Frontiers of Environmental Science & Engineering

ISSN 2095-2201

ISSN 2095-221X(Online)

CN 10-1013/X

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Evaluate HAA removal in biologically active carbon filters using the ICR database
Hsin-hsin TUNG, Yuefeng F. XIE
Front Envir Sci Eng Chin. 2011, 5 (4): 489-496.

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The effects of biologically active carbon (BAC) filtration on haloacetic acid (HAA) levels in plant effluents and distribution systems were investigated using the United States Environmental Protection Agency’s Information Collection Rule (ICR) database. The results showed that average HAA5 concentrations in all locations were 20.4 μg·L-1 and 29.6 μg·L-1 in ICR plants with granular activated carbon (GAC) and ICR plants without GAC process, respectively. For plants without GAC, the highest HAA levels were observed in the quarters of April to June and July to September. However, for plants with GAC, the highest HAA levels were observed in the quarters of April to June and January to March. This HAA level profile inversely correlated well with water temperature, or biologic activity. For GAC plants, simulated distribution samples matched well with distribution system equivalent samples for Cl3AA and THMs. For plants with and without GAC, simulated distribution samples overestimated readily biodegradable HAAs in distribution systems. The study indicated that through HAA biodegradation, GAC process plays an important role in lowering HAA levels in finished drinking water.

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Low-temperature CO oxidation over Au-doped 13X-type zeolite catalysts: preparation and catalytic activity
Qing YE, Donghui LI, Jun ZHAO, Jiansheng ZHAO, Tianfang KANG, Shuiyuan CHENG
Front Envir Sci Eng Chin. 2011, 5 (4): 497-504.

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Au-supported 13X-type zeolite (Au/13X) was synthesized using a common deposition–precipitation (DP) method with a solution of sodium carbonate as a precipitate agent. Further testing was conducted to test for catalytic oxidation of CO. A study was conducted on the effects of different preparation conditions (i.e., chloroauric acid concentration, solution temperature, pH of solution, and calcinations temperature) on Au/13X for CO oxidation. In respect to the catalytic activity, the relationship between different the preparation conditions and gold particles in 13X zeolite was analyzed using X-ray diffraction, TEM and XPS. The activity of Au/13X catalysts in CO oxidation was dependent on the chloroauric acid concentration. From XRD results, a higher chloroauric acid concentration induced larger gold nanoparticles, which resulted in lower catalytic activity. Results revealed that higher temperatures induced higher Au loading, homogeneous deposit, and smaller gold clusters on the support of 13X, resulting in higher CO activity. Furthermore, a pH of 5 or 6 generated greater amounts of Au loading and smaller Au particles on 13X than at a pH of 8 or 9. This may be a result of an effective exchange between Au(OH)2Cl2- and Au(OH)3Cl- on specific surface sites of zeolite under the pH’s 5 and 6. The sample calcined at 300°C showed the highest activity, which may be due to the sample’s calcined at 200°C inability to decompose completely to metallic gold while the sample calcined at 400°C had larger particles of gold deposited on the support. It can be concluded from this study that Au/13X prepared from a gold solution with an initial chloroauric acid solution concentration of 1.5 × 10-3 mol·L-1 gold solution pH of 6, solution temperature of around 90°C, and a calcination temperature of 300°C provides optimum catalytic activity for CO oxidation.

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Application of quantum chemical descriptors into quantitative structure-property relationship models for prediction of the photolysis half-life of PCBs in water
Yueping BAO, Qiuying HUANG, Wenlong WANG, Jiangjie XU, Fan JIANG, Chenghong FENG
Front Envir Sci Eng Chin. 2011, 5 (4): 505-511.

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Quantitative structure-property relationship (QSPR) models were developed for prediction of photolysis half-life (t1/2) of polychlorinated biphenyls (PCBs) in water under ultraviolet (UV) radiation. Quantum chemical descriptors computed by the PM3 Hamiltonian software were used as independent variables. The cross-validated Qcum2 value for the optimal QSPR model is 0.966, indicating good prediction capability for lg t1/2 values of PCBs in water. The QSPR results show that the largest negative atomic charge on a carbon atom (QC-) and the standard heat of formation (ΔHf) have a dominant effect on t1/2 values of PCBs. Higher QC- values or lower ΔHf values of the PCBs leads to higher lg t1/2 values. In addition, the lg t1/2 values of PCBs increase with the increase in the energy of the highest occupied molecular orbital values. Increasing the largest positive atomic charge on a chlorine atom and the most positive net atomic charge on a hydrogen atom in PCBs leads to the decrease of lg t1/2 values.

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Migration of manganese and iron during the adsorption-regeneration cycles for arsenic removal
Fangfang CHANG, Jiuhui QU, Xu ZHAO, Wenjun LIU, Kun WU
Front Envir Sci Eng Chin. 2011, 5 (4): 512-518.

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Fe-Mn binary oxide incorporated into porous diatomite (FMBO-diatomite) was prepared in situ and regenerated in a fixed-bed column for arsenite [As(III)] and arsenate [As(V)] removal. Four consecutive adsorption cycles were operated under the following conditions: Initial arsenic concentration of 0.1 mg·L-1, empty bed contact time of 5 min, and pH 7.0. About 3000, 3300, 3800, and 4500 bed volumes of eligible effluent (arsenic concentration≤0.01 mg·L-1) were obtained in four As(III) adsorption cycles; while about 2000, 2300, 2500, and 3100 bed volumes of eligible effluent were obtained in four As(V) adsorption cycles. The dissection results of FMBO-diatomite fixed-bed exhibited that small amounts of manganese and iron were transferred from the top of the fixed-bed to the bottom of the fixed-bed during As(III) removal process. Compared to the extremely low concentration of iron (<0.01 mg·L-1), the fluctuation concentration of Mn2+ in effluent of the As(III) removal column was in a range of 0.01–0.08 mg·L-1. The release of manganese suggested that manganese oxides played an important role in As(III) oxidation. Determined with the US EPA toxicity characteristic leaching procedure (TCLP), the leaching risk of As(III) on exhausted FMBO-diatomite was lower than that of As(V).

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Advances in the study of directed evolution for cellulases
Hailong LIN, Weiguang LI, Changhong GUO, Sihang QU, Nanqi REN
Front Envir Sci Eng Chin. 2011, 5 (4): 519-525.

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If cellulose can be effectively hydrolyzed into glucose by cellulase, the production costs of hydrogen, ethanol or other chemicals from cellulosic materials will be greatly decreased, and economically viable production of biohydrogen and bioethanol will become feasible. Cellulose is degraded into glucoses by multi-component enzyme systems. Nowadays cellulases are widely used in brewing, food, bioenergy, fodder, textiles, paper, pharmaceuticals, environmental protection and other industries. However, existing cellulases have several problems that limit their wider applications, including the low turnover number for solid cellulosic materials, and low stability in adapting to various application conditions. For example, high temperature, low pH, and so on. Application of directed evolution technology may be one of the most effective ways for improving the characteristics of cellulases. This paper presents a brief review of the cellulose hydrolysis mechanism by cellulase, advances in cellulases (endoglucanase and β-glucosidase) improvement by directed evolution for several characteristics (for instance, thermal stability, pH adaptability and enzyme activity), limitations of directed evolution for cellulases, and the outlook for directed evolution for cellulase.

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Microcystin-LR biodegradation by Sphingopyxis sp. USTB-05
Chengbin XIAO, Hai YAN, Junfeng WANG, Wei WEI, Jun NING, Gang PAN
Front Envir Sci Eng Chin. 2011, 5 (4): 526-532.

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A promising bacterial strain for biodegrading microcystin-LR (MC-LR) as the sole carbon and nitrogen source was successfully isolated from Lake Dianchi, China. The strain was identified as Sphingopyxis sp. USTB-05, which was the first isolated MCs-biodegrading Sphingopyxis sp. in China. The average biodegradation rate of MC-LR by Sphingopyxis sp. USTB-05 was 28.8 mg·L-1 per day, which was apparently higher than those of other bacteria reported so far. The optimal temperature and pH for both strain USTB-05 growth and MC-LR biodegradation were 30°C and 7.0, respectively. The release of MC-LR from the cyanobacterial cells collected from Lake Guishui and the biodegradation of MC-LR by both strain and cell-free extract (CE) were investigated. The results indicated that MC-LR with the initial concentration of 4.0 mg·L-1 in water was biodegraded by Sphingopyxis sp. USTB-05 within 4 d, while MC-LR with the initial concentration of 28.8 mg·L-1 could be completely removed in 3 h by CE of Sphingopyxis sp. USTB-05 containing 350 mg·L-1 protein. During enzymatic biodegradation of MC-LR, two intermediate metabolites and a dead-end product were observed on an HPLC chromatogram. Moreover, the similar scanning profiles of MC-LR and its metabolic products indicate that the Adda side-chain of MC-LR was kept intact in all products.

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Conceptual study on incorporating user information into forecasting systems
Jiarui HAN, Qian YE, Zhongwei YAN, Meiyan JIAO, Jiangjiang XIA
Front Envir Sci Eng Chin. 2011, 5 (4): 533-542.

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The purpose of improving weather forecast is to enhance the accuracy in weather prediction. An ideal forecasting system would incorporate user-end information. In recent years, the meteorological community has begun to realize that while general improvements to the physical characteristics of weather forecasting systems are becoming asymptotically limited, the improvement from the user end still has potential. The weather forecasting system should include user interaction because user needs may change with different weather. A study was conducted on the conceptual forecasting system that included a dynamic, user-oriented interactive component. This research took advantage of the recently implemented TIGGE (THORPEX interactive grand global ensemble) project in China, a case study that was conducted to test the new forecasting system with reservoir managers in Linyi City, Shandong Province, a region rich in rivers and reservoirs in eastern China. A self-improving forecast system was developed involving user feedback throughout a flood season, changing thresholds for flood-inducing rainfall that were responsive to previous weather and hydrological conditions, and dynamic user-oriented assessments of the skill and uncertainty inherent in weather prediction. This paper discusses ideas for developing interactive, user-oriented forecast systems.

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A building-based data capture and data mining technique for air quality assessment
Front Envir Sci Eng Chin. 2011, 5 (4): 543-551.

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Recently, a building-based air quality model system which can predict air quality in front of individual buildings along both sides of a road has been developed. Using the Macau Peninsula as a case study, this paper shows the advantages of building-based model system in data capture and data mining. Compared with the traditional grid-based model systems with input/output spatial resolutions of 1–2 km, the building-based approach can extract the street configuration and traffic data building by building and therefore, can capture the complex spatial variation of traffic emission, urban geometry, and air pollution. The non-homogeneous distribution of air pollution in the Macau Peninsula was modeled in a high-spatial resolution of 319 receptors·km-2. The spatial relationship among air quality, traffic flow, and urban geometry in the historic urban area is investigated. The study shows that the building-based approach may open an innovative methodology in data mining of urban spatial data for environmental assessment. The results are particularly useful to urban planners when they need to consider the influences of urban form on street environment.

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Source apportionment of ambient PM10 in urban areas of Wuxi, China
Bo HAN, Xiaohui BI, Yonghua XUE, Jianhui WU, Tan ZHU, Baogui ZHANG, Jianqing DING, Yuanxin DU
Front Envir Sci Eng Chin. 2011, 5 (4): 552-563.

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A total of 168 PM10 samples were collected during the year of 2005 at eight sites in the city of Wuxi in China. Fifteen chemical elements, three water-soluble ions, total carbon and organic carbon were analyzed. Six source categories were identified and their contributions to ambient PM10 in Wuxi were estimated using a nested chemical mass balance method that reduces the effects of colinearity on the chemical mass balance model. In addition, the concentrations of secondary aerosols, such as secondary organic carbon, sulfate and nitrate, were quantified. The spatially averaged PM10 was high in the spring and winter (123 μg·m-3 and low in the summer–fall (90 μg·m-3). According to the result of source apportionment, resuspended dust was the largest contributor to ambient PM10, accounting for more than 50% of the PM10 mass. Coal combustion (14.6%) and vehicle exhaust (9.4%) were also significant source categories of ambient PM10. Construction and cement dust, sulfates, secondary organic carbon, and nitrates made contributions ranging between 4.1% and 4.9%. Other source categories such as steel manufacturing dust and soil dust made low contributions to ambient PM10.

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Effect of land use and land cover change on soil erosion and the spatio-temporal variation in Liupan Mountain Region, southern Ningxia, China
Bin QUAN, M. J. M. R?MKENS, Rui LI, Fang WANG, Jie CHEN
Front Envir Sci Eng Chin. 2011, 5 (4): 564-572.

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The Liupan Mountains are located in the southern Ningxia Hui Autonomous Region of China, that forms an important divide between landforms and bio-geographic regions. The populated part of the Liupan Mountain Region has suffered tremendous ecological damage over time due to population pressure, excessive demand and inappropriate use of agricultural land resources. To present the relationship between land use/cover change and spatio-temporal variation of soil erosion, data sets of land use between the late 1980s and 2000 were obtained from Landsat Thematic Mapper (TM) imagery, and spatial models were used to characterize landscape and soil erosion conditions. Also, soil erosion in response to land use and land cover change were quantified and analyzed using data from geographical information systems and remote sensing. Soil erosion by water was the dominant mode of soil loss, while soil erosion by wind was only present on a relatively small area. The degree of soil erosion was classified into five severity classes: slight, light, moderate, severe, and very severe. Soil erosion in the Liupan Mountain Region increased between the late 1980s and 2000, both in terms of acreage and severity. Moderate, severe, and very severe eroded areas accounted for 54.86% of the total land area. The lightly eroded area decreased, while the moderately eroded area increased by 368817 ha (22%) followed by severe erosion with 146552 ha (8.8%), and very severe erosion by 97067.6 ha (5.8%). Soil loss on sloping cropland increased with slope gradients. About 90% of the cropland was located on slopes less than 15°. Most of the increase in soil erosion on cropland was due to conversion of steep slopes to cropland and degradation of grassland and increased activities. Soil erosion was severe on grassland with a moderate or low grass cover and on dry land. Human activities, cultivation on steep slopes, and overgrazing of pastures were the main reasons for the increase in erosion severity.

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Restoration of hyper-eutrophic water with a modularized and air adjustable constructed submerged plant bed
Jinzhong LI, Xueju LI, Shujuan SUN, Xuegong LIU, Suiliang HUANG
Front Envir Sci Eng Chin. 2011, 5 (4): 573-584.

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A modularized and air adjustable constructed submerged plant bed (CSPB) which can be used to restore the eutrophic water is introduced in this paper. This plant bed helps hydrophyte grow under poor conditions such as frequently changed water depth, impaired water transparency, algae bloom and substantial duckweed in summer, which are not naturally suitable for growing hydrophyte. This pilot study in Waihuan River of Tianjin, China, revealed that reduction of Chemical Oxygen Demand (COD), Total Nitrogen (TN) and Total Phosphorus (TP) by the use of CSPB could be reached 30%–35%, 35%–40%, 30%–40% respectively in the growing season (from March to October) and 5%–10%, 5%–15%, 7%–20% respectively in the winter (from November to February) when the detention time was 6 d. The relationships between the concentration of COD, TN, TP and the detention time fit the first-order kinetic equation well and the coefficients of determination (R2) were all above 0.9. The attenuation coefficients k of the kinetic equation were a function of the water temperature. When the water temperature was quite low or quite high, k was not significantly changed with increasing or decreasing water temperature. While when the temperature was in a moderate range, an increase or decrease of water temperature would lead to a rapid increase or decrease in k.

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Quantification of energy related industrial eco-efficiency of China
Jiansu MAO, Yanchun DU, Linyu XU, Yong ZENG
Front Envir Sci Eng Chin. 2011, 5 (4): 585-596.

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Improving eco-efficiency is propitious for saving resources and reducing emissions, and has become a popular route to sustainable development. We define two energy-related eco-efficiencies: energy efficiency (ENE) and greenhouse gas (GHG) emission-related eco-efficiency (GEE) using energy consumption and the associated GHG emissions as the environmental impacts. Using statistical data, we analyze China’s energy consumption and GHG emissions by industrial subsystem and sector, and estimate the ENE and GEE values for China in 2007 as 4.871×107?US$/PJ and 4.26×108 US$/TgCO2eq, respectively. Industry is the primary contributing subsystem of China’s economy, contributing 45.2% to the total economic production, using 79.6% of the energy consumed, and generating 91.4% of the total GHG emissions. We distinguish the individual contributions of the 39 industrial sectors to the national economy, overall energy consumption, and GHG emissions, and estimate their energy-related eco-efficiencies. The results show that although ferrous metal production contributes only 3.5% to the national industrial economy, it consumes the most industrial energy (20% of total), contributes 16% to the total industrial global warming potential (GWP), and ranks third in GHG emissions. The power and heat sector ranks first in GHG emissions and contributes one-third of the total industrial GWP, although it only consumes about 8% of total industrial energy and, like ferrous metal production, contributes 3.5% to the national economy. The ENE of the ferrous metal and power and heat sectors are only 8 and 2.1×107 US$/PJ, while the GEE for these two sectors are 9 and 4×104 US$/GgCO2eq, respectively; these are nearly the lowest ENE and GEE values among all 39 industry sectors. Finally, we discuss the possibility of eco-efficiency improvement through a comparison with other countries.

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Environmental dispersivity in free-water-surface-effect dominated wetland: multi-scale analysis
Zi WU, Zhi LI, Li ZENG, Ling SHAO, Hansong TANG, Qing YANG, Guoqian CHEN
Front Envir Sci Eng Chin. 2011, 5 (4): 597-603.

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Distinct from the case with width-dominated shallow wetland flows, the longitudinal evolution of contaminant concentration in the most-typical pattern of wetland as dominated by free-water-surface-effect is characterized by a multi-scale analysis in the present study. An environmental dispersion model for the evolution of the mean concentration is deduced as an extension of Taylor's classical formulation by Mei’s multi-scale analysis. Corresponding environmental dispersivity is found identical to that determined by the method of concentration moments.

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Preliminary study of groundwater denitrification using a composite membrane bioreactor
Lihui ZHANG, Guomin CAO, Yulei FEI, Hong DING, Mei SHENG, Yongdi LIU
Front Envir Sci Eng Chin. 2011, 5 (4): 604-609.

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A composite membrane bioreactor (CMBR) integrating the immobilized cell technique and the membrane separation technology was developed for groundwater denitrification. The CMBR had two well mixed compartments with one filled with the nitrate- containing influent and the other with a dilute ethanol solution; the compartments were separated by the composite membrane consisting of a microporous membrane facing the influent and an immobilized cell membrane facing the ethanol solution. Nitrate and ethanol molecules diffused from the respective compartments into the immobilized cell membrane where nitrate was reduced to gaseous nitrogen by the denitrifying bacteria present there with ethanol as the carbon source. The microporous membrane was attached to one side of the immobilized cell membrane for retention of the disaggregated bacteria. Relative to the single dose of external ethanol, the two-dose supplementation produced better treatment results as evidenced by the lower concentrations of NO3--N and ethanol (as measured by total organic carbon) of the effluent. The batch treatment in CMBR removed most of the nitrate in the influent and attained a stable denitrification rate of 0.1 g·m-2·h-1 for most of the 96-h cycles during the 30-cycle study. The effluent was essentially free of ethanol and nitrite nitrogen.

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Technical feasibility study of an onshore ballast water treatment system
Shengjie LIU, Manxia ZHANG, Xiang LI, Xiaojia TANG, Lingling ZHANG, Yimin ZHU, Chengyu YUAN
Front Envir Sci Eng Chin. 2011, 5 (4): 610-614.

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To fulfill the requirements of Guidelines for approval of ballast water management system (G8), a set of onshore ballast water treatment equipment utilizing micro-pore ceramic filtration (MPCF) and UV radiation (MPCF&UV) system was designed and set up with a maximum flow rate of 80 m3·h-1. Technical feasibilities of MPCF&UV system were evaluated in three areas: removal efficiencies of indicator organism and oceanic bacteria, perdurability of a ceramic filter, and application on native seawater. The results showed that no indicator organism (Dunaliella) or oceanic bacteria was detected after treatment of 20 L MPCF and UV radiation at 1.3× 104 μW·s·cm-2. A 20 L ceramic filter can run continuously for 5.3 h at the flow rate of 15 m3·h-1 before its pressure drop up to 0.195 MPa. The removal percentage of total plankton amounts were 91.9% at a flow rate of 70 m3·h-1 by 80 L MPCF and UV radiation at 1.3× 104 μW·s·cm-2.

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Influence of aeration intensity on the performance of A/O-type sequencing batch MBR system treating azo dye wastewater
Xinhua WANG, Jingmei LI, Xiufen LI, Guocheng DU
Front Envir Sci Eng Chin. 2011, 5 (4): 615-622.

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Among the numerous parameters affecting the membrane bioreactor (MBR) performance, the aeration intensity is one of the most important factors. In the present investigation, an anoxic/aerobic-type (A/O-type) sequencing batch MBR system, added anoxic process as a pretreatment to improve the biodegradability of azo dye wastewater, was investigated under different aeration intensities and the impact of the aeration intensity on effluent quantity, sludge properties, extracellular polymeric substances (EPS) amount generated as well as the change of permeation flux were examined. Neither lower nor higher aeration intensities could improve A/O-type sequencing batch MBR performances. The results showed 0.15 m3·h-1 aeration intensity was promising for treatment of azo dye wastewater under the conditions examined. Under this aeration intensity, chemical oxygen demand (COD), ammonium nitrogen and color removal as well as membrane flux amounted to 97.8%, 96.5%, 98.7% and 6.21 L·m-2·h-1, respectively. The effluent quality, with 25.0 mg·L-1COD, 0.84 mg·L-1 ammonium nitrogen and 8 chroma, could directly meet the reuse standard in China. In the meantime, the sludge relative hydrophobicity, the bound EPS, soluble EPS and EPS amounts contained in the membrane fouling layer were 70.3%, 52.0 mg·g-1VSS, 38.8 mg·g-1VSS and 90.8 mg·g-1VSS, respectively, which showed close relationships to both pollutant removals and membrane flux.

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Co-fermentation of waste activated sludge with food waste for short-chain fatty acids production: effect of pH at ambient temperature
Leiyu FENG, Yuanyuan YAN, Yinguang CHEN
Front Envir Sci Eng Chin. 2011, 5 (4): 623-632.

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Effect of pH ranging from 4.0 to 11.0 on co-fermentation of waste activated sludge (WAS) with food waste for short-chain fatty acids (SCFAs) production at ambient temperature was investigated in this study. Experimental results showed that the addition of food waste significantly improved the performance of WAS fermentation system, which resulted in the increases of SCFAs production and substrate reduction. The SCFAs production at pH 6.0, 7.0, 8.0, and 9.0 and fermentation time of 4 d was respectively 5022.7, 6540.5, 8236.6, and 7911.7 mg COD·L-1, whereas in the blank tests (no pH adjustment, pH 8.0 (blank test 1), no food waste addition, pH 8.0 (blank test 2), and no WAS addition (blank test 3)) it was only 1006.9, 971.1, and 1468.5 mg COD·L-1, respectively. The composition of SCFAs at pH from 6.0 to 9.0 was also different from other conditions and propionic acid was the most prevalent SCFA, which was followed by acetic and n-butyric acids, while acetic acid was the top product under other conditions. At pH 8.0 a higher volatile suspended solids (VSS) reduction of 16.6% for the mixture of WAS and food waste than the sole WAS indicated a synergistic effect existing in fermentation system with WAS and food waste. The influence of pH on the variations of nutrient content was also studied during anaerobic fermentation of the mixture of WAS and food waste at different pH conditions. The release of NH4+-N increased with fermentation time at all pH values investigated except 4.0, 5.0 and in blank test one. The concentrations of soluble phosphorus at acidic pHs and in the blank test one were higher than those obtained at alkaline pHs. Ammonia and phosphorus need to be removed before the SCFAs-enriched fermentation liquid from WAS and food waste was used as the carbon source.

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Micro-analysis of nitrogen transport and conversion inside activated sludge flocs using microelectrodes
Lei WANG, Yongtao LV, Xudong WANG, Yongzhe YANG, Xiaorong BAI
Front Envir Sci Eng Chin. 2011, 5 (4): 633-638.

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To investigate the nitrogen transport and conversion inside activated sludge flocs, micro-profiles of O2, NH4+, NO2, NO3, and pH were measured under different operating conditions. The flocs were obtained from a laboratory-scale sequencing batch reactor. Nitrification, as observed from interfacial ammonium and nitrate fluxes, was higher at pH 8.5, than at pH 6.5 and 7.5. At pH 8.5, heterotrophic bacteria used less oxygen than nitrifying bacteria, whereas at lower pH heterotrophic activity dominated. When the ratio of C to N was decreased from 20 to 10, the ammonium uptake increased. When dissolved oxygen (DO) concentration in the bulk liquid was decreased from 4 to 2 mg·L-1, nitrification decreased, and only 25% of the DO influx into the flocs was used for nitrification. This study indicated that nitrifying bacteria became more competitive at a higher DO concentration, a higher pH value (approximately 8.5) and a lower C/N.

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18 articles