Enhanced Fenton's degradation of real naphthalene dye intermediate wastewater containing 6-nitro-1-diazo-2-naphthol-4-sulfonic acid: A pilot scale study

The production of dye intermediates made from naphthalene compounds such as 6-nitro-1-diazo-2-naphthol-4-sulfonic acid (6-nitro-1,2,4-Acid) caused a major environmental concern, mainly due to their nature of being highly toxic concentrated organics. In this work, an enhanced Fenton process integrating the multi-staged Fenton reaction with inner circulation was practiced in a pilot scale. This creative design exhibited a particular advantage in treating the wastewater with high amount of organic substances. Experiments showed a higher COD removal efficiency (93%) and oxidation efficiency (62%) when two-staged Fenton reaction with inner circulation (flow-to-influent ratio of 5) was applied, whereas only 40.9% of COD reduction was obtained when using the single-staged Fenton without any circulation. It was demonstrated experimentally that the wastewater color went through a fast change via different stages of the reaction. The main intermediates generated along the two-staged reaction have been identified as aromatic and aliphatic acids, but their concentrations demonstrated regular changes in each stage, indicating an enhanced oxidation effect of staged Fenton process.

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► An enhanced Fenton with inner circulation is introduced to treat high concentrated dye intermediate wastewater.
► Treated water recycled to the influent distribution system could increase the oxidation efficiency.
► Staged Fenton could decrease the scavenging effect of hydroxyl radicals.