Advanced Oxidation of a Nonionic Surfactant: Examination of the Degradation Products – Acute Toxicity Relationship

Degradation products formed during removal of an aqueous nonylphenol ethoxylate compound (NP-10) by the H2O2/UV-C, Fenton (Fe/H2O2) and photo-Fenton (Fe/H2O2/UV) advanced oxidation processes and their relationship with the acute toxicity toward Vibrio fischeri photobacteria were investigated. Polyethylene glycols with 3-8 ethoxy units, aldehydes and carboxylic acids were identified as the primary degradation products of the studied treatment processes. A strong correlation was found between the acute toxicity and the aldehydes and carboxylic acids formed during the H2O2/UV-C and photo-Fenton processes. Higher concentrations of aldehydes and carboxylic acids in the H2O2/UV-C process (1.24 and 32 mg L, respectively) than in the photo-Fenton oxidation (0.36 and 21 mg L, respectively) were speculated to cause the higher inhibitory effect (24% relative inhibition) observed in the H2O2/UV-C process. The Fenton process was rather inefficient for the removal of NP-10 (20% removal), resulting in the generation of only low concentrations of degradation products (0.14 mg L aldehyde and 4.58 mg L carboxylic acid) and a residual toxicity (10% relative inhibition) nearly at the same level with that of the untreated pollutant (9% relative inhibition). A positive relationship was evidenced between the concentration of degradation products and the level of acute toxicity.