Electrochemical disinfection of secondary effluent from a wastewater treatment plant: Removal efficiency of ARGs and variation of antibiotic resistance in surviving bacteria

Laboratory-scale electrochemical (EC) disinfection experiments were carried out to investigate its removal efficiency for 23 antibiotic resistance genes (ARGs) that confer against 8 classes of antibiotics and its effects on the antibiotic resistance of surviving bacteria. EC treatments were conducted at different current densities (D treatment) and with different reaction times (T treatment). Prolonged electrolysis resulted in a higher inactivation rate than an increased current density, while the former was less efficient in the removal of ARGs. For example, the inactivation ratios for the T20 and D80 treatments were both > 99%, while the decrease in the relative abundance of ARGs with D80 (from 0.54 to 4.1) was greater than that with T20 (from 5.4 to 5.2). The detection frequency of bacteria resistant to the tested antibiotics decreased by 9-100% after EC treatment. This was mainly attributed to a change in bacterial composition. The proportion of bacteria with high antibiotic resistance frequencies decreased (such as Escherichia), while that with low resistance frequencies (like Acinetobacter and Pseudomonas) increased. In addition, fewer multi-antibiotic-resistant bacteria survived EC disinfection, which also contributed to the significant decrease in the frequency of antibiotic resistant bacteria as well as in the multi-antibiotic-resistance indices of wastewater samples (from 0.47 to 0.35) after EC treatment (P < 0.05). In total, EC disinfection not only reduced the relative abundance of ARGs, but also impaired the antibiotic resistance of surviving bacteria. So it might be a promising disinfection method for controlling the dissemination of antibiotic resistance.