Coking wastewater treatment by coagulation coupled with Fenton and hydrodynamic cavitation/Fenton

In the present study, chemical oxygen demand (COD) was taken as the primary aspect of investigation in order to evaluate the efficiency of advanced treatment of coking wastewater by coagulation-flocculation coupled with Fenton and hydrodynamic cavitation (HC)/Fenton. The coagulation process had a COD removal rate of 71.49% with the FeCl3 = 800 mg/L, pH of raw water, and no flocculant polyacrylamide (PAM) added. Further treatment of Fenton and HC/Fenton was carried out on the coagulated effluent. Using Fenton processes, it was investigated the dosage, reaction time and the influence of mole ratio of H2O2:Fe2+. It was proven, that the molar ratio of H2O2:F-e(2+) = 4:1, H2O2 = 50 mM, reaction for 80min, the total removal rate was 88.83%, met emission standards. HC/Fenton process was applied at the same Fenton ratio and dosage, and the total removal rate was 98.51% at 40 min, with a remaining COD = 3.4 mg/L, being almost completely removed. Fenton dosage was 30 mM for a 50 mM reaction in HC/Fenton process, the obtained total removal rate being 87.91%, with a remaining of COD = 27.66 mg/L, which meets the 40 mg/L stipulated in the Emission standard of pollutants for coking chemical industry (GB16171-2012). HC/Fenton increased the reaction rate, which was three times higher than that of Fenton process, and reducing in this way the amount of applied Fenton reagent. Meanwhile, the cost-efficiency of each process is calculated, the coagulation-Fenton process cost reaching 4.205 CNY/m(3), and the coagulation-HC/Fenton cost of 7.75 CNY/m(3).