Frontiers of Environmental Science & Engineering

ISSN 2095-2201

ISSN 2095-221X(Online)

CN 10-1013/X

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Air pollution and its control in China
HAO Jiming, HE Kebin, DUAN Lei, LI Junhua, WANG Litao
Front.Environ.Sci.Eng.. 2007, 1 (2): 129-142.

Abstract   PDF (391KB)
The rapid growth of China s economy has led to severe air pollution characterized by acid rain, severe pollution in cities, and regional air pollution. High concentrations are found for various pollutants such as sulfur dioxides (SO2), nitrogen oxides (NOx), and fine particulates. Great efforts have thus been undertaken for the control of air pollution in the country. This paper discusses the development and application of appropriate technologies for reducing the major pollutants produced by coal and vehicles, and investigates air quality modeling as an important support for policy-making.
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Selective catalytic reduction of NOx from exhaust of lean-burn engine over Ag-Al2O3/cordierite catalyst
LI Junhua, KANG Shoufang, FU Lixin, HAO Jiming
Front.Environ.Sci.Eng.. 2007, 1 (2): 143-146.

Abstract   PDF (360KB)
A highly effective Ag-Al2O3 catalyst was prepared using the in-situ sol-gel method, and characterized by surface area using nitrogen adsorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The catalyst performance was tested on a real lean-burn gasoline engine. Only unburned hydrocarbons and carbon monoxide in the exhaust were directly used as reductant (without any external reductant), the maximum NOx conversion could only reach 40% at 450?C. When an external reductant, ethanol was added, the average NOx conversion was greater than 60%. At exhaust gas temperature range of 350 500?C, the maximum NOx conversion reached about 90%. CO and HC could be efficiently oxidized with Pt-A2O3 oxidation catalyst placed at the end of SCR converter. However, NOx conversion drastically decreased because of the oxidation of some intermediates to NOx again. The possible reaction mechanism was proposed as two typical processes, nitration, and reduction in HC-SCR over Ag-Al2O3.
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Chemical speciation and anthropogenic sources of ambient volatile organic compounds (VOCs) during summer in Beijing, 2004
LU Sihua, LIU Ying, SHAO Min, HUANG Shan
Front.Environ.Sci.Eng.. 2007, 1 (2): 147-152.

Abstract   PDF (478KB)
Volatile organic compounds (VOCs) were measured at six sites in Beijing in August, 2004. Up to 148 VOC species, including C3 to C12 alkanes, C3 to C11 alkenes, C6 to C12 aromatics, and halogenated hydrocarbons, were quantified. Although the concentrations differed at the sites, the chemical compositions were similar, except for the Tongzhou site where aromatics were significantly high in the air. Based on the source profiles measured from previous studies, the source apportionment of ambient VOCs was preformed by deploying the chemical mass balance (CMB) model. The results show that urban VOCs are predominant from mobile source emissions, which contribute more than 50% of the VOCs (in mass concentrations) to ambient air at most sites. Other important sources are gasoline evaporation, painting, and solvents. The exception is at the Tongzhou site where vehicle exhaust, painting, and solvents have about equal contribution, around 35% of the ambient VOC concentration. As the receptor model is not valid for deriving the sources of reactive species, such as isoprene and 1,3-butadiene, other methodologies need to be further explored.
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NO conversion by positive streamer discharge—effects of gas compositions and reaction conditions
HE Wei, ZHU Tianle, LI Jing
Front.Environ.Sci.Eng.. 2007, 1 (2): 153-158.

Abstract   PDF (561KB)
The effects of gas compositions and reaction conditions on NO conversion by positive streamer discharge were experimentally investigated by using a link tooth wheel-cylinder reactor. The results showed that NO conversion increased w
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Characteristics of mass distributions of aerosol particle and its inorganic water-soluble ions in summer over a suburb farmland in Beijing
ZHAO Peng, ZHU Tong, LIANG Baosheng, HU Min, KANG Ling, GONG Jicheng
Front.Environ.Sci.Eng.. 2007, 1 (2): 159-165.

Abstract   PDF (522KB)
Agricultural activity is one of the most important sources of aerosol particles. To understand the mass distribution and sources of aerosol particles and their inorganic water-soluble ions in a suburb farmland of Beijing, particle samples were collected using a microorifice uniform deposit impactor (MOUDI) in the summer of 2004 in a suburb vegetable field. The distribution of the particles and their inorganic water-soluble ions in the diameter range of 0.18 18 mm were measured. The dominant fine particle ions were SO42-, NO3-, and NH4+. The association of day-to-day variation of the concentration of these ions with temperature, humidity, and solar radiation suggested that they are formed by the reaction of NH3 released from the vegetable field with the acid species produced from photochemical reactions. Fine particle K+ is likely from vegetation emission and biomass burning. Coarse particles like Ca2+, Mg2+, NO3-, and SO42- are suggested to come from the mechanical process by which the soil particle entered the atmosphere, and from the reaction of the acid species at the surface of the soil particle. The results show that fertilizer and soil are important factors determining the aerosol particle over agricultural fields, and vegetable fields in suburban Beijing contribute significantly to the aerosol particle.
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Dynamic fate modeling of γ-hexachlorocyclohexane in the lower reaches of the Liao River
LIU Zhenyu, YANG Fenglin, QUAN Xie, ZHANG Xiaohong
Front.Environ.Sci.Eng.. 2007, 1 (2): 166-171.

Abstract   PDF (436KB)
A QWASI model dependent on temperature is parameterized to describe the long-term fate of persistent organic pollutants (POPs) in the Liao River. The model parameters, namely fugacity capacity, degradation rate, and transfer coefficient, are profoundly affected by temperature. This model is used to simulate the fate of γ-hexachlorocyclohexane (γ-HCH) in the lower reaches of the Liao River from 1998 to 2008. Modeling results show that γ-HCH fugacity capacities in air, water, and sediment increase as temperature decreases, and the transfer and transformation rate coefficients increase as temperature increases. The variations of transfer and transformation parameter D values depend on fugacity capacities, and transfer and transformation coefficients simultaneously. The performance of the model is evaluated by comparing the predicted and observed concentrations in the water and sediment of the Liao River. The predicted values agree well with the observed value in the order of magnitude, in most cases within the factor of 3. It is believed that the model is appropriate for simulating the long term fate of POPs in the Liao River.
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Adsorption and partition of benzo(a)pyrene on sediments with different particle sizes from the Yellow River
XIA Xinghui, HU Lijuan, MENG Lihong
Front.Environ.Sci.Eng.. 2007, 1 (2): 172-178.

Abstract   PDF (376KB)
Experiments have been carried out to study the sorption of Benzo(a)pyrene(Bap) on sediment particles from the Yellow River using a batch equilibration technique. Effects of particle size on the adsorption and partition of Bap were investigated with the particle content of 3 g/L. Several significant results were obtained from the study. (1) Isotherms of Bap could be fitted with the dual adsorption-partition model under different particle sizes, and the measured value of the adsorption and partition was in agreement with the theoretical value of the dual adsorption-partition model. (2) When the particle diameter was d "e 0.025 mm, the adsorption was predominant in the sorption of Bap, which accounted for 68.7% 82.4% of the sorption. For the particles with the size of 0.007 mm "e d < 0.025 mm, the adsorption was predominant when the equilibrium concentration of Bap was 0 8.87 μg/L in the water phase; and the partition was predominant when the equilibrium concentration of Bap was higher than 8.87 μg/L in the water phase. When the particle diameter was d<0.007 mm, the partition was predominant. (3) On the point of particle size, the contribution of adsorption to sorption followed the order: d"e0.025 mm > 0.007 mm "dd<0.025 mm  > d<0.007 mm . (4) The partition coefficients of Bap in solids with different particle sizes were linearly correlated with the organic content, and the Koc of Bap was about 1.26 x 105 (L/kg).
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Pathway of the ozonation of 2,4,6-trichlorophenol in aqueous solution
PI Yunzheng, WANG Jianlong
Front.Environ.Sci.Eng.. 2007, 1 (2): 179-183.

Abstract   PDF (317KB)
The reaction mechanism and pathway of the ozonation of 2,4,6-trichlorophenol (2,4,6-TCP) in aqueous solution were investigated. The removal efficiency and the variation of H2O2, Cl-, formic acid, and oxalic acid were studied during the semi-batch ozonation experiments (continuous for ozone gas supply, fixed volume of water sample). The results showed that when there was no scavenger, the removal efficiency of 0.1 mmol/L 2,4,6-TCP could reach 99% within 6 min by adding 24 mg/L ozone. The reaction of molecular ozone with 2,4,6-TCP resulted in the formation of H2O2. The maximal concentration of H2O2 detected during the ozonation could reach 22.5% of the original concentration of 2,4,6-TCP. The reaction of ozone with H2O2 resulted in the generation of a lot of OH° radicals. Therefore, 2,4,6-TCP was degraded to formic acid and oxalic acid by ozone and OH° radicals together. With the inhibition of OH°radicals, ozone molecule firstly degraded 2,4,6-TCP to form chlorinated quinone, which was subsequently oxidized to formic acid and oxalic acid. Two reaction pathways of the degradation of 2,4,6-TCP by ozone and O3/OH° were proposed in this study.
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Nitrifying and denitrifying bacteria in aerobic granules formed in sequencing batch airlift reactors
WANG Fang, YANG Fenglin, QI Aijiu
Front.Environ.Sci.Eng.. 2007, 1 (2): 184-189.

Abstract   PDF (442KB)
The purpose of this study was to investigate nitrifying bacteria and denitrifying bacteria isolated from aerobic granules. Aerobic granules were formed in an internal-circulate sequencing batch airlift reactor (SBAR) and biodegradation of NH3--N was analyzed in the reactor. Bacteria were isolated and determined from aerobic granules using selected media. The growth properties and morphology of bacteria colonies were observed by controlling aerobic or anaerobic conditions in the culture medium. It was found that bacteria in aerobic granules were diverse and some of them were facultative aerobes. The diversity of bacteria in aerobic granules was a premise of simultaneous nitrification and denitrification.
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Preparation of rare-earth metal complex oxide catalysts for catalytic wet air oxidation
LI Ning, LI Guangming, YAO Zhenya, ZHAO Jianfu
Front.Environ.Sci.Eng.. 2007, 1 (2): 190-195.

Abstract   PDF (401KB)
Catalytic wet air oxidation (CWAO) is one of the most promising technologies for pollution abatement. Developing catalysts with high activity and stability is crucial for the application of the CWAO process. The Mn/Ce complex oxide catalysts for CWAO of high concentration phenolcontaining wastewater were prepared by coprecipitation. The catalyst preparation conditions were optimized by using an orthogonal layout method and single-factor experimental analysis. The Mn/Ce serial catalysts were characterized by Brunauer Emmett Teller (BET) analysis and the metal cation leaching was measured by inductively coupled plasma torch-atomic emission spectrometry (ICP-AES). The results show that the catalysts have high catalytic activities even at a low temperature (80?C) and low oxygen partial pressure (0.5 MPa) in a batch reactor. The metallic ion leaching is comparatively low (Mn<6.577 mg/L and Ce<0.6910 mg/L, respectively) in the CWAO process. The phenol, CODCr, and TOC removal efficiencies in the solution exceed 98.5% using the optimal catalyst (named CSP). The new catalyst would have a promising application in CWAO treatment of high concentration organic wastewater.
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Pollution of NPEOs in four municipal sewage treatment plants in the north of China
HOU Shaogang, SUN Hongwen
Front.Environ.Sci.Eng.. 2007, 1 (2): 196-201.

Abstract   PDF (368KB)
The concentration and distribution of nonylphenol polyethoxylates (NPEOs represents the mixture, and NPnEO represents the monomer) and its metabolites in the influent and effluent of four municipal sewage treatment plants (STPs) in the north of China were measured. Moreover, the concentration and distribution of the above chemicals in the sludge of two STPs were also determined, and the transfer and fate of NPEOs in the sewage treatment process were discussed primarily by analyzing the distribution of the products in the effluent and the sludge. The results showed that NPEOs and its metabolites existed in all the samples of the influent, effluent, and sludge. NPEOs were degraded in the sewage treatment process with the removal efficiency in the range of 23.38% 77.11%, or an average of 52.86%. However, the large analogs of NPnEO were only degraded to small ones, whose degradation rate was rather slow, and consequently the degradation was not complete. Hence, the concentrations of some small metabolites, such as nonylphenol (NP), nonylphenol monoethoxylate (NP1EO), and nonylphenol diethoxylate (NP2EO) were elevated in the effluent. These small metabolites are more toxic than the large NPnEO analogs, and some of them were reported to exhibit environmental endocrine disrupting activity. From this point of view, the process of sewage treatment does not reduce but elevate the risk of NPEOs, which becomes the main source of these small NPnEO in the environment. The sludge exhibited good adsorption ability for NPEOs, especially for the small analogs, which led to the high level of NPEOs in the sludge. Hence, reasonable disposal of the surplus sludge to avoid re-pollution is very important.
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Sediment environmental capacity of 137Cs in Daya Bay
ZHANG Junli, CHEN Jiajun, XU Jialin, LI Yuanxin, HUANG Naiming
Front.Environ.Sci.Eng.. 2007, 1 (2): 202-206.

Abstract   PDF (328KB)
Sediment environmental capacity of pollutants is very important for marine environmental management. Based on the methodology of a study on water, soil environmental capacity, and mass conservation theory in a system, the concept and model on sediment environmental capacity for 137Cs in Daya Bay were developed. The static capacity for 137Cs in the upper sediment near the shore at a shallow area was calculated, and the annual dynamic capacity and total dynamic capacity were also calculated through determination of the typical biomass in the sediment. The results showed that the estimated environmental capacity for 137Cs in sediments was approximately equal to the current input of 137Cs into the sediments. Controlling the input of 137Cs in the sediments within the environmental capacity guarantees the sustainability of the current situation of the Daya Bay ecosystem and avoidance of a significant degradation of the system.
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Electrochemical reduction characteristics and the mechanism of chlorinated hydrocarbons at the copper electrode
XU Wenying, GAO Tingyao, ZHOU Rongfeng, MA Lumin
Front.Environ.Sci.Eng.. 2007, 1 (2): 207-212.

Abstract   PDF (347KB)
The electrochemical reduction characteristics of chlorinated hydrocarbons were investigated by cyclic voltammetry technique. The reduction mechanism and activity of the chlorinated hydrocarbons at the copper electrode were explored. The relationship between the structure of chlorinated hydrocarbons and their reductive activity were discussed. The experimental results showed that chlorinated alkanes and a portion of chlorinated aromatic hydrocarbons could be reduced directly at the copper electrode. However, chlorinated aromatic hydrocarbons were not easy to reduce at the copper electrode. The results provided a theoretical basis for the catalyzed iron inner electrolysis method.
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Use of zeolitized coal fly ash in the simultaneous removal of ammonium and phosphate from aqueous solution
WU Deyi, HU Zhanbo, WANG Xinze, HE Shengbing, KONG Hainan
Front.Environ.Sci.Eng.. 2007, 1 (2): 213-220.

Abstract   PDF (466KB)
Discharge of wastewater containing nitrogen and phosphate can cause eutrophication. Therefore, the development of an efficient material for the immobilization of the nutrients is important. In this study, a low calcium fly ash and high calcium fly ash were converted into zeolite using the hydrothermal method. The removal of ammonium and phosphate that coexist in aqueous solution by the synthesized zeolites were studied. The results showed that zeolitized fly ash could efficiently eliminate ammonium and phosphate at the same time. Saturation of zeolite with Ca2+ rather than Na+ favored the removal of both ammonium and phosphate because the cation exchange reaction by the NH4+ resulted in the release of Ca2+ into the solution and precipitation of Ca2+ with PO43- followed. An increase in the temperature elevated the immobilization of phosphate whereas it abated the removal of ammonium. Nearly 60% removal efficiency for ammonium was achieved in the neutral pH range from 5.5 to 10.5, while the increase or decrease in pH out of the neutral range lowered the adsorption. In contrast, the removal of phosphate approached 100% at a pH lower than 5.0 or higher than 9.0, and less phosphate was immobilized at neutral pH. However, there was still a narrow pH range from 9.0 to 10.5 favoring the removal of both ammonium and phosphate. It was concluded that the removal of ammonium was caused by cation exchange; the contribution of NH3 volatilization to immobilization at alkaline conditions (up to pH level of 11.4) was limited. With respect to phosphate immobilization, the mechanism was mainly the formation of precipitate as Ca3(PO4)2 within the basic pH range or as FePO4 and AlPO4 within acidic pH range.
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Relationship between sludge settleability and membrane fouling in a membrane bioreactor
SUN Yujiao, WANG Yong, HUANG Xia
Front.Environ.Sci.Eng.. 2007, 1 (2): 221-225.

Abstract   PDF (485KB)
The evolution of activated sludge settleability and its relationship to membrane fouling in a submerged membrane bioreactor were studied at a lab-scale equipment fed with synthetic wastewater. It was found that sludge volume index (SVI) gradually increased and the sludge settleability was reduced, which was caused by the propagation of filamentous bacteria. With increasing SVI, the average increasing rate of trans-membrane pressure increased, the stable filtration period was shortened, and the two stages (smooth stage and accelerating stage) of the trans-membrane pressure were more obvious. At the same time, the increasing rate of trans-membrane pressure at the smooth stage decreased and the rate at the accelerating stage increased with SVI, respectively. The observation by using scanning electronic microscopes showed the cake layer with loose structure and large thickness formed on the membrane surface due to the appearance of filamentous bacteria and high SVI in sludge. Influence of the sludge settleability on the trans-membrane pressure was related to the structure and thickness of the cake layer on the membrane.
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Influence of carbon source and temperature on the denitrifying phosphorus removal process
WANG Yayi, WANG Shuying, PENG Yongzhen, Zhu Guibing, LING Yunfang
Front.Environ.Sci.Eng.. 2007, 1 (2): 226-232.

Abstract   PDF (353KB)
To supply the valuable operating parameters for the popular usage of the new denitrifying phosphors removal process, it is essential to study the dominant biochemical reactions and the characteristics of denitrifying phosphorus removing bacteria (DPB). Thus, parallel batch experiments using DPB sludge were carried out to assess the effect of substrates (sewage, HAc, and endogenous carbon source) on denitrifying dephosphorus removal efficiency in this study. The results showed that the initial specific phosphorus release rate increased with the high concentration of the short-chain volatile fatty acids ratio in the influent, and sufficient phosphorus was released by DPB. This improved the subsequent denitrification and phosphorus uptake efficiency. The specific endogenous denitrification mainly relies on the internal carbon source (PHB) stored by poly-P bacteria. Denitrifying phosphorus removing bacteria were very hungry when the internal PHB was consumed. Consequently, the specific endogenous denitrification rate was low and the phosphorus uptake did not happen. On the other hand, in the experiment, the denitrifying phosphorus removal performance under two temperature conditions (8 10?C and 25 26?C) was also investigated and analyzed. It was found that the lower temperature decreased the specific phosphorus release and uptake rate, but did not inhibit the denitrifying phosphorus removal completely. Therefore, the negative influence of the low temperature on the overall phosphorus removal was not significant.
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Kinetic analysis of anaerobic phosphorus release during biological phosphorus removal process
DOU Junfeng, LIU Xiang, LUO Guyuan
Front.Environ.Sci.Eng.. 2007, 1 (2): 233-239.

Abstract   PDF (298KB)
Enhanced biological phosphorus removal (EBPR) is a commonly used and sustainable method for phosphorus removal from wastewater. Poly-β-hydroxybutyrate (PHB), polyphosphate, and glycogen are three kinds of intracellular storage polymers in phosphorus accumulation organisms. The variation of these polymers under different conditions has an apparent influence on anaerobic phosphorus release, which is very important for controlling the performance of EBPR. To obtain the mechanism and kinetic character of anaerobic phosphorus release, a series of batch experiments were performed using the excessively aerated sludge from the aerobic unit of the biological phosphorus removal system in this study. The results showed that the volatile suspended solid (VSS) had an increasing trend, while the mixed liquid suspended sludge (MLSS) and ashes were reduced during the anaerobic phosphorus release process. The interruption of anaerobic HAc-uptake and phosphorus-release occurs when the glycogen in the phosphorus-accumulating-organisms is exhausted. Under the condition of lower initial HAc-COD, HAc became the limiting factor after some time for anaerobic HAc uptake. Under the condition of higher initial HAc-COD, HAc uptake was stopped because of the depletion of glycogen in the microorganisms. The mean ratio of ΔρP/ΔρPHB, ΔρGLY/ΔρPHB, ΔρP/ΔCOD, and ΔρPHB/ΔCOD was 0.48, 0.50, 0.44, and 0.92, respectively, which was nearly the same as the theoretical value. The calibrated kinetic parameters of the HAc-uptake and phosphorus-release model were evaluated as follows: QHAc,max was 164 mg/(g °h), QP,max was 69.9 mg/(g °h), Kgly was 0.005, and KCOD was 3 mg/L. An apparently linear correlation was observed between the ratio of ΔρP/ΔCOD and pH of the solution, and the equation between them was obtained in this study.
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Adsorptive behaviors of humic acid onto freshly prepared hydrous manganese dioxides
LIU Ruiping, LI Guibai, YANG Yanling, HE Wenjie, HAN Hongda
Front.Environ.Sci.Eng.. 2007, 1 (2): 240-245.

Abstract   PDF (333KB)
This study focused on the adsorptive behaviors of humic acid onto freshly prepared hydrous MnO2(s) (δMnO2), and investigated the feasibility of employing δMnO2 for humic acid removal from drinking water. Effects of such parameters as molecular mass of humic acid, kinds of divalent cations on adsorptive behaviors and possible mechanisms involved were investigated. This study indicated that humic acid with higher molecular mass exhibited more tendency of adsorbing onto &MnO2 than that with lower molecular mass. Ca2+ facilitated more humic acid adsorption than Mg2+; UV-Vis spectra analysis indicated higher capabilities of Ca2+ coordinating with acidic functional groups of humic acid than that of Mg2+. Additionally, ζ potential characterization indicated that Ca2+ showed higher potential of increasing ζ potential of &MnO2 than Mg2+. Ca2+ of 1.0 mmol/L increased ζ potential of δMnO2 from -37 mV (pH 7.9) to +7 mV (pH 7.2), while 1.0 mmol/L Mg2+ increased to lower value as -9 mV (pH 6.5), correspondingly. Fourier transform infrared (FTIR) spectra demonstrated the adsorption of humic acid onto &MnO2, showing the important roles of -COO- functional groups and surface Mn-OH in the adsorption of humic acid onto &MnO2.
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Factors affecting simultaneous nitrification and denitrification in an SBBR treating domestic wastewater
LI Jun, GU Guowei, PENG Yongzhen, WEI Su
Front.Environ.Sci.Eng.. 2007, 1 (2): 246-250.

Abstract   PDF (385KB)
An aerobic sequencing batch biofilm reactor (SBBR) packed with Bauer rings was used to treat real domestic wastewater for simultaneous nitrification and denitrification. The SBBR is advantageous for creating an anoxic condition, and the biofilm can absorb and store carbon for good nitrification and denitrification. An average concentration of oxygen ranging from 0.8 to 4.0 mg/L was proved very efficient for nitrification and denitrification. Volumetric loads of TN dropped dramatically and effluent TN concentration increased quickly when the concentration of average dissolved oxygen was more than 4.0 mg/L. The efficiency of simultaneous nitrification and denitrification (SND) increased with increasing thickness of the biofilm. The influent concentration hardly affected the TN removal efficiency, but the effluent TN increased with increasing influent concentration. It is suggested that a subsequence for denitrification be added or influent amount be decreased to meet effluent quality requirements. At optimum operating parameters, the TN removal efficiency of 74% 82% could be achieved.
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Atomic force microscopy study on the microtopography of natural organic matter and newly formed hydrous MnO2
GUO Jin, MA Jun, SHI Xuehua
Front.Environ.Sci.Eng.. 2007, 1 (2): 251-256.

Abstract   PDF (371KB)
To understand the water purification mechanism of potassium permanganate as a coagulation-aid during the preoxidation process, the microtopography of its reductive products, the newly formed hydrous manganese dioxide and the aged hydrous manganese dioxide, was investigated. The morphology of natural organic matter (NOM) adsorbed by the newly formed hydrous manganese dioxide was also compared with that of NOM alone. By using the tapping mode atomic force microscopy (AFM), the observation results show that the newly formed hydrous manganese dioxide possess a perforated sheet (with a thickness of 0 1.75 nm) as well as some spherical particle structures compared with the hydrous manganese dioxide with 2 h aging time, which demonstrated that the newly formed hydrous manganese dioxide had a large surface area and adsorption capacity. When 1 mmol/L newly formed hydrous manganese dioxide was added, the microtopography of NOM molecules shifted from a loosely dispersed pancake shape (with adsorption height of 5 8.5 nm) to a densely dispersed and uniform spherical structure. These results provide a valid proof that it is the perfect adsorption capability of the newly formed hydrous manganese dioxide that might result in the coagulation aid effect of potassium permanganate preoxidation.
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