Tracking fouling layer formation in membrane distillation of landfill leachate concentrate: Insights from periodic membrane autopsies

Abstract

This study tracked the fouling layer formation in the operation of membrane distillation (MD) for the treatment of landfill leachate concentrate. At periodic intervals, the membrane fouling layer was autopsied by spectroscopic and compositional analyses, to provide insight into foulant evolution and interaction mechanisms. Results show that water flux declined rapidly at the beginning of MD operation as protein and sodium chloride (NaCl) preferentially attached and crystalized onto the membrane surface, respectively, to initiate the formation of fouling layer. Such decline became relatively smooth between the water recovery of 20–30% due to the interaction of humic acid with protein which slightly aggravated organic fouling and thus increased membrane surface hydrophilicity. Nevertheless, the enrichment of calcium (Ca2+) and magnesium (Mg2+) ions with further water recovery from leachate concentrate bridged organic foulants, particularly polysaccharide and humic acid, to further thicken the hydrophilic fouling layer to reduce water flux. Indeed, compositional quantification also evidenced a considerable increase in the content of humic acid and divalent cations (Ca2+ and Mg2+) in the fouling layer after a water recovery of 30%.