Efficient separation of Fenton ferric flocs by optimized-design hydrocyclone

• A hydrocyclone for Fenton floc was optimized via single factor, RSM, and NSGA-II. • Wide-angle hydrocyclone surpassed mini-hydrocyclone and Rietema hydrocyclone. • Four key structural parameters were identified. • Optimized hydrocyclone achieved 96.09% SS removal and 5.62 concentration factor. • Optimized hydrocyclone cuts footprint and costs by 41∼89% vs sedimentation. Efficient separation of ferric flocs is a critical challenge in iron-based homogeneous Fenton treatment due to the poor settleability and shear sensitivity of the generated flocs. In this study, a hydrocyclone-based separation strategy was systematically optimized to provide an intensified alternative to conventional gravity-driven sedimentation. Among the investigated hydrocyclone outlines, a wide-angle design exhibited superior separation performance and was further optimized by integrating single-factor experiments, response surface modeling, and NSGA-II optimization. The optimized hydrocyclone achieved a suspended solids removal efficiency of 96.09% and a concentration factor of 5.62. Mechanistic analysis based on flocs morphology revealed that coordinated structural modifications, including elimination of vortex finder insertion, enlargement of the cylindrical diameter, extension of the cylindrical length, and increase of underflow pipe diameters, effectively alleviated shear-induced flocs breakage and enhanced separation efficiency. The optimized hydrocyclone demonstrated robust performance within the recommend operating conditions, which are a feed flow rate below 15 L/h, a split ratio of 14%, and a FeSO 4 concentration below 7 mM. The effectiveness of the optimized hydrocyclone was successfully validated using real refractory industrial wastewaters without inducing organic matter release. Economic evaluation showed that, compared with typical gravity-driven sedimentation, the optimized hydrocyclone reduced footprint by 50%∼88.6%, capital cost by 51.28%∼80.65%, and operation cost by 40.99%∼83.11%. Overall, this study presents a compact, cost-effective, and environmentally sustainable solution for Fenton ferric floc separation, with strong potential for practical engineering application.