Identification and fate of halogenated PAHs formed during electrochemical treatment of saline aqueous solutions.

Halogenations of polycyclic aromatic hydrocarbons (PAHs) comprise a serious problem, when electrochemical oxidation (EO) is applied for treatment of chloride and bromide containing polluted sea water. In this study, the possible non-polar halogenated byproducts formed were identified in a series of chemical hypochlorination experiments using GC-MS, and the analytical information from these experiments was used in the primary EO treatment tests. An electrochemical cell equipped with a Ti/Pt(90)-Ir(10) anode was used in a batch recirculation setup with naphthalene, pyrene, and fluoranthene as the parent PAHs. Contrary to the chemical hypochlorination experiments, naphthalene as the most soluble compound was the only one to be halogenated in detectable amounts during EO. In a single sodium chloride electrolyte, up to 13% of the initial naphthalene was chlorinated at the peak concentration during treatment before it was subsequently removed. Even small concentrations of added bromide in a mixed electrolyte completely dominated the byproduct pattern with formation of primarily mono brominated naphthalene in peak concentrations up to 30-39% of the initial naphthalene. All of the considered byproducts were despite a more recalcitrant behavior degraded at prolonged treatment times, which need to be applied to ensure a safe discharge of the treated water.