Performance of anoxic and aerobic flocs in anoxic/aerobic-membrane bioreactor (A/O–MBR) for the treatment of printing and dyeing wastewater (PDW)

This study compared and elucidated the performance and mechanisms of aerobic and anoxic flocs in anoxic/aerobic-membrane bioreactor (A/O–MBR) for the printing and dyeing wastewater (PDW) treatment. The batch experiments were conducted with aerobic and anoxic flocs from our continuous laboratory-scale A/O–MBR for the PDW remediation. A distinct discrepancy between aerobic and anoxic activated sludge flocs for chemical oxygen demand (COD) and adsorbable organic halogens (AOX) removal was demonstrated. Specifically, the aerobic flocs exhibited considerable higher COD removal efficiencies (O1 59.0 %, O2 76.4 %) than the anoxic flocs (A1 56.5 %, A2 61.0 %) owing to the stronger organic biodegradability of aerobic respiration, while anoxic flocs exhibited greater performance on the AOX removal (A1 87.8 %) than aerobic flocs (O1 76.8 %) after 12 h biodegradation due to the greater abundance of AOX degradation relevant gene in anoxic flocs. Meanwhile, the study also revealed that the biodegradation was the principal mechanism for COD removal in PDW, whereas, both biodegradation and biosorption contributed to the AOX removal. This study provides valuable insights into the upgrading and reconstruction of A/O process in PDW treatment plants.