Synergistic effect of combined colloidal and organic fouling in membrane distillation: Measurements and mechanisms

We examined the synergistic effect of combined fouling in MD process with three organic foulants - alginate, bovine serum albumin (BSA), and humic acid - in the presence of colloidal silica particles. Membrane fouling profiles were quantified by water flux decline and permeate conductivity. Mechanisms of the synergistic effect of combined fouling were revealed by light scattering measurements and infrared spectra of foulant-foulant interaction and foulant- membrane interaction. Membrane fouling morphology and element mapping provided further details of transport of colloidal silica particles and elucidated the mechanisms for silica-induced pore wetting. Specially, gelation of alginate formed an alginate layer on membrane surface and prevented penetration of silica particles into the membrane matrix, which was confirmed by silicon element mapping as well as infrared spectra. Adsorption of BSA protein by colloidal silica aggregates led to a sharp water flux decline and a partial pore wetting. Humic acid, forming a coil structure in high salinity, exhibited limited interaction with colloidal silica that penetrated into the membrane matrix and wetted membrane pores, thereby compromising the product water quality. Results showed that the combined organic fouling with colloidal silica particle not only deteriorated water production, but also compromised product quality by partial membrane wetting.