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Feng X.,Guangzhou Sewage Treatment Co. | Deng J.-C.,Zhongkai University of Agriculture and Engineering | Li B.-Q.,Guangzhou Sewage Treatment Co. | Luo G.,Guangzhou Sewage Treatment Co. | Lei H.-Y.,Sun Yat Sen University
Huanjing Kexue/Environmental Science | Year: 2011

Seven ultrasonic energy levels ranging from 0 to 26000 kJ·kg-1 were used to disintegrate excess sludge to investigate the changes in physical characteristics. The results indicated that the ultrasonication process destroys floc structure, facilitates the transfer of matter into the aqueous phase, and breaks up cell walls, which facilitated the improvement of settleability and biodegradability. Low ultrasonic energies could improve the settleability and supernatant turbidity. When the energy of 1000 kJ·kg-1 was applied into the sludge, the maximal settling velocity of sludge at 45 min was increased by 18.58% and the supernatant turbidity at 24 h was decreased by 43.52%, compared to the control. However, high ultrasonic energies deteriorated the characteristics. The maximal settling velocity was reduced by 37.03% and the supernatant turbidity was increased by 10 times in comparison to the control when the energy dose of 26000 kJ·kg-1 was applied. With the increases in ultrasonic energies, the particle size was significantly decreased, the soluble solids increased and the floc clusters dispersed. These changes in sludge characteristics were directly dependent upon the amount of ultrasonic energy applied. Furthermore, these characteristics correlated significantly to the ultrasonic energy. 1000 kJ·kg-1 was the optimal energy that improved the settleability and the supernatant turbidity, and that destructed the floc structure of sludge. On the other hand, particle size was an important factor affecting sludge settleability and supernatant turbidity. The optimal values led to best settleability and turbidity. Source

Liu L.,Sun Yat Sen University | Liu L.,Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology | Liu L.,Guangzhou Sewage Treatment Co. | Guan D.,Sun Yat Sen University | And 2 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2013

In this study, we selected eighteen species of common street trees along main roads in Guangzhou Municipality to observe and compare their leaf surface morphology using Scanning Electron Microscopy (SEM), and to evaluate how the contact angle of water droplet on leaf surfaces measured by goniometer influence the dust-retaining capability. It was found that the maximum leaf dust-retaining capabilities per unit area of the eighteen species of trees 26 days after rainfall were 0. 066-1. 831g/ m2, indicating significant differences (up to 27 times) among different trees. The plants with network structure on leaf surface, having high stomatal density and large opening of stomata, such as Mangifera Indica, have strong dust-retaining capability; while those whose leaf surfaces are smooth and covered by epicuticular wax with stomata arranged regularly without obvious undulation, such as Bauhinia blakeana, Swietenia mahogani, Lagerstroemia indica Linn. and Scheffera arboricola, have poor dust-retaining capability. There was a significant negative relationship between leaf contact angle and dust-retaining capability (r = -0. 614). Leaves with contact angle smaller than 90 ° demonstrate hydrophilicity. Their maximum dust-retaining capabilities 26 days after rainfall ranged from 1. 0 to 1. 831 g/ m2. For leaves with rugged morphological structure, hook or ridge-shaped rumple, prominence and stomata density ranging from 20 to 60, the measured contact angles are smaller, making the contact area between leaf and dust larger. Therefore, it is not easy for dust on such trees as Mangifera Indica, Bischofia Polycarpa and Ficus altissima Bl., to detach from leaf surface and these species have a strong dust-retaining capability. On the contrary, the special surface structure and hydrophobic wax of tree leaves with larger contact angle, such as Alstonia scholaris, Chukrasia tabularis, Lagerstroemia indica Linn., Scheffera arboricola and Bauhinia blakeana, make it difficult for dust particles to attach to leaves, resulting in small dust-retaining capabilities of less than 1. 0g/ m2. This study has shown that the wax content of surface foliage, stomata density and contact angle of leaves factors controlling the dust-retaining capability. It is therefore advisable to consider choosing tree species morphology enhances dust-retaining capability for urban greening and thus to improve the environmental urban vegetation. Source

Liu J.,Guangzhou University | Wang J.,Guangzhou University | Chen Y.,Guangzhou University | Yang C.,Guangzhou University | And 6 more authors.
Proceedings - International Conference on Computer Distributed Control and Intelligent Environmental Monitoring, CDCIEM 2011 | Year: 2011

This study dealed with the distribution and the origin of trace elements (Co, Cd, Mn, Ni, Zn, Tl and Pb) in two soil profiles from a site near a plant roasting pyrite for sulfuric acid production. Chemical partitioning of the trace elements showed that Tl and Pb in each individual extractable fraction (i.e. weak acid exchangeable, reducible and oxidizable) presented increasing trend upward through the depth in both profiles. Meanwhile, Co, Cd, Mn, Ni and Zn in all the above fractions revealed no general consistent trend across the depth. Results of the profile distribution of heavy metals in the chemical fractions combined with the principle component analysis indicated that the contamination of Tl and Pb is mainly from the percolation of pyrite slag particles in the studied soils, while the contamination of Co, Cd, Mn, Ni and Zn is predominantly due to the leaching of wastewaters in the soils. © 2011 IEEE. Source

Liu L.,Sun Yat Sen University | Liu L.,Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology | Liu L.,Guangzhou Sewage Treatment Co. | Guan D.,Sun Yat Sen University | And 8 more authors.
Environmental Science and Pollution Research | Year: 2013

Urban vegetation increasingly plays an important role in the improvement of the urban atmospheric environment. This paper deals with the dust retention capacities of four urban tree species (Ficus virens var. sublanceolata, Ficus microcarpa, Bauhinia blakeana, and Mangifera indica Linn) in Guangzhou. The dust-retaining capacities of four tree species are studied under different pollution intensities and for different seasons. Remote sensing imagery was used to estimate the total aboveground urban vegetation biomass in different functional areas of urban Guangzhou, information that was then used to estimate the dust-retaining capacities of the different functional areas and the total removal of airborne particulates in urban Guangzhou by foliage. The results showed that urban vegetation can remove dust from the atmosphere thereby improving air quality. The major findings are that dust retention, or capture, vary between the four species of tree studied; it also varied between season and between types of urban functional area, namely industrial, commercial/road traffic, residential, and clean areas. Dust accumulation over time was also studied and reached a maximum, and saturation, after about 24 days. The overall aboveground biomass of urban vegetation in Guangzhou was estimated to be 52.0 × 105 t, its total leaf area 459.01 km2, and the dust-retaining capacity was calculated at 8012.89 t per year. The present study demonstrated that the foliage of tree species used in urban greening make a substantial contribution to atmospheric dust removal and retention in urban Guangzhou. © 2013 Springer-Verlag Berlin Heidelberg. Source

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