How to clean the MBR membrane from Suez/Zenon/Ge/Veolia?

Today I would like to talk to you about the cleaning of MBR membrane, although we have a certain degree of pretreatment of sewage, but after long-term use of the MBR system, MBR membrane separation is generally highly polluted wastewater containing organic matter, inorganic matter is more, the pores will be clogged, so that the water production declined, resulting in a decline in the membrane flux, and therefore the need to clean the membrane module, to restore the flux of the membrane, to extend the service life.

So many customers ask how to clean our membranes when they buy them? When customers want to replace Suez zeeweed 500D, Mitsubishi 5000 series, etc., they will worry about whether our membrane cleaning is different. In fact, it is almost the same. Because our membrane material is basically the same, they are all reinforced PVDF membrane filament. Flux is also 10L to 20L or so. Although many companies publicize when the flux is very large, in fact, when used in specific projects, the flux will not choose so large, because we have to consider the water quality, service life.

How to clean MBR membrane

Now we take a customer’s project as an example.

The customer’s project design is 750 tons of water per day, the actual use of 350 tons of water per day.

Cleaning Methods

When using membrane separation of activated sludge, in order to carry out long-term stable operation, pharmaceutical cleaning is indispensable, pharmaceutical cleaning is divided into regular cleaning, on-line cleaning and out-of-system impregnation cleaning.

5.1 Online maintenance cleaning

5.1.1Brief

Regular cleaning is a cleaning method in the online state, using a pump to reverse the prescribed medicinal solution to the raw water side of the membrane, to decompose the organic matter adhering to the membrane surface, to flush out the sludge adsorbed on the membrane surface, and to restore the pressure difference between the membranes in the method, at which time the filtration and aeration should be stopped first. Regular cleaning should be carried out once a day.

5.1.2 Cleaning way

(1) The solution used for on-line cleaning is 300-500mg/L sodium hypochlorite solution.

(2) The amount of liquid used for on-line cleaning is 2L/m2 plus the amount of piping.

(3) Firstly, stop the water discharge and aeration, and then pump the chemical solution into the membrane filament from the water discharge side within 2min, and then leave it for 10min.

(4) After the injection of the liquid and resting, the aeration was turned on again and continued for 30 minutes, and then filtration was started.

5.1.3 Attention

Regular cleaning beforehand to stop the aeration, this is to ensure that the liquid in the membrane surface adhesion of the contact time is long enough, if the liquid in the liquid injection process of continuous aeration of liquid diffusion and dilution to the whole reactor, resulting in the membrane surface cleaning effect is not good.

5.2 On-line enhanced cleaning

5.2.1 Brief

On-line cleaning refers to the method of reversing the flow of the prescribed liquid from the treatment water pipe to the inside of the hollow fibre membrane and penetrating into the raw water side through the membrane micropores to kill bacteria on the internal and external surfaces of the membrane and decompose and flush out the organics attached to the membrane surface, etc., so as to restore the pressure difference between the membranes.

When the membrane module is higher than 0.3 atm negative pressure is difficult to achieve the design flow rate for online cleaning, the module normal operation after three months even if it can meet the requirements of water production also need to carry out online cleaning.

5.2.2 Cleaning way

(1) On-line cleaning should drain the sewage from the membrane tank, firstly rinse the membrane surface with clean water, and then fill up the clean water.

(2) The solution used for online cleaning is 3000mg/L sodium hypochlorite solution.

(3) The amount of chemical solution used for online cleaning is 2L/m2.

(4) As in the case of periodic cleaning, the water discharge and aeration are stopped, and the chemical solution is injected into the membrane filament from the water discharge side within 30 min, and then left to stand for 90 min. After the injection of liquid and resting, the aeration was turned on again and continued for 30 min, and then filtration was started.

5.2.3 Washing Equipment

。On-line cleaning using the liquid pump dosage is relatively small, so the liquid pump should be used to easily control the flow of diaphragm pumps and so on. When the system is relatively small, you can choose the first will be prepared and then pumped directly into the inner side of the membrane method.

5.2.4 Attention

Regular cleaning and online cleaning is best to stop the aeration beforehand, this is to ensure that the liquid in the membrane surface adhesion of the contact time is long enough, if the liquid in the liquid injection process of continuous aeration of liquid diffusion and dilution to the whole reactor, resulting in the membrane surface cleaning effect is not good.

5.3 Off-lining washing

5.3.1 Brief

Out-of-system impregnation cleaning is a method of removing the components from the sludge tank and placing them in the impregnation cleaning tank for a certain period of time, so that the sludge attached to the membrane surface can be dislodged, the attached organic matter can be decomposed, and the pressure difference between the membranes can be restored.

When it is difficult to maintain the stable water output of the system through regular cleaning and on-line cleaning, it is adopted to use external impregnation cleaning.

5.3.2 Cleaning way

When the first two cleaning methods fail to restore membrane performance, offline cleaning is performed to lift the membrane module out and submerge it in a special cleaning tank to remove contaminants and restore the membrane performance to a state close to the initial value. Immersion cleaning is generally able to significantly restore membrane performance.

For off-line cleaning, the whole membrane module or individual membrane sheet is immersed in an alkaline cleaning agent (NaClO solution with an effective chlorine concentration of 2,000-3,000 mg/L and a pH of 10-11) or an acidic cleaning agent (1-2% oxalic acid or citric acid, 0.1-0.5% sulphuric acid or hydrochloric acid). The immersion time is 6 to 24 h hours for NaClO and 2 h for acid.

Membrane components in the cleaning pool before immersed in water to the membrane surface attached to the sludge cleaning off, can reduce the amount of cleaning chemicals used to improve the cleaning effect. Immersion cleaning can be intermittent aeration, so that the agent is fully mixed to maintain the concentration of the agent on the membrane surface, if necessary, intermittent addition of NaClO and other agents to maintain the concentration of the cleaning solution.

The types of membrane cleaning, concentration of agents, cleaning methods and types of pickling agents are listed in the table below.

5.3.3 Cleaning solution

The following table should be referred to when selecting cleaning objects:

The solution should be able to completely submerge the membrane module. The appropriate cleaning agent needs to be examined for specific contaminant cleaning.