Zhaokun Xiong

Comparative study on the reactivity of Fe/Cu bimetallic particles and zero valent iron (ZVI) under different conditions of N2, air or without aeration.

In order to further compare the degradation capacity of Fe(0) and Fe/Cu bimetallic system under different aeration conditions, the mineralization of PNP under different aeration conditions has been investigated thoroughly. The results show that the removal of PNP by Fe(0) or Fe/Cu system followed the pseudo-first-order reaction kinetics. Under the optimal conditions, the COD removal efficiencies obtained through Fe(0) or Fe/Cu system under different aeration conditions followed the trend that Fe/Cu (air)>Fe/Cu (N2: 0-30 min, air: 30-120 min)>control-Fe (air)>Fe/Cu (without aeration)>Fe/Cu (N2)>control-Fe (N2). It revealed that dissolved oxygen (DO) could improve the mineralization of PNP, and Cu could enhance the reactivity of Fe(0). In addition, the degradation of PNP was further analyzed by using UV-vis, FTIR and GC/MS, and the results suggest that Fe/Cu bimetallic system with air aeration could completely break the benzene ring and NO2 structure of PNP and could generate the nontoxic and biodegradable intermediate products. Meanwhile, most of these intermediate products were further mineralized into CO2 and H2O, which brought about a high COD removal efficiency (83.8%). Therefore, Fe/Cu bimetallic system with air aeration would be a promising process for toxic refractory industry wastewater.

Mineralization of ammunition wastewater by a micron-size Fe0/O3 process (mFe0/O3)

A micron-size Fe0/O3 process (mFe0/O3) was set up to mineralize the pollutants in ammunition wastewater, and its key operational parameters (e.g., initial pH, ozone flow rate, and mFe0 dosage) were optimized by the batch experiments, respectively. Under the optimal conditions, COD removal efficiency obtained by the mFe0/O3 process (i.e., 92.6% after 30 min treatment) was much higher than those of ozone alone (46.5%), mFe0 alone (38.3%) or mFe0/air (58.5%), which confirm the synergetic effect between mFe0 and ozone. In addition, the BOD5/COD (B/C) ratio was elevated from 0 to 0.54 after 30 min treatment by the mFe0/O3 process, which indicates the significant improvement of biodegradability. Furthermore, the analysis results of the UV-vis and excitation–emission matrix (EEM) fluorescence spectra further confirm that the toxic and refractory pollutants in ammunition wastewater had been completely decomposed or transformed into smaller molecule organic compounds. Meanwhile, the superiority of the mFe0/O3 process has been confirmed according the analysis results of COD removal, B/C ratio, UV-vis and EEM. Therefore, the mFe0/O3 process could be proposed as a promising treatment technology for toxic and refractory ammunition wastewater.

Insight into a highly efficient electrolysis-ozone process for N,N -dimethylacetamide degradation: Quantitative analysis of the role of catalytic ozonation, fenton-like and peroxone reactions

A highly efficient electrolysis catalyzed ozone (ECO) process was developed for N,N-dimethylacetamide (DMAC) degradation. The pseudo-first-order rate constants (kobs) of DMAC degradation by ECO process were 1.73-19.09 times greater than those by ozonation and electrolysis processes in a wide pH range of 3.0-10.0. Interestingly, we found O2•- could be generated from ozone decomposition by a radical chain mechanism instead of monovalent reduction of O2 in ECO system at the initial pH of 3.0. Subsequently, the H2O2 derived from O2•- could participate in Fenton-like and peroxone reactions with the released Fe2+ from iron anode and the aerated O3, respectively. Therefore, the extraordinary DMAC removal efficiency was mainly caused by the more generation of •OH through the multiple reactions of homogeneous catalytic ozonation, Fenton-like and peroxone in ECO system. Importantly, the roles of involved reactions in ECO system at various initial pH were quantitatively evaluated according to a series of trapping experiments. The results reveal that the solution pH could significantly affect the contributions of various reactions and convert the reaction mechanisms of multiple reactions in ECO system. Finally, the degradation intermediates were detected to propose a possible DMAC oxidation pathway in the ECO system. This work provides a deep insight into the quantitative analysis of the role of multiple oxidation reactions mechanism and the design of efficient electrochemical advanced oxidation technology for recalcitrant organic pollutant removal.

Treatment of wastewater derived from dinitrodiazophenol (DDNP) manufacturing by the Fe/Cu/O3 process

In this paper, the Fe/Cu bimetallic particles and ozone were combined to decompose or transform the toxic and refractory pollutants in dinitrodiazophenol (DDNP) wastewater. Firstly, operational parameters including theoretical Cu mass loading (TMLCu), Fe/Cu dosage, initial pH, O3 flow rate and treatment time were optimized respectively. The maximum COD removal efficiency (85.3%) and color removal efficiency (95.0%) were obtained under the optimal conditions (i.e., theoretical Cu mass loading (TMLCu) = 0.02 g Cu per g Fe, Fe/Cu dosage = 20 g L−1, initial pH = 5.0, O3 flow rate = 0.3 L min−1, treatment time = 15 min). Then, in order to confirm the superiority of the Fe/Cu/O3 process, three control experiment systems including Fe/Cu, O3 and Fe0/O3 processes were set up under the same conditions. In addition, the UV-vis and FTIR results confirm the main pollutants in DDNP wastewater were oxidized and generated intermediates, which revealed the superiority of Fe/Cu/O3 process. Thus, the DDNP wastewater could be treated by Fe/Cu/O3 process in a promising way.

Enhancing the efficiency of zero valent iron by electrolysis: Performance and reaction mechanism

Electrolysis was applied to enhance the efficiency of micron-size zero valent iron (mFe0) and thereby promote p-nitrophenol (PNP) removal. The rate of PNP removal by mFe0 with electrolysis was determined in cylindrical electrolysis reactor that employed annular aluminum plate cathode as a function of experimental factors, including initial pH, mFe0 dosage and current density. The rate constants of PNP removal by Ele-mFe0 were 1.72-144.50-fold greater than those by pristine mFe0 under various tested conditions. The electrolysis-induced improvement could be primarily ascribed to stimulated mFe0 corrosion, as evidenced by Fe2+ release. The application of electrolysis could extend the working pH range of mFe0 from 3.0 to 6.0 to 3.0-10.0 for PNP removal. Additionally, intermediates analysis and scavengers experiments unraveled the reduction capacity of mFe0 was accelerated in the presence of electrolysis instead of oxidation. Moreover, the electrolysis effect could also delay passivation of mFe0 under acidic condition, as evidenced by SEM-EDS, XRD, and XPS analysis after long-term operation. This is mainly due to increased electromigration meaning that iron corrosion products (iron hydroxides and oxides) are not primarily formed in the vicinity of the mFe0 or at its surface. In the presence of electrolysis, the effect of electric field significantly promoted the efficiency of electromigration, thereby enhanced mFe0 corrosion and eventually accelerated the PNP removal rates.