# Wastewater Treatment by Polymeric Microspheres: A Review
## 3 Natural Polymer
### Alginate
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**S. No** & **Polymer** & **Adsorbate** & **Adsorbent Capacity** & **Kinetic Model** & **Isotherm Model** & **Reference** \\ \hline \multirow{2}{*}{1} & Fe\({}_{3}\)O\({}_{4}\)@HCO in SA & & & & & \\  & microbead & & & & & \\ \hline
2 & HA@SA & Sb(III) & 195.7 mg/g & PSO & Langmuir & [57] \\ \hline
3 & zeolite/alginate & Ni(II) & 98\% & PFO & Freundlich & [58] \\ \hline \multirow{2}{*}{4} & CSM/SA hybrid & & & & & \\  & bead & & & & & \\ \hline
5 & PAM/SA & MB dye & 1070.54 mg/g & PFO & Langmuir & [60] \\ \hline
6 & NRGO/SA/PVA & ANT, 2-MAQ & 0.72, 0.70 mg/g & PSO & Freundlich, D-R & [61] \\ \hline \end{tabular} HCO: hydrous cerium oxide, HA: hyperbranched polyamide, CM, CSM: chitosan microsphere, NRGO: N-doped reduced graphene oxide, ANT: anthracene, 2-MAQ: 2-methylanthraquinone, D-R: Dubinin-Radushkevich.  
\end{table} 
Table 6: Summary efficiency of alginate as adsorbent. removal rate is dependent on the number of free active sites. An isotherm study shows the sorption process follows the Freundlich model, indicating a heterogeneous surface. The Dubinin-Kaganer-Radushkevich (DKR) model study proves that removal reaction is endothermic and the sorption process is chemical. The Zeolite/alginate microspheres can be reused five times without deformation and with the same efficacy. SA can improve adsorbent in other ways; for instance, it can be used as matrix for different microsphere to produce hybrid beads. Chitosan microsphere/sodium alginate hybrid beads (CSM/SA) were fabricated for the removal of heavy metal ions from aqueous solution [59]. The microsphere was applied in the removal of Cr(VI) and Pb(II). The properties of the hybrid beads were enhanced via mutual interaction between original chitosan microspheres and SA. Additionally, the effects of different metal concentrations, pH solutions, and contact times were evaluated. The maximum adsorption capacity obtained from atomic absorption spectrophotometer was 180 mg/g for Pb(II) and 16 mg/g for Cr(VI). EDX results confirmed that the amount of adsorbate is proportionate to the quantity of Ca\({}^{2+}\) on the surface of CSM/SA hybrid beads, but Cr retention is dependent on electrostatic attraction, and the proposed mechanism is drawn in Figure 10. TGA-DTA analysis showed the high thermal stability of the CSM/SA. The first step of the four thermal degradation was from 25 to 240 \({}^{\circ}\)C and showed a 9.7 wt% loss. The adsorption kinetics were evaluated using the PFO and PSO models. The sorption of both Pb(II) and Cr(VI) fit the Langmuir model, indicating that it was monolayer adsorption. A PAM/SA adsorbent with double network structure was prepared for adsorption of MB dye, while the MB concentration was determined using a UV-vis spectrophotometer [60]. The PAM/SA microsphere was prepared via emulsion polymerization of acrylamide and SA. The double network structure was formed from the entanglements between PAM and SA molecular chains. TGA results revealed that adding SA decreases the thermal stability and crystallinity of PAM, but the adsorption capacity of microsphere increased. The microsphere had a smooth surface, the particle size was in range of 1-10 \(\upmu\)m, the pore size was in range of 0-200 nm, the mesoporous structure was uniform, and the ion crosslinking point was uniformly distributed. At pH 6, 25 \({}^{\circ}\)C, and 0.1 g adsorbent dosage, the maximum adsorption capacity reached 75 mg/g. -COO\({}^{-}\) on SA has hydrogen bond with -OH and -NH\({}_{2}\) and has electrostatic interaction with -C=N\({}^{+}\) of MB,  
Figure 10: Proposed mechanism of adsorption of Cr(VI) and Pb(II) ions onto CSM/SA hybrid beads (Reproduced from [PERSON] et al. [59], 2019, BioMed Central Ltd.). which is beneficial for MB molecule to agglomerate and be adsorbed on the surface of SA/PAM composite microspheres. The adsorption followed PFO kinetics and the Langmuir isotherm model, indicating that it was physical adsorption and that the maximum capacity was 1070.54 mg/g.