Effects of step-feeding and internal recycling on nitrogen removal in ceramic membrane bioreactors, and their hydraulic backwashing characteristics

• Both lab and pilot scale CMBR were operated with step-feeding and internal recycling.
• Both step-feeding and internal recycling in CMBRs were effective in denitrification.
• Hydraulic backwashing successfully removed the fouling of ceramic membrane.

Both lab-scale (50 L/day) and pilot-scale (10 m3/day) ceramic membrane bioreactors (CMBRs), equipped with two additional implements (step-feeding and internal recycling), have been tested for the removal of nitrogen and organic matter from municipal wastewater. During the 180 days of operation, 0.5Q of step-feeding increased the removal rate of total nitrogen by 46.2% in the lab-scale CMBR, whereas a 59.0% increase was observed with the additional 3Q internal recycling in the pilot-scale CMBR. This was presumably due to the supply of insufficient carbon source as an electron donor in the denitrification stage. The ceramic membrane also exhibited high rigidity sufficient for periodic backwashing using the highly-pressurized permeate. A constant flux test with 30 s of backwashing after every 9.5 min of filtration successfully removed foulants from the pores of the ceramic membrane, and instantaneously restored the trans-membrane pressure (TMP). During the test, the TMP in case of without the hydraulic backwashing steadily increased (20–80 kPa) for 40 min, whereas it took more than two times to reach the same TMP in the case of with the hydraulic backwashing, which eventually doubled the time span between required chemical washings.

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