Electro-Fenton treatment of soil washing solution of phenanthrene with cyclodextrin using different kind of anode materials: impacts on toxicity and biodegradability

摘要

Electro-Fenton (EF) degradation and mineralization of highly loaded synthetic phenanthrene (PHE) solutions were performed (COD = 11,150 mg O_2 L~(-1) and TOC = 4,500 mg C L~(-1)). Phenanthrene was chosen as a polycyclic aromatic hydrocarbon (PAH) representative and hydroxypropyl-beta-cyclodextrin (HPCD), which is one of the most cost-effective cyclodextrin, was applied as a solubilizing agent. Toxicity and biodegradability of treated solutions were evaluated during the treatment. Different anode materials such as platinum (Pt), dimensional stable anode (DSA; Ti-(RuO_2/IrO_2)) and boron doped diamond (BDD) were employed to carry out the degradation. At optimal catalyst (Fe~(2+)) concentration (i.e., 0.2 mM), the Pt anode was found to be the more efficient one in degradation of PHE. On the other hand, the BDD anode has given the best mineralization performance. PHE and HPCD solutions exhibit high toxicity values vs Vibrio fischeri bacteria (about 80-99% inhibition of luminescence) in the beginning of the treatment. This toxicity decreases after 60% of mineralization (end of HPCD degradation) and reach an almost non-toxic value at the end of treatment. Biodegradability results have shown a great enhancement of BOD_5/COD ratio compared to the initial one (0.001). After 40% of mineralization with BDD anode (about 10 h of treatment), the BOD_5/COD ratio was higher than 0.6, which is sufficient when considering a biological step as post-treatment.