清洗前记录纳滤膜的运行参数，将纳滤进膜盐水的PH值调节到4.5-6.5之间，在操作压力和温度不变的情况下，让膜系统运行3小时左右，观察膜的运行变化，观察膜的渗透液有无变化，在系统运行期间每隔约1小时，记录下膜的出水情况和操作情况。

化学清洗步骤和方法

一、酸洗（清洗时间3-4小时）

1、确认所有阀门位置正确，不会产生背压等不良状况。

2、先用纯水对系统进行低压冲洗；冲洗至膜系统浓缩液电导小于100us/cm。

3、清洗液罐中加入纯水，开启清洗液泵，调节浓缩液阀门，观测并记录测试膜系统纯水通量和操作压力。

4、配置化学清洗液2%柠檬酸（重量比），用氨水回调PH值在2.0-2.5以内，控制溶液温度约30℃-45℃。

5、打开清洗液泵及全开清洗液回流阀和浓缩液回流阀，进行循环混合，保证柠檬酸完全溶解和PH稳定在2.0-2.5以内。

6、打开清洗液泵进膜系统的阀门，适当关小回流阀，使药液进入纳滤膜过滤系统。

7、循环清洗液最初的10%-15%应排放。

8、开启浓缩液侧回流阀和渗透液侧回流阀，调节清洗液泵出口阀门开度（开启1/2）和回流阀门开度（开启1/2），进行低速循环15min；然后逐步关小回流阀门至1/4开度和调节清洗液泵出口阀门开度（开启3/4），进行中速循环15min；再调节清洗液泵出口阀门至全开，关闭回流阀，进行高速循环30min，整个过程检测清洗液温度，在容许的范围内，温度越高清洗效果越好。

9、循环清洗结束后停掉清洗液泵，对纳滤膜过滤系统进行1-2小时浸泡。

10、浸泡结束后，重复步骤（8）。

11、浸泡结束，排放掉清洗液储罐中的酸清洗液，将清洗液储罐清洗干净后，注满纯水，并用纯水冲洗纳滤过滤膜直至PH值接近中性。

12、开启清洗液泵，调节浓缩液出口阀，观测并记录测试膜系统纯水通量和操作压力与（酸洗3）的操作条件相同，同时记录出此时膜系统纯水通量和操作压力。

   Before cleaning, record the operating parameters of the nanofiltration membrane. Adjust the pH value of the brine entering the nanofiltration membrane to between 4.5-6.5. Under constant operating pressure and temperature, let the membrane system run for about 3 hours to observe the changes in membrane operation and whether there are any changes in the permeate of the membrane. During system operation, record the effluent and operation of the membrane every approximately 1 hour.

 Chemical cleaning steps and methods

 一、 Pickling (cleaning time 3-4 hours)

 1. Confirm that all valve positions are correct and there will be no adverse conditions such as back pressure.

 2. First, rinse the system with pure water at low pressure; Flush until the conductivity of the concentrated solution in the membrane system is less than 100us/cm.

 3. Add pure water to the cleaning solution tank, turn on the cleaning solution pump, adjust the concentrate valve, observe and record the pure water flux and operating pressure of the testing membrane system.

 4. Prepare a chemical cleaning solution of 2% citric acid (by weight), adjust the pH value to within 2.0-2.5 with ammonia water, and control the solution temperature to about 30-45 ℃.

 5. Open the cleaning solution pump and fully open the cleaning solution reflux valve and concentrated solution reflux valve, and carry out circulating mixing to ensure complete dissolution of citric acid and stable pH within 2.0-2.5.

 6. Open the valve of the cleaning solution pump entering the membrane system, and appropriately close the reflux valve to allow the solution to enter the nanofiltration membrane filtration system.

 7. The initial 10% -15% of the circulating cleaning solution should be discharged.

 8. Open the concentrated liquid side reflux valve and the permeate side reflux valve, adjust the outlet valve opening (1/2 open) and reflux valve opening (1/2 open) of the cleaning solution pump, and perform a low-speed cycle for 15 minutes; Then gradually close the reflux valve to 1/4 of the opening and adjust the outlet valve of the cleaning solution pump to 3/4 of the opening, and perform a medium speed cycle for 15 minutes; Adjust the outlet valve of the cleaning solution pump to fully open, close the reflux valve, and perform a high-speed cycle for 30 minutes. Check the temperature of the cleaning solution throughout the process, and within the allowable range, the higher the temperature, the better the cleaning effect.  

9. After the cycle cleaning is completed, stop the cleaning solution pump and soak the nanofiltration membrane filtration system for 1-2 hours.

10. After soaking, repeat step (8).

11. After soaking, discharge the acid cleaning solution from the cleaning solution storage tank. After cleaning the cleaning solution storage tank, fill it with pure water and rinse the nanofiltration membrane with pure water until the pH value is close to neutral.

12. Turn on the cleaning solution pump, adjust the concentrated solution outlet valve, observe and record the pure water flux and operating pressure of the testing membrane system under the same operating conditions as (acid washing 3), and record the pure water flux and operating pressure of the membrane system at this time.