Mid-Term Report Summary - AFFIRM (Analysis of Biofilm Mediated Fouling of Nanofiltration Membranes)
Nanofiltration (NF) is becoming an increasingly important process for the production of clean water. The performance of this process is however routinely affected by biofouling, which involves the initial adhesion of microorganisms and their subsequent biofilm development on the membranes. Biofilms are dynamic, often structurally complex communities of surface-adhering microorganisms that are embedded within an extracellular polymeric matrix. The complexity of biofilm metabolic behaviour has limited our complete understanding of why biofouling occurs. It is believed that a number of factors influence biofilm formation in NF processes including the physical conditions in the intensified environment of the membrane module and the organic carbon and nutrient conditions. The overall objective of this project is to investigate the role of biofilm in the fouling of nanofiltration membranes and to develop strategies to enhance the removal of such biofilm.
The AFFIRM project had several achievements in the context of the overall project objectives.
1. Identification of the role of calcium on biofilm mechanical properties. This is relevant because elevated concentrations of calcium exist at the membrane interface in nanofiltration where biofouling develops. This is important because biofilm removal strategies depend on the biofilm mechanical properties.
2. It was shown experimentally that for a range of different membranes and for different microorganisms that bacterial adhesion (the critical precursor to biofouling) is dependent solely on the permeate flux and not on the physico-chemical properties of the bacteria and membranes. This is important because it highlights the critical need to assess novel anti-fouling membranes under permeate flux conditions, which currently is not the case.
3. A follow on study has shown that adhered Pseudomonas fluorescens cells under high permeate flux conditions are met with high fluid shear and convective fluxes at the membrane-liquid interface, resulting in their structural damage and collapse. This study was the first to show cell damage and death during the initial phases of bacterial adhesion to NF membranes, and raises a key question about the role of this observed phenomena during early stage biofilm formation under permeate flux and cross flow conditions.
4. Biofouling does not occur in isolation, we have examined the effect of conditioning films of natural organic matter (NOM) on biofilm development. Previous studies in this area gave contradictory conclusions. We set out to use state-of-the art techniques to investigate why this was the case. Out results provide researchers with a new analysis approach that will allow new insights into composite fouling of nanofiltration.
5. The relationship between biofilm growth conditions (hydrodynamic shear, nutrient levels) and microbial characteristics (extracellular polymer production, surface characteristics, growth rates) is critical in determining biofilm properties. A full understanding of this relationship will help develop strategies for biofouling control. We have used flow cells, confocal microscopy and analysis of biofilm detachment rate under highly controlled conditions to gain a better insight into these relationships that we expect will provide evidence for the development of rational biofouling control strategies.
The AFFIRM project had several achievements in the context of the overall project objectives.
1. Identification of the role of calcium on biofilm mechanical properties. This is relevant because elevated concentrations of calcium exist at the membrane interface in nanofiltration where biofouling develops. This is important because biofilm removal strategies depend on the biofilm mechanical properties.
2. It was shown experimentally that for a range of different membranes and for different microorganisms that bacterial adhesion (the critical precursor to biofouling) is dependent solely on the permeate flux and not on the physico-chemical properties of the bacteria and membranes. This is important because it highlights the critical need to assess novel anti-fouling membranes under permeate flux conditions, which currently is not the case.
3. A follow on study has shown that adhered Pseudomonas fluorescens cells under high permeate flux conditions are met with high fluid shear and convective fluxes at the membrane-liquid interface, resulting in their structural damage and collapse. This study was the first to show cell damage and death during the initial phases of bacterial adhesion to NF membranes, and raises a key question about the role of this observed phenomena during early stage biofilm formation under permeate flux and cross flow conditions.
4. Biofouling does not occur in isolation, we have examined the effect of conditioning films of natural organic matter (NOM) on biofilm development. Previous studies in this area gave contradictory conclusions. We set out to use state-of-the art techniques to investigate why this was the case. Out results provide researchers with a new analysis approach that will allow new insights into composite fouling of nanofiltration.
5. The relationship between biofilm growth conditions (hydrodynamic shear, nutrient levels) and microbial characteristics (extracellular polymer production, surface characteristics, growth rates) is critical in determining biofilm properties. A full understanding of this relationship will help develop strategies for biofouling control. We have used flow cells, confocal microscopy and analysis of biofilm detachment rate under highly controlled conditions to gain a better insight into these relationships that we expect will provide evidence for the development of rational biofouling control strategies.