Controlling Biofilm Growth and Its Antibiotic Resistance in Drinking Water by Combined UV and Chlorination Processes

Abstract

Combined use of light-emitting diodes (LED) ultraviolet (UV) and chlorination provides alternative disinfection in drinking water, which could affect the biofilm formed subsequently. Two sequential integrations (UV-Cl and Cl-UV) and one simultaneous combination (UV/Cl) were adopted to investigate their impacts on biofilm formation. Natural organic matter after combined processes was more accessible for microbes. This might explain the promoted growth of culturable biofilm bacteria—biofilm bacteria stabilized at 104 CFU/mL without disinfection while increasing continuously to 105 CFU/mL in 106 days after combined processes. Contrarily, the viable biofilm bacteria were efficiently suppressed by combined processes, with the least bacteria observed in UV/Cl. The culturable ciprofloxacin-resistant bacteria in biofilm was suppressed by combined processes, with the survival reduced from 49.9% in the control to 27.7%, 16.0% and 10.8% in UV-Cl, Cl-UV and UV/Cl, respectively. The survival of sulfamethoxazole/trimethoprim-resistant bacteria was lower in UV/Cl (16.8%) than others (43.6–55.0%), consistent with the little sul1 and sul2 detected in UV/Cl. Although combined processes reduced most detected antibiotic resistance genes (i.e., blaTEM-1, tetA, sul1 and sul2), UV-Cl showed the potential to enrich tetA and sul2 in biofilm. Overall, UV/Cl outperformed the sequential combinations in the control of viable bacteria and the antibiotic resistance in the subsequently formed biofilm.