Huijiao Wang

Electro-peroxone treatment of Orange II dye wastewater.

Degradation of a synthetic azo dye, Orange II, by electro-peroxone (E-peroxone) treatment was investigated. During the E-peroxone process, ozone generator effluent (O2 and O3 gas mixture) was continuously sparged into an electrolysis reactor, which was equipped with a carbon-polytetrafluorethylene (carbon-PTFE) cathode to electrochemically convert the sparged O2 to H2O2. The in-situ generated H2O2 then reacted with the sparged O3 to produce •OH, which can oxidize ozone-refractory organic pollutants effectively. Thus, by simply combining conventional ozonation and electrolysis processes, and using a cathode that can effectively convert O2 to H2O2, the E-peroxone process degraded Orange II much more effectively than the two processes individually. Complete decolorization and 95.7% total organic carbon (TOC) mineralization were obtained after 4 and 45 min of the E-peroxone treatment, respectively. In comparison, only 55.6 and 15.3% TOC were mineralized after 90 min of the individual ozonation and electrolysis treatments, respectively. In addition to its high efficiency, the E-peroxone process was effective over a wide range of pH (3-10) and did not produce any secondary pollutants. The E-peroxone process can thus provide an effective and environmentally-friendly alternative for wastewater treatment.

Mechanisms of enhanced total organic carbon elimination from oxalic acid solutions by electro-peroxone process

Electro-peroxone (E-peroxone) is a novel electrocatalytic ozonation process that combines ozonation and electrolysis process to enhance pollutant degradation during water and wastewater treatment. This enhancement has been mainly attributed to several mechanisms that increase O3 transformation to ·OH in the E-peroxone system, e.g., electro-generation of H2O2 from O2 at a carbon-based cathode and its subsequent peroxone reaction with O3 to ·OH, electro-reduction of O3 to ·OH at the cathode, and O3 decomposition to ·OH at high local pH near the cathode. To get more insight how these mechanisms contribute respectively to the enhancement, this study investigated total organic carbon (TOC) elimination from oxalic acid (OA) solutions by the E-peroxone process. Results show that the E-peroxone process significantly increased TOC elimination rate by 10.2-12.5 times compared with the linear addition of the individual rates of corresponding ozonation and electrolysis process. Kinetic analyses reveal that the electrochemically-driven peroxone reaction is the most important mechanism for the enhanced TOC elimination rate, while the other mechanisms contribute minor to the enhancement by a factor of 1.6-2.5. The results indicate that proper selection of electrodes that can effectively produce H2O2 at the cathode is critical to maximize TOC elimination in the E-peroxone process.

Kinetics and energy efficiency for the degradation of 1,4-dioxane by electro-peroxone process

Degradation of 1,4-dioxane by ozonation, electrolysis, and their combined electro-peroxone (E-peroxone) process was investigated. The E-peroxone process used a carbon-polytetrafluorethylene cathode to electrocatalytically convert O2 in the sparged ozone generator effluent (O2 and O3 gas mixture) to H2O2. The electro-generated H2O2 then react with sparged O3 to yield aqueous OH, which can in turn oxidize pollutants rapidly in the bulk solution. Using p-chlorobenzoic acid as OH probe, the pseudo-steady concentration of OH was determined to be ∼0.744×10(-9)mM in the E-peroxone process, which is approximately 10 and 186 times of that in ozonation and electrolysis using a Pt anode. Thanks to its higher OH concentration, the E-peroxone process eliminated 96.6% total organic carbon (TOC) from a 1,4-dioxane solution after 2h treatment with a specific energy consumption (SEC) of 0.376kWhg(-1) TOCremoved. In comparison, ozonation and electrolysis using a boron-doped diamond anode removed only ∼6.1% and 26.9% TOC with SEC of 2.43 and 0.558kWhg(-1) TOCremoved, respectively. The results indicate that the E-peroxone process can significantly improve the kinetics and energy efficiency for 1,4-dioxane mineralization as compared to the two individual processes. The E-peroxone process may thus offer a highly effective and energy-efficient alternative to treat 1,4-dioxane wastewater.

Investigation of the synergistic effects for p-nitrophenol mineralization by a combined process of ozonation and electrolysis using a boron-doped diamond anode

Electrolysis and ozonation are two commonly used technologies for treating wastewaters contaminated with nitrophenol pollutants. However, they are often handicapped by their slow kinetics and low yields of total organic carbon (TOC) mineralization. To improve TOC mineralization efficiency, we combined electrolysis using a boron-doped diamond (BDD) anode with ozonation (electrolysis-O3) to treat a p-nitrophenol (PNP) aqueous solution. Up to 91% TOC was removed after 60 min of the electrolysis-O3 process. In comparison, only 20 and 44% TOC was respectively removed by individual electrolysis and ozonation treatment conducted under similar reaction conditions. The result indicates that when electrolysis and ozonation are applied simultaneously, they have a significant synergy for PNP mineralization. This synergy can be mainly attributed to (i) the rapid degradation of PNP to carboxylic acids (e.g., oxalic acid and acetic acid) by O3, which would otherwise take a much longer time by electrolysis alone, and (ii) the effective mineralization of the ozone-refractory carboxylic acids to CO2 by OH generated from multiple sources in the electrolysis-O3 system. The result suggests that combining electrolysis with ozonation can provide a simple and effective way to mutually compensate the limitations of the two processes for degradation of phenolic pollutants.

Electro-peroxone treatment of the antidepressant venlafaxine: Operational parameters and mechanism

Degradation of the antidepressant venlafaxine by a novel electrocatalytic ozonation process, electro-peroxone (E-peroxone), was studied. The E-peroxone treatment involves sparging ozone generator effluent (O2 and O3 gas mixture) into an electrolysis reactor that is equipped with a carbon-polytetrafluoroethylene cathode to electrocatalytically transform O2 in the bubbled gas to H2O2. The in-situ generate H2O2 then reacts with the bubbled O3 to yield OH, which can non-selectively degrade organic compounds rapidly in the solution. Thanks to the significant OH production, the E-peroxone treatment greatly enhanced both venlafaxine degradation and total organic carbon (TOC) removal as compared to ozonation and electrolysis alone. Under optimal reaction conditions, complete venlafaxine degradation and TOC elimination could be achieved within 3 and 120 min of E-peroxone process, respectively. Based on the by-products (e.g., hydroxylated venlafaxine, phenolics, and carboxylic acids) identified by UPLC-UV and UPLC/Q-TOF-mass spectrometry, plausible reaction pathways were proposed for venlafaxine mineralization by the E-peroxone process. The results of this study suggest that the E-peroxone treatment may provide a promising way to treat venlafaxine contaminated water.

Electro-peroxone degradation of diethyl phthalate: Cathode selection, operational parameters, and degradation mechanisms.

This study compares the degradation of diethyl phthalate (DEP) by the electro-peroxone (E-peroxone) process with three different carbon-based cathodes, namely, carbon-polytetrafluorethylene (carbon-PTFE), carbon felt, and reticulated vitreous carbon (RVC). Results show that the three cathodes had different electrocatalytic activity for converting sparged O2 to H2O2, which increased in order of carbon felt, RVC, and carbon-PTFE. The in-situ generated H2O2 then reacts with sparged O3 to yield OH, which can in turn oxidize ozone-refractory DEP toward complete mineralization. In general, satisfactory total organic carbon removal yields (76.4-91.8%) could be obtained after 60min of the E-peroxone treatment with the three carbon-based cathodes, and the highest yield was obtained with the carbon-PTFE cathode due to its highest activity for H2O2 generation. In addition, the carbon-PTFE and carbon felt cathodes exhibited excellent stability over six cycles of the E-peroxone treatment of DEP solutions. Based on the intermediates (e.g., monoethyl phthalate, phthalic acid, phenolics, and carboxylic acids) identified by HPLC-UV, plausible reaction pathways were proposed for DEP mineralization by the E-peroxone process. The results of this study indicate that carbon-based cathodes generally have good electrocatalytic activity and stability for application in extended E-peroxone operations to effectively remove phthalates from water.

Pilot-scale evaluation of micropollutant abatements by conventional ozonation, UV/O 3 , and an electro-peroxone process

The electro-peroxone (E-peroxone) process is an emerging ozone-based advanced oxidation process (AOP) that has shown large potential for micropollutant abatement in water treatment. To evaluate its performance under more realistic conditions of water treatment, a continuous-flow pilot E-peroxone system was developed and compared with conventional ozonation and a UV/O3 process for micropollutant abatements in various water matrices (groundwater, surface water, and secondary wastewater effluent) in this study. With a specific ozone dose of 1.5 mg O3/mg DOC, micropollutants that have high and moderate reactivity with ozone (O3) (diclofenac, naproxen, gemfibrozil, and bezafibrate) could be sufficiently abated (>90% abatement) in the various waters by all three processes. However, ozone-resistant micropollutants (ibuprofen, clofibric acid, and chloramphenicol) were abated only by ∼32-68%, 68-91%, and 73-90% during conventional ozonation of the selected groundwater, surface water, and secondary wastewater effluent, respectively. By electro-generating H2O2 or applying UV irradiation to enhance O3 transformation to •OH during ozonation, the E-peroxone and UV/O3 processes similarly enhanced the abatement efficiencies of ozone-resistant micropollutants by ∼15-43%, ∼5-15%, and ∼5-10% in the groundwater, surface water, and secondary wastewater effluent, respectively. In addition, the E-peroxone and UV/O3 processes significantly reduced bromate formation during the treatment of the three waters compared to conventional ozonation. Due to its higher efficiency, the E-peroxone process reduced ∼10-53% of the energy consumption required to abate the concentration of chloramphenicol (the most ozone-resistant micropollutant spiked in the waters) by 1 order of magnitude in the three waters compared to conventional ozonation. In contrast, the UV/O3 process consumed approximately 4-10 times higher energy than conventional ozonation. This pilot-scale study demonstrates that the E-peroxone process can provide a feasible, effective, and energy-efficient alternative for micropollutant abatement and bromate control in water and wastewater treatment.

Prediction of micropollutant abatement during homogeneous catalytic ozonation by a chemical kinetic model

Prediction of micropollutant abatements by catalytic ozonation is critical for its process design and optimization in water treatment. In this study, a chemical kinetic model based on ozone (O3) and hydroxyl radical (OH) rate constants (kO3 and kOH) and O3 and OH exposures is proposed for the generalized prediction of micropollutant abatement by homogeneous catalytic ozonation. Several micropollutants with kO3 ranging from <0.15 to 1.0 × 106 M-1 s-1 were spiked in water matrices (deionized water and surface water) and then treated by ozonation alone and homogeneous catalytic ozonation with varying transition metals (Ti2+, Co2+, Ni2+, Zn2+, Cu2+, Mn2+, Fe2+, and Fe3+). The addition of the varying catalysts enhanced the kinetics and yield of OH formation from O3 decomposition to different extent. Consequently, for the same applied O3 doses, higher OH exposures can generally be obtained at the expense of lower O3 exposures during catalytic ozonation with the varying catalysts compared to ozonation alone. The changes in O3 and OH exposures did not considerably influence the abatement of micropollutants with high and moderate O3 reactivities (diclofenac, gemfibrozil, and bezafibrate), whose abatement efficiencies were generally >90% during both ozonation alone and catalytic ozonation with the varying catalysts. In contrast, ozone-resistant micropollutants (2,4-dichlorophenoxyacetic acid, clofibric acid, and ibuprofen) were less effectively abated during ozonation (∼40-60% abatement), and the addition of the varying catalysts could enhance their absolute abatement efficiencies to various extent (∼0-10% in the deionized water and ∼0-22% in the surface water) during catalytic ozonation. Despite the differing catalytic mechanisms of the varying transition metals, the abatement efficiencies of micropollutants by catalytic ozonation could be satisfactorily predicted by the chemical kinetic model using the O3 and OH rate constants of the micropollutants reported in literature and the O3 and OH exposures determined during the treatment processes. These results demonstrate that the chemical kinetic model can provide a useful tool for the generalized prediction of micropollutant abatement by homogeneous catalytic ozonation.