Microplastic–cyanobacteria heteroaggregates enhance membrane fouling and disinfection by-product generation: Species-dependent effects and treatment implications

The increasing pollution of water sources by microplastics and cyanobacteria has promoted the formation of microplastic–cyanobacteria heteroaggregates, which can enter drinking water treatment plants. This study investigated the effects of these heteroaggregates on filtration and NaClO disinfection processes. The results showed that the interfacial interactions between microplastics and cyanobacteria increased cell membrane permeability by 19.9%–54.8% and augmented the malondialdehyde content of cyanobacteria from 9.8 nmol/mg to 46.5 nmol/mg. These interactions induced the release of intracellular substances and reduced the normalized membrane flux from 1.000 to 0.178 for microplastic– Oscillatoria heteroaggregates and from 1.000 to 0.124 for microplastic– Microcystis aeruginosa heteroaggregates. More severe membrane fouling caused by microplastic– M. aeruginosa heteroaggregates was attributed to the fact that unicellular M. aeruginosa led to more serious membrane pore blockage compared with filamentous Oscillatoria sp. After NaClO disinfection, water pollution caused by microplastic–cyanobacteria heteroaggregates became more severe than that caused by cyanobacteria alone. Specifically, the content of dissolved organic carbon increased from 7.5 mg/L to 25.2 mg/L for M. aeruginosa -containing systems and from 2.9 mg/L to 15.9 mg/L for Oscillatoria -containing systems. Meanwhile, the concentration of microcystins increased from 6.3 μg/L to 11.4 μg/L in M. aeruginosa systems, and the cylindrospermopsin concentration increased from 2.5 μg/L to 11.2 μg/L in Oscillatoria sp. systems. Furthermore, the levels of disinfection by-product formation potentials, especially the trichloronitromethane formation potential, in water containing microplastic–cyanobacteria heteroaggregates were higher than those in microplastic-free algal water. Therefore, drinking water treatment plants must fully consider the impact of microplastic–cyanobacteria heteroaggregates on filtration and disinfection processes.