Ping Yang

Removal of high concentration p-nitrophenol in aqueous solution by zero valent iron with ultrasonic irradiation (US-ZVI)

In this study, the US-ZVI system was used to produce the strong reductants including H and nascent Fe(2+) ions to eliminate the toxicity of the high concentration p-nitrophenol (PNP) wastewater. The effect of the reactor structure, initial pH, ZVI dosage, ultrasonic power and initial PNP concentration on the removal efficiency of PNP from water was investigated intensively. The results show that a higher removal rate can be obtained by using a conical structure reactor, and the lower initial pH can aid the acceleration of PNP removal rate by using US-ZVI system. Furthermore, the removal efficiencies of PNP increased obviously with the increase of initial ZVI concentration from 0 to 15 gL(-1). Also, the treatment capacity of ZVI was enhanced remarkably by the ultrasonic irradiation, and the US-ZVI system can maintain high treatment efficiency for the high concentration PNP wastewater (500-10,000 mgL(-1)). Meanwhile, the high removal efficiency of PNP was mainly resulted from the synergistic reaction of ZVI and US. At last, the main degradation product (i.e., p-aminophenol) was detected by gas chromatography-mass spectrum (GC-MS). Thus, the reaction pathway of PNP in the US-ZVI system is proposed as a reducing process by the H and nascent Fe(2+) ions.

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.

Comprehensive analysis of the toxic and refractory pollutants in acrylonitrile-butadiene-styrene resin manufacturing wastewater by gas chromatography spectrometry with a mass or flame ionization detector

Acrylonitrile-butadiene-styrene (ABS) resin manufacturing wastewater is a complicated, toxic and refractory industrial wastewater. Comprehensive and accurate analysis of the typical pollutants in ABS resin manufacturing wastewater is critical to develop cost-effective wastewater treatment technologies. In this paper, a comprehensively qualitative analysis combined with three complementary methods has been developed for the detection of typical pollutants in ABS resin manufacturing wastewater from three production sections, and thirty-seven compounds had been detected and further confirmed by this analysis method with standards. Simultaneous chromatographic separation and quantification of seven representative pollutants, including three mononuclear aromatics, three acrylonitrile dimers and one acrylonitrile derivative, were achieved by GC-FID system. The detection limits of this method for seven representative pollutants were in the range of 0.007-0.89 mg/L. The within-day and between-day precisions of this method were less than 6.5% (RSD, n=6). The recoveries of the representative pollutants reached 90-120%. The ABS resin manufacturing wastewater from E zone was successfully determined by this method, with two mononuclear aromatics and three acrylonitrile dimers accounting for 57.73% and 40.63% of the selected seven compounds, respectively. These results reveal that the removal of mononuclear aromatics and acrylonitrile dimers is a key to treat this wastewater.

Removal of FePO4 and Fe3(PO4)2 crystals on the surface of passive fillers in Fe0/GAC reactor using the acclimated bacteria

As past studies presented, there is obvious defect that the fillers in the Fe(0)/GAC reactor begin to be passive after about 60 d continuous running, although the complicated, toxic and refractory ABS resin wastewater can be pretreated efficiently by the Fe(0)/GAC reactor. During the process, the Fe(3)(PO(4))(2) and FePO(4) crystals with high density in the passive film are formed by the reaction between PO(4)(3-) and Fe(2+)/Fe(3+). Meanwhile, they obstruct the formation of macroscopic galvanic cells between Fe(0) and GAC, which will lower the wastewater treatment efficiency of Fe(0)/GAC reactor. In this study, in order to remove the Fe(3)(PO(4))(2) and FePO(4) crystals on the surface of the passive fillers, the bacteria were acclimated in the passive Fe(0)/GAC reactor. According to the results, it can be concluded that the Fe(3)(PO(4))(2) and FePO(4) crystals with high density in the passive film could be decomposed or removed by the joint action between the typical propionic acid type fermentation bacteria and sulfate reducing bacteria (SRB), whereas the PO(4)(3-) ions from the decomposition of the Fe(3)(PO(4))(2) and FePO(4) crystals were released into aqueous solution which would be discharged from the passive Fe(0)/GAC reactor. Furthermore, the remained FeS and sulfur (S) in the passive film also can be decomposed or removed easily by the oxidation of the sulfur-oxidizing bacteria. This study provides some theoretical references for the further study of a cost-effective bio-regeneration technology to solve the passive problems of the fillers in the zero-valent iron (ZVI) or Fe(0)/GAC reactor.

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.

Treatment of ultra-high concentration 2-diazo-4,6-dinitrophenol (DDNP) industry wastewater by the combined Fe/Cu/air and Fenton process

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.

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.

Effect of C/N ratio and aeration rate on performance of internal cycle MBR with synthetic wastewater

AbstractEffect of C/N ratio and aeration rate on performance of continuously operated internal circulation membrane bioreactor (ICMBR) was investigated thoroughly using synthetic domestic wastewater. The results show that COD and total nitrogen (TN) removal efficiencies were improved with the increase of C/N ratio under certain conditions (T = 25 °C, MLSS = 10 g/L, aeration rate was 0.15 m3/h, influent NH3-N concentration was 20 mg/L, influent -N concentration was 100 mg/L, and HRT = 12 h). Meanwhile, a steady ammonia nitrogen (AN) removal rate (~80%) was obtained when C/N ratio increased from 2:1 to 6:1. Furthermore, when C/N ratio was 6:1 and aeration rate was 0.15 m3/h, average removal rates of COD, AN, and TN reached 98.5, 97.4, and 52.6%, respectively. Additionally, the improvement in activity of denitrifying bacteria could increase TN removal rate at a lower aeration rate. Under the optimal operation parameters (C/N ratio of 6:1 and aeration rate of 0.05 m3/h), the high average removal efficiencies ...

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.

Pretreatment of ultra-high concentrated wastewater from phthalonitrile resin manufacturing by chemical precipitation, reduction and oxidation.

To remove the toxic and refractory pollutants in the phthalonitrile resin wastewater and improve its biodegradability, a combined process (i.e., CaCl2+AA+Fe/Cu/air) was developed to pretreat this wastewater obtained from a phthalonitrile resin manufacturing plant in southwestern China. First, CO3(2-) was precipitated and removed by adding CaCl2. Furthermore, its ultra-high concentrated NO2(-) (22.7±0.1 g/L) was reduced into N2 by adding amidosulphonic acid (AA). Meanwhile, two control experiments were setup to confirm the superiority of the combined process (i.e., CaCl2+AA). Subsequently, the wastewater was further treated by Fe/Cu/air process after the removal of CO3(2-) and NO2(-). The results suggest that the developed method not only could effectively remove the ultra-high concentrated CO3(2-) (>99%) and NO2(-) (>99%), but also could obtain high COD (58.8%) and colority (95.2%) removal efficiencies. Meanwhile, B/C ratio of this wastewater increased from 0.19 to 0.45, which suggests the biodegradability also was improved significantly. Finally, the high treatment efficiency was mainly attributed to the synergistic effects of CaCl2, AA and Fe/Cu/air. Therefore, the combined process is a promising pretreatment process for the ultra-high concentrated wastewater from phthalonitrile resin manufacturing.