Abstract
Electrochemical advanced oxidation experiments were conducted to investigate the degradation of total petroleum hydrocarbons (TPH), nC12 to nC23 alkanes and priority pollutants such as polycyclic aromatic hydrocarbons (PAHs) in petroleum-contaminated water using an inexpensive Ti/Sb-SnO2/PbO2 anode. The influence of electrolyte, applied current, treatment time, and electrode surface area was assessed. Under optimal conditions of energy and 2.5 h of treatment, the TPH removal percentages were 85.44% and 85.61% in Na2SO4 and NaCl electrolytes, respectively. The effect of external electrolyte on TPH degradation was marginal at smaller electrodes (12 cm2) and found to be negligible at larger electrodes (30 cm2). Results demonstrated that TPH degradation was not significantly influenced by active chlorine species (Cl2, HOCl) generated in the NaCl electrolyte other than hydroxyl radicals. The lighter n-alkanes (nC12 to nC14) had exhibited greater removal percentages (90.65% to 98.8%) than medium alkanes (nC15 to nC18: 81% to 89%) and heavier alkanes (nC19 to nC23: 81% to 84.3%). n-Alkanes were resistant to oxidation at low concentrations, possibly due to the inter-phase mass transfer resistance between polar free-radicals and non-polar alkanes. PAHs were completely disappeared (~99.99%) owing to their high reactivity towards free radicals. GC–MS analysis revealed that the n-alkanes had transformed to alcohols, aldehydes, carboxylic acids, and esters before mineralization. The degradation pathway for PAHs involves the formation of hydroxylated products, chlorinated products, aromatic ring-opening products, acids, and esters. The toxicity, as evaluated by Vibrio-fischeri inhibition tests, was decreasing in Na2SO4 medium and increasing in NaCl medium following the electrochemical oxidation treatment. This increase in toxicity in NaCl medium was found to be due to electro-generated active chlorine species.
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