BIOFILM DEFOULING USING MICROBUBBLES GENERATED BY FLUIDIC OSCILLATIONS

The physical separation offered by membrane filters such as Reverse Osmosis (RO), Microfiltration (UF), Ultrafiltration (UF), and Nanofiltration (NF) has reduced the operating cost of such processes compared to distillation and chemical extraction. The advantages of the membrane such as high selectivity, high capacity, feasibility and cost effectiveness make them very good alternatives in separation industries especially cleaning technologies. Membranes, however, are easily fouled. Since the methods developed to defoul a membrane such as ultrasonic and chemical backflushing are always damaging to the membrane, this study is to explore the potential of microbubbles to restore the membrane to its operational condition. Microbubble clouds generated using fluidic oscillation produce non-coalescent bubbles, smaller and more uniform in size. Fluidic oscillation generated microbubbles are influenced by adjusting flow rate and oscillation frequency in conjunction with the diffuser pore size. The size of the microbubble produced is ranging from 30μm to 500μm at the lowest flow rate of air. The effect for cleaning purposes of microbubble injection with and without fluidic oscillation is explored by examination using Scanning Electron Microscopy (SEM), Total Suspended Solid (TSS) and system operational pressure drop (TMP). The smaller microbubble means higher surface contact area to remove the biofilm on the membrane filter. To further validate the effect of microbubbles on detaching and cleaning, FO generated microbubbles were sparged on biofilm (Chlamydomonas algae and HeLa cells) cultured on microscope slide surface. The detachment rates were compared by observing the density of algae and cells removed from the surface using lux meter and cell counting method. It is found that microbubbles generated using Higher Oscillation frequency of Fluidic Oscillator (HOFO) has a higher detachment and defouling rate. The highest defouling rate recorded for MF filter was 9.53mbar/min using HOFO, followed by 6.22mbar/min of microbubbles generated using Lower Oscillation frequency of Fluidic Oscillator (LOFO). Similar trends were observed in algae and cell detachment, the highest oscillation frequency of 335Hz has the highest detachment rate of 1.775lx/min and 1.7 104 cell/ml respectively. For MF systems, microbubbles generated using Higher Oscillation Frequency Oscillator (HOFO), increased the defouling rate by 64%. Similar observation recorded where HOFO increased detachment rate of Chlamydomonas algae and HeLa cells by 42% and 95% respectively.