In this study, pure and poly(ethylene glycol) grafted silica nanoparticles (PEG-g-silica NPs) were synthesized using sol-gel method and used to fabricate microporous mixed matrix high density polyethylene (HDPE) membranes via TIPS method. A set of characterization tests including FE-SEM, BSE, EDS, AFM, contact angle, membrane pore size and pure water flux (PWF) were carried out. Furthermore, the governing fouling mechanisms were determined using classic models as well as combined fouling models. In addition, the effect of pre-coagulation with polyaluminium chloride (PAC) on the humic acid (HA) filtration was also investigated. FE-SEM images of synthesized nanoparticles showed that the particles size decreased from 70 nm to 35 nm by increasing the PEG concentration. It was seen that the water flux of PEG-g-silica NPs/HDPE membrane was about 7.45 times higher than that of pure HDPE membrane. Also, the contact angle test confirmed reducing of membrane contact angle to 96 in the presence of PEG-g-silica NPs. Bubble point measurements showed that the largest pore diameter of the membranes had no discernable change after embedding nanoparticles. The results obtained from the fouling study indicated an excellent performance in mitigating fouling for nanocomposite membranes. Also, it was found that pre-treatment with PAC can significantly mitigate fouling and improve humic acid removal. (c) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.