Membrane filtration is an effective technique used in water treatment to remove particles, organic pollutants, inorganic compounds, and microorganisms to accomplish a biologically safe and consistently high quality drinking water. One significant challenge to membrane separation technologies is membrane fouling causing pressure drop, flux decline and eventually significant cost of membrane replacement. Specifically, membrane biofouling is considered a major problem due to the capabilities of microorganisms to adapt their growth rate, multiply, and relocate even if they were 99.99% removed from the feed stream. The objective of this research was to determine the impact of metabolic activity of the pure culture of biofoulants on the membrane biofilm metabolic activity, biofilm formation rate, and operational flux decline.
In this study, the metabolic activity of Pseudomonas fluorescens in active, inactive, and different growth phases were investigated during cross-flow filtration using a cellulose acetate ultrafiltration (UF) membrane at different sampling times (4, 11, and 24 hours) of filtration. In accordance with previous biofilm studies, ATP was used to determine the metabolical activity of the biomass. Dehydrogenase activity assessment of the membrane biofilm using CTC was also carried out on intact biofilms.
Our results showed that after 10-12 hours of filtration, the biofilm ATP levels reach an equilibrium concentration (avg. 8 amol/cell) and do not appear to be related to biofoulant ATP levels from cells harvested in the late exponential growth phase regardless of initial ATP level. However, the bacterial growth phase affected the ATP activity of cells. Membrane biofilms formed from biofoulants in the lag and stationary phase of growth contained similar levels of ATP (avg. 1.8 amol/cell), and the exponential phase cells resulted in significant higher activity. Flux decline does not appear to be related to metabolic activity of the biofoulant or biofilm following 24 hours of filtration. Notably, there was much less (ca. 2.5%) flux decline when the biofoulant cells were inactive. Since metabolic activity determines the substrate conversion rate and the biofilm growth rate, the knowledge of the metabolic activity of the biofoulants and membrane biofilm is essential for understanding the biofilm accumulation mechanism for applying appropriate countermeasures to control membrane biofouling.