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Frontiers of Environmental Science & Engineering

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ISSN 2095-2201 (Print)
ISSN 2095-221X (Online)
CN 10-1013/X
Postal Subscription Code 80-973
Formerly Known as Frontiers of Environmental Science & Engineering in China
2019 Impact Factor: 4.053

, Volume 10 Issue 3

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Chemical poison and regeneration of SCR catalysts for NOx removal from stationary sources
Junhua LI,Yue PENG,Huazhen CHANG,Xiang LI,John C. CRITTENDEN,Jiming HAO
Front. Environ. Sci. Eng.. 2016, 10 (3): 413 -427 .
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Selective catalytic reduction (SCR) of NOx with NH3 is an effective technique to remove NOx from stationary sources, such as coal-fired power plant and industrial boilers. Some of elements in the fly ash deactivate the catalyst due to strong chemisorptions on the active sites. The poisons may act by simply blocking active sites or alter the adsorption behaviors of reactants and products by an electronic interaction. This review is mainly focused on the chemical poisoning on V2O5-based catalysts, environmental-benign catalysts and low temperature catalysts. Several common poisons including alkali/alkaline earth metals, SO2 and heavy metals etc. are referred and their poisoning mechanisms on catalysts are discussed. The regeneration methods of poisoned catalysts and the development of poison-resistance catalysts are also compared and analyzed. Finally, future research directions in developing poisoning resistance catalysts and facile efficient regeneration methods for SCR catalysts are proposed.

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A photolysis coefficient for characterizing the response of aqueous constituents to photolysis
Front. Environ. Sci. Eng.. 2016, 10 (3): 428 -437 .
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UV photolysis and UV based advanced oxidation processes (AOPs) are gaining more and more attention for drinking water treatment. Quantum yield (?) and molar absorption coefficient (?) are the two critical parameters measuring the effectiveness of photolysis of a compound. The product of the two was proposed as a fundamental measure of a constituent’s amenability to transformation by photolysis. It was shown that this product, named the photolysis coefficient, kp, can be determined using standard bench tests and captures the properties that govern a constituent’s transformation when exposed to light. The development showed the photolysis coefficient to be equally useful for microbiological, inorganic and organic constituents. Values of kp calculated by the authors based on quantum yield and molar absorption coefficient data from the literature were summarized. Photolysis coefficients among microorganisms ranged from 8500 to more than 600000 and are far higher than for inorganic and organic compounds, which varied over a range of approximately 10 to 1000 and are much less sensitive to UV photolysis than the microorganisms.

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Degradation of carbon tetrachloride in thermally activated persulfate system in the presence of formic acid
Minhui XU,Xiaogang GU,Shuguang LU,Zhouwei MIAO,Xueke ZANG,Xiaoliang WU,Zhaofu QIU,Qian SUI
Front. Environ. Sci. Eng.. 2016, 10 (3): 438 -446 .
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The thermally activated persulfate (PS) degradation of carbon tetrachloride (CT) in the presence of formic acid (FA) was investigated. The results indicated that CT degradation followed a zero order kinetic model, and CO2-· was responsible for the degradation of CT confirmed by radical scavenger tests. CT degradation rate increased with increasing PS or FA dosage, and the initial CT had no effect on CT degradation rate. However, the initial solution pH had effect on the degradation of CT, and the best CT degradation occurred at initial pH 6. Cl- had a negative effect on CT degradation, and high concentration of Cl- displayed much strong inhibition. Ten mmol·L-1HCO3- promoted CT degradation, while 100 mmol·L-1NO3- inhibited the degradation of CT, but SO42- promoted CT degradation in the presence of FA. The measured Cl- concentration released into solution along with CT degradation was 75.8% of the total theoretical dechlorination yield, but no chlorinated intermediates were detected. The split of C-Cl was proposed as the possible reaction pathways in CT degradation. In conclusion, this study strongly demonstrated that the thermally activated PS system in the presence of FA is a promising technique in in situ chemical oxidation (ISCO) remediation for CT contaminated site.

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Catalytic activities and mechanism of formaldehyde oxidation over gold supported on MnO2 microsphere catalysts at room temperature
Guanglong PANG,Donghui WANG,Yunhong ZHANG,Chunyan MA,Zhengping HAO
Front. Environ. Sci. Eng.. 2016, 10 (3): 447 -457 .
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MnO2 microspheres with various surface structures were prepared using the hydrothermal method, and Au/MnO2 catalysts were synthesized using the sol-gel method. We obtained three MnO2 microspheres and Au/MnO2 samples: coherent solid spheres covered with wire-like nanostructures, solid spheres with nanosheets, and hierarchical hollow microspheres with nanoplatelets and nanorods. We investigated the properties and catalytic activities of formaldehyde oxidation at room temperature. Crystalline structures of MnO2 are the main factor affecting the catalytic activities of these samples, and γ-MnO2 shows high catalytic performance. The excellent redox properties are responsible for the catalytic ability of γ-MnO2. The gold-supported interaction can change the redox properties of catalysts and accelerate surface oxygen species transition, which can account for the catalytic activity enhancement of Au/MnO2. We also studied intermediate species. The dioxymethylene (DOM) and formate species formed on the catalyst surface were considered intermediates, and were ultimately transformed into hydrocarbonate and carbonate and then decomposed into CO2. A proposed mechanism of formaldehyde oxidation over Au/MnO2 catalysts was also obtained.

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Enhanced performances in catalytic oxidation of o-xylene over hierarchical macro-/mesoporous silica-supported palladium catalysts
Nanli QIAO,Xin ZHANG,Chi HE,Yang LI,Zhongshen ZHANG,Jie CHENG,Zhengping HAO
Front. Environ. Sci. Eng.. 2016, 10 (3): 458 -466 .
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A series of hierarchical macro-/mesoporous silica supports (MMSs) were successfully synthesized using dual-templating technique employing polystyrene (PS) spheres and the Pluronic P123 surfactant. Pd was next loaded on the hierarchical silica supports via colloids precipitation method. Physicochemical properties of the synthesized samples were characterized by various techniques and all catalysts were tested for the total oxidation of o-xylene. Among them, the Pd/MMS-b catalyst with tetraethoxysilane/polystyrene weight ratio of 1.0 exhibited superior catalytic activity, and under a higher gas hourly space velocity (GHSV) of 70000 h-1, the 90% conversion of o-xylene has been obtained at around 200°C. The BET and SEM results indicated that Pd/MMS-b catalyst possesses high surface area and large pore volume, and well-ordered, interconnected macropores and 2D hexagonally mesopores hybrid network. This novel ordered hierarchical porous structure was highly beneficial to the dispersion of active sites Pd nanoparticles with less aggregation, and facilitates diffusion of reactants and products. Furthermore, the Pd/MMS-b catalyst possessed good stability and durability.

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Utilization of aluminum hydroxide waste generated in fluoride adsorption and coagulation processes for adsorptive removal of cadmium ion
Jiawei JU,Ruiping LIU,Zan HE,Huijuan LIU,Xiwang ZHANG,Jiuhui QU
Front. Environ. Sci. Eng.. 2016, 10 (3): 467 -476 .
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Although Al-based coagulation and adsorption processes have been proved highly efficient for fluoride (F) removal, the two processes both generate large amount of Al(OH)3 solid waste containing F (Al(OH)3-F). This study aimed to investigate the feasibility of utilizing Al(OH)3-F generated in Al(OH)3 adsorption (Al(OH)3-Fads) and coagulation (Al(OH)3-Fcoag) for the adsorption of cadmium ion (Cd(II)). The adsorption capacity of Al(OH)3-Fads and Al(OH)3-Fcoag for Cd(II) was similar as that of pristine aluminum hydroxide (Al(OH)3), being of 24.39 and 19.90 mg·g-1, respectively. The adsorption of Cd(II) onto Al(OH)3-Fads and Al(OH)3-Fcoag was identified to be dominated by ion-exchange with sodium ion (Na+) or hydrogen ion (H+), surface microprecitation, and electrostatic attraction. The maximum concentration of the leached fluoride from Al(OH)3-Fads and Al(OH)3-Fcoag is below the Chinese Class-I Industrial Wastewater Discharge Standard for fluoride (<10 mg·L-1). This study demonstrates that the Al(OH)3 solid wastes generated in fluoride removal process could be potentially utilized as a adsorbent for Cd(II) removal.

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Trace analysis of off-flavor/odor compounds in water using liquid-liquid microextraction coupled with gas chromatography—positive chemical ionization-tandem mass spectrometry
Front. Environ. Sci. Eng.. 2016, 10 (3): 477 -481 .
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A rapid, inexpensive and laboratory friendly method was developed for analysis of off-flavor/odor compounds in fresh and salt water using gas chromatography with chemical ionization-tandem mass spectrometry. Off-flavor/odor compounds included geosmin, 2-methylisoborneol (MIB), 2-isobutyl-3-methyoxypyrazine (IBMP), and 2-isopropyl-3-methoxypyrazine (IPMP). Using this method, a single sample can be extracted within minutes using only 1 mL of organic solvent. The ion transitions for IPMP, IBMP, MIB, and geosmin were 153>121, 167>125, 152>95, and 165>109, respectively. The linearity of this method for analyzing MIB ranged from 4 to 200 ng·L-1, and from 0.8 to 200 ng·L-1 for the other analytes. Method recoveries ranged from 97% to 111% and percent relative standard deviations ranged from 3% to 9%, indicating that the method is accurate, precise, and reliable.

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The prediction of adsorption isotherms of ester vapors on hypercrosslinked polymeric adsorbent
Liuyan WU,Lijuan JIA,Xiaohan LIU,Chao LONG
Front. Environ. Sci. Eng.. 2016, 10 (3): 482 -490 .
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Adsorption isotherms of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate and ethyl propionate on hypercrosslinked polymeric resin (ND-100) were measured at 303K, 318K and 333K,respectively, and well fitted by Dubinin–Astakhov (DA) equation. The plots of the adsorbed volume (qv) versus the adsorption potential (?) at three different temperatures all fell basically onto one single curve for every ester. A predicted model based on DA equation was obtained on the basis of adsorption equilibrium data of methyl acetate, ethyl acetate and ethyl propionate at 318K. The model equation successfully predicted the adsorption isotherms of methyl acetate, ethyl acetate and ethyl propionate on ND-100 at 303K, and 333K, and also gave accurate predictive results for adsorption isotherms of the other two ester compounds (propyl acetate and isopropyl acetate) on ND-100 at 303K, 318K and 333K. The results proved the effectiveness of DA model for predicting the adsorption isotherms of ester compounds onto ND-100. In addition, the relationship between physico-chemical properties of adsorbates and their adsorption properties was also investigated. The results showed that molecular weight, molar volume and molar polarizability had good linear correlations with the parameter E (which represents adsorption characteristic energy) of DA equation.

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Fate and removal of typical pharmaceutical and personal care products in a wastewater treatment plant from Beijing: a mass balance study
Jie GAO,Jun HUANG,Weiwei CHEN,Bin WANG,Yujue WANG,Shubo DENG,Gang YU
Front. Environ. Sci. Eng.. 2016, 10 (3): 491 -501 .
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The fate and removal of pharmaceuticals and personal care products (PPCPs) in wastewater treatment plants (WWTPs) has received great attention during the last decade. Numerous data concerning concentrations in the water phase can be found in the literature, however corresponding data from sludge as well as associated mass balance calculations are very limited. In the present study, the adsorbed and dissolved concentrations of 9 PPCPs were investigated in each unit of a WWTP in Beijing, China. Based on the calculation of mass balance, the relative mass distribution and removal efficiency of each target compound was obtained at each process. The amount of PPCPs entering into the WWTP ranged from 12 g·d-1 to 3848 g·d-1. Five target compounds (caffeine, chloramphenicol, bezafibrate, clofibric acid, and N,N-diethyl-meta-toluamide) were effectively removed, with rates of 57%–100%. Negative removal efficiencies were obtained for sulpiride, metoprolol, nalidixic acid, and carbamazepine, ranging from -19% to -79%. PPCPs mainly existed in dissolved form (≥92%) in both the raw influent and the final effluent. The sludge cake carried a much lower amount of PPCPs (17 g·d-1) compared with the discharged effluent (402 g·d-1). In A2/O treatment tanks, the anaerobic and anoxic tanks showed good performance for PPCPs removal, and the amount of adsorbed PPCPs was increased. The results reveal that both the dissolved and the adsorbed phases should be considered when assessing the removal capacity of each A2/O tank.

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Enhanced degradation of trichloroethene by calcium peroxide activated with Fe(III) in the presence of citric acid
Xiang ZHANG,Xiaogang GU,Shuguang LU,Zhouwei MIAO,Minhui XU,Xiaori FU,Muhammad DANISH,Mark L. BRUSSEAU,Zhaofu QIU,Qian SUI
Front. Environ. Sci. Eng.. 2016, 10 (3): 502 -512 .
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Trichloroethene (TCE) degradation by Fe(III)-activated calcium peroxide (CP) in the presence of citric acid (CA) in aqueous solution was investigated. The results demonstrated that the presence of CA enhanced TCE degradation significantly by increasing the concentration of soluble Fe(III) and promoting H2O2 generation. The generation of HO? and O2-? in both the CP/Fe(III) and CP/Fe(III)/CA systems was confirmed with chemical probes. The results of radical scavenging tests showed that TCE degradation was due predominantly to direct oxidation by HO?, while O2-? strengthened the generation of HO? by promoting Fe(III) transformation in the CP/Fe(III)/CA system. Acidic pH conditions were favorable for TCE degradation, and the TCE degradation rate decreased with increasing pH. The presence of Cl-, HCO3-, and humic acid (HA) inhibited TCE degradation to different extents for the CP/Fe(III)/CA system. Analysis of Cl- production suggested that TCE degradation in the CP/Fe(III)/CA system occurred through a dechlorination process. In summary, this study provided detailed information for the application of CA-enhanced Fe(III)-activated calcium peroxide for treating TCE contaminated groundwater.

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Vacuum promotes metabolic shifts and increases biogenic hydrogen production in dark fermentation systems
Haifa RAJHI,Daniel PUYOL,Mirna C. MARTÍNEZ,Emiliano E. DÍAZ,José L. SANZ
Front. Environ. Sci. Eng.. 2016, 10 (3): 513 -521 .
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The successful operation of any type of hydrogen-producing bioreactor depends on the performance of the microorganisms present in the system. Both substrate and partial gas pressures are crucial factors affecting dark fermentation metabolic pathways. The main objective of this study was to evaluate the impact of both factors on hydrogen production using anaerobic granular sludge as inoculum and, secondly, to study the metabolic shifts of an anaerobic community subjected to low partial gas pressures. With this goal in mind, seven different wastewater (four synthetic media, two industrial wastewater, and one domestic effluent) and the effect of applying vacuum on the systems were analyzed. The application of vacuum promoted an increase in the diversity of hydrogen-producing bacteria, such as Clostridium, and promoted the dominance of acetoclastic- over hydrogenotrophic methanogens. The application of different media promoted a wide variety of metabolic pathways. Nevertheless, reduction of the hydrogen partial pressure by application of vacuum lead to further oxidation of reaction intermediates irrespective of the medium used, which resulted in higher hydrogen and methane production, and improved the COD removal. Interestingly, vacuum greatly promoted biogenic hydrogen production from a real wastewater, which opens possibilities for future application of dark fermentation systems to enhance biohydrogen yields.

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Effect of ultraviolet irradiation and chlorination on ampicillin-resistant Escherichia coli and its ampicillin resistance gene
Yuchen PANG,Jingjing HUANG,Jinying XI,Hongying HU,Yun ZHU
Front. Environ. Sci. Eng.. 2016, 10 (3): 522 -530 .
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Antibiotic resistance is a serious public health risk that may spread via potable and reclaimed water. Effective disinfection is important for inactivation of antibiotic-resistant bacteria and disruption of antibiotic resistance genes. Ampicillin is a widely prescribed antibiotic but its effectiveness is increasingly undermined by resistance. In this study, changes in ampicillin resistance for Escherichia coli (E. coli) CGMCC 1.1595 were analyzed after exposure to different doses of ultraviolet (UV) or chlorine, and damage incurred by the plasmid encoding ampicillin resistance gene blaTEM-1 was assessed. We reported a greater stability in ampicillin-resistant E. coli CGMCC 1.1595 after UV irradiation or chlorination when compared with previously published data for other E. coli strains. UV irradiation and chlorination led to a shift in the mortality frequency distributions of ampicillin-resistant E. coli when subsequently exposed to ampicillin. The ampicillin hemi-inhibitory concentration (IC50) without disinfection was 3800 mg·L-1, and an increment was observed after UV irradiation or chlorination. The IC50 of ampicillin-resistant E. coli was 1.5-fold higher at a UV dose of 40 mJ·cm-2, and was 1.4-fold higher when exposed to 2.0 mg·L-1 chlorine. These results indicate that UV irradiation and chlorination can potentially increase the risk of selection for E. coli strains with high ampicillin resistance. There was no evident damage to blaTEM-1 after 1–10 mg Cl2·L-1 chlorination, while a UV dose of 80 mJ·cm-2 yielded a damage ratio for blaTEM-1 of approximately 1.2-log. Therefore, high UV doses are required for effective disruption of antibiotic resistance genes in bacteria.

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Mechanisms behind the accelerated extracellular electron transfer in Geobacter sulfurreducens DL-1 by modifying gold electrode with self-assembled monolayers
Feng ZHANG,Shengsong YU,Jie LI,Wenwei LI,Hanqing YU
Front. Environ. Sci. Eng.. 2016, 10 (3): 531 -538 .
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Modification of electrode surface with carboxylic acid terminated alkanethiol self-assembled monolayers (SAMs) has been found to be an effective approach to improve the extracellular electron transfer (EET) of electrochemically active bacteria (EAB) on electrode surface, but the underlying mechanism behind such enhanced EET remains unclear. In this work, the gold electrodes modified by mercapto-acetic acid and mercapto-ethylamine (Au-COOH, Au-NH2) were used as anodes in microbial electrolysis cells (MECs) inoculated with Geobacter sulfurreducens DL-1, and their electrochemical performance and the bacteria-electrode interactions were investigated. Results showed that the Fe(CN)63-/4- redox reaction occurred on the Au-NH2 with a higher rate and a lower resistance than that on the Au or the Au-COOH. Both the MECs with the Au-COOH and Au-NH2 anodes exhibited a higher current density than that with a bare Au anode. The biofilm formed on the Au-COOH was denser than that on bare Au, while the biofilm on the Au-NH2 had a greater thickness, suggesting a critical role of direct EET in this system. This work suggests that functional groups such as –COOH and-NH2 could promote electrode performance by accelerating the direct EET of EAB on electrode surface.

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Changes of microbial composition during wastewater reclamation and distribution systems revealed by high-throughput sequencing analyses
Yiwen LIN,Dan LI,Siyu ZENG,Miao HE
Front. Environ. Sci. Eng.. 2016, 10 (3): 539 -547 .
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This study employed 454-pyrosequencing to investigate microbial and pathogenic communities in two wastewater reclamation and distribution systems. A total of 11972 effective 16S rRNA sequences were acquired from these two reclamation systems, and then designated to relevant taxonomic ranks by using RDP classifier. The Chao index and Shannon diversity index showed that the diversities of microbial communities decreased along wastewater reclamation processes. Proteobacteria was the most dominant phylum in reclaimed water after disinfection, which accounted for 83% and 88% in two systems, respectively. Human opportunistic pathogens, including Clostridium, Escherichia, Shigella, Pseudomonas and Mycobacterium, were selected and enriched by disinfection processes. The total chlorine and nutrients (TOC, NH3-N and NO3-N) significantly affected the microbial and pathogenic communities during reclaimed water storage and distribution processes. Our results indicated that the disinfectant-resistant pathogens should be controlled in reclaimed water, since the increases in relative abundances of pathogenic bacteria after disinfection implicate the potential public health associated with reclaimed water.

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Selection and characterization of eight freshwater green algae strains for synchronous water purification and lipid production
Jingjing ZHAN,Qiao ZHANG,Momei QIN,Yu HONG
Front. Environ. Sci. Eng.. 2016, 10 (3): 548 -558 .
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The objective of this study is to select and characterize the candidate for synchronous water purification and lipid production from eight freshwater microalgae strains (Chlorella sp. HQ, C. emersonii, C. pyrenoidosa, C. vulgaris, Scenedesmus dimorphus, S. quadricauda, S. obiquus, Scenedesmus sp. LX1). The strains Chlorella sp. HQ, C. pyrenoidesa, and S. obliquus showed superiority in biomass accumulation, while the top biomass producers did not correspond to the top lipid producers. S. quadricauda achieved higher lipid content (66.1%), and Chlorella sp. HQ and S. dimorphus ranked down in sequence, with lipid content above 30%. Considering nutrient removal ability (total nitrogen (TN): 52.97%; total phosphorus (TP): 84.81%), the newly isolated microalga Chlorella sp. HQ was the possible candidate for water purification coupled with lipid production. To further investigate the lipid producing and nutrient removal mechanism of candidate microalga, the ultra structural changes especially the lipid droplets under different water qualities (different TN and TP concentrations) were characterized. The results elucidate the nutrient-deficiency (TN: 3.0 mg·L-1; TP: 0.3 mg·L-1) condition was in favor of forming lipid bodies in Chlorella sp. HQ at the sub-cellular level, while the biomass production was inhibited due to the decrease in chloroplast number which could further suppress the nutrient removal effect. Finally, a two-phase cultivation process (a nutrient replete phase to produce biomass followed by a nutrient deplete phase to enhance lipid content) was conducted in a photo-bioreactor for Chlorella sp. HQ to serve for algae-based synchronous biodiesel production and wastewater purification.

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Chemical characteristics of fine particulate matter emitted from commercial cooking
Bing PEI,Hongyang CUI,Huan LIU,Naiqiang YAN
Front. Environ. Sci. Eng.. 2016, 10 (3): 559 -568 .
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The chemical characteristics of fine particulate matter (PM2.5) emitted from commercial cooking were explored in this study. Three typical commercial restaurants in Shanghai, i.e., a Shanghai-style one (SHS), a Sichuan-style one (SCS) and an Italian-style one (ITS), were selected to conduct PM2.5 sampling. Particulate organic matter (POM) was found to be the predominant contributor to cooking-related PM2.5 mass in all the tested restaurants, with a proportion of 69.1% to 77.1%. Specifically, 80 trace organic compounds were identified and quantified by gas chromatography/mass spectrometry (GC/MS), which accounted for 3.8%–6.5% of the total PM2.5 mass. Among the quantified organic compounds, unsaturated fatty acids had the highest concentration, followed by saturated fatty acids. Comparatively, the impacts of other kinds of organic compounds were much smaller. Oleic acid was the most abundant single species in both SCS and ITS. However, in the case of SHS, linoleic acid was the richest one. ITS produced a much larger mass fraction of most organic species in POM than the two Chinese cooking styles except for monosaccharide anhydrides and sterols. The results of this study could be utilized to explore the contribution of cooking emissions to PM2.5 pollution and to develop the emission inventory of PM2.5 from cooking, which could then help the policy-makers design efficient treatment measures and control strategies on cooking emissions in the future.

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Effects of carrier-attached biofilm on oxygen transfer efficiency in a moving bed biofilm reactor
Yanling WEI,Xunfei YIN,Lu QI,Hongchen WANG,Yiwei GONG,Yaqian LUO
Front. Environ. Sci. Eng.. 2016, 10 (3): 569 -577 .
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Three laboratory-scale moving bed biofilm reactors (MBBR) with different carrier filling ratios ranging from 40% to 60% were used to study the effects of carrier-attached biofilm on oxygen transfer efficiency. In this study, we evaluated the performance of three MBBRs in degrading chemical oxygen demand and ammonia. The three reactors removed more than 95% of NH4+-N at an air flow-rate of 60 L·h-1. The standard oxygen transfer efficiency (αSOTE) of the three reactors was also investigated at air flow-rates ranging from 60 to 100 L·h-1. These results were compared to αSOTE of wastewater with a clean carrier (no biofilm attached). Results showed that under these process conditions, αSOTE decreased by approximately 70% as compared to αSOTE of wastewater at a different carrier-filling ratio. This indicated that the biofilm attached to the carrier had a negative effect on αSOTE. Mechanism analysis showed that the main inhibiting effects were related to biofilm flocculants and soluble microbial product (SMP). Biofilm flocs could decrease αSOTE by about 20%, and SMP could decrease αSOTE by 30%–50%.

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Recovering humic substances from the dewatering effluent of thermally treated sludge and its performance as an organic fertilizer
Yuning YANG,Huan LI
Front. Environ. Sci. Eng.. 2016, 10 (3): 578 -584 .
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The biologic treatment of the dewatering effluent from thermally treated sludge is difficult due to the high concentration of refractory humic substances. On the other hand, humic substances are an important source of organic fertilizer. In this study, a novel process using ferric coagulant was developed to recover humic substances from dewatering effluent for use as an organic fertilizer. When ferric coagulant was applied to raw dewatering effluent, up to 70% of humic substances were enmeshed by hydrolyzed ferric ions at an optimum pH of 4.5. The proper mass ratio of iron ions to humic substances was 0.6. In the recovered material, humic substances accounted for 24.2% of the total dry solids, and the amount of phosphorus (equivalent phosphorus pentoxide) was 6.2%. Heavy metals and other components all met the legal requirements for organic fertilizer. When the recovered material was applied to soybeans, the germination and growth of the seeds was significantly improved.

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18 articles