Most of the ion exchange resins can be polluted or mixed with suspended solids. When pH changes, bicarbonate and other relatively insoluble salts will precipitate. In addition, when some substances are adsorbed or ion exchanged, they are not easy to be removed by normal regeneration steps, so they will be deposited on the resin and cause pollution.

Normal cleaning can prevent pollutant deposition and prolong the service life of resin.

Increasing regeneration dose and times (increasing temperature) can reduce pollution and prevent permanent adsorption of inclusions.

It is a very beneficial practice to make the ion exchange resin in the exchanger contact with enough regenerant and adopt normal cleaning steps.

1. Loss of resin in running equipment.

2. If the nature of water supply is changed, if the amount of ions to be removed is increased, the output of equipment will be reduced.

3. Operation error; regeneration conditions are not met, and operation is not in accordance with regulations.

4. Factory engineering hardware failure.

5. Resin contamination or degradation.

Among the above items, 1 is the most difficult to judge; 2 is to analyze the water quality of the water supply regularly and adjust the corresponding operation in time; 3 is easy to check, check the backwashing steps, washing volume and regenerant concentration, so as to meet the requirements of the operating procedures. If 1, 2, 3 and 4 are normal, the resin shall be sampled and analyzed.

Resin sampling

For resin evaluation and conclusion, the key lies in how to sample, and the sample must be representative. If this point cannot be mastered, the analyst shall provide the sampling method. If the mixed bed resin or other air mixing devices are installed, the resin in the bed is generally distributed in layers after backwashing. According to the regeneration and operation mode, the pollution of top resin can vary greatly, so the sample will not be representative. Therefore, it is necessary to take samples at different bed heights and mix them, or take core samples and mix them before sending them for analysis.

Cleaning steps

According to the nature of pollutants, different steps are adopted to clean the polluted resin, which will be discussed in this paper.

Sterilization steps

Sometimes the polluted water enters the ion exchange system, and the resin will be polluted by bacteria or algae. If the resin bed is found to be polluted, the following methods can be used:

Peracetic acid

Peracetic acid, a derivative of hydrogen peroxide, has a broad-spectrum bactericidal effect on microorganisms. Research work shows that peracetic acid is increasingly used in human medicine for bactericidal and antiviral effects on bacteria, molds and spores.

Due to the broad-spectrum bactericidal performance of peracetic acid, it is also used as a broad-spectrum bactericide for resin (the joint development of Degussa technology application department and homdury chemical plant). The use of 0.2% Peracetic acid solution (aqueous solution, reaction time of 1 hour) can make 104-105 / ml including mould sludge, eliminate to zero. It is useful to wash the bed with peracetic acid for a short time (generally 45 minutes or 10-15 bed volume).

In addition to good bactericidal effect, peracetic acid (according to the test) has no effect on the exchange performance of cation resin and anion resin.

If peracetic acid is used as disinfectant, whether it is cation resin or anion resin, the following steps can be used:

1. If it is used in anion resin, the resin shall be completely invalid first, because peracetic acid shall be used below pH8.

2. Prepare 1 bed volume (BV) (i.e. 1 L / L resin) peracetic acid solution with a concentration of 2%.

3. 1BV disinfectant was injected at a flow rate of 5vb / hour, and the replaced water was discharged from the trench.

4. When all peracetic acid is injected, close all valves, soak for at least 1 hour, and immerse the resin and piping with peracetic acid solution.

5. Wash out the bactericide, use raw water, flow rate of 5bv / h, at least 60 minutes, and then quickly wash for 30 minutes.

6. Regenerate the resin and put it into operation.

formaldehyde

If formaldehyde is used as disinfectant, the following steps can be used:

Three bed volume (BV) formaldehyde solutions were prepared. Therefore, they must be diluted 80 times. The solution can be injected into the bed by using regenerant injection system, so that the concentration is 0.5%.

1BV bactericide was injected at a flow rate of 5bv / h and the displaced water was drained to the trench.

If possible, drain to a level of 50 mm above the resin surface.

Inject the second 1BV bactericide solution at the same flow rate as before, leave it in the equipment for at least 8 hours and preferably overnight, and there should be formaldehyde smell at each drain valve.

Flush and discharge with raw water until formaldehyde cannot be detected by Schiff test at the discharge point.

Regenerate the resin twice (double regeneration) and put it into operation.