Photocatalytic degradation of polyamide 66: evaluating the feasibility of photocatalysis as a microfibre-targeting technology

Wastewater treatment plants (WWTPs) have been identified as main contributors to releasing microfibres into the environment, however, WWTPs do not have microfibre-targeting technologies. In this study, photocatalysis is evaluated as a potential technology to treat microfibres in WWTPs by studying the degradation of polyamide 66 (PA66) microfibres using ultraviolet (UV) and titanium dioxide (TiO2). PA66 microfibres suspended in deionised water were exposed to different combinations of UV and TiO2. The degradation of the PA66 microfibres was monitored by changes in mass, carbonyl index and morphology using microbalance, infrared spectroscopy, and scanning electron microscopy. The formation of by-products from the degradation of the fibres was evaluated by measuring the chemical oxygen demand (COD) of the treated water. The degradation efficiency was optimised under UVC with a dose of 100 mg TiO2/L. Under these conditions, the PA66 microfibres presented a 97% mass loss within 48 h. The photocatalytic conditions applied generated a relatively low level of by-products (10 mg/L of COD). Therefore, photocatalysis with TiO2 an UVC could potentially be a feasible technology to treat microfibres in WWTPs, although more investigation is required to establish if this treatment leads to the formation of nanofibres. Further work is needed to translate the present optimised conditions to WWTPs.