The pH dependence of Escherichia coli O157:H7 adsorption on kaolinite and goethite surfaces

Abstract

Understanding the adsorption processes of Escherichia coli O157:H7 in the soil–water system is important in order to protect public health from waterborne diseases. The aim of this study was to investigate the role of pH on E. coli O157:H7 adsorption on kaolinite and goethite. The adsorption of E. coli O157:H7 on kaolinite and goethite over a wide range of pH levels (3–10) was determined. Confocal microscopy, zeta potential, classic Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, and Fourier transform infrared spectrometry were used to provide insights into the mechanisms that affect E. coli O157:H7 adsorption. E. coli O157:H7 adsorption was greater on the positively charged goethite than on the negatively charged kaolinite. The maximum adsorption of E. coli O157:H7 occurred on goethite at pH 3, and increasing pH resulted in decreased adsorption on kaolinite and goethite. Confocal microscopy images confirmed that higher affinities of E. coli O157:H7 occurred on kaolinite and goethite at low pH. Zeta potential, interaction energy, and Fourier transform infrared analysis indicated that electrostatic forces between the E. coli O157:H7 and goethite surfaces controlled the extent of E. coli O157:H7 adsorbed onto goethite surfaces at low pH, and hydrogen bonding and inner-sphere complexation play majors roles in E. coli O157:H7 adsorption to goethite at high pH levels. However, electrostatic force is not the main force for E. coli O157:H7 adsorption to kaolinite. Goethite displayed a larger adsorption capacity for E. coli O157:H7 than kaolinite. The adsorption of bacteria on kaolinite and goethite was pH dependent, and high percentages of E. coli O157:H7 adsorption to kaolinite and goethite occurred at low pH levels.