Effect of Fe/Al Hydroxides on Transport and Retention of Escherichia coli in Saturated Sand Media

The transport of bacteria has been investigated extensively using iron (Fe) (hydr) oxide-coated quartz. However, few studies have investigated the effects of aluminum (Al) (hydr) oxide on the transport of bacteria. In this study, column experiments were conducted to investigate the effects of Fe/Al hydroxides on the transport of Escherichia coli (E. coli) in saturated quartz sand at different pH levels, ionic strengths (IS), and ionic compositions. Fe/Al hydroxide coatings increased the positive charge of quartz, reduced the negative charge, shifted zeta potential in a positive direction, and thus enhanced the retention of E. coli on quartz. The retention of E. coli decreased with increasing pH and increased with increasing IS. These findings were consistent with the theoretical prediction of the Derjaguin, Landau, Verwey and Overbeek (DLVO) interaction energy. Calcium ions improved the retention of E. coli in the column. Since Alhydroxide-coated quartz had a more positive charge, the retention of E. coli was higher in Al-hydroxidecoated quartz than in Fe-hydroxide-coated quartz. When compared with quartz alone, Fe/Al hydroxide coatings significantly reduced the transport of E. coli, and the inhibitory effect of Al hydroxide was greater than that of Fe hydroxide.