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. 2024 Mar 6;9(11):12635-12642.
doi: 10.1021/acsomega.3c07627. eCollection 2024 Mar 19.

Sequential Approach for Water Purification Using Seashell-Derived Calcium Oxide through Disinfection and Flocculation with Polyphosphate for Chemical Pollutant Removal

Yuuki Hata  1   2 , Sumiyo Hiruma  2 , Hiromi Miyazaki  2 , Shingo Nakamura  2
Affiliations

Sequential Approach for Water Purification Using Seashell-Derived Calcium Oxide through Disinfection and Flocculation with Polyphosphate for Chemical Pollutant Removal

Yuuki Hata et al. ACS Omega. .

Abstract

Safe water supply is usually inadequate in areas without water treatment plants and even in a city under emergency conditions due to a disaster, even though safe water is essential for drinking and other various purposes. The purification of surface water from a river, lake, or pond requires disinfection and removal of chemical pollutants. In this study, we report a water purification strategy using seashell-derived calcium oxide (CaO) via disinfection and subsequent flocculation with polyphosphate for chemical pollutant removal. Seashell-derived CaO at a concentration (2 g L-1) higher than its saturation concentration caused the >99.999% inactivation of bacteria, mainly due to the alkalinity of calcium hydroxide (Ca(OH)2) produced by hydration. After the disinfection, the addition of sodium polyphosphate at 2 g L-1 allowed for the flocculation of CaO/Ca(OH)2 particles with adsorbing chemical pollutants, such as Congo red, dichlorodiphenyltrichloroethane, di(2-ethylhexyl)phthalate, and polychlorinated biphenyls, for removing these pollutants; purified water was obtained through filtration. Although this purified water was initially highly alkaline (pH ∼ 12.5), its pH decreased into a weak alkaline region (pH ∼ 9) during exposure to ambient air by absorbing carbon dioxide from the air with the precipitating calcium carbonate. The advantages of this water purification strategy include the fact that the saturation of CaO/Ca(OH)2 potentially serves as a visual indicator of disinfection, that the flocculation by polyphosphate removes excessive CaO/Ca(OH)2 as well as chemical pollutants, and that the high pH and Ca2+ concentrations in the resulting purified water are readily decreased. Our findings suggest the usability of seashell-derived material-polymer assemblies for water purification, especially under emergency conditions due to disasters.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Schematic illustration of the water purification process using seashell-derived CaO via disinfection and subsequent flocculation with polyphosphate involving chemical pollutants.
Figure 2
Figure 2
Characterization of CaO/Ca(OH)2 suspensions and the aggregates with polyphosphate. (a) Optical microscopy image of CaO/Ca(OH)2 suspensions at 2 g L–1. (b) ζ Potential of CaO/Ca(OH)2 particles. (c) Photograph of CaO/Ca(OH)2 suspensions and aggregates with polyphosphate. The samples were shaken by hand for resuspension and left to stand for 1 min before photographing. (d) Optical microscopy image and (e) XRD profile of the aggregates with polyphosphate. The symbols unfilled circle and asterisk in panel (e) denote peaks assignable to crystalline Ca(OH)2 and sodium triphosphate phase II, respectively.
Figure 3
Figure 3
Removal of Congo red by the CaO/Ca(OH)2–polyphosphate aggregates. Photographs of the Congo red solutions (a) before and (b) after the addition of the aggregates and (c) subsequent filtration. (d) UV–vis spectra of Congo red solutions before and after the treatment.
Figure 4
Figure 4
Disinfection of the model-contaminated water with seashell-derived CaO. CFU mL–1 values of E. coli before and after the addition of chemical pollutants (DDT, DEHP, and PCBs) and seashell-derived CaO are presented. N.D. denotes not detected (CFU mL–1 < 10). The error bars represent the standard deviation of three individual trials.
Figure 5
Figure 5
Decreases in (a) pH and (b) Ca2+ concentration of the filtrate during exposure to ambient air with stirring.
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