Behavior and removal of microplastics during desalination in a lab-scale direct contact membrane distillation system
Mariana N. Miranda, Rita Fernandes, Adrián M.T. Silva, M. Fernando R. Pereira
Abstract
The behavior of microplastic particles (MPPs) is explored in a lab-scale direct contact membrane distillation (DCMD) system used to produce drinking water from seawater, while also analyzing the impact of their presence on the process performance. Commercial MPPs (LDPE, PET and uPVC) were first studied under temperature stress (TS) tests (using amber bottles) to mimic the exposure to the high temperatures commonly used in DCMD (~80 °C), which led to uPVC being selected to be tested under different loads and aging degrees in the DCMD system. By analyzing uPVC MPPs samples before and after the TS and DCMD experiments by ATR-FTIR, UV–Visible spectroscopy and SEM, it was concluded that minor aging is expected to occur. High loads (>0.1 g L−1) of uPVC MPPs decreased the DCMD performance in terms of permeate flux (from 32.8 ± 0.3 with filtered seawater to 28.7 ± 0.3 kg m−2 h−1 with a load of 0.2 g L−1), although no signs of inferior treated water quality were found based on the conductivity and salinity results. The removal of MPPs (size > 1.2 μm) in DCMD applications with seawater was analyzed by μRaman, with all the results suggesting very high removal efficiencies (≥99 %).