The general chemical cleaning steps are as follows. The specific matters are determined according to the working conditions at the site and the requirements for cleaning.
1 Rinse the membrane element. Rinse with a reverse osmosis water or ion exchange water for a few minutes.
2 Configure the medicine. Ensure that the drug is completely dissolved.
3 loops. The water in the membrane element is replaced with a low flow rate, and a part of the washing liquid is discharged, and then circulated. The circulating flow rate is based on the range of Table 8. When the pollution is severe, if a large flow cycle is selected, there is a possibility that the pressure difference is too high, and the membrane element is damaged (the maximum pressure drop of the single membrane element is 0.07 MPa). At this point, the following methods are more reliable:
- The cycle starts 5 minutes and the cycle is 1/3 of the set flow rate;
- Cycle 5 – 10 minutes, according to the set flow 2 / 3 cycle flow cycle;
- Cycle through the flow requirements after 10 minutes.
The time of the cycle should be determined on a case-by-case basis. Usually 1 hour is subject to change. During this time, always check if the pH changes. The pressure should be kept as low as possible, with as little water as possible. Also monitor whether the pressure difference changes.
4 Soak and recycle. Slowly close the valve at the inlet of the reverse osmosis membrane element and close the circulation pump when the circulation is close to zero. In order to prevent liquid from flowing out of the pressure vessel, the relevant valve can be closed during soaking. The time of soaking is determined by the degree of contamination. Generally in the 1 - 12 hour range. After soaking, open the relevant valve and cycle.
5 Rinse. The membrane element and the liquid in the cleaning device are rinsed with reverse osmosis water or ion exchange water. At this time, the system is replaced from the cycle state to the discharge state. Rinse the membrane system with feed water. The rinse time is approximately 20 – 60 minutes. The pH of the drainage and the conductivity can be determined to determine whether the flushing is complete. The values of pH and conductivity are similar to the values of the influent, and the flushing can be stopped when there is no change.
7 trial run. In the normal starting system, the initial production water should be discharged until the water quality of the produced water meets the requirements. In order to obtain a stable reverse osmosis water quality, the recovery time sometimes takes several hours to several days. Especially after washing with an alkaline solution (high pH), it takes a long time to recover the water.