Electrochemically Generated Sulfate Radicals and Singlet Oxygen for Enhanced Tetracycline Degradation and Sewage Disinfection

Electrochemical degradation of tetracycline (TC) using a mixed metal oxide (MMO) anode was investigated in the present study. The inefficiency of hydroxyl radicals for TC degradation was revealed by the minimal pollutant degradation observed in anodic oxidation and electro-Fenton processes. The addition of peroxymonosulfate (PMS) and peroxydisulfate (PDS) resulted in effective TC degradation, and PDS showed higher efficiency than PMS. The efficiency of the electrochemically activated PDS process was improved with the addition of iron-loaded biochar (FBC) as a catalyst; and the optimal efficiency of 78% was observed at the natural pH of a 100 ppm TC solution (pH 5.6), operated at 1 V, with 250 ppm PDS and 100 mg/L FBC. The process was effective over a wide pH range, from 3 to 9. In situ-generated sulfate radicals and singlet oxygen were found to be the predominant oxidants responsible for TC degradation, even in sewage, with 73.7% TC removal. The process also resulted in sewage disinfection, with a reduction in total coliforms from 1.48 × 1012 CFU/mL to 2.8 × 1011 CFU/mL, and in fecal coliforms from 6.9 × 1011 CFU/mL to 1.2 × 1011 CFU/mL, in addition to cell wall damage to nematodes and rotifers. Overall, electrochemical degradation is an effective approach for TC removal from aqueous media .