# Wastewater Treatment by Polymeric Microspheres: A Review
## 4 Photocatalytic Degradation
### Chitosan  
Photodegradation is also used for the removal of organic pollutants besides dyes. Chitosan beads can provide protection for nanoparticle catalysts that are highly reactive in air or aqueous solution. Chitosan beads modified with Tiourea-Magnetite-TiO\({}_{2}\) (Cs-T-M-Ti) beads were prepared for the adsorption of Naphthalene [83]. However, it did not present significant differences from the Cs-T model. Therefore, converting it as photocatalyst, making use of TiO\({}_{2}\), one of the most popular substances used as photocatalyst, is suggested. ZnFe\({}_{2}\)O\({}_{4}\)-CS beads were fabricated for the removal of chlorodimeform insecticide (CDM) from wastewater [84]. The beads were made using the alkaline coprecipitation method. The bead had a saturation magnetization intensity of 6.42 emu/g and a coercivity of 0.93 mT. Overall, 1 g of ZnFe\({}_{2}\)O\({}_{4}\)-CS beads reached complete degradation for CDM within 7 min at optimal conditions, pH 3, an initial CDM dosage of 20 mg/L, and a molar ratio of Zn/Fe at 0.35. The removal of complete TOC removal required 2 h. H\({}_{2}\)O\({}_{2}\) concentration could shorten the time for TOC removal, as over 80% of removal was possible within 1 h at H\({}_{2}\)O\({}_{2}\) concentration of 8.8 mM. The catalytic degradation for CDM is majorly attributed to the activation of H\({}_{2}\)O\({}_{2}\) under UVC irradiation. The ZnFe\({}_{2}\)O\({}_{4}\)-CS beads catalyst could be reused for at least four cycles with small metal leaching. However, the treatment  
Figure 20: (**a**) UV light irradiated photocatalytic degradation curves, (**b**) the corresponding K parameters in the presence of 2 wt% BOC-CA beads and (**c**) cyclic degradation curves of RhB (Reproduced with permission from [PERSON] et al. [82], Copyright 2021, Elsevier).  
for real wastewater did not always present perfect results. Chitosan beads were used as solid catalysts for the photo-Fenton process [85]. The beads were crosslinked with glutaraldehyde and mixed with FeSO\({}_{4}\cdot\)H\({}_{2}\)O to obtain the iron-adsorbed chitosan beads. The degradation experiment treated the biological treatment effluent (E2). The effluent carried strong purple coloring, and the chitosan bead aimed to decolorize and remove the toxins. The degradation of color achieved 91.91% after 105 min and the degradation of aromatic compound reached 70.87% indicating that those compounds were fragmented into smaller compounds. However, the total dissolved solids (TDS) concentration remained at 5993.88 mg/L, which was only a 12.70% reduction. The D. magna toxicity for E2 after treatment for 105 min was presented by the effective concentration that affects 50% of the population of the organisms (EC50), EC50 increased from 63.12% to 76.57%, indicating that the toxicity decreased but the effluent remained slightly toxic. The result did not satisfy the required standard for toxicity test. It indicates that even though the decolorization was successful, this does not always imply the successful removal of toxic substances. Intermediates could be made through the removal process that may carry toxicity.