Characterization and removal of humic substances in ultra- and nanofiltration

Sixty percent of the Finnish lakes can be described as humic waters. Humic-free water is required in industry; for instance, in the paper making process the brightness may decrease because of humic water. One aim of this investigation was to study the removal of humic substances from different waters with ultrafiltration (UF) and nanofiltration (NF) using salts and retention aids as pretreatments. The other aim was to characterize humic acids with different methods. In both UF and NF of moorland water, retention was good without any pretreatment, but a small positive effect was obtained with AlCl3, NaCl, KCl and FeCl3. Retention aids did not improve the retention, but the cationic ones were affected slightly positively. In NF a higher pressure evidently improved retention. In every case pH had a great influence because at a low pH the structure of humic acid is more compact and no fouling occurs. Humic acid was analyzed using GOD, TOC, UV/VIS, SEM-EDAX, FTIR and zeta potential methods. Adsorption of humic acid was tested with polymer films using contact angle measurements and also with active carbon and carrot adsorbents. Adsorption was strongest at pH 3 in every trial and active carbon adsorbed humic acid much more than carrot adsorbents.