Remediation of water contaminated with diesel oil using a coupled process: Biological degradation followed by heterogeneous Fenton-like oxidation

•Diesel oil was removed by biodegradation and Fenton oxidation.•78% diesel oil was degraded by Acinetobacter venetianus in 96 h.•Total COD removal increased from 56.8% to 90% by nZVI.•It is a potential remediation for hard degradable contaminants.

The treatment of a synthetically prepared wastewater containing diesel oil has been investigated using combined treatment schemes based on the biological treatment followed by an advanced oxidation process. 78% of diesel oil was degraded by Acinetobacter venetianus in 96 h, while the removal efficiency of chemical oxygen demand (COD) in the aqueous phase was only 56.8%, indicating that degraded metabolites existed in solution. To solve this problem, a Fenton-like system consisting of nanoscale zero-valent iron (nZVI) and hydrogen peroxide was used for further oxidation of the metabolites after biodegradation. Results showed that the total COD removal increased from 56.8% to 89% under the optimal condition. In addition, effects of initial pH (2.0-9.0), ZVI dosage (0-2.0 g L-1), hydrogen peroxide (H2O2) dosage concentration (0-15 mmol L-1) and temperature (298-308 K) on the treatment efficiency of the combined process were studied. Scanning electron microscopy (SEM) demonstrated that changes to the surface of nZVI occurred. GC-MS revealed that the degraded metabolites were mineralized practically by nZVI/H2O2 system. The results points towards the potential of Fenton-like oxidation as a short post-treatment after a biological process for the treatment of organic pollutants in wastewater.