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Analysis of Postconsumer Plastic Wash Water From Different Washing Methods
Summary
Researchers assessed chemical contaminants in wash water from five different plastic recycling washing methods applied to postconsumer polypropylene, finding that ultrasonic and surfactant-based washing produced the most contaminated wastewater, and raising concerns that surfactant degradation products like 4-tert-octylphenol—a known endocrine disruptor—may accumulate in recycled plastic.
The quality of postconsumer (PC) plastic wash water is essential for safe recycled plastic production, especially for food‐contact applications. This study assesses the proliferation of chemicals of concern (CoCs) (e.g., phthalates and bisphenols) in waste wash water. To conduct the research work, various washing methods, for example, trommel, friction (only water), surfactant‐caustic, caustic, and ultrasonic‐assisted washing, are applied to PC polypropylene (PP). The phthalate and bisphenol concentration in PC PP wastewater has been determined by gas chromatography–triple quadrupole mass spectrometry and revealed di(2‐ethylhexyl) phthalate and di‐cyclohexyl phthalate. Wash water from ultrasonication‐assisted washing and surfactant‐based washing contains the highest CoC concentrations compared to other methods. Surfactant‐containing wash water is reused for 15 batches of PC PP, determining no significant rise in phthalates or bisphenols until the 10 th batch. Surfactant concentration declines over subsequent plastic batch washing. It is hypothesized that surfactant is adsorbed to the plastic’s surface as it is removed from the wash water. This is concerning because Triton X‐100 (surfactant) can degrade into 4‐tert‐octylphenol, a known endocrine disruptor. Hypothetically, surfactant availability influences the targeted analyte’s accumulation in PC PP wash water. This study highlights that ultrasonication and surfactant‐based washing generate more contaminated wastewater, potentially due to higher PC PP cleaning efficiency.