## 8 Remediation Strategies and Methods
### Chemical Remediation Methods  
In WW treatment, chemical methods can be combined with other treatment techniques to completely clean up the MPs from the target environment. The extensive study of AOPs for the chemical treatment of contaminants back-dates to their proposal in the 1980s [233]. These processes involve various methods such as light, heat, plasma, sonication, and catalysts to effectively produce reactive oxygen species (ROS), commonly known as radicals, during the treatment process. Recently, AOPs have gained attention as effective methods for eliminating persistent contaminants in water by generating diverse ROS, including sulfate radical (SO4\(\bullet-\)), hydroxyl radical (\(\bullet\)OH) and chloride radicals, enabling them to readily break down a wide range of contaminants [199; 234]. AOPs based on sulfate radicals have shown great potential for catalytic degradation of MPs, particularly those composed mainly of PE. AOPs offer advantages such as the removal of specific organic matter, enhancement of biodegradation, and complete conversion of hazardous pollutants. While AOPs can be associated with high costs, utilizing them as a pretreatment for biodegradation, focusing on the surface degradation of MPs, can be a practical and environment-friendly approach [178]. AOPs have different types of processes originating from different sources like UV/photocatalytic reactions, ozone, and Fenton-based AOP. Photolysis is a degradation reaction caused by light, particularly UV radiation, and it is the basis for all photo driven AOPs. Photolysis can be used alone or within AOPs for the degradation of plastics. When polymers are exposed to light, both physical and chemical changes occur in their structure [235]. Many organic polymers are sensitive to visible and UV irradiation [236]. The photolysis of plastics generally requires high irradiation energy. Different wavelengths of UV light can cause the scission of specific bonds in different polymers. Vacuum UV irradiation can also lead to the degradation of water molecules, resulting in the formation of highly reactive hydroxyl radicals and hydrogen radicals [237]. PET strongly absorbs UV irradiation below 315 nm, while PS is considered relatively stable when exposed to vacuum UV irradiation due to the energy transfer from the aliphatic backbone to the phenyl ring, which can distribute the absorbed energy to aromatic bonds and thermally released or by fluorescence [235]. In addition to the direct photolysis of plastics, photolysis is also applied to the degradation of pollutants in environmental pollution treatment facilities. Reactive intermediates and radicals, such as hydroxyl radicals, triplet organic matter, singlet oxygen, hydrated electrons, superoxide radical anions, carbonate radicals, and organoperoxy radicals, are generated through photolysis, especially under UV irradiation [238]. These reactive species can attack and decompose various recalcitrant contaminants. The physicochemical properties of plastics can be altered, leading to their decomposition [195]. Cracks can form on the surface of plastic samples, causing them to become rougher and eventually break down into smaller pieces ranging from nanometers to micrometers. Over time, the size of plastics or MPs can be further reduced to nano-sized particles. Another UV-based technology called UV/H\({}_{2}\)O\({}_{2}\) utilizes the reaction between UV light and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) to generate hydroxyl radicals (\(\bullet\)OH) [236]. This process offers an additional approach to the treatment of pollutants, and it can be used alone or in combination with other AOPs, utilizing various reactive species generated through UV irradiation. In the context of decomposing recalcitrant contaminants, UV is commonly employed to activate photocatalysts, which generate ROS like hydroxyl radicals and superoxide radicals during photocatalysis. ROS attack MPs, leading to polymeric chain rupture, branching, crosslinking, and even mineralization into CO\({}_{2}\) and H\({}_{2}\)O.