Comparison of ozone-based AOPs on the removal of organic matter from the secondary biochemical effluent of coking wastewater.

Advanced oxidation processes (AOPs) based on ozone are gaining continuously growing popularity in wastewater treatment. This study explored the treatment of coking wastewater using a combination of ozonation (O3), ultraviolet (UV), and hydrogen peroxide (H2O2) process expressed by % chemical oxygen demand (COD) removal, % total organic carbon (TOC), % UV254, % fluorescence intensity removal and its electrical energy consumption. The obtained results demonstrated that, the combination of O3, UV, and H2O2 which is denoted by O3/UV/H2O2 in this study achieved great success in COD removal (92.08%), TOC removal (78.25%), and reduction of fluorescence intensity (99.82%). Compared with the O3 and O3/UV processes, O3/UV/H2O2 improved the COD removal by approximately 54-69% and 38-51%, respectively. In addition, the energy consumption was reduced by 53-67%. The TOC removal rate in the effluent ranged 71% and 83%, while the UV254 removal rate was up to 90%. The fluorescence spectroscopy showed that the O3/UV/H2O2 combination process reduced the fluorescence intensity by almost 97% within 10 min. Furthermore, the total polycyclic aromatic hydrocarbons (PAHs) concentration in the effluent was less than 10µg/L (removal efficiency > 80%) and the most toxic benzo(a)pyrene (BaP) was less than 0.03 µg/L (0.018µg/L). In addition, the energy consumption of the O3/UV/H2O2 process was 53-67% lower than those of O3 and O3/UV processes. Furthermore, the energy consumption was 80.26 kWh m-3 after 60 min of reaction time when the COD (69.3 mg/L) met the standard discharge. Finally, the O3/UV/H2O2 process could be an effective method for improving the mineralisation of refractory organic matter.

Preparation of Tin-Antimony anode modified with carbon nanotubes for electrochemical treatment of coking wastewater.

To improve the electrocatalytic activity, carbon nanotubes (CNTs) were used to modify a titanium-supported tin-antimony anode (Ti/SnO2-Sb). Compared to a Ti/SnO2-Sb anode, the Ti/SnO2-Sb-CNTs anode exhibited a higher oxygen evolution potential (1.62 V), smaller crystalline volume (71.23 Å3), larger active surface area (0.371 mC cm-2), lower charge transfer resistance (8.24 Ω), and longer service life (291 h). The CNTs provided the Ti/SnO2-Sb anode with effective electrocatalytic activity, conductivity and stability. To evaluate its performance, the Ti/SnO2-Sb-CNTs anode was utilized for the treatment of coking wastewater. The chemical oxygen demand (COD) and total organic carbon (TOC) removal yields of the coking wastewater reached 83.05% and 74.56% under the optimal current density of 25 mA m-2, Na2SO4 concentration of 35 mM, and plate spacing of 10 mm. UV254, ultraviolet-visible absorption spectroscopy, excitation-emission matrix spectra spectroscopy, and Fourier-transform infrared spectroscopy analyses showed that the aromatic and nitrogenous compounds in the coking wastewater were degraded. Furthermore, the electrochemical treatment could effectively reduce the toxicity of the coking wastewater. The energy consumption of the coking wastewater treatment was reduced to 396.56 kWh (kg COD)-1. This study provides a basis engineering application of the electrochemical oxidation of coking wastewater.