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Volume 43 Number 3 Volume 43 Number 4

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Research articles

ScienceAsia 43(2017): 244-253 |doi: 10.2306/scienceasia1513-1874.2017.43.244

The effect of ultrasonic algae inhibition on the concentration and state changes of heavy metals in sediments

Shucong Zhena, Niegui Lib, Shuai Guc, Xiao Tand,*

ABSTRACT:     To evaluate the effect of ultrasound on the release of heavy metals in sediments during the ultrasonic algae inhibition and elimination process, low-frequency and low-power ultrasound at 35 kHz, 0.105 W/cm2 was used to irradiate a simulated water body for 60 min. Water samples were extracted at 10 min intervals to detect the concentration changes of Cu, Zn, Pb, and Cr. Samples from the sediment surface and 10 cm below the surface were extracted to determine the changes of total amounts for the four heavy metals, as well as the corresponding concentration changes of exchangeable, carbonate binding, Fe-Mn binding, organic binding, and residue states. The test results showed that the concentrations of the four heavy metals in water increase rapidly during the first 20 min of ultrasonic treatment, decreasing thereafter. The concentrations approach a stable level after 50 min. The concentrations of all the four metals increased by over 80%. During the first 20 min of ultrasonic treatment, the release rates of Cu, Zn, Pb, and Cr at the sediment surface were 27%, 24%, 29%, and 29%, respectively, while the concentrations of the Fe-Mn binding state and exchangeable state decreased by 25% and 47%, 22% and 43%, 29% and 28%, and 29% and 29%, respectively. The release rate of the four heavy metals at 10 cm below the surface was 34%, 34%, 32%, and 39%, respectively. Meanwhile, the concentrations of the Fe-Mn binding state of Cu, Zn, and the Fe-Mn binding state and organic bonding state of Pb and Cr decreased significantly. After 50 min of ultrasonic treatment, the total amount of heavy metals and the five states approached a stable level. These findings suggest that ultrasonic treatment can accelerate the release of metal elements from sediments to the water body; thus the ultrasonic algae inhibition technology is not sufficiently safe and reliable, involving the risk of secondary pollution.

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a School of Architecture and Construction, Yancheng Institute of Technology, Yancheng 224051, China
b Nanjing Automation Institute of Water Conservancy and Hydrology, Nanjing 210012, China
c College of Earth Science and Engineering, Hohai University, Nanjing 210098, China
d Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing 210098, China

* Corresponding author, E-mail: yczhqi@163.com

Received 23 Feb 2017, Accepted 22 Oct 2017