in organic matter composition, COD value of influent water, and water temperature. It is necessary to ensure that the residual chlorine at the inlet of the reverse osmosis system is below 0.05mg/L to ensure that the water penetrating through the reverse osmosis membrane does not contain other chlorinated substances. When the value is higher than normal, the amount of reducing agent input should be increased on the basis of controlling the quality and concentration of the reducing agent.

3. PH value

When testing the pH value at the inlet of the security filter, it should be ensured that it is within the range of 8.0 to 8.4. If the pH value is too low, it may cause microbial contamination. Therefore, it is important to focus on observing the changes in the first stage pressure difference and the pressure difference of the security filter. If the pH value is too high, attention should be paid to the specific changes in the second stage pressure difference. If an increase in aluminum and iron content is found at the same time, it may be due to the subsequent reduction in the dispersion of aluminum and iron, It may cause a period of alternating pollution, so it is necessary to strengthen the control of pH value.