Humic acid desorption from a positively charged nanocellulose surface

Trimethyl-ammonium functionalized cellulose nanofibers (CNF) display a positively charged surface over a wide pH and ionic strength range, and constitute therefore not only an interesting biobased sorbent material, but also a positively charged model surface to investigate sorption phenomena. In the current work, CNF were totally or partially covered by humic acid (HA) at pH ∼6, and the desorption process of HA from CNF was thereafter studied in batch and continuous filtration experiments at various pH and ionic strength. It is found that the desorbed amount of HA increases and the kinetic of desorption is faster via increasing the pH and ionic strength of the solution. Moreover, the desorption is affected by the extent of CNF coverage with HA and by the presence of free HA in solution. The present work gives insights into the interaction of HA with permanently positively charged surfaces and was successfully exploited for the removal of HA from CNF filters for regeneration allowing multiple filter utilization.