Enhancing cleaning of microfiltration membranes fouled by food oily wastewater using microbubbles

Abstract

Food processing generates wastewater containing high contents of fat, oil and grease. As a widely used wastewater treatment method, the process efficiency of membrane filtration can be hindered by membrane fouling, hence periodic cleaning is needed. However, clean-in-place (CIP) operations performed in food processing plants consume large amounts of water, energy, and chemicals. This study incorporated microbubbles (MBs) with the mean diameter of 4.48 µm into liquids at the density of 1431 bubbles/mL as alternative cleaning agents, and investigated their performance of cleaning microfiltration membranes used for food oily wastewater treatment. Palm oil-in-water emulsions were used as model wastewater, increasing the oil concentration from 0.05 to 0.1% w/v changed the dominant fouling mechanism from intermediate blocking to cake formation. MB incorporation into water rinse did not recover the flux of membranes fouled with reversible oil layer, but adding MBs into NaOH solution for cleaning increased the flux recovery by 235%. Increasing the crossflow velocity of MB-incorporated liquids from 0.65 to 0.92 m/s reduced their enhancing effect on cleaning, but further increase to 1.20 m/s had the highest level of enhancement. Moreover, MBs did not significantly enhance the removal of oil deposits irreversibly blocking the membrane pores. MB-assisted cleaning proved a promising technology for integration into current CIP operations to improve their cleaning efficiency with reduced water and chemical usage.