Reverse osmosis membrane autopsy in coal chemical wastewater treatment: Evidences of spatially heterogeneous fouling and organic-inorganic synergistic effect

Abstract

Abstract Although fouling on reverse osmosis (RO) membrane has been studied widely, few focused on coal chemical industry where RO is indispensable for water reclamation. The complexity of the wastewater further makes the synergistic mechanism of inorganic and organic foulants unclear. Besides, spatial heterogeneity of fouling at different positions of RO module needs more investigation. This study analyzed samples from a two-stage RO module applied in a full-scale plant for coal chemical wastewater reclamation. Scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM-EDS), inductively coupled plasma optical emission spectrometer (ICP-OES), X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR), confocal laser scanning microscopy (CLSM), three-dimensional excitation-emission matrix (3D-EEM) and 16S sequencing were applied. Results showed that fouling gradually mitigated along the axial direction of the elements. Additionally, from stage-1 to stage-2, although organic fouling constantly dominated, inorganic fouling was aggravated while biofouling was alleviated with declined microbial diversity and population. The structure of microbial community also varied, which was due to the selectivity of higher salinity of the 2nd stage influent and interception of particular species in the 1st stage. Moreover, experimental evidences were provided for the bridging effect of Ca2+ and polysaccharides, as well as the synergistic effect of silicon and organic matters in fouling. The detailed foulant analysis on real membrane samples in this study may lay foundation for improving fouling control strategies in coal chemical industry.