Ultrafiltration Equipment Operation and Ultrafiltration Membrane Cleaning

2022-05-09


1. Ultrafiltration membrane online cleaning

During the operation of the Ultrafiltration Membrane Module, the surface of the membrane will be covered by various harmful impurities retained by it to form a filter cake layer, and even the membrane pores will be blocked by finer impurities, increasing the permeation pressure of water. . The quality of raw water can only solve the problem of the speed and speed of membrane pollution, but cannot fundamentally solve the pollution problem. Even if the pretreatment is thorough, very few impurities in the water will gradually affect the separation performance of the membrane due to the accumulation of time. Therefore, when the ultrafiltration membrane is fouled to a certain extent, it should be cleaned.

 

2. The selection of chemical cleaning agents In general, no matter what the pollution is, it should be pickled first and then alkaline washed, or sterilized first, then pickled and alkaline washed, and the effect is the best. Alkaline washing alone is not effective. First acid washing and then alkali washing can also prevent the solution from PH>9 and scaling.

Chemical cleaning agents are sodium hypochlorite (NaClO), sodium hydroxide (NaOH), and hydrochloric acid (HCl).

A. The purpose of backwashing with hydrochloric acid: to remove metal ion attachments on the membrane, such as calcium salts, magnesium salts, and iron salts.

B. The purpose of adding sodium hypochlorite for backwashing: sterilization and virus elimination.

C. The purpose of backwashing with sodium hydroxide: to clean impurities such as organic matter.

 

3. Determination of pollutants

In the early stage of Ultrafiltration Membrane System operation (about half a year, the water source is urban tap water), the operating pressure difference rose rapidly. One UF end cap was sampled to open, and the UF membrane was removed. It was found that there was a thin layer of yellow viscose on the end surface of the UF membrane and the outer shell. The material cannot be completely dissolved in HCl or NaOH, but it fades in acid, and it is judged that the pollutants are mainly inorganic salt scale and colloid fouling.

As urban reclaimed water is used as the water source for demineralized water, the fouling in the ultrafiltration operation is aggravated, especially when the heating ultrafiltration is continuously operated in winter, the operating pressure difference rises rapidly. Smell, sticky and slippery inner wall attachments, black, yellow, black and green in color. This substance can be slowly dissolved in high concentrations of NaClO and HCl. It is judged that the pollutants are mainly bacterial microorganisms, organic matter and inorganic salt scale.

Add HCl and add NaOH+NaClO for cleaning, and backwash the operation mode of 360t/h.

 

4. Determination of cleaning plan

Due to the pollution characteristics of Ultrafiltration Membrane Equipment, the pollutants of ultrafiltration membranes are mainly organic matter, microbial pollution, and inorganic salt scale. After a long period of research, an alternate cleaning plan with HCL cleaning and NaOH+NaClO cleaning has been formulated, that is, acid cleaning first and then alkali cleaning. wash. The ultrafiltration equipment adopts a backwashing integrated chemical cleaning, which is to add appropriate drugs to the backwash inlet pipeline of the ultrafiltration equipment to ensure the normal cleaning and operation of the ultrafiltration equipment.

When carrying out chemical cleaning of ultrafiltration equipment, the cleaning method must ensure that there is no air in the Ultrafiltration System, the concentration of the drug, the temperature and time of immersion, and every 1 to 2 months according to the pressure difference of the operating equipment. To strengthen cleaning, the chemical is twice that of normal chemical cleaning. The soaking time depends on the pollution and blockage. The general soaking time should not exceed 6h.