Concentration and characterization of groundwater colloids from the northwest edge of Sichuan basin, China

•Cross-flow ultrafiltration (CFUF) system equipped with 100 kDa cartridges was used for the concentration of groundwater colloids.•Two different morphologies of colloids existed which seemed to have hollow and platy structure.•The mineralogical composition of colloids consisted of albite, orthoclase, clinochlore, lepidocrocite, muscovite, calcite and quartz.•The predominance of dissolved organic matter (DOM) was protein-like matter probably secreted by Thermomonas and other bacteria.

Natural groundwater colloids are significantly important since they are closely related with toxic substances migration in subsurface systems. In this paper, a cross-flow ultrafiltration (CFUF) system equipped with 100 kDa cartridges was developed to enrich groundwater colloids and multiple analytical techniques were used to characterize colloid properties. Analytical techniques included scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM) with energy dispersive X-ray spectra (EDS), excitation-emission matrix (EEM) fluorescence spectra, inverted fluorescence microscopy (IFM), and 16S rDNA sequencing. SEM and AFM results indicated that the mean diameter and height of colloids were 322 ± 90 nm and 10.4 ± 2.1 nm respectively and two different morphologies of colloids existed which seem to be hollow and platy structure. XRD analysis showed that the mineralogical composition of inorganic colloids consisted of albite (NaAlSi3O8), orthoclase (KAlSi3O8), clinochlore ((Mg,Fe)6(Si,Al)4O10(OH)8, lepidocrocite (FeIIIO(OH)), muscovite (KAl2(Si3Al)O10(OH,F)2), calcite (CaCO3) and quartz (SiO2), most of which was confirmed by TEM-EDS information. Different types of dissolved organic matter (DOM) were characterized by EEM fluorescence spectra, while a larger fraction of 'protein-like' fluorescent DOM was found. Bacteria was observed under 488 nm laser excitation by IFM and 16S rDNA sequencing revealed that Thermomonas was the most likely genus the bacteria may belong to.

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