Fouling control of a ceramic microfiltration membrane for direct sewer mining by backwashing with ozonated water

• MF filtration of primary wastewater resulted in severe irreversible fouling.
• Fouling could not be fully removed by conventional backwashing.
• Backwashing using ozonated RO filtered water fully removed fouling.
• Extending the ozone backwashing time enhanced fouling removal efficiency.

Backwashing using ozonated water was investigated to control fouling during direct sewer mining using a ceramic microfiltration (MF) membrane. Primarily treated municipal wastewater was filtered and backwashing was performed using RO filtered tap water in this study. Direct MF filtration in the dead-end filtration mode using the ceramic MF membrane resulted in fouling that could not be fully removed by conventional backwashing. A steady increase in transmembrane pressure (TMP) was observed after each filtration cycle and could be attributed mostly to cake formation. In contrast, backwashing using ozonated water for 2.5 min was effective at removing the fouling cake layer; thus, resulting in a stable TMP value after multiple filtration cycles. The effectiveness of ozonated water backwashing could be enhanced by extending the backwashing time. Indeed, the permeability of a heavily fouled membrane was fully restored after 3.5 min of ozonated water backwashing. Results reported here suggest that backwashing using ozonated water has the ability to remove most foulants deposited on the membrane surface and can be used for sewer mining, where severe cake formation occurs.