Degradation of antibiotic ampicillin on boron-doped diamond anode using the combined electrochemical oxidation - Sodium persulfate process

In this work, the electrochemical oxidation of antibiotic ampicillin (AMP) on a boron-doped diamond anode in the presence of sodium persulfate (SPS) was investigated (EO/SPS process). Experiments were conducted at AMP concentrations between 0.8 and 3 mg/L, SPS concentrations between 100 and 500 mg/L, current densities between 5 and 110 mA/cm2, in three water matrices (ultrapure water, bottled water and secondary treated wastewater), using 0.1 M Na2SO4 as the supporting electrolyte. AMP degradation follows a pseudo-first order kinetic expression with the apparent rate constant increasing with (i) increasing SPS concentration (from 0.08 min−1 to 0.36 min−1 at 0 and 500 mg/L SPS, respectively, 1.1 mg/L AMP, 25 mA/cm2), (ii) increasing current (from 0.08 min−1 to 0.6 min−1 at 5 and 110 mA/cm2, respectively, 1.1 mg/L AMP, 250 mg/L SPS), and (iii) decreasing AMP concentration (from 0.16 min−1 to 0.31 min−1 at 3 and 0.8 mg/L, respectively, 250 mg/L SPS, 25 mA/cm2). The presence of various anions (mainly bicarbonates) in bottled water did not impact AMP degradation. The observed kinetic constant decreased by 40% in the presence of 10 mg/L humic acid. On the other hand, process efficiency was enhanced almost 3.5 times in secondary effluent due to the electrogeneration of active chlorine species that promote indirect oxidation reactions in the bulk solution. The efficacy of the EO/SPS process was compared to and found to be considerably greater than a process where SPS was activated by simulated solar irradiation at an intensity of 7.3 × 10−7 E/(L.s) (SLR/SPS process). Coupling the two processes (EO/SLR/SPS) resulted in a cumulative, in terms of AMP degradation, effect. The combined process was tested for AMP degradation, mineralization and inhibition to Vibrio fischeri in wastewater; fast AMP removal was accompanied by low mineralization and incomplete toxicity removal.