Comparison of Nitrilotriacetic Acid and [S,S]-Ethylenediamine-N,N′-disuccinic Acid in UV–Fenton for the Treatment of Oil Sands Process-Affected Water at Natural pH

The application of UV–Fenton processes with two chelating agents, nitrilotriacetic acid (NTA) and [ S, S ]-ethylenediamine- N, N ′-disuccinic acid ([ S, S ]-EDDS), for the treatment of oil sands process-affected water (OSPW) at natural pH was investigated. The half-wave potentials of Fe(III/II)NTA and Fe(III/II)EDDS and the UV photolysis of the complexes in Milli-Q water and OSPW were compared. Under optimum conditions, UV–NTA–Fenton exhibited higher efficiency than UV–EDDS–Fenton in the removal of acid extractable organic fraction (66.8% for the former and 50.0% for the latter) and aromatics (93.5% for the former and 74.2% for the latter). Naphthenic acids (NAs) removals in the UV–NTA–Fenton process (98.4%, 86.0%, and 81.0% for classical NAs, NAs + O (oxidized NAs with one additional oxygen atom), and NAs + 2O (oxidized NAs with two additional oxygen atoms), respectively) under the experimental conditions were much higher than those in the UV–H 2 O 2 (88.9%, 48.7%, and 54.6%, correspondingly) and NTA–Fenton (69.6%, 35.3%, and 44.2%, correspondingly) processes. Both UV–NTA–Fenton and UV–EDDS–Fenton processes presented promoting effect on the acute toxicity of OSPW toward Vibrio fischeri . No significant change of the NTA toxicity occurred during the photolysis of Fe(III)NTA; however, the acute toxicity of EDDS increased as the photolysis of Fe(III)EDDS proceeded. NTA is a much better agent than EDDS for the application of UV–Fenton process in the treatment of OSPW.