If you mean that your membranes are fouled, so that little or no water passes through them there are a number of possible causes.
1) Membranes are fouled because they have not been cleaned. In this case you will need to follow the CIP procedures.
2) Insufficient air scour frequency or air flow. The air moving across the surface on the outside of the membranes causes the fouling layer/particles to shear off and break away into the bulk liquid. It also helps to reduce concentration polarization by reducing the opportunity to form a boundary layer.
3) Insufficient back pulse volume or frequency. The back pulse pushes treated water backwards through the membrane to break off the fouling cake. Not all membrane systems have this but certainly most do.
4) Insufficient pump suction causing low flow through the membrane. This would give the appearance of a membrane blockage.
5) Vacuum leak caused by leaks in the manifolds or pump suction pipework. Same as 4) above.
6) It might also be as a result of trying to treat wastewater outside your design parameters. Without more information it is impossible to comment further on this.
If one of those does not cover your situation you will have to provide more information.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
Hi ashtree, thanks for the wide experience you shared for the mbr possible fouling causes. The wastewater came from a soda making company with a COD content of 2,000ppm, TSS=50-100ppm, BOD=1500ppm & O&G=10ppm. Flow is 5000 m3/d. It has a coarse bar screen before it goes to EQ tank, AX, AE chamber. THen water overflows to MBR tank.
One of the reasons above could be one of the causes of frequent fouling of the MBR. Let me know if you have still some explanation to share on above set-up.
Do you have any data on:
1) the airflow rates
2) back pulse flow rates and frequency ,
3) trans-membrane pressures,
4) flux rates,
5) when you last performed a CIP and what is the usual CIP frequency and with what chemicals.
6) MLSS values
If you collect this sort of data i would suggest that you go back and see if if there has been any major changes. This might not tell you what is wrong but at least it may point to a starting point.
Even if there have been no changes there could be a problem with some of these factors: eg insufficient air flow rate. This may never have been optimized for the conditions.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
