Solar disinfection of fungal spores in water: Kinetics, influencing factors, mechanisms and regrowth

Abstract

Water contamination with fungi has gained attention increasingly, while solar disinfection (SODIS) is a potential method, especially for developing countries. In this work, inactivation kinetics, influencing factors, mechanisms and regrowth of fungal spores in the SODIS process were firstly investigated. The inactivation fitted well with the Geeraerd and Van Impe inactivation model-fitting tool and P. polonicum was more sensitive to simulated sunlight than A. niger. The pH value within the range of 5–9 and low concentration humic acid did not affect the solar inactivation of fungal spores, while HA at the concentration above 5.0 mg/L inhibited the solar inactivation efficiency. Over the tested range, the inactivation efficiency was obtained at the temperature near the optimal growth temperature (30-40 °C for A. niger, 20–30 °C for P. polonicum). According to the results of flow cytometry, ATP concentration and scanning electron microscopy, the solar inactivation of fungal spores was ascribed to endogenous actions. During the SODIS process, the DNA and respiratory chain of fungal spores were attacked. Subsequently, esterase activity was induced. As a result, the spores lost the culturability firstly, accompanied by the exhaustion of ATP, finally the membrane became permeable. Although no fungal spore regrowth was observed in ground water and surface water after SODIS, they remained a certain regrowth potential in nutrient-rich water like R2A. This work uncovered the control of waterborne fungi by SODIS.