Part 5. Degradation of microplastics
Plastics with sizes < 5mm are termed microplastics (MPs)1. MPs are found in the environment, in particular in water-bodies where physical abrasion of longer plastic pieces occurs. Due to the small sizes, they may infiltrate the food chain introducing an additional risk. Although its removal is not an easy target, wastewater treatment plants can retain a MP via conventional activated sludge process and membranes; however, they remain in filers, adsorbents and membranes. Therefore, strategies and technologies to their final destruction are in constant search2. However, most of them have been focus on solid state treatment methods. Better results are reported combining methods and using two phases: MPs-water.
Advance Oxidation Processes (AOPs) as Fenton3 reagent accompanied of heat treatment can efficiently mineralize MPs. Fenton´s reagent (Fe+2/H2O2) generates hydroxyl radical (OH.): Fe+2 + H2O2 = Fe+3 + OH. + OH– . This radical with high oxidation power degrades persistent organic pollutants with advantages of high performance and non-toxicity. The heterogeneity of the MPs- Fenton (solid-liquid) reaction affects its efficiency; however, the MPs small size and high surface area contribute to a better interaction of the reagent with the solid. In any case if the reaction is accompanied by heat treatment (hydrothermal) and acid media quite good results in degradation are reported4. For instance, after 16 h of MPs polyethylene (PE) treatment yields 95.9% weight loss and 75.6% mineralization efficiency. MPs of Polystyrene (PS), Polypropylene (PP), Polyethylene terephthalate (PET) and Polyvinyl chloride (PVC) were also hydrothermal-Fenton treated yielding 90 % (PS and PP), 30 % (PET) and 25 % (PVC) weight loss. The efficiency of the degradation system is maintained in practical water bodies.
MPs have been found even at the Weddell Sea in the Antarctica. 65 % of the samples taken at the surface water contained 0.01 MP/m3 and 11.4 % of the sub surface contained 0.04 MP/m3. However, it was also found5 using micro X-ray Fluorescence Spectroscopy (XRF) that the 45 % of the MPs contamination came from the research vessel.
1.- B .Nguyen, D . Claveau-Mallet,. L. M. Herandez. E. G Xu, J. M Farner, N. Tufenkji, Acc. Chem. Res., 52(2019) 858−866.
2.- K. Hu, W. Tian,. Y. Yang,. G. Nie, P. Zhou, Y. Wang,.; X .Duan, S. Wang, Water Res. 198, (2021), , No. 117144.
3.- N. N. Wang,. T. Zheng, G. S. Zhang, P. Wang, J. Environ.Chem. Eng., 4 (2016) 762−787.
4.- K. Hu, P. Zhou, Y. Yang, T. Hall, G. Nie, Y. Yao, X. Duan, S. Wang, ACS EST Engg. 2 (2022) 110−120
5.- C. Leistenschneider, P. Burkhardt-Holm, T. Mani, S. Primpke, H. Taubner, G. Gerdts, Environ. Sci. Technol. 55, (2021) 15900−15911
