Pollutants in the water attached the surface of membrane during the running of MBR，due to the sludge environment and its filtration characteristics, which will affect the permeable ability of membrane modules. In order to keep the continuous permeable ability when membrane modules are used, removing pollutants from the surface of membrane needs to be done in time by related ways, preventing the aggravation of membrane fouling. Methods commonly used include: Air scrubbing, hydraulic backwash, maintenance chemical cleaning, recovery chemical cleaning, off-line cleaning, etc.

Cleaning Conditions And Methods Of Membrane Modules

1：Air Scrubbing

During the running of membrane modules, the aeration produced by the bottom aeration tank of the membrane module creates an upward flow of air inside the module, with the stir of air flow，the membrane filaments oscillate freely in the water, to reduce the attached pollutants. At the same time, the produced bubble water flow has a certain washing and stripping effect on the pollutants on the surface of the membrane filaments .Air scrubbing is the basic way for MBR to control the pollution , In principle, the entire aeration is required for air scrubbing（Except chemical cleaning and stopped running）.

Aeration Intensity：Recommended aeration volume is 0.24-0.5Nm³/㎡.h（Membrane area），in actual operation, it is advisable to control the Liquid Level Rolling 5-10cm above the membrane frame.

2：Hydraulic Backwash

Hydraulic backwash is needed after sustained running of membrane modules for a time. When hydraulic backwash, through the backwash pump, the tap water or permeating liquid is reverse injected into the membrane modules from the water outlet port, the backwash water passes through the membrane apertures from inside to outside, and rinses the attached  pollutants in the membrane apertures out to recover the membrane filter channel, at the same time , the inside-to-ouside backwash liqquid can make pollutants attached on the surface of membranes loose or dicharged, it’s beneficial to the recovery of membrane water permeability. Hydraulic backwash is a basic method for MBR to control pollution(Gas scrubbing when backwash)，hydraulic backwash needs to  run for 3-4 hours.

Backwash Flux：30-50L/㎡.h（According to the membrane area），generally 2-3 times the water  yield;
Backwash Pressure：Be controlled about 0.1MPa;
Backwash Time：2-3min/time.

3：Maintenance Cleaning

Maintenance cleaning is the regular removal of dirt and clogs on the membrane surface through the role of chemicals, to prevent the thickening of the bonding layer and the aggravation of pollution,  for stable running. Keep the MBR membrane modules soaked in the membrane tank during maintenance chemical cleaning, the relevant chemicals are injected into the backwash water by a dosing pump, and flow back to the raw water side of MBR mambrane modules from the water production pipe with backwash water, decomposing  organic matter attached on the membrane surface, to recover the water permeability. When cleaning, filtration and aeration should be stopped in advance.If continuous aeration is performed during the injection of liquid and rest, which will make medical solution diffuse and dilute to the whole tank, resulting in the low effect of cleaning membrane surface.

Maintenance cleaning is devided into acid cleaning and chlorine cleaning,the citric acid cleaning mainly aims at the inorganic salt pollution，the NaCIO cleaning  mainly aims at organic pollutants. When the type of pollution is uncertain, it’s suggested that both parts are to be implemented. Certain types of organic pollutants can only be chlorine washed for maintenance.

Maintenance Cleaning Frequency: NaCIO Cleaning (1 time every 1-3 days)，Citric acid (1 time every 3 days);

Cleaning Medcine And Concentration: 300-500ppm NaCIO（Available chlorine）or citric acid.

4：Recovery Cleaning

When the amount of sludge attached to the membrane surface is larger, the membrane fouling is more serious, and the membrane water permeability can not be recovered by aeration and maintenance chemical cleaning, recovery chemical cleaning needs to be done to MBR membrane modules.When cleaning, filtration and aeration should be stopped in advance.If continuous aeration is performed during the injection of liquid and rest, which will make medical solution diffuse and dilute to the whole tank, resulting in the low effect of cleaning membrane surface.

Recovery chemical cleaning includes acid cleaning and chlorine cleaning. Still keep the MBR membrane modules soaked in the membrane tank during recovery chemical cleaning.

Please clean membrane modules thoroughly with conventional cleaning ways before recovery cleaning, to  reduce the residual sludge as much as possible.Inject the prepared NaCIO cleaning liquid slowly from produced water outlet into the membrane module by using dosing pump and then soak for a long time.

The concentration of cleaning medicine used for immersion is usually 3000-5000ppm NaCIO (available chlorine), or the suitable concentration of chemical medicine can also be selected according to the actual situation.The dosage of medicine is calculated according to the unit membrane area（2L/m2） +the capacity of the ingress pipe, the injected time should be controlled about 15-30min usually, after then soak for 30-90min. When it is finished, acid cleaning needs to be done if it doesn’t have a good recovery effect , by using 0.1-0.3% hydrochloric acid,1% citric acid. The way of cleaning is the same with chlorine cleaning .

Recovery Cleaning Frequency: 1 time every 1-3 months or can not be recovered by maintenancecleaning;
Cleaning Medcine And Concentration: 3000ppm NaCIO（Available chlorine）/1% citric acid;
Dosage: 2-3L/㎡（According to the membrane area）;
Cleaning Time: Drug injection 30min+Soak in 30-90min.

Important Note：

a. Rinse the residual medicine thoroughly after NaCIO cleaning and then it can be done for acid cleaning, otherwise, NaCIO will  react with the acid and produces chlorine gas, which can cause poisoning.

b. Most of the medicine used for recovery cleaning will enter into the membrane tank, reducing the activity of residual chlorine by using activated sludge, making little effect on treated water. If the amount of residue is large and influence the running of other systems, it’s suggested that doing reduction treatment with sodium bisulfite or sodium thiosulfate.

c. Be sure to empty the membrane modules and pipe when cleaning, otherwise, the air lock is easy to happen during cleaning, resulting in that the medicine liquid can not be evenly immersed into the membrane wire.

d.  Acid will make the PH in membrane tank change, but it has little effect on treated water because the amount is small, If the amount of residue is large and influence the running of other systems, it’s suggested that doing neutralization treatment with  sodium carbonate.

e.  For the medicine liquid in membranes and equipped pipes, generally increase the amount of backwash water to reduce the impact of the system running on the outlet water.

5：Off-line Cleaning

When the membrane water permeability can not be recovered by recovery cleaning, Off-line chemical cleaning needs to be done. Off-line recovery chemical cleaning is the way that remove membrane modules out of acitvated sludge tank, then put them into the immersion cleaning tank soak for a certain time, so that the organic matter attached to the membrane surface can be decomposed and the membrane water permeability can be recovered. 

Cleaning Methods： 
a. Remove the suction pipe, air pipe for aeration, etc. from the membrane modules, then lift the whole membranes out of the mambrane tank, and put them into immersion cleaning tank.（The Max hoisting angle of lanyard is 60°）

b. Clean the inside of the membrane modules with a nozzle and remove the activated sludge attached to the inside of the membrane.Pay attention to that don’t let the sludge on the unloaded suction pipe pollute the inside of suction pipe（It may bring damages to membranes if high pressure cleaning machine is used to clean the membrane, don’t use high pressure cleaning machine)

c. Completely soak membrane modules in the immersion cleaning tank filled with the prescribed medicine liquid.Keep that for 6～24 hours (If the pollution is serious,the soak time can be added, if the temperature of medicine liquid comes down, the cleaning effect will come down. Heating the liquid to about 30 ° C  will improve the cleaning effect）.

Off-line Cleaning Medicine And Dosage

Cleaning Solution	Medicine And Dosage
Acid Cleaning	1～2% Citric Acid / 0.2～0.4% Hydrochloric Acid
Alkaline Cleaning	0.1～0.4% NaOH + 0.1～0.3% NaClO（Available Chlorine）
Chlorine Cleaning	0.3～0.5% Sodium Hypochlorite

d. After the immersion, take the membrane modules(Mebrane) out of the immersion cleaning tank, and clean them adequately with water, removing the medicine liquid attached the membrane modules(Mebrane), and then install mebrane to the membrane modules.

e. Install membrane modules in the membrane tank, in the case of stopping filtration, only allow aeration to run for more than 30 minutes, and then start filtering.

f. Before discarding the medicine liquid, recover sodium hypochlorite with sodium thiosulfate or sodium bisulfite, and then discard.