Removal of tetracyclines from aqueous solutions by electrocoagulation/pecan nutshell coupling processes: synergistic effect and mechanism.

The present work compared electrocoagulation (EC)/pecan shell (PS) coupling process with a simple electrocoagulation (EC) process for the removal of tetracyclines (TCs). The results indicated that the addition of appropriate PS could lead to the enhancement of the removal efficiency and decrease of operating time via synergistic influence, including conventional EC process, biomass materials adsorption, charge neutralization and coordination adsorption. The ideal condition for the coupling process was 2.5 mA/cm2 for current density and 3 cm for plate spacing. Based on the optimum condition, when the dosage of PS was 5 g/L, the initial concentration of tetracycline hydrochloride (TC), oxytetracycline hydrochloride (OTC) and chlortetracycline hydrochloride (CTC) was 250 mg/L, the removal rate of PS was 55.90%, 45.10% and 14.98% higher than those of EC process after 40 min treatment. In addition, compared to conventional EC process, the unit energy demand (UED) decreased by 49.62%, 53.2 4% and 26.35% and the unit electrode material demand (UEMD) decreased by 49.80%, 85.65% and 44.37%, respectively, which means more energy conservation and environmental protection.