# Wastewater Treatment by Polymeric Microspheres: A Review
## 5 Conclusions and Future Prospects  
Polymer microspheres are rising candidates as adsorbents for wastewater treatment. The removal of pollutants is a critical issue because they can cause severe health problems and drinking water shortages. MBs are extensively used in industrial procedures including textile, manufacturing, and bio industries in aquatic conditions. Their toxicity can cause cancer, mutation, and many other diseases. Therefore, the decolorization of dyes and the removal of other pollutants such as heavy metal ions, organic pollutants, and oil are urgent issues. Among several ways to remove the pollutants, adsorption is effective because it is relatively cost-effective, can operate in mild conditions, and does not produce secondary pollution. Currently, activated carbon is widely used as the adsorbent, but due to its high cost, research to substitute AC is ongoing. The next adsorbents require chemical and mechanical stability, high recyclability, cost-effectiveness, eco-friendliness, non-toxicity, effective performance at low pollutant concentration, the ability to scale up for commercial use, and so on. To increase the adsorption capacity, abundant adsorption sites and high selectivity for the adsorbate are needed as well. We reviewed various research that used polymer microsphere as adsorbents. Synthetic polymers (including vinylic polymers and PDA polymers) and natural polymers (including cellulose, algae, and chitosan) were used. Some were made into a magnetic microsphere and photocatalyst. Most were conducted in batch experiments with UV-vis spectroscopy to measure the adsorption capacity. The \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**S. No** & **Polymer** & **Catalyst** & **Adsorbate** & \
\begin{tabular}{c} **Degradation** \\ **Efficiency (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Reaction Time** \\ **(min)** \\ \end{tabular} & **Reference** \\ \hline
1 & Chitosan & Fe & MB & 98.8 & 6 & [77] \\ \hline
2 & PDA-PVDF & Fe species & MO & \(\sim\)100 & 60 & [78] \\ \hline
3 & PVA/SA & SA-FeCl\({}_{3}\) & TC & 90.5 & 60 & [80] \\ \hline
4 &
\begin{tabular}{c} Alg-HAP, Alg-m, \\ Alg-mHAP \\ \end{tabular} & HAP, Fe\({}_{3}\)O\({}_{4}\) & MO & 71.42, 79.41, 84.28 & 90 & [81] \\ \hline
5 & CA & BiOCl & RhB & 100 & 75 & [82] \\ \hline
6 & Chitosan & ZnFeO\({}_{4}\) & CDM & \(\sim\)100 & 7 & [84] \\ \hline \multirow{3}{*}{7} & \multirow{3}{*}{Chitosan} & \multirow{3}{*}{FeSO\({}_{4}\)} & Strong purple & \multirow{3}{*}{91.92, 70} & \multirow{3}{*}{105} & \multirow{3}{*}{[85]} \\  & & & coloration, aromatic & & \\ \cline{1-1}  & & compound & & & \\ \hline \hline \end{tabular}
\begin{tabular}{c} PVDF: polyvinylidene fluoride, Alg: alginate, mHAP: magnetic hydroxyapatite, m: magnetite, CA: calcium alginate, CDM: chlorodimer insecticide. \\ \end{tabular}
\end{table} 
Table 8: Summary efficiency of photocatalytic spheres. optimal conditions for adsorption, recyclability, and regeneration ratio were also measured to evaluate effectiveness. RSM modeling was used in some research to find the influence of several factors such as pH, time, temperature, pollutant concentration, etc. Adsorption mechanisms, isotherm, and kinetic models were investigated. Magnetic adsorbents can be made with various polymer microspheres by introducing magnetic nanoparticles. They showed potential for ecological adsorbents. Magnetic adsorbents have high recyclability due to their easy separation. Magnetic separation is a facile way to recover the adsorbent after it reaches equilibrium. Adsorbents can be easily recovered if an external magnetic field is given. Therefore, it can be used for several adsorption-desorption cycles. Additionally, because it is easily retrieved from wastewater, it does not drive secondary pollution from the remaining adsorbents. The polymer microsphere strengthens magnetic adsorbent by increasing adsorption capacity and stability.