Synergistic utilization of inherent halides and alcohols in hydraulic fracturing wastewater for radical-based treatment: A case study of di-(2-ethylhexyl) phthalate removal

The degradation of di-(2-ethylhexyl) phthalate (DEHP) was examined as an example to capitalize on the potential interactions of peroxydisulfate (PS) and ferrous iron (Fe2+) in the model Day-1/Day-90 and on-site hydraulic fracturing wastewater (FWW). The primary oxidative radicals in the Fe2+/PS system (i,e., SO(4)(center dot- )and (OH)-O-center dot) were less effective for the degradation of DEHP (6.45%) in ultrapure water. Both chloride (Cl-) and bromide (Br-) at equivalent molar ratio with PS enhanced DEHP degradation (15.6% and 45.5%, respectively) via the generation of Cl-center dot and Br-center dot radicals, whereas the degradation rate was inhibited by the excessive amount of Cl(- )or Br- in the Day-1/Day-90 FWW. However, the co-presence of ethylene glycol (C2H4 (OH)(2), 0.043% v/v in the FWW) and halide ions (Cl- or Br-, 0.05 mM) resulted in the highest removal efficiency of 82.6 - 88.5% within 10 min by Fe2+/PS. Further investigation revealed that the formation of reductive alcohol radicals (center dot C2H3 (OH)(2)) slowed down or replenished the Fe2+ exhaustion. This study demonstrated that the Fe2+/PS-based advanced oxidation may show a synergistic interplay with Cl-/Br(- )and C2H4(OH)(2) in the FWW, which depends on their relative concentrations. Thus, the inherent constituents in the fracturing wastewater can be utilized for the catalytic degradation of co-existing organic contaminants.