Chemical oxygen demand oxidation via sustained-release persulfate balls: a rate-compatibility study of flow velocity, releasing, and oxidation

Identification of chemical oxygen demand (COD) in municipal solid waste (MSW) landfill leachates is a challenging problem. This paper investigated the feasibility of using sodium persulfate (PS), a strong oxidant, as a permeable reactive barrier (PRB) filling material. Firstly, sustained-release persulfate balls were manufactured to adjust the release rate of persulfate, the oxidation agent. In addition, Fe(II)-loaded activated carbon (Fe-AC) was used to help with an even distribution of Fe(II) in the porous medium (PRB in this case). Then, the oxidation efficiency and kinetic rate of COD removal by the sustained-release balls were subjected to batch tests. A mass ratio of 1:1.4:0.24:0.7 for PS:cement:sand:water was the most efficient for COD removal (95%). The breakthrough curve for a 5 mm sustained-release ball revealed that the retardation factor was 1.27 and that the hydrodynamic dispersion coefficient was 15.6 cm²/d. The corresponding half-life of COD oxidation was 0.43 d, which was comparable with the half-life of PS release from sustained-release balls (0.56 d). The sustained-release persulfate balls were shown to be an economical material with a simple recipe and production method when catalyzed by Fe-AC. Compared with cutting-edge methods, sustained-release balls used in PRBs offer significant advantages in terms of both effectiveness and economy for the preparation of sustained-release and catalytic materials. These results verified the feasibility of using sustained-release persulfate balls as a PRB material for COD removal.