Treatment of high-strength wastewater by Fe(2+)-activated persulphate and hydrogen peroxide

Oxidation of nine petroleum hydrocarbon compounds by combined hydrogen peroxide/sodium persulfate catalyzed by siderite

A system consisting of hydrogen peroxide/persulfate (H₂O₂/S₂O₈^2-) catalyzed by siderite was attempted to oxidize nine representative petroleum hydrocarbon compounds [benzene, toluene, ethylbenzene, m-xylene, p-xylene, o-xylene, 1,2,4-trimethylbenzene, methyl-tert-butyl ether, and naphthalene] that tend to persist in the environment. Oxidation under different siderite dosages, H₂O₂:S₂O₈^2- ratios, and pH conditions were investigated. Results indicated that oxidation rates increased from 1.21-4.62 to 1.77-8.94 d^-1 as siderite increased from 0.16 to 0.48 g/40 mL (H₂O₂:Na₂S₂O₈ = 5:1, initial pH = 3.0), except for naphthalene (decreased from 0.58 to 0.45 d^-1 with increased siderite dosage). When the H₂O₂:S₂O₈^2- ratio was increased from 1:1 to 5:1 (siderite = 0.16 g, initial pH = 3.0), the oxidation rates increased from 0.02-0.73 to 0.33-2.19 d^-1. However, as pH increased to > 5.5 (siderite = 0.16 g, H₂O₂:Na₂S₂O₈ = 2.5:1), the oxidation rates of petroleum hydrocarbons decreased to 0.003-0.09 d^-1, which was approximately 90% less than that at pH = 3.0. The partial correlations and principal component analysis of the experimental data were conducted. Overall, both siderite dosage and H₂O₂:S₂O₈^2- ratio correlated positively with oxidation efficiency. The oxidation potential by H₂O₂/S₂O₈^2- mixtures towards the target petroleum hydrocarbon compounds seemed to be more sensitive to pH conditions than to siderite dosages or H₂O₂:S₂O₈^2- ratios.

Application of heterogeneous photo-Fenton process for the mineralization of imidacloprid containing wastewater

The imidacloprid was mineralized by heterogeneous photo-Fenton process in a three-phase fluidized bed reactor using waste iron oxide as catalyst. The effects of catalyst loading, dosage of H₂O₂ and pH were investigated to determine the optimal experiments conditions. The results revealed that TOC removal efficiency increases with an increase in H₂O₂ dosage of up to 105.0 mM, an increase in catalyst dosage from 1.0 to 5.0 g L^-1, and a decrease in pH from 5.0 to 3.5. Under the optimal conditions, 97.7% TOC removal was achieved in 6 h under 254-nm UV irradiation. Moreover, recycling experiments indicated that the waste iron oxide had a good stability and the TOC removal of pesticide yielded more than 80% under the fourth recycles.