Developments of efficient dithionite-zerovalent iron/persulfate systems with accelerated Fe(III)/Fe(II) cycle for PAHs removal in water and soils

Iron-activated persulfate (PS) systems commonly suffer from the poor Fe(III)/Fe(II) redox cycle in groundwater and soils, due to the rapid oxidation of Fe(II) by both PS-related and naturally occurring oxidative substances. Maintaining the Fe(III)/Fe(II) redox cycle is necessary to achieve the high efficiency and stability of iron -activated persulfate systems toward aromatic contaminants (e.g., PAHs) in groundwater and soils. Herein, we discover the mixtures of dithionite (DTN) and zerovalent iron (ZVI) to synergistically activate PS, and develop highly efficient, stable DTN-ZVI/PS systems for PAHs removal in groundwater and soils. DTN and intermediates sulfite/thiosulfate initiated reduction of ZVI-derived Fe(III) species in DTN-ZVI/PS systems. This reaction accelerated the Fe(III)/Fe(II) redox cycle and coated ZVI with FeSx, both favoring the generation of HO center dot and SO4213;center dot. DTN-ZVI/PS exhibited Nap removal of >90% in water during 11 of 15 supplementations of Nap and/or PS, 1.4-2.4 times ZVI/PS. Similarly, 0.47-4.3 fold increments of Nap removal kobs were obtained in five chemical types of groundwater, and 1.3-2.4 fold increments of PAHs removal in soils. This study may provide a technical basis to develop new Fe-activated oxidation systems for groundwater and soil remediation.

Automated summary

By mixing dithionite (DTN) and zerovalent iron (ZVI) with persulfate (PS), a highly efficient and stable DTN-ZVI/PS system was developed for the removal of PAHs in groundwater and soils. This study may contribute to the development of new iron-activated oxidation systems for groundwater and soil remediation.