# Biosorption Potential of Sargassum for Removal of Aqueous Dye Solutions
## 3 Results  
_Effect of CaCl\({}_{2}\) Treatment on the Biosorption of Methylene Blue_  
At a biosorbent dose of 0.1 g, removal efficiencies of 89.98% and 82.55% were achieved in the initial 30 min of biosorption for CaCl\({}_{2}\)-treated and untreated \(S\). _muticum_, respectively. The difference between the treated and untreated biomass after 30 min was found to be significant (\(p\) = 0.003, \(t\)-test, unequal variance, two-tailed). When the biosorbent was increased to 0.4 g, the removal efficiency increased to 95.48% within the initial 30 min for CaCl\({}_{2}\)-treated \(S\). _muticum_ but remained fairly constant at 81.19% for the untreated \(S\). _muticum_, indicating that the pretreatment may have some effect on the biosorption capacity of methylene blue (Figure 2). For the untreated \(S\). _muticum_, no significant difference was observed between biosorbent doses of 0.1 g and 0.4 g after 30 min (\(p\) = 0.762) and 60 min (\(p\) = 0.299); however, after 120 min at 0.4 g, the concentration in the solution increased, indicating desorption of the dye, decreasing the removal efficiency to 76.09% compared to 82.91% at 0.1 g, which was a significant difference (\(p\) = 0.048).  
The three-way ANOVA showed that species, Sargassum concentration and treatment (CaCl\({}_{2}\)) were statistically highly significant factors (_p_ < 0.001) in the MB removal. The interactions between the species and Sargassum concentration (_p_ < 0.05) and Sargassum concentration and CaCl\({}_{2}\) (_p_ < 0.001) were also statistically significant factors in the removal of MB.  
To describe the adsorption of MB on Sargassum, a first-order kinetic model was fitted with a high coefficient of determination (Table 1). It was generally seen that the amount of dye adsorbed at equilibrium was higher in CaCl\({}_{2}\)-treated seaweed compared to untreated seaweed, with a maximum difference of 17.29% between the 0.4 g CaCl\({}_{2}\)-treated and untreated mixed Sargassum. For the CaCl\({}_{2}\)-treated seaweed samples (0.1 g biomass), the adsorption constant differed by only 0.008 between _S. muticum_ and mixed Sargassum. There was a relatively higher difference in the adsorption constants between using 0.1 g or 0.4 g of CaCl\({}_{2}\)-treated mixed Sargassum (difference of 0.066). The decrease in adsorption over time limited the fitting of this model for 0.4 g CaCl\({}_{2}\)-treated _S. muticum_.  
\begin{table}
\begin{tabular}{c c c c} \hline  & \(q_{e}\) & \(k\) & \(\mathbf{R^{2}}\) \\ \hline
0.1 _S. muticum_ CaCl\({}_{2}\) & 93.641 & 0.107 & 0.999 \\ \hline
0.4 _S. muticum_ CaCl\({}_{2}\) & 94.538 & - & 0.999 \\ \hline
0.1 Mixed Sarg CaCl\({}_{2}\) & 88.700 & 0.099 & 1.000 \\ \hline
0.4 Mixed Sarg CaCl\({}_{2}\) & 91.892 & 0.165 & 0.999 \\ \hline \end{tabular}
\end{table}
Table 1: Kinetic parameters \(q_{e}\) is the amount of dye adsorbed at equilibrium, \(k\) is the adsorption rate constant and \(\mathbf{R^{2}}\) is the coefficient of determination between calculated and average experimental results.  
Figure 2: Biosorption of methylene blue over 120 min using CaCl\({}_{2}\)-pretreated or untreated Sargassum muticum (SM) (0.1 and 0.4 g). Standard deviation n = 3.  
Figure 4: Biosorption of methylene blue over 120 min using _Sargassum multicum_ (SM) at different concentrations. Concentration of dye remained constant at 10 mg L\({}^{-1}\) (80 mL). Standard deviation, n = 3.  
Figure 5: Biosorption of methylene blue over 120 min using mixed _Sargassum_ spp. at different concentrations. Concentration of dye remained constant at 10 mg L\({}^{-1}\) (80 mL). Standard deviation, n = 3.