Partial oxidation of phenolic wastewater using NaOH and Ni addition for hydrogen production and phenolics degradation in supercritical water

Abstract

Phenolic wastewater is a challenge for traditional microbial treatment because of complex pollutant constituents and high concentration of aromatic hydrocarbons. Using H2O2 as oxidant, partial oxidation of phenolic wastewater using NaOH and Ni addition for hydrogen production and phenolics degradation in supercritical water was explored. It was found that higher oxygen ratio was advantageous for phenolics and other organic pollutants converting to gaseous products from supercritical water partial oxidation without any catalyst addition, but hydrogen production peaked at 0.5 oxygen ratio. Hydrogen gasification efficiency were raised to 75.68% within 0.5 oxygen ratio and 3.0% NaOH addition. Although separate Ni catalyst effectively enhanced the production of the gasifiable intermediate, hydrogen gasification efficiency appeared to a balance due to the enhancement of hydrogenation and methanation reactions. Both organic pollutants removal and hydrogen production enhancement were significantly improved under the combined NaOH-Ni catalyst, 85.24% TOC removal and 86.39% hydrogen gasification efficiency achieved within 1.0 NaOH + 2.0 Ni catalyst. There was very little cyclic compounds detected in liquid phase from combined NaOH-Ni catalytic partial oxidation, compared with individual addition. S, O and Si elements deposited in the surface of Ni catalyst, which have some negative effect on reuse. The positive effect of combined NaOH-Ni catalyst on organic pollutants removal and hydrogen production enhancement was demonstrated, which provided novel results and information that help to solve the problems in the process of toxic and high concentration organic wastewater treatment and facilitate the engineering application of supercritical water partial oxidation technology in the future.