Abstract A wide variety of biopolymeric materials have been studied as flocculants in wastewater treatment to replace oil-based synthetic polymers. However, derivatives of cellulose, the most abundant biopolymer on earth, are still rarely used to treat wastewater. In this work, we first tested the flocculation performance of three anionic sulfonated (ADAC) nanocellulose flocculants, with variable charge densities in combined coagulation–flocculation treatment of municipal wastewater and compared the results with the performance of a commercial coagulant and a synthetic polymeric flocculant. Second, using an optical monitoring device (MOFI), we followed the morphology and strength of the formed flocs with three ADAC and two previously studied dicarboxyl acid nanocellulose (DCC) flocculants and a synthetic polymer. The decrease in turbidity and the COD removal performance of the ADAC nanocelluloses were similar to those of a commercial reference polymer in low dosages, with considerably decreased chemical consumption relative to coagulation with ferric sulfite alone. The wastewater flocs produced with the nanocellulose flocculants were smaller and rounder than those produced with the commercial reference polymer, but the flocs produced with the anionic nanocelluloses were more stable under shear than the flocs produced with the reference polymer.