Abstract: To achieve the green and efficient treatment of high-strength biogas slurry from livestock and poultry farming, this study investigated the coagulation–flocculation performance of cationic starch-based bioflocculants in treating CSTR-processed pig manure digestate. Commercial bioflocculants were screened, followed by comparative evaluation against PAM, single-factor tests, and response surface methodology (RSM) optimization. Bioflocculant A exhibited the best performance among ten candidates, achieving SS and TP removal efficiencies of 94% and 93.5%, respectively, with a treatment cost of 3.85 CNY·t^-1, comparable to PAM (97.3% and 97.5% at 4.1 CNY·t^-1), indicating its potential to replace PAM for digestate flocculation. RSM analysis identified the optimal operating conditions as a bioflocculant dosage of 150 + 500 mg·L^-1 , an SS concentration of 25 000 mg·L^-1, and pH 7.07, under which a comprehensive performance score of 0.96 was obtained. Furthermore, an engineering-oriented economic model revealed that regions with high comprehensive scores were mainly located in the intersection of neutral to slightly alkaline conditions (pH 7.0~7.6), low SS concentrations (25 000~30 000 mg·L^-1 ), and low-cost ranges (3.8~4.7 CNY·t^-1 water). Mechanistic investigations using FT-IR, SEM-EDS, and adsorption kinetics showed that the introduction of quaternary ammonium groups generated cationic active centers, establishing a multi-mechanism synergistic flocculation-adsorption process. The adsorption behavior conformed to the pseudo-second-order kinetic model (R²≥0.999), consisting of a rapid stage dominated by charge neutralization and ion exchange, followed by a slower equilibrium stage governed by polymer bridging and floc growth. Overall, this study provides reliable theoretical and technical support for replacing traditional synthetic flocculants with bioflocculants in high-strength organic wastewater treatment, and offers theoretical guidance and engineering reference for the practical application of bioflocculants in digestate management.