Molecular transformation of dissolved organic matter in process water from oil and gas operation during UV/H2O2, UV/chlorine, and UV/persulfate processes

Abstract

This paper reported the impact of UV/H2O2, UV/chlorine, and UV/persulfate advanced oxidation processes on the molecular transformations of dissolved organic matter (DOM), removal of naphthenic acids (NAs) and acute toxicity in oil sands process water (OSPW). The UV/persulfate process exhibited the highest removal (81.2% with 2 mM dose) towards classical NAs and highest reduction in acute toxicity to Vibrio fischeri among the three processes. The fraction of DOM such as CHOS class species decreased along with the increase of the oxidant doses in all processes. The increase in O/C ratio and lack of change in the H/C and double bond equivalence indicated that H-abstraction followed by the OH-addition was the main reaction pathway for all processes. This observation aligned with previous studies using model compounds and proved that OSPW DOM reacted similarly to model compounds. Sulfur containing organic matters were the most liable compounds in OSPW NOM, while UV/chlorine was the most effective process to oxidize nitrogen containing organic matters. Overall results revealed that the UV/persulfate process could be used as a promising technique for the removal of OSPW NA and reduction of acute toxicity towards Vibrio fischeri. In addition, this DOM characterization approach could be utilized to investigate the transformation of complicated OSPW DOM and to identify the byproducts generated during different water treatment processes.