Simulation of equilibrium system and release behaviors of both oxytetracycline and copper on aerobic granules in a sequencing batch reactor

Accumulation of hard-to-degrade or nondegradable chemicals may be created in a long-time granule sludge treatment process. The excess accumulation of target chemicals on aerobic granules (AG) might induce inevitable release in sequencing batch reactors. In order to investigate the combined extent on AG with oxytetracycline (OTC) and copper as well as the better understanding of the environmental fate of chemicals, the saturated and equilibrated system was simulated by an adsorption test, and then a release experiment was conducted to study the influence of concentration, pH, ionic strength, and temperature. The results showed that isotherms of OTC and Cu(II) with high correlation coefficients (R2 = 0.991–0.996) and (R2 = 0.992–0.996) fit well with the Redlich–Peterson model (RPM). The bonding amounts of both OTC and Cu(II) increase in the coexisting system, indicating that the OTC–Cu(II) complex had stronger binary ability with AG. Relying on different initial concentrations, release of OTC from AG was 0.799–10.758% with decrease in coexisting Cu(II) ion concentration from 40 mg/L to 0 mg/L and 0.08–6.21% for Cu(II) with decrease in coexisting OTC concentration from 10 mg/L to 0 mg/L, indicating that decrease in coexisting ion concentration has adverse effect on their combined ability with AG.