Paper Title
OPTIMAL MODIFICATION OF EGGSHELL PROTEINS FOR ADSORBING METALS IN WATER

Abstract
Factories—including high-tech factories, chemical factories, and electroplating factories—frequently generate heavy metal wastewater during their manufacturing processes and consequently easily results in river, reservoir, and underground water pollution. Because heavy metals are durable and toxic and bioaccumulate, they harm the environment and compromise human health. Heavy metals in wastewater mostly contain positive charges. Removal of such metals necessitates the identification of economical recycling materials with negative charges for heavy metal absorption. Eggshell membranes are rich in proteins and contain negatively charged sulfur groups after undergoing reduction treatment. Therefore, eggshells are a potential candidates for capturing positively charged metals. This study adopted a factorial experimental design to verify the critical factors affecting the metal adsorption efficiency of eggshell membranes. These factors included water temperature, pH level, reducing agents used, and reaction time. In addition, we utilized a response surface methodology to determine the optimal metal adsorption conditions for modified eggshells. Finally, multiple models, including the isothermal and kinetic adsorption models, were used to investigate the modified eggshells’ silver, copper, and chromium adsorption efficiencies in water. Specifically, metals in the sample solutions were digested by using aqua regia and analyzed through inductively coupled plasma atomic emission spectroscopy. The results revealed that thioglycol 2-mercaptoethanol (a reducing agent) and reaction time were the most crucial factors influencing metal adsorption. We employed the response surface methodology and found that an initial reducing agent concentration and reaction time of 9.75 M and 1.9 h, respectively, were the optimal operating conditions enabling the modified eggshells to achieve a mixed metal (i.e., silver, copper, and chromium combined) adsorption efficiency of 96.8%. The proposed method demonstrates the potential use of eggshells as a biological adsorption material that can purify metals in water, making their use a topic meriting further investigation in studies related to objectives of green cycles and environmental sustainability. Keywords - Eggshell Membrane; Reducing Agent; Disulfide Bond Metal Adsorption; Factorial Design And Response Surface Methodology; Adsorption Model Regression.