AIST observed the fouling process of water treatment membranes non-destructively. A phenomenon was discovered in which the lipids present in a biofilm caused membrane fouling. The researcher proposed a new model for the membrane fouling process under high loads.

Cell-derived macromolecules in biofilms causing membrane fouling

Under low loads there are more polysaccharides, while under high loads there are more lipids.

Two types of model wastewater with different concentrations of organic substances (low load and high load) were treated using a membrane bioreactor (MBR) to identify the substances and microorganisms that cause membrane fouling. Using a confocal reflection microscope combined with fluorescent probes, it was found that polysaccharides are the primary component under low loads while lipids are the primary component under high loads. It was also found using a next-generation sequencer that the microorganisms constituting the biofilm are different when the concentrations of organic substances differ. These findings led to the proposal of a new model for the membrane fouling process under high loads.

In recent years, global water shortages have become more serious and the need for reclaimed water is rapidly rising. By the MBR method, high-quality water can be obtained in a narrower space than the conventional method (the precipitation method), but the cause of treatment membrane fouling and the details of the mechanism are unknown, and the methods for detection and control of membrane fouling were issues. Until now, the timing to replace the membrane was based on uniform countermeasures using the amount of permeated water through the membrane and differential pressure as indicators.

The developed analysis method will be applied to individual MBR operations with different organic substance concentrations and wastewater types to accumulate information on components and microorganisms causing membrane fouling. Using the information, AIST will work to propose appropriate operation management methods for MBR, and maintenance and management methods for water treatment membranes.