Zeyu Guan

Degradation of refractory dibutyl phthalate by peroxymonosulfate activated with novel catalysts cobalt metal-organic frameworks: Mechanism, performance, and stability.

In this work, a new effective and relatively stable heterogeneous catalyst of Metal-Organic Framework Co3(BTC)2·12H2O (Co-BTC) has been synthesized and tested to activate peroxymonosulfate (PMS) for removal of refractory dibutyl phthalate (DBP). Co-BTC(A) and Co-BTC(B) were synthesized by different methods, which resulted in different activity towards PMS. The results indicated that Co-BTC(A) showed better performance on DBP degradation. The highest degradation rate of 100% was obtained within 30min. The initial pH showed respective level on DBP degradation with a rank of 5.0>2.75>9.0>7.0>11.0 in PMS/Co-BTC(A) system. No remarkable reduction of DBP was observed in the catalytic activity of Co-BTC(A) at 2nd run as demonstrated by recycling. However, the DBP degradation efficiency decreased by 8.26%, 10.9% and 25.6% in the 3rd, 4th, and 5th runs, respectively. The loss of active catalytic sites of Co(II) from Co-BTC(A) is responsible for the activity decay. Sulfate radicals (SO4(-)) and hydroxyl radicals (OH) were found at pH 2.75. Here, we propose the possible mechanism for activation of PMS by Co-BTC(A), which is involved in homogeneous and heterogeneous reactions in the solutions and the surface of Co-BTC(A), respectively.

Metal–organic frameworks MIL-88A with suitable synthesis conditions and optimal dosage for effective catalytic degradation of Orange G through persulfate activation

MIL-88A was synthesized in diverse preparation conditions and characterized by various techniques. The catalytic performance of MIL-88A series for degrading Orange gelb (OG) through persulfate activation were also tested at temperature of 25 °C and the results were shown in the following sequence: 85 °C/2 h > 65 °C/2 h > 105 °C/2 h > 65 °C/6 h > 65 °C/12 h. MIL-88A produced at the synthesis temperature of 85 °C and in the crystallization time of 2 h (85 °C/2 h) was the best one with a removal rate of 96.4% mainly due to high SBET and much greater leach-out of Fe. An optimal dosage (0.3 g L−1) for MIL-88A in the MIL-88A/PS/OG system exists because of inhibition and promotion by fumaric acid. The filtrate experiment indicated that the catalytic activation involved heterogeneous reactions on the surface of the catalyst and homogeneous reactions in solutions. But the heterogeneous reaction occupied the principal position and the probable mechanism was obtained. Moreover, only solution pH < 4 could show a high degradation effect without the help of temperature. Comparing two different methods in the recycling experiment, the removal rate of OG decreased after the fourth run in both. Loss of active catalytic sites for Fe(III) in MIL-88A in the process of separating and sampling was responsible for activity decay.

Synthesis of iron-based metal-organic framework MIL-53 as an efficient catalyst to activate persulfate for the degradation of Orange G in aqueous solution

A series of MIL-53(Fe) materials were synthesized using a solvothermal method under different temperature and time conditions and were used as catalysts to activate persulfate and degrade Orange G (OG). Influences of the above conditions on the crystal structure and catalytic behavior were investigated. Degradation of OG under different conditions was evaluated, and the possible activation mechanism was speculated. The results indicate that high synthesis temperature (larger than 170 °C) leads to poor crystallinity and low catalytic activity, while MIL-53(Fe) cannot fully develop at low temperature (100 or 120 °C). The extension of synthesis time from 5 h to 3 d can increase the crystallinity of the samples, but weakened the catalytic activity, which was caused by the reduction of BET surface area and the amount of Fe (II)-coordinative unsaturated sites. Among all the samples, MIL-53(Fe)-A possesses the best crystal structure and catalytic activity. In optimal conditions, OG can be totally decolorized after degradation for 90 min, and a removal rate of 74% for COD was attained after 120 min. The initial solution pH had great influence on OG degradation, with the greatest removal in acidic pH environment. ESR spectra showed that sulfate radical (SO4- ·), hydroxyl radical (OH·), persulfate radical (S2O8- ·), and superoxide radical (O2·) exist in this system under acidic conditions. Furthermore, with the increase of pH, the relative amount of O2· increases while that of OH· and SO4- · decreases, resulting in a reduced oxidizing capacity of the system.

Structure and Succession of Bacterial Communities of the Granular Sludge during the Initial Stage of the Simultaneous Denitrification and Methanogenesis Process

Batch experiment at COD/NO3−-N ratio of 8.0 was conducted to investigate the initial performance of the simultaneous denitrification and methanogenesis (SDM) process and corresponding granular sludge (SDMGS). The results showed a high level of inhibition of methanogenesis activity with nitrate addition, and the particle size, settling performance, and morphologies of the SDMGS were also different from conventional methanogenesis granular sludge. The structure and succession of bacterial communities of the granular sludge during the initial stage of the SDM process were determined using the high-throughput sequencing method. Sequence analysis indicated that diversity of bacterial communities was significantly decreased due to nitrate addition. Proteobacteria, Bacteroidetes, Firmicutes, and Spirochaetes were identified to be the dominant bacterial communities (96.06%) of the SDMGS samples, and microbes associated with anaerobic fermentation were reorganized. Alpha-, Beta- and Gamma-proteobacteria, and Bacteroides might be the sources of denitrificans. Lastly, species associated with animal and human infections, such as Enterobacteriaceae, Bacteroides, and other common human enteric pathogens, were found to be recovered during the initial stage. Short-term assessment of bacterial communities of the SDMGS would strengthen understandings of the effects of nitrate contamination in water bodies and provide vital guidance for operation of nitrate-containing wastewater treatment.

Lithium iron phosphate (LiFePO4) as an effective activator for degradation of organic dyes in water in the presence of persulfate

Lithium iron phosphate (LiFePO4) was prepared and applied in the heterogeneous activation of persulfate (PS) for Orange G (OG) degradation in water. Scanning electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to characterize the properties of the material before and after activation. The effects of several parameters on its catalytic activity were also investigated. It was found that the catalyst presented ultrafast activity for OG and other organic dye degradations. The results from XPS further suggested that the highly catalytic efficiency possibly involved the activation of PS to sulfate radicals as main radical meditated by the redox pair of Fe(II)/Fe(III) of LiFePO4/FePO4.

Application of Novel Amino-Functionalized NZVI@SiO2 Nanoparticles to Enhance Anaerobic Granular Sludge Removal of 2,4,6-Trichlorophenol.

A novel amino-functionalized silica-coated nanoscale zerovalent iron (NZVI@SiO2-NH2) was successfully synthesized by using one-step liquid-phase method with the surface functionalization of nanoscale zerovalent iron (NZVI) to enhance degradation of chlorinated organic contaminants from anaerobic microbial system. NZVI@SiO2-NH2 nanoparticles were synthesized under optimal conditions with the uniform core-shell structure (80–100 nm), high loading of amino functionality (~0.9 wt%), and relatively large specific surface area (126.3 m2/g). The result demonstrated that well-dispersed NZVI@SiO2-NH2 nanoparticle with nFe0-core and amino-functional silicon shell can effectively remove 2,4,6-trichlorophenol (2,4,6-TCP) in the neutral condition, much higher than that of NZVI. Besides, the surface-modified nanoparticles (NZVI@SiO2-NH2) in anaerobic granule sludge system also showed a positive effect to promote anaerobic biodechlorination system. More than 94.6% of 2,4,6-TCP was removed from the combined NZVI@SiO2-NH2-anaerobic granular sludge system during the anaerobic dechlorination processes. Moreover, adding the appropriate concentration of NZVI@SiO2-NH2 in anaerobic granular sludge treatment system can decrease the toxicity of 2,4,6-TCP to anaerobic microorganisms and improved the cumulative amount of methane production and electron transport system activity. The results from this study clearly demonstrated that the NZVI@SiO2-NH2/anaerobic granular sludge system could become an effective and promising technology for the removal of chlorophenols in industrial wastewater.

Modeling and multi-objective optimization for ANAMMOX process under COD disturbance using hybrid intelligent algorithm

Anaerobic ammonium oxidation (ANAMMOX) has been regarded as an efficient process to treat nitrogen-containing wastewater. However, the treatment process is not fully understood in terms of reaction mechanisms, process simulation, and control. In this paper, a multi-objective control strategy mixed soft-sensing model (MCSSM) is developed to systematically design the operating variations for multi-objective control by integrating the developed model, a least square support vector machine optimized with principal component analysis (PCA-LSSVM) and non-dominated sorting genetic algorithm-II (NSGA-II). The results revealed that the PCA-LSSVM model is a feasible and efficient tool for predicting the effluent ammonia nitrogen concentration (CNH4+−N,eff

An accuracy model for on-line prediction of effluent ammonia nitrogen in anammox treatment system based on pca-bp algorithm

{C}_{NH_4^{+}-N, eff}