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The ZVI/HO process was applied for cosmetic wastewater treatment. Two commercial zero-valent iron (ZVI) types with different granulations were chosen: Hepure Ferrox PRB and Hepure Ferrox Target. In addition, the pH and stirring method influence on ZVI/HO process efficiency was studied. During the ZVI and ZVI/HO processes, linear Fe ions concentration increase was observed. The addition of HO significantly accelerated the iron dissolution process. The highest COD removal was obtained using finer ZVI (Hepure Ferrox Target) for doses of reagents ZVI/HO 1500/1600 mg/L, in a HO/COD weight ratio 2:1, at pH 3.0 with stirring on a magnetic stirrer. After 120 min of the process, 84.0% COD removal (from 796 to 127 mg/L) was achieved. It was found that the efficiency of the process depends, as in the case of the Fenton process, on the ratio of the reagents (ZVI/HO) and their dose in relation to the COD (HO/COD) but does not depend on the dose of the iron itself. Statistical analysis confirms that COD removal efficiency depends primarily on HO/COD ratio and ZVI granulation, but ZVI dose influence is not statistically significant. The head space, solid-phase microextraction, gas chromatography, mass spectrometry results confirm high efficiency of the ZVI/HO process.

Hydraulic fracturing flow-back fluid (HFFBF) was treated by a zero-valent iron (ZVI)/H 2 O 2 process. The initial HFFBF chemical oxygen demand (COD) was 3,440 mg/L and the 5-d biochemical oxygen demand (BOD 5)/COD ratio was 0.259. Under the optimal 500/6,884 mg/L of ZVI/H 2 O 2 reagent doses, and a 120-min process time, COD was decreased to 680 mg/L (80.2% removal). Additionally, as a result of pollutants' chemical oxidation, the wastewater's susceptibility for biodegradation was essentially increased to BOD 5 /COD 0.971. To assess the maximum share of coagulation in the total ZVI/H 2 O 2 process treatment effect, a coagulation process was additionally employed. The coagulation for an optimal 1.5mL/L of iron-based PIX 111 coagulant dose obtained 1,200 mg/L of COD, 65.1% removal. The use of coagulation only allowed an increase in BOD 5 /COD to 0.625. As a result of the oxidation step during ZVI/H 2 O 2 process, the persistent compounds were transformed to more vulnerable ones.

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