In order to improve the biodegradability of delay explosive wastewater (DEW), a combined Fe0/air and Fenton oxidation process (i.e., first Fe0/air-Fenton-secondFe0/air) was developed to decompose the refractory organic pollutants and remove heavy metals (i.e., Pb and Cr) in this wastewater. Effect of the initial solution pH, Fe0 dosage, H2O2 dosage, aeration rate, and treatment time on the treatment efficiency of the firstFe0/air-Fenton-secondFe0/air process were investigated, respectively. Meanwhile, two control experiments were setup to confirm the synergistic reaction between Fe0/air and Fenton. The results show that the maximum COD removal efficiency was approximately 50.0% under the optimal conditions. Also, Pb, Cr, and poly(vinyl alcohol) (PVA) in the DEW could be completely removed. Therefore, its BOD5/COD ratio was enhanced from 0.20 to 0.56. Finally, FTIR and EEM fluorescence spectroscopy were used to analyze the decomposition and transformation of the refractory pollutants, which could further confirm the high efficiency of the firstFe0/air-Fenton-secondFe0/air process.

Fe0 particles were passivated by concentrated nitric acid, and a Fe0/(passivated Fe0) system was setup for p-nitrophenol (PNP) removal. First, the characteristics of passivated Fe0 particles were analyzed. The results suggest that the passivated Fe0 particles have an iron oxide passivation film on their surface with inertness and high electrode potential (0.57 V). Besides, the optimal conditions were obtained according to the significant parameters optimization. In addition, control experiments were set up to investigate the advantage of reactivity and operational life of the Fe0/(passivated Fe0) system, and the results confirmed that the new system had higher reactivity and longer operational life. Meanwhile, the reaction mechanism of Fe0/(passivated Fe0) system for PNP removal was proposed. Finally, with an analysis of preparation cost, the Fe0/(passivated Fe0) system could also be seemed as a cost-effective technology. Consequently, the developed Fe0/(passivated Fe0) system in this study is a promising technology for treatment of contaminated water.

•Parameters optimization was studied firstly by single-factor experiments.•Optimization conditions was obtianed through response surface methodology (RSM).•Degradation pathway of PNP was proposed.•Synergistic mechanism of Fe0-PM-PS system was investigated thoroughly.To develop a technology for the degradation of the toxic and refractory pollutants, the Fe0-PM-PS system and 6 control experiments were setup in this study. First, effects of Fe0 dosage (0–18.3 g/L), PM dosage (0–25.0 mmol/L), PS dosage (0–30.0 mmol/L), initial pH value (3.0-11.0), air flow rate (0–2.0 L/min), and feeding times of PM and PS (1–5) on the degradation of PNP in aqueous solution by the Fe0-PM-PS system were studied through the single-factor experiment. Furthermore, the optimized experimental conditions (i.e., Fe0 dosage of 11.9 g/L, PM dosage of 15.0 mmol/L, PS dosage of 18.1 mmol/L and feeding times of oxidants of 4) were obtained through response surface methodology (RSM). The result shows that the maximum COD removal efficiency (89.0%) was obtained by the Fe0-PM-PS system under the optimal conditions, which was mainly attributed to the strong synergistic effect among Fe0, PM and PS. In addition, PNP degradation pathway was proposed according to the intermediates detected by HPLC. According to the analysis results of SEM-EDS, XRD and XPS, the reaction mechanism of the Fe0-PM-PS system has been clarified thoroughly. In short, these results suggest that the Fe0-PM-PS system should be proposed as an effective pretreatment process for the toxic and refractory PNP wastewater.Download high-res image (167KB)Download full-size image

•Shale gas drilling flowback fluid (SGDF) was treated by the mFe0/PS/O3 system.•Degradation of the typical pollutants in SGDF was evaluated by GC-MS analysis.•Superiority of the mFe0/PS/O3 process was investigated through the control experiments.•Synergetic action between Fe0 and oxidants (i.e., PS and ozone) was investigated.Shale gas drilling flowback fluid (SGDF) generated during shale gas extraction is of great concern due to its high total dissolved solid, radioactive elements and organic matter. To remove the toxic and refractory pollutants in SGDF and improve its biodegradability, a microsacle Fe0/Persulfate/O3 process (mFe0/PS/O3) was developed to pretreat this wastewater obtained from a shale gas well in southwestern China. First, effects of mFe0 dosage, O3 flow rate, PS dosage, pH values on the treatment efficiency of mFe0/PS/O3 process were investigated through single-factor experiments. Afterward, the optimal conditions (i.e., pH = 6.7, mFe0 dosage = 6.74 g/L, PS = 16.89 mmol/L, O3 flow rate = 0.73 L/min) were obtained by using response surface methodology (RSM). Under the optimal conditions, high COD removal (75.3%) and BOD5/COD ratio (0.49) were obtained after 120 min treatment. Moreover, compared with control experiments (i.e., mFe0, O3, PS, mFe0/O3, mFe0/PS, O3/PS), mFe0/PS/O3 system exerted better performance for pollutants removal in SGDF due to strong synergistic effect between mFe0, PS and O3. In addition, the decomposition or transformation of the organic pollutants in SGDF was analyzed by using GC-MS. Finally, the reaction mechanism of the mFe0/PS/O3 process was proposed according to the analysis results of SEM-EDS and XRD. It can be concluded that high-efficient mFe0/PS/O3 process was mainly resulted from the combination effect of direct oxidation by ozone and persulfate, heterogeneous and homogeneous catalytic oxidation, Fenton-like reaction and adsorption. Therefore, mFe0/PS/O3 process was proven to be an effective method for pretreatment of SGDF prior to biological treatment.Download high-res image (257KB)Download full-size image

•PS could effectively enhance the reactivity of mFe/Cu for PNP removal.•Performance of mFe/Cu-PS system was comparatively investigated.•Reduction was proposed as the main PNP removal pathway.•Major reactions in the heterogeneous system of mFe/Cu-PS were proposed.In this study, batch experiments were conducted to examine the enhanced reactivity of microscale Fe/Cu bimetallic particles (mFe/Cu) with persulfate (PS) for p-nitrophenol (PNP) removal in aqueous solution. The key operating parameters (i.e., theoretical Cu mass loadings (TMLCu), mFe/Cu dosage, PS dose, initial pH and temperature) were optimized by the batch experiments, respectively. The experimental data were followed well the pseudo-first-order kinetic model. Result reveals that refractory PNP (500 mg L−1) was effectively degraded by mFe/Cu-PS system with removal of 98.4% and kobs of 1.91 min−1 after only 3 min treatment under the optimal operating conditions. Moreover, compared with control experiments (i.e., mFe/Cu, microscale Fe0 with PS (mFe0-PS), and PS alone), mFe/Cu-PS system exerted better performance for PNP removal due to the strong synergistic effect between PS and mFe/Cu. According to the analysis results of degradation kinetics of PNP, COD (chemical oxygen demand) removal, UV–vis absorption spectra and the intermediates formed, the results reveal that the PNP removal by mFe/Cu-PS system was mainly attributed to reduction accompanied slight oxidation. And based on the analysis of surface characteristics of mFe/Cu particles, it is further demonstrated that PS could enhance the reactivity of mFe/Cu through rapid corrosion of iron surface and decrease of surface passivation of mFe/Cu surface when the low molar ratio of PS to mFe/Cu (i.e., 1:43) was used in this study. These results also illustrates mFe/Cu-PS can be as a high efficient pretreatment technology for the removal of toxic refractory PNP from wastewater.Download high-res image (281KB)Download full-size image

•Dispel the concern of Cu2+ pollution of the effluent in Fe/Cu-based systems.•Relation between Cu2+ release and PNP removal in Fe/Cu-based systems was studied.•Structure and composition of Fe and Cu corrosion products were detected.•Proposed Cu transfer mechanisms and pathways in various Fe/Cu-based systems.In this study, six different Fe/Cu-based systems (e.g., Fe/Cu, Fe/Cu/N2, Fe/Cu/air, Fe/Cu/H2O2, Fe/Cu/O3, and Fe/Cu/PS) were set up to investigate the Cu2+ release during wastewater treatment. Results indicated that the concentration of Cu2+ could maintain the equilibrium state and the concentrations were less than 0.157 mg/L in different Fe/Cu-based systems except in Fe/Cu/air system (0.919 mg/L). The concentration of Cu2+ could come up to the integrated wastewater discharge level standard. Meanwhile, the relatively inverse correlation between Cu2+ release and pollutant removal efficiency was found in different Fe/Cu-based systems. Furthermore, the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) were used to systematically characterize the structure and composition of Fe/Cu bimetallic particles after different Fe/Cu-based systems reaction. Finally, the mechanisms of Cu2+ transfer pathway between the surface of iron and solution in different Fe/Cu-based were proposed. The different Cu2+ transfer mechanisms in Fe/Cu-based reduction systems and Fe/Cu-based oxidation systems were found. This study provided potent evidence to dispel the environmental concern of heavy metal pollution and also shed light on the Cu2+ transfer mechanisms in different kinds of Fe/Cu-based systems.Download high-res image (129KB)Download full-size image

•Optimal conditions were obtained and control experiments were setup to confirm the performance of Fe0/H2O2/persulfate system.•The fresh and used Fe0 have been characterized by SEM, EDS, XRD and XPS.•Degradation pathway of PNP was proposed according to the detected intermediates.•Synergistic mechanism of Fe0/H2O2/persulfate system was investigated thoroughly.In this study, a Fe0/H2O2/persulfate system was developed to degrade p-nitrophenol (PNP) in aqueous solution, and 7 control experiments were setup to evaluate the synergistic effects in Fe0/H2O2/persulfate system. First, effects of Fe0 dosage (0–4.0 g/L), H2O2 dosage (0–30.0 mM), persulfate dosage (0–25.0 mM) and initial pH value (3.0–13.0) on PNP removal by the Fe0/H2O2/persulfate system were investigated through single-factor experiments. Furthermore, the optimal parameters (i.e., 1.3 g/L Fe0, 24.8 mM H2O2, 6.7 mM persulfate and initial pH of 5.1) were obtained through response surface methodology (RSM). Meanwhile, a high PNP removal (99.9%) obtained under the optimal conditions was mainly ascribed to the strong synergistic effects among Fe0, H2O2 and persulfate. Furthermore, PNP degradation pathway was proposed according to the detected intermediates. In addition, the reaction mechanism of Fe0/H2O2/persulfate system was proposed according to iron corrosion products detected by using SEM-EDS, XRD and XPS. In a word, all the results suggest that Fe0/H2O2/persulfate system should be recommended as a valid method for the treatment of toxic and intractable industrial wastewater.Download high-res image (171KB)Download full-size image

•Coagulation-flocculation as pre-treatment combined with mFe/Cu/O3 process.•Operating parameters of CF-mFe/Cu/O3 process were optimized thoroughly.•Degradation process of pollutants was analyzed by UV–vis, EEM and GC/MS.•Improvement of the biodegradability of wastewater by the combined process.A coagulation-flocculation as pre-treatment combined with mFe/Cu/O3 (CF-mFe/Cu/O3) process was developed to degrade the pollutants in automobile coating wastewater (ACW). In coagulation-flocculation (CF) process, high turbidity removal efficiency (97.1%) and low COD removal efficiency (10.5%) were obtained under the optimal conditions using Al2(SO4)3·18H2O and CaO. The effluent of CF process (ECF) was further disposed by mFe/Cu/O3 process, and its key operating parameters were optimized by batch experiments. Optimally, COD removal efficiency of ECF obtained by the mFe/Cu/O3 process (i.e., 87.6% after 30 min treatment) was much higher than those of mFe/Cu alone (8.3%), ozone alone (46.6%), and mFe/Cu/air (6.1%), which confirms the superiority of the mFe/Cu/O3 process. In addition, the analysis results of UV–vis, excitation-emission matrix (EEM) fluorescence spectra and GC/MS further confirm that the phenol pollutants of ECF had been effectively decomposed or transformed after CF-mFe/Cu/O3 process treatment. Meanwhile, B/C ratio of ACW increased from 0.19 to 0.56, which suggests the biodegradability was improved significantly. Finally, the operating cost of CF-mFe/Cu/O3 process was about 1.83 USD t−1 for ACW treatment. Therefore, the combined process is a promising treatment technology for the coating wastewater from automobile manufacturing.

•Good performance for the degradation of PNP was obtained in an ABFB reactor.•Variation of microbial EPS during the whole operation process was investigated.•Richness and diversity for bacteria and fungi in aerobic sludge were analyzed.•Dominant phyla Proteobacteria and Ascomycota were identified in this reactor.Biodegradability of PNP has been reported widely in recent years, but the community composition of PNP-degrading microorganisms was still unclear today. In this paper, the biodegradation process with continuously PNP loading from 0 to 6.50 kg m−3 d−1 in 58 days in an aerobic biological fluidized bed (ABFB) reactor has been investigated. The results show that COD and PNP removal stabilized at 95% and 99% during the operation period with a maximum PNP concentration of 1250 mg/L. The high concentration of PNP in substrate led to a significant increase in extracellular polymeric substances (EPS) component of biomass and obvious morphological changes of microbial colonies during the degradation process. In addition, high-throughput sequencing was employed to reveal the highly diverse bacterial and fungal populations in the reactor. At the same time, genera Sphingobium, Penicillum and Debaryomyces belonging to phyla Proteobacteria and Ascomycota were identified to be the dominant species in high concentration PNP degradation process. This work investigated the tolerable degree of aerobic microbes to PNP toxicity as well as the characteristics of microbial communities at different PNP concentration levels. It might add some new insights into bacterial and fungal communities in high p-nitrophenol concentration degradation processes.Download high-res image (168KB)Download full-size image

•Premagnetization process was used for Fe0/(Fe/Cu) enhancement for nitrate reduction.•Significant parameters of premagnetization Fe0/(Fe/Cu) system were optimized.•The advantages and the duration of premagnetization of the new system were confirmed.•The mechanism of the new system was proposed.•The new system was used to treat multi-pollutants wastewater and real wastewater.In order to develop a better Fe0 based system, premagnetization was used to enhance the reactivity of Fe0 particles and Fe/Cu bimetallic particles micro-electrolysis (Fe0/(Fe/Cu)) system for nitrate wastewater treatment. In this study, the significant parameters (i.e., initial pH, premagnetization time and intensity of magnetic field) were optimized firstly. Under the optimal conditions, the premagnetization Fe0/(Fe/Cu) system could obtain a high rate (kobs = 0.732 min−1) and better selectivity ([TN removal]/[NO3−-N removal] ratio = 54.3%) for nitrate reduction, which were much superior to the 7 control experiments (i.e., Fe0/(Fe/Cu) system, premagnetization Fe0 particles and Cu0 particles micro-electrolysis (premagnetization Fe0/Cu0) system, Fe0/Cu0 system, premagnetization Fe0 system, Fe0 system, premagnetization Fe/Cu system and Fe/Cu system). Meanwhile, it was confirmed that the prepared Fe0/(Fe/Cu) could keep the high reactivity even after vacuum drying and longtime storage. Furthermore, the operational life of premagnetization Fe0/(Fe/Cu) system is better than that of Fe0/(Fe/Cu) system (for more than 12.6 L wastewater treatment). The used Fe0/(Fe/Cu) could recover high reactivity after acid washing as well. Moreover, the characteristics of the medium materials before and after employment were analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Besides, the reasonable mechanism of premagnetization improving the rate and selectivity for nitrate reduction of Fe0/(Fe/Cu) system was also proposed. The possible reasons why premagnetization process could strengthen both rate and selectivity for nitrate reduction and why premagnetization could strengthen the Fe0/(Fe/Cu) system better were also given. Finally, it was proved that the new developed system not only could effectively treat different pollutants but also is suitable for different quality wastewater treatment. As a conclusion, the premagnetization Fe0/(Fe/Cu) system is a promising Fe0 based technology for wastewater treatment.Download high-res image (127KB)Download full-size image

•The effects of CuFe2O4 dosages, PS dosages, initial pH and co-existing inorganic ions were investigated thoroughly.•The materials characterization of CuFe2O4 nano-particles were analyzed by TEM, BET, VSM, XRD and XPS.•The main radical specie (i.e., SO4-) and the stability of CuFe2O4 nano-particles were proved.•Degradation pathway of PNP was proposed according to the detected intermediates.•Mechanism of CuFe2O4/PS system was investigated comprehensively.To evaluate the heterogeneous degradation of p-nitrophenol (PNP) in aqueous solution by catalytic oxidation process involving persulfate (PS) activated by CuFe2O4 magnetic nano-particles, the CuFe2O4/PS system was investigated in this study. CuFe2O4 magnetic nano-particles were synthesized with a sol-gel combustion method and then used as heterogeneous catalysts for PS activation. First, effects of CuFe2O4 dosage (0–40 g/L), PS dosage (0–10 mM), initial pH value (3.0–11.0) and co-existing inorganic ions on the degradation of PNP in aqueous solution by CuFe2O4/PS system were investigated comprehensively. In particular, the maximum PNP removal (89%) and total organic carbon (TOC) removal (81%) were obtained under the optimal conditions. Meanwhile, two control experiments (i.e., CuFe2O4 alone and PS alone systems) were carried out to confirm the performance in CuFe2O4/PS system. Furthermore, the reasonable PNP degradation pathway was proposed based on the intermediates detected by high performance liquid chromatography (HPLC). Finally, the mechanism of the CuFe2O4/PS system was proposed thoroughly according to the characterization of catalyst, the analysis results of metal leaching and radical scavenging studies. In a word, this study provides an effective oxidative system for PNP removal by CuFe2O4/PS heterogeneous process at ambient temperature.Download high-res image (102KB)Download full-size image

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.

In this study, an electroless (electrode-less) copper plating technology was developed to prepare the high-reactive and robust iron–copper (Fe/Cu) bimetallic particles. First, effect of pretreatment and key preparation parameters (e.g., complexant, H3BO3, NiSO4·7H2O, pH and plating time) on the reactivity of Fe/Cu bimetallic particles were investigated, respectively. Their reactivity was evaluated according to the obtained Kobs for PNP removal. Also, the characteristics of Fe/Cu bimetallic particles prepared by electroless plating and displacement plating were comparatively observed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The analysis results show that when Fe/Cu bimetallic particles were prepared by electroless plating, copper was uniformly deposited on the surface of Fe0 substrate, and only a few bulky particles were observed. However, plenty of loose copper blocks were heterogeneously distributed on the surface of Fe0 substrates when the Fe/Cu bimetallic particles were prepared by the conventional displacement plating. Furthermore, the operational life and reactivity of Fe/Cu bimetallic particles prepared by electroless and displacement plating process were comparatively investigated by the recycling experiment. The results suggest that the new Fe/Cu bimetallic particles have a longer operational life than that of the conventional Fe/Cu bimetallic particles. Meanwhile, it can be seen from the control experiments that the new Fe/Cu bimetallic particles have a stronger reactivity for the PNP removal both in Fe/Cu/air and Fe/Cu/N2 processes. As results, the new electroless plating for the preparation of Fe/Cu bimetallic particles is superior to the conventional displacement plating. In other words, the electroless copper plating is a promising technology to prepare the high-reactive and robust Fe/Cu bimetallic particles.

Treatment of 2-diazo-4,6-dinitrophenol (DDNP) industry wastewater by 1stFe/Cu/air–2ndFenton–3rdFe/Cu/air was studied to degrade the toxic refractory pollutants and improve the biodegradability. Three control experiments (i.e., 1stFe0/air–2ndFenton–3rdFe0/air, Fe/Cu/air, and Fenton) were set up to confirm the superiority of 1stFe/Cu/air–2ndFenton–3rdFe/Cu/air and the synergistic reaction between Fe/Cu/air and Fenton process. Furthermore, the key operating parameters including initial pH (1.5–7.0), Fe/Cu dosage (5–50 g L−1), aeration rate (0–2.0 L min−1), reaction time (0–180 min) and H2O2 dosage (0–40 mmol L−1) were optimized, respectively. The results showed that high COD removal (87.1%), decolority (99.9%), DDNP removal (100%) and B/C ratio (0.58) was obtained by 1stFe/Cu/air–2ndFenton–3rdFe/Cu/air process. It has a higher treatment efficiency than 1stFe0/air–2ndFenton–3rdFe0/air due to the high reactivity Fe/Cu bimetallic particles. Therefore, the developed method in this study is a promising process for treatment of DDNP industry wastewater. Finally, the analysis results of UV-vis and FTIR reveal that the main groups (e.g., benzene ring, nitro and azo groups) of the pollutants could be decomposed effectively after 4.5 h treatment by 1stFe/Cu/air–2ndFenton–3rdFe/Cu/air. The results also further confirm the superiority of 1stFe/Cu/air–2ndFenton–3rdFe/Cu/air and the synergistic reaction between Fe/Cu/air and Fenton process. Thus, it is a promising technology for the treatment of ultra-high concentrated DDNP industry wastewater.

The effect of the preparation conditions on the physicochemical characteristics, operating life, and reactivity of Fe/Cu bimetallic particles was studied significantly by using a model pollutant (p-nitrophenol), scanning electron microscopy–energy dispersive spectrometry, and X-ray diffraction spectrometry. The results suggest that the higher reactivity and longer operating life of Fe/Cu bimetallic particles were obtained under the optimal preparation conditions. Furthermore, under the optimal preparation conditions, Cu was not easily dropped from the Fe0 particle, and the weight ratio of Cu on the surface of the Fe/Cu bimetallic particles increased significantly. Moreover, their optimal theoretical Cu mass loading could be decreased from 0.89 to 0.41 g Cu/g Fe, which favors the reduction of production costs. In addition, two batch experiments with Fe/Cu bimetallic particles prepared under optimal and nonoptimal conditions were set up to comparatively investigate the improvement of operating life and reactivity of Fe/Cu particles when optimized preparation conditions were carried out. As a result, it was proven that the reactivity and operating life of Fe/Cu bimetallic particles could be improved significantly through the optimization of preparation conditions.