Ultrasound Treatment Reducing the Production of VBNC Bacteria in the Process of Chlorine Disinfection: Efficiency and Mechanisms

The production and reactivation of viable but nonculturable(VBNC) bacteria by chlorine disinfection leads to an overestimation of the disinfection effect and brings health risks. Therefore, this study is to evaluate the disinfection efficiency of combined ultrasound(US) and chlorine in inhibiting the production and reactivation of VBNC bacteria and to clarify the mechanisms. The number of culturable cells was effectively reduced by 99.97% after US/chlorine treatments. The number of VBNC bacteria introduced by US treatment and chlorine treatment was 10 CFU/ mL and 10 CFU/mL, respectively. However, US/chlorine disinfection produces fewer VBNC bacteria(10 CFU/mL), and the dark reactivation of the VBNC bacteria was effectively inhibited. Ultrasound and chlorine have synergistic effects in disinfection-ultrasound further enhancing bacterial membrane permeability and chlorine-induced oxidative stress, causing the bacterial antioxidant system to collapse. In addition, single cell Raman spectroscopy and gas chromatography-tandem mass spectrometry(GC-MS/MS) analysis revealed that US/chlorine treatment inhibits more strongly or even destroys the metabolism of bacteria. The significantly perturbed metabolic pathways mainly involved the amino acid, carbohydrate and lipid metabolisms. Thus, the combined US/chlorine treatment is a promising cleaner and a more efficient disinfection technology to remove VBNC bacteria in the field of water purification. [Figure not available: see fulltext.].