Application of coagulant obtained through charge reversal of sawdust-derived cellulose nanocrystals in the enhancement of water turbidity removal

Sawdust-derived cellulose nanocrystals (CNC) were functionalized using hexadecyltrimethylammonium bromide (HDTMA-Br) as a cationic surfactant to produce novel coagulant for application in reducing water turbidity. The modified CNC was characterized using Fourier transform infra-red spectroscopy, x-ray diffraction, scanning electron microscopy, transmission electron microscopy and zetametry. Upon functionalization, the surface charge was reversed from −39 mV to +22 mV by introducing amine group to the CNC matrix. The microscopic analyses revealed that CNC has a narrow particle size range and rod-like morphology. The XRD analysis showed increased peak intensity upon modification, indicating enhanced crystallinity of the CNC; and an additional peak around 30.1° appeared, which was attributed to the presence of HDTMA on the surface of CNC. Turbidity tests was conducted using both simulated and environmental water samples, and the effects of CNC modification reaction time, solution pH, coagulant dosage and initial turbidity levels were evaluated. Results reveal that turbidity reduction increased with an increase in reaction time and coagulant dosage, and decreases in initial turbidity level and solution pH. The performance of the modified CNC coagulant in turbidity reduction complied with the South African national standard (SANS 241:2015) for drinking water quality. (paper)