Achieved deep-dewatering of dredged sediments by Fe(II) activating persulfate pretreatment: Filtrating performance and mechanistic insights

Abstract

The dredged sediments, being produced from sediment dredging process, would cause serious second environmental pollution without being disposed appropriately. Dewatering could effectively reduce the volume of dredged sediments before their disposal. Here, we for the first time achieved the deep-dewatering of dredged sediments with Fe(II)/Persulfate pretreatment and unraveled the involved mechanism. Fe(II)/Persulfate pretreatment was found to dramatically elevate the dewatering of dredged sediments, with water content of dredged sediments decreased from 84.8% ± 0.5% (the blank) to 39.5% ± 1.3% after pretreatment with 8 mg/g total suspended solids (TSS) Fe(II) and 20 mg/g TSS Persulfate. Mechanism investigation indicated that SO4−, OH, and Fe(III) were produced during Fe(II)/Persulfate process in the presence of H2O, while these species possibly resulted in the advanced dewaterability of dredged sediments. SO4− and OH broke extracellular polymeric substances (EPS) matrix and decomposed their main components in dredged sediments, which caused the disengagement of bound water in EPS, benefited to the reduction in hydrophilcity of sediments, and facilitated decrement of their viscidity. Furthermore, these radicals likely affected the proteic conformation in EPS and therefore stretched the proteic hydrophobic sites, which drove the increment in hydrophobicity of dredged sediments, availing to the escape of unbound water. Additionally, the electrostatic repulsions were reduced and the double electric layers round particles were compressed under the influence of Fe(III), which facilitated aggregating the dredged sediments particulates. Furthermore, the aggregated sediments particles were kept by Fe(III) combination with carboxyl and hydroxyl groups in sediments. After Fe(II)/Persulfate pretreatment of dredged sediments, their bound water content, surface area, electronegativity, and viscidity were alleviated while their flocculation, hydrophobicity, and water-draining structure were strengthened, which facilitated the deep-dewatering of dredged sediments.