Sequential advanced oxidation-biodegradation of simple aqueous solutions of aromatic compounds

A comparative study was conducted on the effects of advanced oxidation on the subsequent biodegradability of naphthalene, phenanthrene and pentachlorophenol in aqueous solution as single solutes and as a mixture. Mixed cultures were developed for each parent compound, capable of growing on (as sole carbon source) and mineralizing the respective compound. Biodegradation by degrader enrichments and by municipal activated sludge bacteria was measured by mineralization and cell uptake of {dollar}sp{lcub}14{rcub}{dollar}C from parent compounds. Parent compounds were oxidized by ozone in the presence of hydrogen peroxide at pH 7.4 at 25{dollar}spcirc{dollar}C. Naphthalene and pentachlorophenol were removed from solution by O{dollar}sb3{dollar}/H{dollar}sb2{dollar}O{dollar}sb2{dollar} in 15 minutes, while phenanthrene disappeared after 10 minutes of oxidation. The Microtox{dollar}circler{dollar} toxicity of oxidized solutions decreased in parallel with parent compound disappearance, indicating that oxidation products were significantly less toxic than parent compounds. Naphthalene and its oxidation products were readily degradable, by both degraders and activated sludge, irrespective of the presence of other solutes. Phenanthrene was mineralized only by degraders and only before oxidation; products were not mineralized by degraders or by activated sludge. Thus, oxidation did not increase the biodegradability of readily degradable compounds naphthalene and phenanthrene. However, naphthalene was converted from volatile to soluble material, and phenanthrene was converted from adsorbable to soluble material by oxidation, so oxidation may have some utility for increasing the solubility, and thus bioavailability, of volatile or strongly sorbed chemicals. Pentachlorophenol was most affected by oxidation-biodegradation, Pentachlorophenol was 30% mineralized after 60 minutes of oxidation. After 30 minutes of oxidation, activated sludge mineralized label from pentachlorophenol to the same extent as did degraders, indicating a dramatic reduction in the recalcitrance of pentachlorophenol by advanced oxidation.