Coagulation enhancement of nonylphenol ethoxylate by partial oxidation using zero-valent iron/hydrogen peroxide

Abstract

Coagulation enhancement of nonionic surfactant nonylphenol polyethoxylate with 9 mol of ethoxylate (NP9EO), was conducted by partial oxidation using zero-valent iron (ZVI)/hydrogen peroxide (H₂O₂) since coagulation is a typical process in many small-scale wastewater treatment plants but it is difficult to remove NP9EO due to micelle formation, and partial oxidation as pretreatment using the proposed process might be adequate and economically feasible. In this study, effects of pH, ZVI dosage, and H₂O₂ concentration were all investigated. The results show, highest NP9EO removal was observed at pH 2 instead of pH 1.5, since the presence of extra ferrous ion in the lower pH consumed the hydroxyl radicals, resulting in low removal efficiency. In addition, ferrous ion was converted to ferric ion for pH higher than 2 which reduced the efficiency of Fenton reaction. NP9EO removal efficiency by coagulation with ZVI/H₂O₂ pretreatment was as high as 99%, which is 40% higher than that without ZVI/H₂O₂ pre-treatment. The optimum dosages for ZVI/H₂O₂ oxidation were about 125 mg/L of H₂O₂ and 3 g/L of ZVI with NP9EO removal higher than 85%. But considering the following coagulation, the optimum dosages were about 125 mg/L of H₂O₂ and 2.5 g/L of ZVI with NP9EO removal efficiency of 95%. Besides, the dissolution of ferric ion from ZVI/H₂O₂ was able to reduce/replace the requirement of the traditional ferric chloride.

Keywords:

• Coagulation
• Partial oxidation
• Nonylphenol polyethoxylate
• Zero-valent iron
• H₂O₂

Notes

Presented at the International Conference on Desalination for the Environment, Clean Water and Energy, European Desalination Society, 23–26 April 2012, Barcelona, Spain