Inactivation of E. coli, Legionella and Pseudomonas in Tap Water Using Electrochemical Disinfection

Abstract

Disinfection of hot water systems is critical in reducing the incidence of disease outbreaks caused by pathogenic bacteria. Electrochemical disinfection (ED) has been identified as an economical, low-maintenance and chemical-free alternative in the fight against waterborne pathogenic microorganisms. It also provides the residual disinfection needed to inactivate the planktonic bacteria released by the biofilm. The work presented here includes fundamental small scale laboratory optimisation experiments in a flask where platinum coated electrodes were immersed in 3.5 litre of tap water contaminated with Escherichia coli (NCT10418) with an initial population density between 3x105 and 1.6x105 Colony Forming Units/ml (CFU/ml) or Legionella pneumophila serogroup 1 (NCTC12821) ranging from 180 to 244 CFU/ml. Voltage, electrode area, inter-electrode distance, spiking time, volume of contaminated water and mixer speed were varied to determine the optimal geometrical and operational requirements needed to kill bacteria. Experimental results indicate ED to be an effective control method, with a >4-log inactivation of E. coli and a >5-log inactivation of Legionella in 10 min. and 45 min., respectively, at a current density of ≈ 4 mA/cm2. The findings of the flask experiments were translated into real-world conditions by evaluating the long-term performance of an optimised ED prototype device installed in the hot water recirculation system of a small-size health-care centre building. The results showed that ED is effective at minimising pathogen contamination of the hot water distribution system from initial values, with total bacteria levels and Pseudomonas species being reduced in all of the samples over a 15 month period following activation of the ED device.