E. coli – MS2 bacteriophage interactions during solar disinfection of wastewater and the subsequent post-irradiation period

Abstract

In this study, the effect of MS2 bacteriophage on the inactivation of its Escherichia coli host was evaluated in an effort to recreate some the main factors governing solar disinfection of wastewater (namely microbial growth, infection, photonic flux). As such, the kinetics of sole MS2 bacteriophage or Escherichia coli and their simultaneous inactivation were investigated in synthetic secondary effluent wastewater and accurately modeled by log-linear and shoulder-log linear models, respectively. The observed inactivation kinetics revealed a minor influence between the microorganisms during the solar treatment phase. However, the simultaneous presence of both strains affected bacterial regrowth during the post-irradiation period. Specifically, our results show minor MS2 increase (1-log) in presence of E. coli, but bacterial survival restriction in presence of the bacteriophage (24- vs. 48-h decay). Experiments conducted at three different temperatures (4, 20 and 37 °C) and two discharge matrices (lake water, seawater) indicate that both healthy cells and non-cultivable bacteria influence population dynamics, with (re)growth under mesophilic temperatures and support of the viral life cycle. Noteworthy cases were observed in lake water (high regrowth levels) and in seawater (no growth). In overall, this study contributes to the deeper understanding of population dynamics (i.e. coliphage-bacteria interactions). In extension, it unveils the capacity of solar exposure as disinfection method and indicates possible health risks associated with enteric viral and bacterial-related diseases due to incomplete solar wastewater disinfection or post-irradiation mishandling.