Application of high frequency ultrasound in the destruction of DDT in contaminated sand and water.
High frequency ultrasound, as an alternative to high cost incineration, has been investigated to remediate DDT from sand and soil slurries. In this study, low power high frequency ultrasound (1.6 MHz; 150 W/L), with operating costs much lower than low frequency ultrasound, has been used to remediate DDT in liquid solution and in sand slurries. At 1.6 MHz, the wavelength, cycle time, bubble size and bubble life time are much smaller and the number of bubbles per litre is much larger than at frequencies below 50 kHz. These large differences affect the effective mass transfer to the bubbles and subsequent energy release, hydrolysis of water and degradation mechanism. Based on DDT measurement, using high frequency ultrasound, 90% of 8 mg/L of DDT from liquid solution was destroyed in 90 min. Removal efficiency from 32.6 mg/L of DDT in a 40 wt.% sand slurry was 22% in 90 min. Other slurry and DDT combinations are reported. Incremental chloride measurements indicated that combination of ultrasound and iron powder helps to increase the remediation rate of DDT from sand slurry, e.g. 46% cf. 32% for a 20 wt.% slurry. The results show that high frequency ultrasound is effective in degrading the non-polar pollutant DDT dispersed in water and in sand slurry. In practice, due to intensity limitations in currently available equipment and higher attenuation of energy, high frequency ultrasound has a low volume coverage and would require circulation of the slurry past the sonotrode, multiple sonotrodes, larger sonotrode area and lower slurry densities may still be required.
Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, SA 5095, Australia.
Kandasamy
K
Thangavadivel
Mallavarapu
M
Megharaj
Roger St C
RS
Smart
Peter J
PJ
Lesniewski
Ravi
R
Naidu
D003634:DDT / Q000737:chemistry*; D010575:Pesticides / Q000737:chemistry*; D012822:Silicon Dioxide; D014465:Ultrasonics; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D010575:Pesticides; D014874:Water Pollutants, Chemical; D012822:Silicon Dioxide; D003634:DDT