Chemical cleaning guidelines for pressure-type membrane components

1. Overview

During the long-term operation of the ultrafiltration device, the impurities in the water will accumulate over time, and the separation performance of the membrane is gradually affected. Therefore, the ultrafiltration device needs to chemical clean the membrane components regularly and irregularly to restore the performance of the membrane. Compared with normal operation, the water production of the ultrafiltration system decreases by more than 10%~20% or the transmembrane pressure difference increases by 0.08~0.1MPa (the transmembrane pressure difference shall not exceed 0.2MPa at any time), and the membrane flux cannot be restored by backwashing, the ultrafiltration system should be cleaned chemically.

Chemical cleaning is using a certain concentration of specific chemical agents in the membrane system for circulation and soak, to clean the dirt on the surface of the membrane wire. Chemical agents are selected according to the type of water quality and the pollution characteristics of the membrane components.

2. Selection of chemical cleaning agents

(1) Alkali washing: 0.2% sodium hypochlorite (according to the effective chlorine meter) + 0.1% sodium hydroxide solution, that is, the ratio of 10% sodium hypochlorite solution adding 20L and 1kg sodium hydroxide solid per 1 ton of water.

Scope of application: when the organic content in the water is high, it may cause the filter membrane to be organic matter pollution. And when the conditions are conducive to biological survival, some bacteria and algae will also multiply in the ultrafiltration membrane components, resulting in biological contamination.

    (2) pickling: 1~2% citric acid solution or 0.2% hydrochloric acid solution, that is, the ratio of 7kg of industrial hydrochloric acid or 10~20kg of citric acid per ton of water.

Scope of application: when the content of Fe, Mn or other metals in the inlet water exceeds the design standard, or the suspended matter in the inlet water of ultrafiltration membrane components is particularly high, and the non-organic pollution caused to the inlet side of the membrane.

3. Specification table of common agents

Table 1 Specification table of common agents for chemical cleaning

4. Flow chart of chemical cleaning

Figure 1 Flow chart of ultrafiltration chemical cleaning

5. Cleaning steps

A. Close the ultrafiltration device according to the shutdown procedure, and close all the valves on the device;

B. Prepare the acid / base solution in the cleaning solution box and stir well to mix well;C. Open the cleaning water inlet valve (V03) and the cleaning fluid return valve (V04, V05), and then start the cleaning pump.Allow the wash solution into the membrane assembly and return to the wash solution chamber. The cycle cleaning time is60min-120min；

D. Close the cleaning pump, set the static soak, the time depends on the pollution situation, generally more than 60min;

E. Wash in recirculation for 10-20min;

F. Backwash and forward wash of the ultrafiltration device alternately until the drainage PH value of the ultrafiltration device is neutral;

G. Continue the second agent cleaning or return to the production run state.