Effects of Chemical Pretreatment on Natural Fibers Removal and Microplastics Integrity for Wastewater Characterization

Nine digestion protocols were tested to quantify microplastics
in wastewater using nine polymeric and three natural fiber controls
representative of common microplastics in wastewater. Protocols were
also evaluated for their impact on natural fibers, which can interfere
with microplastic quantification. Control size change and visual integrity
were assessed, revealing that a sequential 24-h treatment with 6%
NaClO at room temperature (RT) followed by 24 h with 30% H2O2 at 40 °C preserved polymer integrity while fully
oxidizing natural fibers, even when preincubated in real wastewater
samples. A Fourier-transform infrared spectroscopy (FTIR) validation
using the carbonyl index (CI) and carbon–oxygen index (COI)
showed significant changes in poly(ethylene terephthalate) (PET) and
polyvinyl chloride (PVC) after digestion but did not compromise FTIR
spectrum recognition. The protocol applied to raw wastewater samples
showed optimal performance at 300 mg Cl2/L, achieving up
to 95% Chemical Oxygen Demand (COD) and 92% turbidity reduction. No
further improvements in COD or turbidity removal were observed beyond
this dose, regardless of initial COD levels. The present approach
affords greater comparability with existing studies thanks to a large
range of polymeric, natural controls, and oxidant dose investigations
regarding common water quality parameters.