Disinfection of water with new chitosan-modified hybrid clay composite adsorbent

Abstract

Hybrid clay composites were prepared from Kaolinite clay and <i>Carica papaya</i> seeds via modification with chitosan, Alum, NaOH, and ZnCl₂ in different ratios, using solvothermal and surface modification techniques. Several composite adsorbents were prepared, and the most efficient of them for the removal of gram negative enteric bacteria was the hybrid clay composite that was surface-modified with chitosan, Ch-nHYCA <b>_1:5</b> (Chitosan: nHYCA = 1:5). This composite adsorbent had a maximum adsorption removal value of 4.07 × 10⁶ cfu/mL for <i>V. cholerae</i> after 120 min, 1.95 × 10⁶ cfu/mL for <i>E. coli</i> after ∼180 min and 3.25 × 10⁶ cfu/mL for <i>S. typhi</i> after 270 min. The Brouers-Sotolongo model was found to better predict the maximum adsorption capacity (<i>q_max</i> ) of Ch-nHYCA_1:5 composite adsorbent for the removal of <i>E. coli</i> with a <i>q_max</i> of 103.07 mg/g (7.93 × 10⁷ cfu/mL) and <i>V. cholerae</i> with a <i>q_max</i> of 154.18 mg/g (1.19 × 10⁸ cfu/mL) while the Sips model best described <i>S. typhi</i> adsorption by Ch-nHYCA <b>_1:5</b> composite with an estimated <i>q_max</i> of 83.65 mg/g (6.43 × 10⁷ cfu/mL). These efficiencies do far exceed the alert/action levels of ca. 500 cfu/mL in drinking water for these bacteria. The simplicity of the composite preparation process and the availability of raw materials used for its preparation underscore the potential of this low-cost chitosan-modified composite adsorbent (Ch-nHYCA <b>_1:5</b> ) for water treatment.