Membrane Autopsy

Membrane autopsies are generally considered to reveal the cause of membrane damage, whether it is scaling, fouling or decreased production in quantity or quality. A membrane autopsy can also be a way to monitor the lifecycle of membrane elements. Being the “smoking gun” the inspected membrane element will show mechanical and chemical damage as well as any foulants which can evidently lead to the source of the problem.

  • Mechanical damage such as telescoping, caused trough too high feed pressures, can be observed without opening the membrane element. Delaminating or blistering can be detected after cutting the element open and enrol the sheets.
  • Chemical damage such as oxidation by chlorine can be revealed by the Fujiwara test on the membrane surface. Damage from cleaning procedures beyond the pH-range or temperatures as given by the membrane manufacturers will be easily detectable with a visual observation.
  • More sophisticated equipment such as a Scanning Electroscope (SEM) or  Energy-dispersive X-ray spectroscopy (EDX) can show structures and reveal the elements present on the membrane surface.
  • Biomass as well as bacteria can be quantified and analyzed by Total Organic Compounds (TOC), Adenosine Tri Phosphate (ATP) and DNA technology. Whereas the visual observation of the whole sheets contribute to an impression where the foulants have spread over the membrane surface and if channeling had occurred.

Membrane autopsy and Global Membrains

The know how provided by Global Membrains combined with the data of the plant as recorded by the user and the membrane autopsy proved to be the magic mix. As showed by one example of detected chlorine damage. In this particular case the customer took the feed water for his Reverse Osmoses plant from an industrial cooling water system. The system was treated with chlorine to avoid biofouling in the cooling water.To prevent chlorine damage, calculations were made and adequate and timely dosage of Sodium bi-sulphite (SBS) was engineered and controlled. After the conclusions of the membrane autopsy the plant was checked again on the SBS dosing which proved to be working. However further research revealed that the SBS dose rate was calculated on the average concentration of chlorine. The dose pump on the other hand shock fed the chlorine in the complex cooling system in to short a time to be absorbed by the full volume of the system. This leads to an extreme high peak in only a part of the water.  Once this part came by the feed to the RO system, the SBS dose rate was way too low to neutralize the chlorine and consequently damaged the membranes. The solution was a more spread out in time dosing of the chlorine. The chlorine detector was able to shut down the feed to the RO in case the chlorine excessed a maximum level.