After acid/alkaline pretreatment and gamma-ray irradiation, the UV–vis spectra of EPS are shown in Fig. 1. Compared to the initial samples, a new absorption band from 240 nm to 300 nm existed in all irradiated samples (Fig. 1A, C, and D), apart from acid condition (Fig. 1B). Nucleic acid component is the most important goal of microorganisms irradiation inactivation. It is specific substance in organisms′ cells, and normal cells′ extracellular substance seldom contains nucleic acid. Only cells
