Repurposing waste eggshells for arsenic removal and bacterial inactivation in contaminated water

Arsenic (As) contamination and pathogenic bacteria in drinking water pose serious health risks, emphasizing the need for effective treatment solutions to ensure water safety. The high calcium content in eggshells is expected to enhance As(V) adsorption and bacterial inactivation, making them a promising green material for water treatment. The physicochemical properties of thermally treated eggshells were analyzed, and their As(V) adsorption capacity and antibacterial effectiveness were assessed through batch experiments. Eggshells were thermally treated at 100 to 900 °C to enhance their adsorptive and antimicrobial properties. Thermal treatment altered the pore characteristics and mineral phases of the eggshells, while Ca elution increased markedly at 800 °C and above. These changes correlated with increased As(V) adsorption and bacterial inactivation efficiencies. Adsorption studies showed that eggshells treated at 800 °C (Eggshell-800) had the highest As(V) adsorption capacity, reaching 570.60 mg/g, and fit well with the Langmuir adsorption model. Antimicrobial assessments demonstrated that Eggshell-800 effectively inactivated key waterborne pathogens, including Escherichia coli O157:H7, Salmonella Typhimurium , and Listeria monocytogenes , reducing their populations to below the limit of detection (< 1.0 log CFU/mL) within 30 min. The study highlighted the dual functionality of thermally treated eggshells, offering a cost-effective and sustainable solution for addressing both heavy metal contamination and microbial safety in water treatment.