The electro/Fe3+/peroxydisulfate (PDS) process coupled to activated sludge culture for the degradation of tetracycline

The removal of tetracycline (TC) by electro/Fe3+/peroxydisulfate process combined to the biological treatment is reported in this study. Effect of current density, peroxydisulfate (PDS) concentration, Fe3+ ions concentration and initial tetracycline concentration were investigated. The results indicated that the removal efficiency of TC increased with increasing current density and decreases with tetracycline initial concentration. This effect is attributed to the competition of TC and electrogenerated intermediate compounds for the consumption of oxidizing SO4− radicals. The TC degradation efficiency was improved significantly when the PDS and Fe3+ concentrations increased from 1 to 10 mM and 1-2 mM, respectively. Above 10 mM PDS and 2 mM Fe3+ concentrations, a decrease of TC degradation efficiency was observed. The optimal operating conditions were: 2 mM Fe3+, 0.06 mM TC, 10 mM PDS concentrations and 40 mA cm−2 current density. Under these conditions a total degradation of TC within only 40 min of reaction time and 98% of mineralization yield after 3 h electrolysis were obtained. The biodegradability of the solution after electro/Fe3+/peroxydisulfate pre-treatment showed that BOD5/COD ratio increased from 0.00 initially to 0.42, 0.46 and 0.83 after 4 h, 5 h and 6 h, respectively, namely above the limit of biodegradability (0.4). The enhancement of biodegradability initially from 0.00 to 0.42 and 0.46 after 4 h and 5 h of electrolysis respectively, was confirmed by the biological treatment, since 77.51% and 92.54% of the dissolved organic carbon was removed respectively by coupling Electro/Fe3 +/PDS pre-treatment and a biological treatment.