Coupled fenton-denitrification process for the removal of organic matter and total nitrogen from coke plant wastewater

This work assesses the feasibility of applying a Coupled Fenton-Denitrification (CFD) process for the treatment of wastewater from a coking plant. This highly toxic effluent is characterized by comparable carbon and nitrogen contents and it is usually released into the treatment system at well above room temperature. Recalcitrant organic matter can be easily removed in a first step using Fenton treatment. Working at 50 °C, pH ₀ : 3, and a wastewater obtained from a coking plant, the stoichiometric amount of H ₂ O ₂ relative to COD and a H ₂ O ₂ /Fe ²⁺ weight ratio of 50, around 60% of carbon load was mineralized whereas H ₂ O ₂ was completely depleted. However, no changes were observed in the total nitrogen content. A subsequent denitrification stage led to an additional 80% TOC (overall above 90%) and 75% Total Nitrogen removal. This was done in a batch bioreactor at room temperature over 72 h, using a 40-day pre-acclimated denitrifying biomass. These results point to the possibility of designing a combined chemical oxidation and biological treatment to deal with complex effluents containing refractory organic matter including high concentrations of nitrogen species.