A newly green natural polymer bagasse cellulose based flocculant (PBCF) was synthesized utilizing a grafting copolymerization method for effectively enhancing humic acid (HA) removal from natural water. This work aims to investigate flocculation behavior of PBCF in synthetic water containing HA, and the effects of flocculant dose and initial solution pH on flocculation performance. Results showed that PBCF functioned well at a flocculant dose of 60 mg/L and pH ranging from 6.0 to 9.0. The organic removal efficiency in synthetic water in terms of HA (UV 254) and chemical oxygen demand (COD Mn) were up to 90.6% and 91.3%, respectively. Furthermore, the charge neutralization and adsorption bridging played important roles in HA removal. When applied for lake water, PBCF removed 91.6% turbidity and 50.0% dissolved organic matter, respectively. In short, PBCF demonstrates great potential in water treatment in a safe and environmentally friendly or 'green' way. [Display omitted] • A cationic flocculant (PBCF) was prepared for using agricultural waste as a resource. • PBCF was effective in removing HA at different concentrations. • PBCF is highly efficient for UV 254 , COD Mn and turbidity in lake water. • Dose-pH graphs and correlation analyses confirmed flocculation during HA removal. • Electrical neutralization and adsorption bridging dominated HA removal. [ABSTRACT FROM AUTHOR]