Based on more than 50 related studies in the past 10 years, Professor Hu Hongying and his team at the School of Environmental have systematically summarized the possible health, process and ecological risks caused by Disinfection Residual Bacteria (DRB). They clarified how to identify typical DRB, elucidated the characteristics of DRB in terms of its community structure, growth and secretion, its antibiotic resistance and association with residual bacteria risks. They also emphasized the importance of studying DRB control, and discussed the risk control strategies of DRB.
Since 2020, the ravaging pandemic of Covid-19 has called for more attention on biosecurity. Disinfection is an indispensable part of controlling biological risks in water treatment. However, previous studies on disinfection have mostly focused on its inactivation effects on microorganisms and the risk of byproducts without enough attention on DRB. Hu’s research team collected and summarized literature on the changes in microbial community caused by disinfection in the past 10 years, analyzed the community structure of DRB after three common disinfection methods (chlorine-containing disinfectants (CCD), UV, and Ozone), and identified the dominant phylum and typical genus of DRB in water treatment. α-, β- and γ-Proteobacteria were more frequent in the residual bacteria of all three common disinfection methods. Bacteroidetes and Firmicutes were more frequent in the DRB of CCD disinfection. The relative abundance of γ-Proteobacteria and Firmicutes were on the increase in all three types of disinfection process. The relative abundance of Actinobacteria experienced significant increase during UV disinfection and Cyanobacteria during ozone disinfection. Pseudomonas is a typical genus of DRB common to all three ways of disinfections, while Acinetobacter to UV and ozone disinfection, both of which deserve extra attention in future studies.
Typical Genus of DRB
The study summarized the possible health, process, and ecological risks associated with DRB. DRB may have higher growth potential, larger pathogenic bacteria proportions, stronger secretion and fouling properties, and higher levels of antibiotic resistance genes. These make it necessary to have more focus on DRB.
Health, process, and ecological risks associated with DRB
The study noted that, advancements in disinfection technology offer many possibilities to address DRB problems. Synergic disinfection can effectively counteract some bacteria’s resistance to a single way of disinfection, and secondary disinfection can bring more severe damages to bacterial cells and thus inhibit their regrowth. Some novel disinfection technologies have significant advantages in controlling regrowth and the transmission of hazard gene, such as advanced oxidation techniques, in-electrode filtration disinfection, and nanowire electroporation. All these technologies are great candidates to control DRB risks. Apart from the choice of methods and agents, operating conditions and dosage can also make a difference. There are reports indicating that different disinfectant dosages can lead to hugely varied DRB hazard potentials.
The study also pointed out that DRB problems can exist in air and on solid surface apart from water treatment processes. DRB problems in various media should all be attached great importance to, especially during Covid-19 with an increased use of disinfectants.
Results of the study were published in Water Research as “Risks, characteristics, and control strategies of disinfection-residual-bacteria (DRB) from the perspective of microbial community structure”. The first author of the paper is Hao-Bin Wang, a PhD student in the School of Environment, Tsinghua University, with Professor Hu Hongying and Associate Researcher Wu Yinhu from the School of Environment as corresponding authors. The study was supported by the National Natural Science Foundation of China.
Link of the paper：https://doi.org/10.1016/j.watres.2021.117606
