ABSTRACT Flocculation is one of the most significant conditioning methods for sludge dewatering. In the study, a novel flocculant CSâTA, prepared through free radical-mediated conjugation of tannic acid (TA) and chitosan (CS), was proposed to improve sludge dewatering. The characterisation using Fourier transform infra-red spectroscopy and X-ray diffraction analysis shows that the CS chain was the backbone of CSâTA, and the presence of CSâTA aromatic rings confirmed the conjugation of CS with TA. Moreover, the conditioning of CSâTA yielded the best dewatering performance at 30 mg g TSâ1 with the water content of sludge cake by press filtration (Wsc) of 59.78% ± 0.3% and capillary suction time (CST) of 11.8s ± 0.35 s, compared to 98.2% ± 0.15% and 56.2 s ± 0.16 in raw sludge. The results of different influencing factors (e.g. pH and temperature) on flocculation efficiency indicated that CSâTA possessed the capacity for enhancing sludge dewaterability over a wide range of pH, and the optimal temperature was observed to be 35 °C. Furthermore, the increase of particle size and zeta potential implied the addition of CSâTA favoured the formation of larger particles charge neutralisation and adsorption bridging effect. In addition, extracellular polymer substances (EPS) analysis indicated that the decrease in the polysaccharide and protein contents in EPS after CSâTA addition could increase the relative hydrophobicity of sludge. Moreover, the contents of heavy metals in sludge and their leaching toxicity and environmental risk were reduced. This study provides comprehensive insights into the exploration of CSâTA for sludge dewatering and the maintenance of ecological security in an eco-friendly.