MBR membrane is an important component in the sewage treatment system nowadays, and its treatment object is generally high pollution, sewage containing more organic material and inorganic material. Although we have carried out a certain degree of pretreatment on sewage, there will still be sludge and other dirt after long-term use. Once the MBR membrane is contaminated, it will cause the membrane pore blockage and the water production volume will decrease, resulting in a decrease in the membrane flux. Therefore, we need to clean the MBR membrane module to restore the MBR membrane flux and extend its service life.
The cleaning method of MBR membrane module is generally including air aeration cleaning, maintenance chemical cleaning, backwashing, offline recovery chemical cleaning. We should choose the appropriate cleaning method according to the specific pollution condition of the MBR membrane, in order to achieve better cleaning results at lower cost.
1. Air Aeration Cleaning
Air aeration cleaning is a physical cleaning method that strengthens the circulation of the water flow. When the inlet and outlet valves of the MBR membrane module are closed, the air valve is opened to allow the aeration tube to be continuously aerated for 2-3 days. The sludge layer deposited on the membrane surface is washed away by the upward airflow.
2. Maintenance Chemical Cleaning
Maintenance chemical cleaning is also called chemical enhanced backwash (CEB), which it’s a kind of online maintenance cleaning with low chemical strength. It means that when the MBR membrane suction pump and the blower are stopped, through the backwash pump combined with the dosing pump, the cleaning solution in the dosing box is driven into inside of the PVDF membrane.
The backwashing is divided into water backwashing and air-water backwashing. It refers to apply a backwash pressure to the water outlet of the MBR membrane, and let the produced water or produced water mixed air fluid flushing back through the membrane, in order to flush out the pollutants in the MBR.
4. Offline Recovery Chemical Cleaning
Offline recovery chemical cleaning means that the MBR system is stopped and the MBR membrane module is removed from the MBR membrane bioreactor tank (you can also evacuate the membrane pool, and cleaning on its original place), and place in the chemical cleaning tank that has been configured with cleaning fluid. It is the most effective cleaning method to restore membrane flux. Offline recovery chemical cleaning steps are as following:
(1). Stop the suction pump and blower;
(2). Close the water outlet valve, disassemble the union or flange connection of the water collection pipe and external aeration pipe on the MBR membrane module; take out the MBR membrane module;
(3). Rinse the sludge on the surface of the MBR membrane with tap water (do not use a high-pressure water gun to flush directly and cause membrane damage);
(4). Combine with the nature of sewage to determine the type of membrane module pollution (touch the surface of membrane by hand, generally if it feels sticky, it’s organic pollution, or if it feels hard and roughness, it’s more serious inorganic pollution);
(5). According to the number of membrane modules to estimate the amount of chemical cleaning solution dosage, and according to the type of pollution, configure the corresponding acid or alkaline chemical cleaning solution;
(6). Put the MBR membrane module into the chemical cleaning tank that has been configured with cleaning solution; soak for 6-12 hours (during the soaking period, it is recommended to regularly stir the drug solution and observe through the PH test paper whether an appropriate amount of supplement is needed to ensure the concentration of the drug solution; If there is an aeration tube at the bottom, the aeration valve at the bottom of the chemical cleaning tank can be opened regularly for aeration and agitation);
(7). After soaking, rinse the MBR membrane module with clean water until the PH is neutral, then put it back into the MBR membrane biological reaction tank, and connect the union or flange connection of water collection pipe, inner aeration main pipe and outer aeration pipe on the MBR membrane module;
(8). Turn on the fan, and adjust the air volume, purge the membrane module for 5-10 minutes;
(9). Adjust the air volume to a normal state, turn on the suction pump, and switch to the normal automatic operation model;
Noted The cleaning operation process must be carried out in strict accordance with regulations, otherwise, an unpredictable reaction will occur between the cleaning agent and the filter medium, which will generate heat and damage the ultrafiltration membrane components and piping. In the cleaning operation procedures, the sequence of each cleaning operation should be strictly observed to achieve a high efficiency cleaning effect.