Intimately coupled photocatalysis and biodegradation (ICPB) is a novel wastewater treatment technique that has potential applications in refractory degradation. This paper reports a synergistic degradation protocol that allowing the transfer of photoelectrons between photocatalysts and microbes without supplementary electron donors or improving the loading rate of the photocatalysts. As a result, a degradation rate of ～94% was sustained for 400 h in a perturbation setup with a hydraulic retention time of 4.0 h. We achieved the degradation of β-apo-oxytetracycline, a stable antimicrobial intermediate compound (half-life of 270 d in soil interstitial water), within 10 min, and no accumulation was observed. Moreover, the required loading rate of the photocatalyst was dramatically reduced to 18.3% compared to previous reports which mentioned much higher rates. The results of our study provided a new strategy to improve the degradation efficiency of oxytetracycline and give new insight into the degradation mechanism of the bio-photocatalytic degradation system.

SEM images of the blank sponge carrier (a, b), coated with Bi12O17Cl2 (c, d) and after the synergistic degradation operation for 400 h (e, f).