Decay of Microbial Contaminants in Water Treatment and In
the Environment
Abstract
Faculty: Andrea Silverman
Mentor: Mwanarusi Mwatondo
Monochloramine is typically used in water purification as a secondary step to prevent
the regrowth of micro- organisms that were previously inactivated in the first step of
disinfection. A recent study had shown that bacteria indigenous to the environment
such as those found in wastewater were more resistant to chlorine disinfection (which
is commonly used in the first step of disinfection) as compared to laboratory cultured
bacteria (Mwatondo and Silverman, 2021). An open question is: what is the mechanism of
resistance that is present in the environmental bacteria? Based on isolated experiments
where bacteria from wastewater grown in the lab were more susceptible to disinfection
compared to those in wastewater, it is hypothesized that the mechanism of resistance
to disinfection stems from changes in physiology (Mwatondo and Silverman, 2021).
Since monochloramine is typically used as a residual disinfectant for drinking water, it
is important to understand the mechanism of resistance of indigenous bacteria to it.
Here, we test the hypothesis that disinfection resistance of bacteria in the environment
is induced through physiological factors. Three isolate colonies of Enterococci and
Escherichia coli obtained from wastewater were cultured using the same procedure for
laboratory-cultured bacteria where they were incubated in nutrient broths then rinsed in
phosphate buffer saline (PBS) prior to exposure to monochloramine. This is significant
as Escherichia coli and Enterococci have been classified as biological indicators for the
presence of disease-causing microorganisms in fecal contaminated water. Furthermore,
while there are several papers on disinfection with chlorine or sunlight, very few focus
on monochloramine. Based on preliminary experimental data, we expect that the
wastewater-sourced bacteria grown in the lab will behave like laboratory cultured
bacteria due to a lower resistance to disinfection compared to wastewater-sourced
bacteria. This will further provide critical information on the mechanism of resistance
employed by environmental bacteria so that more effective disinfectants and procedures
are innovated.