When is the right time to replace a membrane module?

There is no uniform standard, no specific property to monitor, or no specific value for judging the life of a membrane module, or the timing of replacement, except for cases of membrane module breakage. In general, modules are replaced when the water permeability falls below the value at the time of design, the quality of treated water cannot be maintained, or the frequency of chemical washing needs to be increased from that at the time of design.
Performance deterioration accompanying use can be broadly classified into the deterioration of members constituting the membrane module, such as membrane, adhesives, and housing, and a decline in filtering performance due to insufficient recovery from clogging by the rinsing process and line clogging.

1.Deterioration of members constituting the membrane module

Major factors that cause deterioration of members (membrane, adhesives, and housing) constituting a member module include:

• Properties of the liquid to treat (water temperature, pH, etc.),
• Pressure used for filtration and backwashing,
• Repetitive stress by pressure changes at each operation process,
• Concentration of chemicals used to recover the water permeability of the membrane module and frequency of use,
• Ambient environment (direct sunlight, etc.) and
• (Even when not used) storage conditions (room temperature, air temperature, duration, etc.).

2.A decline in filtering performance

Particles, suspended substances, soluble macromolecules, poorly soluble compounds, etc. that are removed by the membrane adhere on the feed side of the membrane surface and porous parts of the membrane. Line clogging also causes declines in permeability flow rate and increases in filtration pressure.

To control such declines in filtering performance or to recover the performance, the membrane is periodically back washed, physically or chemically washed using air or chemicals to remove foulant, or/and operated using the feed to which chemicals for preventing clogging are added or special operation method.