Operation performance of an A/A/O process coupled with excess sludge ozonation and phosphorus recovery: A pilot-scale study

• An A/A/O process coupled with sludge ozonation and P recovery was developed.
• The sludge solubilization efficiency was 35.5% at about 100 mg O3 g−1 MLSS.
• The maximum sludge reduction efficiency reached 85% in the combined treatment system.
• Ozonated sludge recycle impacted slightly the removal of pollutants (except P).
• The influent P was recovered by 29% from the supernatant of ozonated sludge.

This study investigated the long-term operation performance of an anaerobic/anoxic/oxic (A/A/O) process coupled with sludge ozonation and phosphorus (P) recovery at pilot scale with a treatment capacity of 1.0 m3 d−1. Batch experiments of sludge ozonation showed that the release of organic substances (expressed as chemical oxygen demand (COD)), nitrogen (N), and P from disintegrated microbial cells was enhanced with an increasing ozone dose. The optimal ozone dose was about 100 mg g−1 MLSS (mixed liquor suspended solids), at which a sludge solubilization efficiency of 35.5% was achieved. The pilot-scale treatment system was continuously operated for 141 days and a maximum sludge reduction efficiency of 85% was reached. Ozonated sludge recycle (OSR) affected slightly the COD and N removal, mixed liquor volatile suspended solids to MLSS ratio, and sludge activity in the bioreactor, and significantly improved the sludge settleability. However, P removal was obviously inhibited because of the reduced discharge of excess sludge. The mass balances of COD and N indicated that OSR improved both organic mineralization and denitrification. The influent P could be recovered by 29% from the supernatant of ozonated sludge, thus notably enhancing its removal in the pilot-scale treatment system. This study demonstrates the operational feasibility of the A/A/O process coupled with excess sludge reduction by ozone and P recovery.

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