Quantifying the surface charges and hydrophobicities of Magnesium and Nitrogen doped biochar, sand and Escherichia coli O157:H7 and K12 cells

Primary Author

Elizabeth Cervantes

Additional Author(s)

Katherine Quinn, Sohrab Haghighi Mood, Manuel Garcia Perez and Nehal I. Abu-Lail

Faculty Mentor

Nehal I. Abu-Lail

Abstract

844 million people lack access to clean drinking water as pollutants like heavy metals and bacterial pathogens can contaminate water and result in waterborne diseases. Biochar is a cheap, charcoal-like material that can be possibly used as an effective filter to retain pathogenic bacteria in subsurfaces. However, utilizing it as a filter has been limited by the lack of knowledge on how it interacts with bacteria and sand amended with biochar. Interactions between cells and materials such as biochar or sand are governed by a variety of forces including electrostatic and van der Waals forces, acid-base interactions, covalent bonds, hydrogen forces as well as steric forces. To quantify such interactions, knowledge of the hydrophobicities and the charges of the interacting materials is essential. With that in mind, the goal of this study was to quantify the hydrophobicities and surface charges of biochar, sand and bacterial cells using contact angle and electrophoretic mobility measurements, respectively. Four types of Magnesium and Nitrogen-doped biochar prepared at four different temperatures (400, 500, 600, and 700 oC) via pyrolysis were investigated. E. coli O157:H7 was the model bacterium selected because it commonly contaminates water in the subsurface. E. coli K-12 was used as the nonpathogenic control. Our results indicated that biochars prepared at 400 and 700 oC are negatively charged with -14.8±1.7 mV and -18.4±2.9 mV, respectively while the biochars prepared at 500 and 600 oC are positively charged with 5.2±0.9 mV and 5.6±1.7 mV, respectively. The sand was also negatively charged with -20.1±0.8 mV. When compared at pH 7, E. coli K12 was approximately 10 fold more negative than E. coli O157:H7. When hydrophobicities were quantified, all biochars were hydrophobic while the sand and bacterial strains were hydrophilic. Our results are expected to guide the design of effective biochar filters capable of retaining bacteria in them through maximizing adhesion forces between bacteria and biochar/sand.

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