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Emission characteristics of dioxins, furans and polycyclic aromatic hydrocarbons during fluidized-bed combustion of sewage sludge

DENG Wenyi,YAN Jianhu,LI Xiaodong,WANG Fei,CHI Yong,LU Shengyong,

环境科学学报(英文版) , 2009,
Abstract: Pre-dried sewage sludge with high sulfur content was combusted in an electrically heated lab-scale fluidized-bed incinerator. The emission characteristics of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polycyclic aromatic hydrocarbons (PAHs) were studied. Coal and calcium oxide (CaO) were added during the sewage sludge combustion tests to optimize combustion conditions and control SO2 emission. The results indicated that the flue gases emitted during mono-combustion of sewage sludge were characterized by relatively high concentrations of SO2, NOx and organic pollutants, due to the high sulfur, nitrogen, and volatile matter content of sewage sludge. The total 16 USEPA priority PAHs and 2,3,7,8-substituted PCDD/Fs produced from sewage sludge combustion were found to be 106.14 g/m3 and 8955.93 pg/m3 in the flue gas, respectively. In the case of cocombustion with coal (msludge/mcoal = 1:1), the 16 PAHs and 2,3,7,8-substituted PCDD/Fs concentrations were markedly lower than those found during mono-combustion of sewage sludge. During co-combustion, a suppressant e ect of CaO on PCDD/Fs formation was observed.
Comprehensive evaluation of municipal sewage sludge combustion characteristics and its combustion kinetics model in Guangzhou

LIU Jingyong,SUN Shuiyu,

环境科学学报 , 2012,
Abstract: Five municipal sewage sludges, KFQ, DTS, LJ, LD and ZZ, from different sources of Guangzhou city and one sewage sludge sample ZQ from Zhaoqing city were collected. The six dried single samples and one mixtures were investigated by a thermogravimetric method analysis (TGA) under different conditions and four combustion indexes of sludge were calculated by using the TG-DTG curves. The results showed that the original municipal sewage sludge was with the characteristics of high volatile mater, low content of fixed carbon and low calorific value. The whole combustion process can be divided into four stages including the water releasing stage, volatile releasing stage, volatile combustion stage and fixed carbon combustion stage. Obvious, differences were discovered from different sludges at the same TG-DTG curves. The volatile separating and combustion dominated the whole combustion process. The combustion characteristics of different sources of sludge were dependent on the wastewater treatment process, the sources of sludge and their physical and chemical properties. The LJ sludge combustion performance was the best while the LD sludge was worst in the six kinds of sludge according to the volatile releasing index D, flammability index C and the comprehensive combustion index S. The index values of KFQ and ZZ mixtures became low except for the volatile releasing index D. The heating rate of the mixture was too fast, therefore cannot significantly improve the overall sludge combustion. Both the combustion reaction equation during different combustion periods and the corresponding kinetics parameter E were calculated by the Coats-Redfern equation. The results indicated that the value of activation energy (E) was corresponded with the combustion stages.
Experimental study on combustion characteristics and its kinetics of paper mill sludge

Liu Jingyong Sun Shuiyu Xu Yanbin Long Laishou Chen Tao Chen Minting,

环境工程学报 , 2010,
Abstract: The combustion characteristics of paper mill sludge and its blends with industrial sewage sludge at different proportions were studied by thermogravimetric analysis(TG-DTG) at different heating rates.The results showed that different DTG curves and peaks of fixed carbon were performed in combustion process between paper mill sludge and industrial sewage sludge.With the increasing of heating rates,the general combustion characteristics were improved.The burning time was shorten accordingly with the combustio...
Biosorption of Toxic Metals from Solid Sewage Sludge by Marine Green Algae  [PDF]
Rafia Azmat,Uzma,Fahim Uddin
Asian Journal of Plant Sciences , 2007,
Abstract: Biosorption of toxic metals from solid sewage sludge by marine green (Codium iyengrii) algae were observed. The process of removal of toxic metals by certain plants species are called biosorption. For this purpose the contaminated sewage sludge from sewage farm of SITE area Karachi from three different places were collected. In these places vegetables like onion (Allium cepa), spinach (Spinacia oleracea) and turnip(Brassica rapa) were cultivated which is commonly supplied to Karachi city. Heavy metals analysis of sewage sludge and plants were performed by atomic absorption spectrophotometry before and after treatment of sludge at laboratory scale. The effect of removal of metal was observed on plant growth. The results were also compared by garden soil. Results showed that concentration of metals in soil decreases by bio-sorption of toxic metal on seaweed. This helps in improving the soil quality by adsorption of metals on seaweeds. Significant improvement in size of leaves of bean plants in treated sewage sludge, were observed due to which chlorophyll contents founds to be increased as compare to non-treated plant. Reduction in metals uptake by plants from sludge as compared with non-treated sludge were recorded due to which nutritional level of plants were enhanced.
Characteristics of sewage sludge and distribution of heavy metal in plants with amendment of sewage sludge
DAI Jia-yin,CHEN Ling,ZHAO Jian-fu,MA Na,
DAI Jia-yin
,CHEN Ling,ZHAO Jian-fu,MA Na

环境科学学报(英文版) , 2006,
Abstract: In order to better understand land application of sewage sludge, the characterization of heavy metals and organic pollutants were investigated in three different sewage sludges in Shanghai City, China. It was found that the total concentrations of Cd in all of sewage sludge and total concentrations of Zn in Jinshan sewage sludge, as well as those of Zn, Cu, and Ni in Taopu sludge are higher than Chinese regulation limit of pollutants for sludge to be used in agriculture. Leachability of Hg in all of studied samples and that of Cd in Taopu sewage sludge exceed the limit values of waste solid extraction standard in China legislation. Based on the characteristics for three kinds of sewage sludge, a pot experiment was conducted to investigate the effect of soil amended with Quyang sewage sludge on the accumulation of heavy metal by Begonia semperflorens-hybr; Ophiopogon japonicus (L.F.) Ker-Gaw; Loropetalum chindense-var. rubrum; Dendranthema morifolium; Viola tricolor; Antirrhinum majus; Buxus radicans Sieb; Viburnum macrocephalum; Osmanthus fragrans Lour; Cinnamomum camphora siebold and Ligustrum lucidum ait. Results showed that 8 species of plant survived in the amended soil, and moreover they flourished as well as those cultivated in the control soil. The heavy metal concentration in plants varied with species, As, Pb, Cd and Cr concentration being the highest in the four herbaceous species studied, particularly in the roots of D. morifolium. These plants, however, did not show accumulator of As, Pb, Cd and Cr. The highest concentration of Ni and Hg was found in the roots of D. morifolium, followed by the leaves of B. semperflorens-hybr. Levels of Zn and Cu were much higher in D. morifolium than in the other plant species. D. morifolium accumulated Ni, Hg, Cu and Zn, which may contribute to the decrease of heavy metal contents in the amended soil. Treatment with sewage sludge did not significantly affect the uptake of heavy metals by the L. chindense-var. rubrum, however, it significantly affected the uptake of heavy metals by D. morifolium.
Study of co-combustion characteristic of sewage sludge and coal gangue mixed with weathered coal

- , 2017, DOI: 10.13738/j.issn.1671-8097.2017.04.008
Abstract: 利用热重分析仪研究不同掺烧比例、不同钙硫比下低热值混矸煤与污泥的着火稳定性和综合燃尽特性。采用Coats-Redfern积分法确定污泥与煤混烧过程中化学动力学参数。结果表明:污泥与煤样的混烧特性从总体上表现为污泥和煤样共同作用的结果,低热值混矸煤中适当掺混污泥可以提高热失重率,改善低热值混矸煤的着火特性,达到更好的燃烧效果,当污泥的掺烧比为10%左右时,综合燃烧性能最好。Ca/S摩尔比对煤和污泥燃烧也有很大的影响,随着Ca/S摩尔比的增加,混合燃料的着火点和燃尽温度均增加,燃烧特性指数先变小再增大,可以得出为了增加脱硫的效果而增加Ca/S摩尔比,对混合燃料的燃烧起到负面的作用,所以需要寻求一个最佳的Ca/S摩尔比。其研究结果可为掺烧污泥的循环流化床锅炉的运行提供参考。
Combustion characteristics of sewage sludge and coal gangue mixed with weathered coal were studied by thermos gravimetric analyzer with different mixng ratios and calcium-sulphur ratios.The kinetics analysis of the mainly weightlessness stage of fuel was conducted using the Coats-Redfern integral method. Results show that, the combustion characteristics reached the highest point with the mixing ratio of 10%.Calcium and sulfur have a great influence on coal and sludge combustion. With the increase of Ga/S molar ratio, the ignition and ignition temperature of the mixed fuel are increased,and the combustion characteristic index increases first and then increases.Increasing the Ca/S molar ratio by increasing the desulfurization effect has a negative effect on the combustion of the mixed fuel,so an optimum Ca/S molar ratio is required.The results of the study can provide a reference for the operation of circulating fluidized bed boiler.
Experimental Investigation on NOx Reduction by Primary Measures in Biomass Combustion: Straw, Peat, Sewage Sludge, Forest Residues and Wood Pellets  [PDF]
Ehsan Houshfar,Terese L?v?s,?yvind Skreiberg
Energies , 2012, DOI: 10.3390/en5020270
Abstract: An experimental investigation was carried out to study the NO x formation and reduction by primary measures for five types of biomass (straw, peat, sewage sludge, forest residues/Grot, and wood pellets) and their mixtures. To minimize the NO x level in biomass-fired boilers, combustion experiments were performed in a laboratory scale multifuel fixed grate reactor using staged air combustion. Flue gas was extracted to measure final levels of CO, CO 2, C xH y, O 2, NO, NO 2, N 2O, and other species. The fuel gas compositions between the first and second stage were also monitored. The experiments showed good combustion quality with very low concentrations of unburnt species in the flue gas. Under optimum conditions, a NO x reduction of 50–80% was achieved, where the highest reduction represents the case with the highest fuel-N content. The NO x emission levels were very sensitive to the primary excess air ratio and an optimum value for primary excess air ratio was seen at about 0.9. Conversion of fuel nitrogen to NO x showed great dependency on the initial fuel-N content, where the blend with the highest nitrogen content had lowest conversion rate. Between 1–25% of the fuel-N content is converted to NO x depending on the fuel blend and excess air ratio. Sewage sludge is suggested as a favorable fuel to be blended with straw. It resulted in a higher NO x reduction and low fuel-N conversion to NO x. Tops and branches did not show desirable NO x reduction and made the combustion also more unstable. N 2O emissions were very low, typically below 5 ppm at 11% O 2 in the dry flue gas, except for mixtures with high nitrogen content, where values up to 20 ppm were observed. The presented results are part of a larger study on problematic fuels, also considering ash content and corrosive compounds which have been discussed elsewhere.
Evaluation of PCDD/Fs and metals emission from a circulating fluidized bed incinerator co-combusting sewage sludge with coal
Gang Zhang,Jing Hai,Jiang Cheng,Zhiqi Cai,Mingzhong Ren,Sukun Zhang,Jieru Zhang,
Gang Zhang
,Jing Hai,Jiang Cheng,Zhiqi Cai,Mingzhong Ren,Sukun Zhang,Jieru Zhang

环境科学学报(英文版) , 2013,
Abstract: The emission characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and heavy metals were evaluated during co-combustion of sewage sludge with coal from a circulating fluidized bed incinerator. The stack gas, slag and fly ash samples were sampled and analyzed. The gas-cleaning system consisted of electrostatic precipitators and a semi-dry scrubber. Results showed that the stack gas and fly ash exhibited mean dioxin levels of 9.4 pg I-TEQ/Nm3 and 11.65 pg I-TEQ/g, respectively, and showed great similarities in congener profiles. By contrast, the slag presented a mean dioxin level of 0.15 pg I-TEQ/g and a remarkable difference in congener profiles compared with those of the stack gas and fly ash. Co-combusting sewage sludge with coal was able to reduce PCDD/Fs emissions significantly in comparison with sewage sludge mono-combustion. The leaching levels of Hg, Pb, Cd, Ni, Cr, Cu, and As in the fly ash and slag were much lower than the limits of the environmental protection standard in China. These suggest that the co-combustion of sewage sludge and coal is an advisable treatment method from an environmental perspective.
The characteristics of heavy metals and PAHs in sewage sludges and their relationships

SUN Feng,WENG Huanxin,MA Xuewen,FU Fengxia,

环境科学学报 , 2008,
Abstract: Polycyclic aromatic hydrocarbons (PAHs) and heavy metals are among the most widespread pollutants found in sewage sludge and impart tremendous potential hazard to human health. Here, we studied the characteristics of PAHs and heavy metals in the sewage sludge from nine different wastewater treatment plants. Zn is the most abundant heavy metal in domestic sewage sludge, followed by Cu, As and Cd. In industrial sewage sludge, the heavy metal profile varies dramatically depending on the source. In tannery sludge, the Cr concentration exceeds 15000 mg·kg-1. The state of heavy metals in sewage sludge varies as well. Cr, Cu and Pb exist predominantly in oxidizable and residual states; Ni and Zn exist mainly in acid soluble and reducible states, whereas Cd can exist in a variety of states. No significant difference in the total content of PAHs was observed between domestic and industrial sewage sludge. The levels of different PAHs follow a pattern of 4 rings > 3 rings > 2 rings > 5 rings > 6 rings. Fuel spills and incomplete combustion of carbon-containing fuels are the major sources of PAHs in sewage sludge. Our results revealed a correlation between heavy metals (e.g. Cd, Ni, and Zn) and low molecular weight PAHs (e.g. 2 or 3-ring PAHs) in sewage sludge. This correlation may be explained by the influence of heavy metals on the bioactivity of microorganisms that are capable of degrading PAHs.
Effects of Cationic Polyacrylamide Characteristics on Sewage Sludge Dewatering and Moisture Evaporation  [PDF]
Jun Zhou, Fenwu Liu, Chengyi Pan
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0098159
Abstract: The effects of the molecular weight (MW) and charge density (CD) of cationic polyacrylamide (CPAM) on sludge dewatering and moisture evaporation were investigated in this study. Results indicated that in sludge conditioning, the optimum dosages were 10, 6, 6, 4, and 4 mg g?1 CPAM with 5 million MW and 20% CD, 5 million MW and 40% CD, 3 million MW and 40% CD, 8 million MW and 40% CD, and 5 million MW and 60% CD, respectively. The optimum dosage of CPAM was negatively correlated with its CD or MW if the CD or MW of CPAM was above 20% or 5 million. In the centrifugal dewatering of sludge, the moisture content in the conditioned sludge gradually decreased with the extension of centrifugation time, and the economical centrifugal force was 400×g. The moisture evaporation rates of the conditioned sludge were closely related to sludge dewaterability, which was in turn significantly correlated either positively with the solid content of sludge particles that were >2 mm in size or negatively with that of particles measuring 1 mm to 2 mm in diameter. During treatment, sludge moisture content was reduced from 80% to 20% by evaporation, and the moisture evaporation rates were 1.35, 1.49, 1.62, and 2.24 times faster in the sludge conditioned using 4 mg g?1 CPAM with 5 million MW and 60% CD than in the sludge conditioned using 4 mg g?1 CPAM with 8 million MW and 40% CD, 6 mg g?1 CPAM with 5 million MW and 40% CD, 6 mg g?1 CPAM with 3 million MW and 40% CD, and 10 mg g?1 CPAM with 5 million MW and 20% CD, respectively. Hence, the CPAM with 5 million MW and 60% CD was ideal for sludge dewatering.
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