A fundamental design study of electrochemical processes for the control of pathogenic bacteria

Abstract

Water systems in buildings have been reported to contribute to pseudomonal infection transmission and have been associated with Legionnaires’ disease (LD) outbreaks, for they provide the perfect conditions for bacteria proliferation and biofilms formation. An overview of the problem has highlighted that the economic burden, the healthcare and mortality costs of both LD and pseudomonal infections are significant. Although critical to the safe delivery of water, pathogen control continues to remain a challenge as current hot water treatments are not always effective, are often energy intensive and require expensive maintenance. This thesis was set out to evaluate the potential use of electrochemical disinfection (ED) in controlling pathogens in hot water systems of buildings. In this project, we performed a fundamental systematic study on the effect of geometrical and operational parameters in a flask, to gather an understanding of the effect of each parameter on the rate of bacteria elimination, crucial for the design and optimization of electrolytic cells. ED prototypes were then installed in in the hot water systems of two different buildings operating at 60°C, the temperature recommended for Legionella control (HSE, 2013), and their efficacy was monitored long term. In one of the buildings, 2 to 4– log reductions in total bacteria counts was observed, while Pseudomonas species counts were reduced by 3 log. The apparent failure in the other building was due to the inadequate operation of the water system. In order to achieve the 2019 zero carbon targets for new non-domestic buildings set by the UK government, the energy demand associated with heating water needs to be addressed, but maintaining systems at such high temperatures renders difficult the use of greener technologies that could further reduce the CO2 impact of heating water. Given that ED generates disinfectants and that the Health and Safety Executive advises that if hot water is treated with biocides, water temperatures can be reduced, the efficacy of the prototype device was evaluated under laboratory conditions at temperatures between 30 and 45˚C. The prototype was found to be effective both on laboratory-grown biofilm and on planktonic Legionella pneumophila serogroup 1, with 5-log reduction on bacteria counts.