# Removal of Contaminants in Water with Scallop Shell Waste
## 3 Results
### Remotion of Water Waste Contaminants  
Water decontamination tests using scallop shell powder were performed with the objective of defining a potential application for this type of waste. Two of the main contaminants of Chilean waters were selected, the first being Caffeic Acid (CA), which is a compound commonly found in wastewater produced by vittiviniculture [49; 50; 51; 52; 53]. The second contaminant selected is Arsenic in the form of As(III), which is present in soil and water bodies [54; 55], as well having been found in potable waters [56; 57]. Figure 9 shows the removal percentage of caffeic acid (CA) and arsenic(III) obtained using different particle size ranges of scallop shell waste (BS, MS, and SS) for 20 and 80 min, respectively. In Figure 9, scallop shell waste with a small diameter (SS) presents a high removal percentage of contaminants. In addition, the waste with a big particle diameter (BS) presents practically zero removal percentage. This behavior can be explained by textural properties (Table 3). The standard deviation (SD) shows no significant differences between the results obtained, which demonstrates that they are precise and reproducible. In order to understand the adsorption process between the scallop shell residues and the caffeic acid contaminant, experiments were carried out by using crushed shell powder with a small particle size (SS) and subjecting them to different operational definitions. This study will, therefore, focus on the effect that variable pH, shell powder concentration, and contaminant concentration have on the adsorption process. Table 4 shows the removal average percentage of caffeic acid by different SS-sized shell powder concentrations. The SD shows no significant differences between the results obtained, and the results indicate that, while adsorption percentages do not deviate significantly between samples after 90 min, they do vary after 20 min, with the 1000 ppm sample having the highest adsorption percentage amongst samples. This behavior clearly suggests that increasing the concentration of northern scallop shell residue would hasten the removal of caffeic acid from the system in this study. Figure 9: Removal percentage of caffeic acid and arsenic(III) using different particle size ranges of scallop shell residues (BS, MS, and SS). It is also important to note that caffeic acid adsorption reaches its maximum value after 80 min, as results from the 500 ppm and 1000 ppm samples are almost identical, with 98.5% and 98.6%, respectively, and remain constant until the end of the experiment at 90 min, implying that the majority of caffeic acid has already been adsorbed by the shell residue. This, in turn, means that increasing shell residue concentration above 500 ppm becomes unnecessary for this system. Furthermore, increasing residue concentration to 1000 ppm has an effect on final sample pH, increasing it well above the limit allowed by international law regarding water reuse. Final pH values of the other two samples are both within the 6.5 to 8.0 range required by law. The post-adsorption pH increase is caused by the calcium carbonate that makes up the scallop shells, as it is an oxysalt that increases pH in contact with water, therefore increasing system pH as the shell residue concentration increases. Results are presented as mean \(\pm\) standard deviation. We compared CA removal percentage and As(III) removal percentage among the three surface area groups (BS, MS, SS) by means of an unifactorial ANOVA model (Table 3). We did likewise for adsorption (Table 4), comparing three levels of sample concentration. Removal percentage of caffeic acid at different initial pH values was compared by a multiple linear regression model, considering time in logarithmic scale. Initial sample pH and its effects on adsorption rates were also studied. Removal percentages remain low at pH 3.0 (34.1 \(\pm\) 0.6%) and pH 8.0 (57.7 \(\pm\) 0.6%), while pH values for 4.6 and 6.5 yielded adsorption percentages of 100.0 \(\pm\) 0.0% and 97.3 \(\pm\) 0.4%, respectively.