A gas–liquid discharge reactor for water disinfection: Electrical properties and microbicidal effects on viruses and bacteria

As an eco-friendly oxidation technique, gas–liquid underwater discharge is considered a promising water disinfection method. In this study, we constructed a gas–liquid discharge reactor, in which the electrical properties, optimized discharging parameters, and microbicidal effects on coliphage virus and two bacteria (E. coli and S. aureus) were investigated. It is shown that, compared to direct underwater discharge without ventilation, gas–liquid discharges can release higher energy and generate more active species, thus resulting in better inactivation performance. A microbicidal reduction of over 99.9% can be achieved in 5 min of treatment for three types of microbes in 600 ml tap water (σ ∼ 590 μS/cm); specifically, 3.34, 3.95, and 3.65 log reductions were achieved for coliphages, E. coli, and S. aureus, respectively. The observations of microbial morphologies indicate that underwater discharges and their products can severely damage the external structures and internal substances of micro-organisms, which is responsible for the working mechanism of microbial inactivation. The reactor can decrease E. coli from 6.2 × 103–6.4 × 106 CFU/ml to ∼1000 CFU/ml in 5 min, suggesting that this gas–liquid discharge reactor has a low sensitivity to the initial density of suspension. In addition, the reactor can also achieve a satisfactory disinfection effect even in water with high conductivity, although the microbicidal performance of E. coli will be attenuated with an increase in solution conductivity (from 3.82 log reduction at 2 mS/cm to 2.22 log at 15 mS/cm). These advantages indicate the broad applicability of the reactor in water disinfection.