Frontiers of Environmental Science & Engineering

ISSN 2095-2201

ISSN 2095-221X(Online)

CN 10-1013/X

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Engineering application of membrane bioreactor for wastewater treatment in China: Current state and future prospect
Kang XIAO, Ying XU, Shuai LIANG, Ting LEI, Jianyu SUN, Xianghua WEN, Hongxun ZHANG, Chunsheng CHEN, Xia HUANG
Front. Environ. Sci. Eng.. 2014, 8 (6): 805-819.

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China has been the forerunner of large-scale membrane bioreactor (MBR) application. Since the first large-scale MBR (≥10 000 m3·d-1) was put into operation in 2006, the engineering implementation of MBR in China has attained tremendous development. This paper outlines the commercial application of MBR since 2006 and provides a variety of engineering statistical data, covering the fields of municipal wastewater, industrial wastewater, and polluted surface water treatment. The total treatment capacity of MBRs reached 1 × 106 m3·d-1 in 2010, and has currently exceeded 4.5 × 106 m3·d-1 with ~75% of which pertaining to municipal wastewater treatment. The anaerobic/anoxic/aerobic-MBR and its derivative processes have been the most popular in the large-scale municipal application, with the process features and typical ranges of parameters also presented in this paper. For the treatment of various types of industrial wastewater, the configurations of the MBR-based processes are delineated with representative engineering cases. In view of the significance of the cost issue, statistics of capital and operating costs are also provided, including cost structure and energy composition. With continuous stimulation from the environmental stress, political propulsion, and market demand in China, the total treatment capacity is expected to reach 7.5 × 106 m3·d-1 by 2015 and a further expansion of the market is foreseeable in the next five years. However, MBR application is facing several challenges, such as the relatively high energy consumption. Judging MBR features and seeking suitable application areas should be of importance for the long-term development of this technology.

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Haloacetic acids in swimming pool and spa water in the United States and China
Xiaomao WANG,Garcia Leal M I,Xiaolu ZHANG,Hongwei YANG,Yuefeng XIE
Front. Environ. Sci. Eng.. 2014, 8 (6): 820-824.

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The objective of this study is to investigate the occurrence of haloacetic acids (HAAs), a group of disinfection byproducts, in swimming pool and spa water. The samples were collected from six indoor pools, six outdoor pools and three spas in Pennsylvania, the United States, and from five outdoor pools and nine indoor pools in Beijing, China. Five HAAs (HAA5), including monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid were analyzed. Total chlorine, pH and total organic carbon concentration were analyzed as well. Results indicated that the levels of HAA5 in swimming pools and spas in the United States ranged from 70 to 3980 μg·L-1, with an arithmetic average at 1440 μg·L-1 and a median level at 1150 μg·L-1. These levels are much higher than the levels reported in chlorinated drinking water and are likely due to organic matters released from swimmers’ bodies. The levels of HAA5 in swimming pools in China ranged from 13 to 332 μg·L-1, with an arithmetic average at 117 μg·L-1 and a median level at 114 μg·L-1. The lower HAA levels in swimming pools in China were due to the lower chlorine residuals. Results from this study can help water professionals to better understand the formation and stability of HAAs in chlorinated water and assess risks associated with exposures to HAAs in swimming pools and spas.

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Recovery of NH4+ by corn cob produced biochars and its potential application as soil conditioner
Yang ZHANG,Zifu LI,Ibrahim B MAHMOOD
Front. Environ. Sci. Eng.. 2014, 8 (6): 825-834.

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NH4+ ion, a main pollutant in aquatic systems, not only causes eutrophication in rivers and lakes but also contributes to fish toxicity. In this study, an eco-friendly biosorbent was prepared from the pyrolysis of corn cob, a low-cost agricultural residue. The biochars produced by pyrolysis of corn cob at 400°C and 600°C were characterized and investigated as adsorbents for NH4+-N from an aqueous solution. The biochars were characterized through elemental analysis, Brunauer–Emmett–Teller–N2 surface area analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. Batch experiments were conducted to investigate the NH4+ adsorption process of the corn cob biochars. The Freundlich isotherm model fitted the adsorption process better than the Langmuir and Dubinin–Radushkevich isotherm models. Moreover, the adsorption process was well described by a pseudo-second-order kinetic model. Results of thermodynamic analysis suggested that adsorption was a nonspontaneous exothermic process. Biochars produced at 400°C had higher adsorption capacity than those produced at 600°C because of the presence of polar functional groups with higher acidity. The exhausted biochar can be potentially used as soil conditioner, which can provide 6.37 kg NH4+-N?t-1 (N fertilizer per ton of biochar).

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Adsorption of benzene and toluene from waste gas using activated carbon activated by ZnCl2
Front. Environ. Sci. Eng.. 2014, 8 (6): 835-844.

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A series of activated carbons with high surface area were prepared from walnut shell using chemical activation with ZnCl2. In this research the carbonization stage was carried out at 500°C. The performance of the synthesized carbons evaluated in adsorption of benzene and toluene from waste gas. The influence of impregnation ratio on the characteristics of synthesized activated carbons as well as their adsorption capacity was investigated. The ratio of activation agent to walnut shell was selected in the range of 0.5–2.0 wt/wt. The synthesized activated carbons were characterized using XRD, SEM, BET and FTIR techniques. The highest activated carbon production yield was obtained at impregnation ratio of 1.5 wt/wt. The XRD analysis illustrated that peaks intensity decreased with increasing impregnation ratio showing that amorphous property of samples was increased. The SEM analysis revealed successful pore development in synthesized activated carbons obtained at high impregnation ratios. The surface area of the activated carbons increased with increasing impregnation ratio and its maximum value reached 2643 m2?g-1 at impregnation ratio of 2/1. FTIR analysis indicated that the relative amount of different acidic surface groups on synthesized carbons was a function of impregnation ratio. Experimental results for benzene and toluene adsorption showed a high potential of employing synthesized impregnated activated carbon for treatment of waste gas. Generally, the amount of VOC adsorbed on the surface was affected by physicochemical properties of synthesized activated carbons.

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A model of 90Sr distribution in the sea near Daya Bay Nuclear Power Plant in China
Jingyu WANG,Hongwei FANG,Guojian HE,Lei HUANG
Front. Environ. Sci. Eng.. 2014, 8 (6): 845-853.

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The impact on the environment of radionuclide release from nuclear power plants has attracted increased attention, especially after the accident at Fukushima Daiichi Nuclear Power Plant in Japan. Based on the mechanisms of adsorption/desorption at solid/liquid interfaces and a surface micromorphology model of sediments, a theoretical expression of the distribution coefficient Kd is derived. This coefficient has significant effects on the distribution of radionuclide in seawater, suspended sediment and seabed sediment. Kd is then used to simulate 90Sr transport in the sea near the Daya Bay Nuclear Power Plant. The simulation results are compared with field measurements of tidal level, current velocity, suspended sediment concentration and 90Sr concentrations in the same period. Overall, the simulated results agree well with the field measured data. Thus, the derived expression for Kd is capable of interpreting realistic adsorption/desorption processes. What’s more, conclusion is drawn that about 40% 90Sr released by Daya Bay Nuclear Power Plant will be adsorbed by suspended sediment and 20% by seabed sediment, only about 40% 90Sr will remain in the sea near Daya Bay Nuclear Power Plant in South China Sea.

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Variation in humic and fulvic acids during thermal sludge treatment assessed by size fractionation, elementary analysis, and spectroscopic methods
Yuning YANG,Huan LI,Jinyi LI
Front. Environ. Sci. Eng.. 2014, 8 (6): 854-862.

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Thermal pretreatment can be applied to sludge anaerobic digestion or dewatering. To analyze the variation in humic substances during thermal sludge treatment, sludge humic and fulvic acids were extracted before and after 30-min thermal treatment at 180°C, and then their contents, molecular weight distributions, elementary compositions, and spectral characteristics were compared. The results showed that the total contents of humic and fulvic acids in the sludge almost remained constant during thermal treatment, but 35% of humic and fulvic acids were dissolved from the sludge solids. Moreover, both humic and fulvic acids were partly decomposed and 32% of humic acids were converted to fulvic acids. The median value of the molecular weights of humic acids decreased from 81 to 41 kDa and that of fulvic acids decreased from 15 to 2 kDa. Besides the reduction in molecular size, the chemical structures of humic and fulvic acids also exhibited a slight change, i.e. some oxygen functional groups disappeared and aromatic structures increased after thermal sludge treatment.

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Laboratory study on high-temperature adsorption of HCl by dry-injection of Ca(OH)2 in a dual-layer granular bed filter
Junjun TAN,Guohua YANG,Jingqiao MAO,Huichao DAI
Front. Environ. Sci. Eng.. 2014, 8 (6): 863-870.

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Combustion-generated hydrogen chloride (HCl) is considered to be a very hazardous acid gaseous pollutant. This paper presents a laboratory study on the dry adsorption of HCl. The experiments were conducted in a dual-layer granular bed filter, at gas temperatures of 500°C–700°C and n(Ca)/n(Cl)molar ratios of 1.0–5.0 using the silver nitrate titration method by dry adsorbent powders Ca(OH)2. Mainly, the adsorption efficiency of HCl and utilization efficiency of Calcium were studied, by varying relevant factors including n(Ca)/n(Cl), temperature, feeding method, water vapor and CO2. With a relatively higher HCl concentration of 1000 ppm, the experimental results revealed that 600°C may be the optimum temperature for HCl adsorption when optimum n(Ca)/n(Cl) was 2.5 in our tests. The results also demonstrated that the feeding at a constant pressure was more effective, and the HCl adsorption efficiency could rapidly reach over 90% with n(Ca)/n(Cl) = 2.5 at 600°C. Furthermore, the HCl adsorption efficiency was found to be slightly promoted by water vapor, while could be impeded by CO2, and the utilization efficiency of calcium could be up to 74.4% without CO2, while was only 36.8% with CO2 when n(Ca)/n(Cl) was 2.5 at 600°C.

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Speciation evolutions of target metals (Cd, Pb) influenced by chlorine and sulfur during sewage sludge incineration
Jingde LUAN,Rundong LI,Zhihui ZHANG,Yanlong LI,Yun ZHAO
Front. Environ. Sci. Eng.. 2014, 8 (6): 871-876.

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In sludge incineration, the thermal behavior of heavy metal is a growing concern. In this work, the combined analysis of metal partitioning behavior between vapor phase and condensed phase, speciation redistribution in condensed phase and the difference of metal species in binding energy was carried out to investigate the possible volatilization-condensation mechanism of heavy metals in high-temperature sludge incineration. It was found that there were two steps in metal volatilization. The initial volatilization of heavy metal originated from their exchangeable (EXC), carbonate bound (CAR) and iron–manganese bound (FM) fractions, which is primarily composed of simple substance, chlorides, oxides and sulfides. With the increase of chlorine and sulfur in sludge, the inner speciation redistribution of heavy metals occurred in condensed phase, which was an important factor affecting the potential volatility of heavy metals. A partial of metal species with complexed (COM) and residual (RES) fractions gradually decomposed into simple substance or ions, oxides and carbonates, which significantly strengthened the second volatility. In presence of chlorine, about 46% of Cd with the RES fraction disappeared when the volatility rate of Cd increased by 44.89%. Moreover, about 9% of Pb with COM fraction disappeared when there was an increase of nearly 10% in the volatilization rate. Thus, the second volatilization was mainly controlled by the decomposition of metal species with COM and RES fractions. By virtue of XRD analysis and the binding energy calculation, it was found that metal complex and silicates were inclined to decompose under high temperature due to poor thermo stability as compared with sulfates.

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Identification of pakchoi cultivars with low cadmium accumulation and soil factors that affect their cadmium uptake and translocation
Lin WANG,Yingming XU,Yuebing SUN,Xuefeng LIANG,Dasong LIN
Front. Environ. Sci. Eng.. 2014, 8 (6): 877-887.

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The selection and use of low-Cd-accumulating cultivar (LCAC) has been proposed as one of the promising approaches in minimizing the entry of Cd in the human food chain. This study suggests a screening criterion of LCACs focusing on food safety. Pot culture and plot experiments were conducted to screen out LCACs from 35 pakchoi cultivars and to identify the crucial soil factors that affect Cd accumulation in LCACs. Results of the pot culture experiment showed that shoot Cd concentrations under the three Cd treatments significantly varied across cultivars. Two cultivars, Hualv 2 and Huajun 2, were identified as LCACs because their shoot Cd concentrations were lower than 0.2 mg·kg-1 under low Cd treatment and high Cd exposure did not affect the biomass of their shoots. The plot experiment further confirmed the consistency and genotypic stability of the low-Cd-accumulating traits of the two LCACs under various soil conditions. Results also showed that soil phosphorus availability was the most important soil factor in the Cd accumulation of pakchoi, which related negatively not only to Cd uptake by root but also to Cd translocation from root to shoot. The total Cd accumulation and translocation rates were lower in the LCACs than in the high-Cd cultivar, suggesting that Cd accumulation in different cultivars is associated with the Cd uptake by root as well as translocation from root to shoot. This study proves the feasibility of the application of the LCAC strategy in pakchoi cultivation to cope with Cd contamination in agricultural soils.

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Occurrence and fate of antibiotics in advanced wastewater treatment facilities and receiving rivers in Beijing, China
Xinwei LI,Hanchang SHI,Kuixiao LI,Liang ZHANG,Yiping GAN
Front. Environ. Sci. Eng.. 2014, 8 (6): 888-894.

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The occurrence and removal of 13 antibiotics were investigated in five wastewater treatment plants (WWTPs) with advanced wastewater treatment processes in Beijing, China. Most of the target antibiotics were detected in the secondary and tertiary effluents, with the concentrations of 4.8–1106.0 and 0.3–505.0 ng·L-1. Fluoroquinolone antibiotics showed relatively high concentrations in all samples (782–1814 ng·L-1). Different tertiary treatment processes showed discrepant antibiotics removal performances. Ozonation process was found more effective in removing target antibiotics compared to the coagulation-flocculation-sedimentation process and sand filtration process. Investigation of the target antibiotics in three typical urban rivers in Beijing was carried out to understand antibiotics occurrence in surface water environment. Eight antibiotics were detected in the studied rivers, with highest concentration of antibiotics in the river which was mainly replenished by reclaimed water. This study showed the necessity of employing more effective advanced treatment facilities to further reduce the discharge amount of antibiotics.

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Assessment of temporal and spatial variations in water quality using multivariate statistical methods: a case study of the Xin'anjiang River, China
Xue LI,Pengjing LI,Dong WANG,Yuqiu WANG
Front. Environ. Sci. Eng.. 2014, 8 (6): 895-904.

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This study evaluated the temporal and spatial variations of water quality data sets for the Xin'anjiang River through the use of multivariate statistical techniques, including cluster analysis (CA), discriminant analysis (DA), correlation analysis, and principal component analysis (PCA). The water samples, measured by ten parameters, were collected every month for three years (2008–2010) from eight sampling stations located along the river. The hierarchical CA classified the 12 months into three periods (First, Second and Third Period) and the eight sampling sites into three groups (Groups 1, 2 and 3) based on seasonal differences and various pollution levels caused by physicochemical properties and anthropogenic activities. DA identified three significant parameters (temperature, pH and E.coli) to distinguish temporal groups with close to 76% correct assignment. The DA also discovered five parameters (temperature, electricity conductivity, total nitrogen, chemical oxygen demand and total phosphorus) for spatial variation analysis, with 80.56% correct assignment. The non–parametric correlation coefficient (Spearman R) explained the relationship between the water quality parameters and the basin characteristics, and the GIS made the results visual and direct. The PCA identified four PCs for Groups 1 and 2, and three PCs for Group 3. These PCs captured 68.94%, 67.48% and 70.35% of the total variance of Groups 1, 2 and 3, respectively. Although natural pollution affects the Xin'anjiang River, the main sources of pollution included agricultural activities, industrial waste, and domestic wastewater.

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Characterization of phosphorus species and modeling for its organic forms in eutrophic shallow lake sediments, North China
Hongguang CHENG,Xiao PU,Yiting CHEN,Fanghua HAO,Liming DONG
Front. Environ. Sci. Eng.. 2014, 8 (6): 905-921.

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Variations of phosphorus (P) and its species in surface sediment of Baiyangdian Lake, a eutrophic shallow lake located in North China, were investigated through combination of field survey and numerical calculation based on cluster analysis. P fractionation was performed by a sequential extraction scheme, categorized as loosely bound P (NH4Cl-P), reductant soluble P (BD-P), metallic oxide bound P (NaOH-P), calcium bound P (HCl-P) and organic P (Org-P). P concentrations exhibited regional similarities and a total of four sub-areas were identified in which the same rank was HCl-P>Org-P>BD-P ≈ NaOH-P>NH4Cl-P. NH4Cl-P, BD-P and Org-P were found to contribute to P enrichment in overlying water column. Specifically, labile Org-P acted as a potential pool with a greater contribution in aerobic layer compared to anaerobic layer. A hysteresis (lag= 4 months) existed when labile Org-P concentration was negatively correlated with aerobic layer thickness. In view of magnitude of identified P contributors in sub-areas, higher potential of P release was present in Fuhe River and Tang River estuary areas. On the basis of calibration and verification, the mathematical model with parameter settings applied in this study was improved to serve as a tool for limnology management and eutrophic control.

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Modeling agricultural non-point source pollution in a high-precipitation coastal area of China
Zhiyi LI,Pengfei DU,Haiwei HUANG,Yong Ge,Xu LI
Front. Environ. Sci. Eng.. 2014, 8 (6): 922-928.

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Non-point source (NPS) pollution simulation in the high-precipitation coastal areas of China is difficult because varying annual typhoon incidence leads to highly contrasting rainfall patterns in dry years and wet years. An IMPULSE (Integrated Model of Non-point Sources Pollution Processes) based NPS model of the Changtan Reservoir watershed, which is a typical high-precipitation coastal area in China, was established based on the analysis of point and NPS pollution data, a digital elevation model, and data on land-use, soil, meteorology, economy, and agricultural management practice. Pre-processed pre-rainfall soil moisture levels were introduced during the simulation to model the effects of typhoons on hydrology. Rainfall events were simulated sequentially through the year and the model was calibrated and verified using hydrological and water quality data. Accuracy of the simulated rainfall runoff and water quality in the Changtan watershed was found to be acceptable. The study showed that the NPS modeling system could be applied to the simulation and prediction of NPS loadings in the Changtan Reservoir watershed.

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Decentralized wastewater treatment technologies and management in Chinese villages
Xuesong GUO,Zehang LIU,Meixue CHEN,Junxin LIU,Min YANG
Front. Environ. Sci. Eng.. 2014, 8 (6): 929-936.

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Problems treating sewage in rural areas in China have attracted increasing attention in recent years. However, only 6% of rural areas had spray drainage and wastewater treatment systems by the end of 2010. It is necessary to assess the technologies currently used so that sewage treatment in rural areas can be developed appropriately, to provide reliable and affordable wastewater treatment, in these areas. We evaluated the sewage treatment technologies currently used in rural areas by conducting case studies on 62 facilities that had each been operating for at least one year. Our study was carried out between 2009 and 2011, and the aim was to assess the situation during that period and assess any problems involved in decentralized sewage treatment in villages. We found that decentralized sewage treatment is the most popular wastewater treatment method in villages, and that the most common primary treatment technology used in rural areas is the septic tank. Our investigation highlights the need to establish standards for assessing effluent quality, including a range of target pollutants. Our results also show that effluents should be reused to meet the local environmental requirements in different areas, especially in ecologically sensitive areas.

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Improvement of nitrification efficiency by bioaugmentation in sequencing batch reactors at low temperature
Di CUI,Ang LI,Tian QIU,Rui CAI,Changlong PANG,Jihua WANG,Jixian YANG,Fang MA,Nanqi REN
Front. Environ. Sci. Eng.. 2014, 8 (6): 937-944.

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Bioaugmentation is an effective method of treating municipal wastewater with high ammonia concentration in sequencing batch reactors (SBRs) at low temperature (10°C). The cold-adapted ammonia- and nitrite- oxidizing bacteria were enriched and inoculated, respectively, in the bioaugmentation systems. In synthetic wastewater treatment systems, the average NH4+-N removal efficiency in the bioaugmented system (85%) was much higher than that in the unbioaugmented system. The effluent NH4+-N concentration of the bioaugmented system was stably below 8 mg·L-1 after 20 d operation. In municipal wastewater systems with bioaugmentation, the effluent NH4+-N concentration was below 8 mg·L-1 after 15 d operation. The average NH4+-N removal efficiency in unbioaugmentation system (about 82%) was lower compared with that in the bioaugmentation system. By inoculating the cold-adapted nitrite-oxidizing bacteria (NOB) into the SBRs after 10 d operation, the nitrite concentration decreased rapidly, reducing the NO2--N accumulation effectively at low temperature. The functional microorganisms were identified by PCR-DGGE, including uncultured Dechloromonas sp., uncultured Nitrospira sp., Clostridium sp. and uncultured Thauera sp. The results suggested that the cold-adapted microbial agent of ammonia-oxidizing bacteria (AOB) and NOB could accelerate the start-up and promote achieving the stable operation of the low-temperature SBRs for nitrification.

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A potentiometric cobalt-based phosphate sensor based on screen-printing technology
Lei ZHU,Xiaohong ZHOU,Hanchang SHI
Front. Environ. Sci. Eng.. 2014, 8 (6): 945-951.

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A potentiometric cobalt-based screen-printing sensor was fabricated by electroplating cobalt on the surface of a screen-printing electrode as the sensitive layer for the determination of dihydrogenphosphate (H2PO4-) in wastewater samples. The electrochemical performance of this sensor was fully examined to determine its detection calibration, detection limit, response time, selectivity, and interference with pH, various ions, and dissolved oxygen (DO). The cobalt-based phosphate sensor showed a phosphate-selective potential response in the range of 10-5 mol·L-1 to 10-1 mol·L-1, yielding a detection limit of 3.16 × 10-6 mol?L-1and a slope of -37.51 mV?decade-1 in an acidic solution (pH 4.0) of H2PO4-. DO and pH were found to interfere with sensor responses to phosphate. Ultimately, the performance of the sensor was validated for detecting wastewater samples from the Xiaojiahe Wastewater Treatment Plant against the standard spectrophotometric methods for H2PO4- analysis. The discrepancy between the two methods was generally ±5% (relative standard deviation). Aside from its high selectivity, sensitivity, and stability, which are comparable with conventional bulk Co-wire sensors, the proposed phosphate sensor presents many other advantages, such as low price, compactness, ease of use, and the possibility of integration with other analytical devices, such as flow injectors.

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Reuse of heavy metal-accumulating Cynondon dactylon in remediation of water contaminated by heavy metals
Dongdong MA,Hongwen GAO
Front. Environ. Sci. Eng.. 2014, 8 (6): 952-959.

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Phytoremediation technology is regarded as a simple and efficient way to remove heavy metals from contaminated soil. A reasonable disposal of metal hyperaccumulators is always a major issue in waste reuse and resource-saving. The heavy metal-accumulating Cynondon dactylon (L.) was investigated where heavy metals were desorbed by a facile acid-treatment. The result indicated that more than 90% of heavy metals (Zn, Pb and Cu) was extracted from Cynondon dactylon with 0.2 mmol·L-1 HCl. The plant residue was used to adsorb heavy metals ions. The adsorption fitted the Langmuir isotherm model with the saturation adsorption capacity of 9.5 mg·g-1 Zn2+, 36.2 mg·g-1 Pb2+ and 12.9 mg·g-1 Cu2+, and the surface complexation and the backfilling of heavy metal-imprinting cavities existed simultaneously during the adsorption. The treatment of wastewaters indicated that the plant residue exhibited a high removal rate of 97% for Cu. Also, the material could be recycled. The method offers a new disposal approach for heavy metal hyperaccumulator.

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Biosorption of Cr(VI) by carbonized Eupatorium adenophorum and Buckwheat straw: thermodynamics and mechanism
Front. Environ. Sci. Eng.. 2014, 8 (6): 960-966.

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High quality and low cost carbon can be prepared from Eupatorium adenophorum (E. adenophorum) and Buckwheat straw. The biosorbent was used for Cr(VI) removal. The effect of experimental parameters, such as pH, sorbent dosage and temperature were examined and the optimal experimental condition was determined. Solution pH is found influencing the adsorption. Cr(VI) removal efficiency is found to be maximum (98%) at pH= 1. Langmuir and Freundlich adsorption isotherms were applicable to the adsorption process and their constants were evaluated. The adsorption data obtained agreed well with the Langmuir sorption isotherm model. The maximum adsorption capacities for Cr(VI) ranged from 46.23 to 55.19 mg·g-1 for temperature between 298 K and 308 K under the condition of pH= 1.0. Thermodynamic parameters such as free energy change (ΔG), enthalpy (ΔH) and entropy (ΔS) indicate a spontaneous, endothermic and increased randomness nature of Cr(VI) adsorption. Studies found that the raw E. adenophorum and buckwheat straw mixed materials with simple treatment had a high efficiency for the removal of Cr(VI) and would be a promising adsorbent.

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Combined biologic aerated filter and sulfur/ceramisite autotrophic denitrification for advanced wastewater nitrogen removal at low temperatures
Tian WAN,Guangming ZHANG,Fengwei DU,Junguo HE,Pan WU
Front. Environ. Sci. Eng.. 2014, 8 (6): 967-972.

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An innovative advanced wastewater treatment process combining biologic aerated filter (BAF) and sulfur/ceramisite-based autotrophic denitrification (SCAD) for reliable removal of nitrogen was proposed in this paper. In SCAD reactor, ceramisite was used as filter and Ca(HCO3)2 was used for supplying alkalinity and carbon source. The BAF-SCAD was used to treat the secondary treatment effluent. The performance of this process was investigated, and the impact of temperature on nitrogen removal was studied. Results showed that the combined system was effective in nitrogen removal even at low temperatures (8 °C). Removal of total nitrogen (TN), NH4+-N, NO3-_N reached above 90% at room temperature. Nitrification was affected by the temperature and nitrification at low temperature (8 °C) was a limiting factor for TN removal. However, denitrification was not impacted by the temperature and the removal of NO3--N maintained 98% during the experimental period. The reason of effective denitrification at low temperature might be the use of easily dissolved Ca(HCO3)2 and high-flux ceramisite, which solved the problem of low mass transfer efficiency at low temperatures. Besides, vast surface area of sulfur with diameter of 2–6 mm enhanced the rate of microbial utilization. The removal of nitrate companied with the production of SO42-, and the average concentration of SO42- was about 240 mg·L-1. These findings would be beneficial for the application of this process to nitrogen removal especially in the winter and cold regions.

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19 articles