## 5 Water Treatment Employing Bioadsorbents
### Bioadsorbents Based on Herbage and Forage  
5.3.1. Heavy Metals  
Heavy metals have been removed from aqueous environments using adsorbents obtained from herbs and forage (Table 5). [PERSON] et al. [88] investigated the potential of SCB for treating Mn(II) present in ground water, considering as optimum conditions an adsorbent dosage of 1.5 g and an initial heavy metal concentration of 2 mg/L at pH 6. Mn(II) was successfully removed with an efficiency of 62.5%, explained under a pseudo-second order kinetic model. Using a ten-fold quantity of raw SCB, it was possible to eliminate a higher concentration of this metal (12 mg/L) with similar efficiency [87]. Additional chemical pretreatment with hydrochloric acid had a significant positive effect on this adsorbent, increasing the removal to 99% due to the increase of carboxyl and hydroxyl groups on its surface. Tea and sunflower wastes were implemented for Mn(II) uptake, obtaining removal efficiencies of 95.5 and 81.6%, respectively, at pH 8 [89; 92]. Particularly, the sunflower residue presented a higher maximum adsorption capacity (47.6 mg/g) than tea waste (0.15 mg/g); the Langmuir isotherm model was employed. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Biowaste** & **Contaminant** & \begin{tabular}{c} **Isothermal Model** \\ **Adjusted** \\ \end{tabular} & \begin{tabular}{c} **Kinetic Model** \\ **Adjusted** \\ \end{tabular} & \begin{tabular}{c} **qm/Qe** \\ **Adjusted** \\ \end{tabular} & \begin{tabular}{c} **Removal** \\ **Efficiency (\%)** \\ \end{tabular} & **Ref.** \\ \hline \multirow{4}{*}{Barley straw} & BBY & Langmuir & Pseudo-second order & 124.3 mg/g & N.R & \\  & CV & Langmuir & Pseudo-second order & 95.8 mg/g & N.R & [69] \\  & MB & Langmuir & Pseudo-second order & 86.5 mg/g & N.R & \\  & SO & Langmuir & Pseudo-second order & 99.7 mg/g & N.R & \\ \hline \multirow{4}{*}{Barley straw (CA/NaOH-modified)} & BBY & Langmuir & Pseudo-second order & 524.3 mg/g & N.R & \\  & CV & Langmuir & Pseudo-second order & 473.2 mg/g & N.R & \\  & MB & Langmuir & Pseudo-second order & 498.1 mg/g & N.R & \\  & SO & Langmuir & Pseudo-second order & 296.6 mg/g & N.R & \\ \hline \multirow{4}{*}{Barley straw (Magnetic)} & BBY & Langmuir & Pseudo-second order & 137.6 mg/g & N.R & \\  & CV & Langmuir & Pseudo-second order & 96.1 mg/g & N.R & \\  & MB & Langmuir & Pseudo-second order & 94.1 mg/g & N.R & \\  & SO & Langmuir & Pseudo-second order & 102 mg/g & N.R & \\ \hline \multirow{4}{*}{Barley straw (Magnetic CA/NaOH-modified)} & BBY & Langmuir & Pseudo-second order & 520.3 mg/g & N.R & \\  & CV & Langmuir & Pseudo-second order & 410.8 mg/g & N.R & \\ \cline{1-1}  & MB & Langmuir & Pseudo-second order & 455.8 mg/g & N.R & \\ \cline{1-1}  & SO & Langmuir & Pseudo-second order & 460.7 mg/g & N.R & \\ \hline \multirow{4}{*}{Black tea} & Cu & Langmuir & Pseudo-second order & 48 mg/g & 77 & [90] \\  & Pb & Freundlich & Pseudo-second order & 65 mg/g & 94 & [70] \\ \hline \multirow{4}{*}{Corn stalks} & Cu & N.R & N.R & 0.059 mmol/g & 35 & \\  & Cd & N.R & N.R & 0.046 mmol/g & 30 & [73] \\  & Ni & N.R & N.R & 0.009 mmol/g & 8 & \\  & Pb & N.R & N.R & 0.029 mmol/g & 20 & \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} Date palm wastes \\ (Surface fibres) \\ \end{tabular} } & Phosphates & N.R & N.R & N.R & 85 & [107] \\ \cline{1-1}  & \multirow{2}{*}{Phosphates} & N.R & N.R & N.R & 87 & [107] \\ \cline{1-1}  & \multirow{2}{*}{Pb} & Langmuir & Pseudo-second order & 88.61 mg/g & 98.6 & [41] \\ \cline{1-1}  & \multirow{2}{*}{
\begin{tabular}{c} Mixed tea waste \\ (\end{tabular} & Cr(VI) & Freundlich & Pseudo-second order & 94.34 mg/g & -97 & [93] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Adsorption parameters and removal efficiencies of different biosorbents derived from herbage and forage for the removal of pollutants in aqueous matrices.