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Featured researches published by Yifei Sun.


Waste Management | 2014

Effects of lipid concentration on anaerobic co-digestion of municipal biomass wastes.

Yifei Sun; Dian Wang; Jiao Yan; Wei Qiao; Wei Wang; Tianle Zhu

The influence of the lipid concentration on the anaerobic co-digestion of municipal biomass waste and waste-activated sludge was assessed by biochemical methane potential (BMP) tests and by bench-scale tests in a mesophilic semi-continuous stirred tank reactor. The effect of increasing the volatile solid (VS) concentration of lipid from 0% to 75% was investigated. BMP tests showed that lipids in municipal biomass waste could enhance the methane production. The results of bench-scale tests showed that a lipids concentration of 65% of total VS was the inhibition concentration. Methane yields increased with increasing lipid concentration when lipid concentrations were below 60%, but when lipid concentration was set as 65% or higher, methane yields decreased sharply. When lipid concentrations were below 60%, the pH values were in the optimum range for the growth of methanogenic bacteria and the ratios of volatile fatty acid (VFA)/alkalinity were in the range of 0.2-0.6. When lipid concentrations exceeded 65%, the pH values were below 5.2, the reactor was acidized and the values of VFA/alkalinity rose to 2.0. The amount of Brevibacterium decreased with increasing lipid content. Long chain fatty acids stacked on the methanogenic bacteria and blocked the mass transfer process, thereby inhibiting anaerobic digestion.


Chemosphere | 2011

Degradation of phenol in mists by a non-thermal plasma reactor.

Guijie An; Yifei Sun; Tianle Zhu; Xiao Yan

A link tooth wheel-cylinder non-thermal plasma reactor was set up to investigate the degradation of phenol in the mists. In addition, the decomposition efficiency of phenol, TOC removal, and byproduct formation were investigated. The stable discharge was achieved in both air and the mist condition. The decomposition efficiency and TOC removal increased with increasing the input power. For the input power of 3.6 W, the phenol decomposition and TOC removal reached 90% and 47%, respectively. Phenol degradation byproducts were identified as small molecular organic acids, including formic acid, acetic acid, and oxalic acid. Their masses in the trapped solutions first increased and then decreased slightly with increasing the input power. Therefore, the biodegradation capacity of the phenol degradation byproducts can be improved.


Journal of Hazardous Materials | 2013

Conversion of carbon disulfide in air by non-thermal plasma

Xiao Yan; Yifei Sun; Tianle Zhu; Xing Fan

Carbon disulfide (CS2), a typical odorous organic sulfur compound, has adverse effects on human health and is a potential threat to the environment. In the present study, CS2 conversion in air by non-thermal plasma (NTP) was systematically investigated using a link tooth wheel-cylinder plasma reactor energized by a DC power supply. The results show that corona discharge is effective in removing CS2. The CS2 conversion increases with the increase of specific input energy (SIE). Both short-living (e.g. O, OH radicals) and long-living species contribute to the CS2 conversion, but the short-living species play a more important role. Both gaseous and solid products are formed during the conversion of CS2. Gaseous products mainly include CO, CO2, OCS, SO2, SO3 and H2SO4. The yields of CO and CO2 increase, the yields of OCS and SO2 follow bell curves while the sum yield of SO3 and H2SO4 remains constant as SIE increases. The solid products, consisting of CO3(2-), SO4(2-) and possible polymeric sulfur, deposit on the inner wall and electrodes of the plasma reactor.


Chemosphere | 2014

Effects of gas compositions on NOx reduction by selective non-catalytic reduction with ammonia in a simulated cement precalciner atmosphere.

Weiyi Fan; Tianle Zhu; Yifei Sun; Dong Lv

The effects of gas compositions on NOx reduction and NH3 slip by selective non-catalytic reduction (SNCR) with NH3 were investigated in a simulated cement precalciner atmosphere. The results show that the presence of H2O improves NOx reduction and widens the reduction temperature window significantly. O2 is indispensable for reducing NOx. The optimum reduction temperature decreases and the temperature window widens to a lower temperature with the increase of O2 content. In addition, the increase of O2 content also results in a decrease of the maximum NOx reduction efficiency. The effect of SO2 on NOx reduction is negligible in the simulated precalciner atmosphere. To increase CO concentration makes NO reduction take place at relatively low temperatures. However, NH3 will tend to be oxidized into NO instead of reducing NO after entering the stream containing O2 at high temperatures if it is initially blended with a high concentration of CO in an oxygen-free environment. The increase of H2O, O2, SO2 or CO concentration is helpful to reduce NH3 slip in the temperature region below 900°C. These effects are resulted from the fact that the generation and consumption of O and OH radicals which are crucial to NO reduction and formation can be influenced by the four gas compositions. In industrial operation of SNCR for cement precalciner, these effects should be taken into account to increase NOx reduction efficiency and avoid NH3 slip.


Journal of Environmental Sciences-china | 2013

Anaerobic co-digestion of municipal biomass wastes and waste activated sludge: Dynamic model and material balances

Yifei Sun; Dian Wang; Wei Qiao; Wei Wang; Tianle Zhu

The organic matter degradation process during anaerobic co-digestion of municipal biomass waste (MBW) and waste-activated sludge (WAS) under different organic loading rates (OLRs) was investigated in bench-scale and pilot-scale semi-continuous stirred tank reactors. To better understand the degradation process of MBW and WAS co-digestion and provide theoretical guidance for engineering application, anaerobic digestion model No.1 was revised for the co-digestion of MBW and WAS. The results showed that the degradation of organic matter could be characterized into three different fractions, including readily hydrolyzable organics, easily degradable particulate organics, and recalcitrant particle organics. Hydrolysis was the rate-limiting step under lower OLRs, and methanogenesisis was the rate-limiting step for an OLR of 8.0 kg volatile solid (VS)/(m3 x day). The hydrolytic parameters of carbohydrate, protein, and lipids were 0.104, 0.083, and 0.084 kg chemical oxygen demand (COD)/(kg COD x hr), respectively, and the reaction rate parameters of lipid fermentation were 1 and 1.25 kg COD/(kg COD x hr) for OLRs of 4.0 and 6.0 kg VS/(m3 x day). A revised model was used to simulate methane yield, and the results fit well with the experimental data. Material balance data were acquired based on the revised model, which showed that 58.50% of total COD was converted to methane.


Chemosphere | 2010

Formation of chlorinated aromatics in model fly ashes using various copper compounds

Masaki Takaoka; Takashi Fujimori; Atsuhiro Shiono; Takashi Yamamoto; Nobuo Takeda; Kazuyuki Oshita; T. Uruga; Yifei Sun; Tsunehiro Tanaka

Various copper compounds found in fly ash are related to the formation of chlorinated aromatics. The formation potentials of chlorinated aromatics in different model fly ashes containing various copper compounds and the chemical behavior of such copper compounds were investigated. In model fly ash with copper metal, hydroxide, carbonate, or oxides, the generated amounts of chlorobenzene (CBz) and polychlorinated biphenyls (PCBs) and the average chlorination numbers were low and at the same level, respectively. The maximum generated amounts of chlorinated aromatics were observed at 300 degrees C. Although X-ray absorption near edge structure (XANES) spectra indicated that the chemical form of copper compounds changed little, they were found to promote the formation of chlorinated aromatics. Therefore, these copper compounds play the same role as CuO. On the other hand, in model fly ash with copper chloride, the generated amounts of CBz and PCBs were quite high and the average chlorination numbers was high. Dynamic changes were observed in XANES spectra, and the pre-edge peak attributed to monovalent copper compounds appeared at around 300 degrees C. A large difference was observed between these two groups in the amount of CuCl generated and the homologs of chlorinated aromatics present, indicating that CuCl played an important role in the formation of chlorinated aromatics.


Chemosphere | 2015

Dechlorination of polychlorinated biphenyls by iron and its oxides

Yifei Sun; Xiaoyuan Liu; Masashi Kainuma; Wei Wang; Masaki Takaoka; Nobuo Takeda

The decomposition efficiency of polychlorinated biphenyls (PCBs) was determined using elemental iron (Fe) and three iron (hydr)oxides, i.e., α-Fe2O3, Fe3O4, and α-FeOOH, as catalysts. The experiments were performed using four distinct PCB congeners (PCB-209, PCB-153, and the coplanar PCB-167 and PCB-77) at temperatures ranging from 180 °C to 380 °C and under an inert, oxidizing or reducing atmosphere composed of N2, N2+O2, or N2+H2. From these three options N2 showed to provide the best reaction atmosphere. Among the iron compounds tested, Fe3O4 showed the highest activity for decomposing PCBs. The decomposition efficiencies of PCB-209, PCB-167, PCB-153, and PCB-77 by Fe3O4 in an N2 atmosphere at 230 °C were 88.5%, 82.5%, 69.9%, and 66.4%, respectively. Other inorganic chlorine (Cl) products which were measured by the amount of inorganic Cl ions represented 82.5% and 76.1% of the reaction products, showing that ring cleavage of PCBs was the main elimination process. Moreover, the dechlorination did not require a particular hydrogen donor. We used X-ray photoelectron spectroscopy to analyze the elemental distribution at the catalysts surface. The O/Fe ratio influenced upon the decomposition efficiency of PCBs: the lower this ratio, the higher the decomposition efficiency. X-ray absorption near edge structure spectra showed that α-Fe2O3 effectively worked as a catalyst, while Fe3O4 and α-FeOOH were consumed as reactants, as their final state is different from their initial state. Finally, a decomposition pathway was postulated in which the Cl atoms in ortho-positions were more difficult to eliminate than those in the para- or meta-positions.


Journal of Hazardous Materials | 2016

Mechanism of unintentionally produced persistent organic pollutant formation in iron ore sintering.

Yifei Sun; Lina Liu; Xin Fu; Tianle Zhu; Alfons G. Buekens; Xiaoyi Yang; Qiang Wang

Effects of temperature, carbon content and copper additive on formation of chlorobenzenes (CBzs) and polychlorinated biphenyls (PCBs) in iron ore sintering were investigated. By heating simulated fly ash (SFA) at a temperature range of 250-500°C, the yield of both CBzs and PCBs presented two peaks of 637ng/g-fly ash at 350°C and 1.5×10(5)ng/g-fly ash at 450°C for CBzs, and 74ng/g-fly ash at 300°C and 53ng/g-fly ash at 500°C. Additionally, in the thermal treatment of real fly ash (RFA), yield of PCBs displayed two peak values at 350°C and 500°C, however, yield of CBzs showed only one peak at 400°C. In the thermal treatment of SFA with a carbon content range of 0-20wt% at 300°C, both CBzs and PCBs obtained the maximum productions of 883ng/g-fly ash for CBzs and 127ng/g-fly ash for PCBs at a 5wt% carbon content. Copper additives also affected chlorinated aromatic formation. The catalytic activity of different copper additives followed the orders: CuCl2∙2H2O>>Cu2O>Cu>CuSO4>CuO for CBzs, and CuCl2∙2H2O>>Cu2O>CuO>Cu>CuSO4 for PCBs.


Chemosphere | 2013

Thermal degradation of hexachlorobenzene in the presence of calcium oxide at 340–400 °C

Keqing Yin; Xingbao Gao; Yifei Sun; Lei Zheng; Wei Wang

Hexachlorobenzene (HCB) in the milligram range was co-heated with calcium oxide (CaO) powder in sealed glass ampoules at 340-400 °C. The heated samples were characterized and analyzed by Raman spectroscopy, elemental analysis, gas chromatography/mass spectrometry, ion chromatography, and thermal/optical carbon analysis. The degradation products of HCB were studied at different temperatures and heated times. The amorphous carbon was firstly quantitatively evaluated and was thought to be important fate of the C element of HCB. The yield of amorphous carbon in products increased with heating time, for samples treated for 8h at 340, 380 °C and 400 °C, the value were 17.5%, 34.8% and 50.2%, respectively. After identification of the dechlorination products, the HCB degradation on CaO at 340-400 °C was supposed to through dechlorination/polymerization pathway, which is induced by electron transfer, generate chloride ions and form high-molecular weight intermediates with significant levels of both hydrogen and chlorine, and finally form amorphous carbon. Higher temperature was beneficial for the dechlorination/polymerization efficiency. The results are helpful for clarifying the reaction mechanism for thermal degradation of chlorinated aromatics in alkaline matrices.


Water Science and Technology | 2012

Treatment of 14 sludge types from wastewater treatment plants using bench and pilot thermal hydrolysis.

Wei Qiao; Yifei Sun; Wei Wang

A total of 14 types of sludge from household sewage, mixture of domestic and industrial wastewater, and industrial and oil wastewater treatment plants were selected to evaluate the effectiveness and adaptability of thermal hydrolysis pre-treatment. Organic solubilization, dewatering improvement, volume reduction, high-strength filtrate biodegradation, and dewatered sludge incineration were investigated using bench and pilot thermal hydrolysis experiments (170 °C/60 min). Results showed that sludge types significantly affected the treatment effects. Organic content has a primary influence on thermal effects. The relationship between suspended solid (SS) solubilization and raw sludge organic content was linear with an R(2) of 0.73. The relationship between raw sludge organic content and treated sludge dewatering was linear with an R(2) of 0.86 and 0.65 for pilot and bench pre-treatments, respectively. Household and oil sludge possessed incineration possibilities with high heat value. Industrial and oil sludge filtrate was unsuitable for digestion to recover bioenergy.

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Wei Qiao

China University of Petroleum

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