Project No: 16301018

Title: The impacts of chlorine disinfection on the diversity, function and gene expression in the bacterial microbiomes of two contrasting types of sewage effluents

PI: Prof. Lau, Stanley C K


Sewage contains a large quantity of pathogens. To protect public health, treated effluents are often disinfected prior to the discharge to the receiving waters. Chlorine is one of the most commonly used disinfectants in the sewage treatment process due to its advantages of being high in efficacy and low in operational requirements. The impacts of chlorine on the metabolism, physiology and survival of effluent-associated bacteria have been an area of active research. However, the investigations have been largely focused on a small number of pathogens or indicator bacteria (pathogen surrogates) that are readily culturable in the lab. It is well-known that the vast majority of the bacterial cells living in the environment, including sewage, are in the viable-but-non-culturable (VBNC) state. Even E. coli, which is a readily culturable bacteria typically used by regulatory agencies as an indicator of effluent quality and water sanitation, could enter the VBNC state upon chlorination, resulting in an overestimation of disinfection efficacy. What has been lacking in the current knowledge is a culture-independent, holistic understanding of the impacts of chlorine disinfection on the entire bacterial microbiome of treated effluent as a genetically and functionally diverse community of hundreds to thousands of species. The response of effluent-associated bacteria to the post-disinfection discharge to the aquatic environment is another important issue that has not been investigated at the microbiome level. To fill the knowledge gap, we propose a culture-independent investigation on (i) the lethal and sublethal impacts of chlorine on the bacterial microbiome of treated effluent, and (ii) the potential bacteriological threats associated with the disposal of the disinfected effluent to the aquatic environment. To achieve this, effluents that are going through actual chlorine disinfection in sewage treatment facilities will be investigated for changes in community composition, functional repertoire and gene expression profile, particularly for the diversity and quantity of pathogens and genes of public health concern (e.g. virulence factors and antibiotic resistance). After that, undisinfected effluents will be brought to the lab to receive chlorine disinfection followed by field mesocosm experiments to simulate the discharge to coastal seawater; the impacts on the community composition of the bacterial microbiome in general and the population dynamics of pathogens in particular will be investigated. Overall, the knowledge obtained in this proposed project will provide for the first time a culture-independent, microbiome-level insight to the bacteriological outcomes of one of the world’s most commonly used effluent disinfection and disposal strategy.