Jeehyeong Khim

Jihoon Cha

Myunghee Lim

Sang-Geon Nam

Sang-Hyun Cho

Younggyu Son

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Analysis of Energy Consumption in Ultrasonic Soil 
Washing Processes for the Diesel-Contaminated Soil
Sang-Geon Nam‡, Younggyu Son, Sang-Hyun Cho, Jihoon Cha, Myunghee Lim, 
Jeehyeong Khim (School of Civil, Environmental and Architectural Engineering, 
Korea Univ.)
1. Introduction 
Ultrasound irradiation in aqueous phase leads 
to cavitation events including the formation, 
oscillation/growth and violent collapse of bubbles 
in micro-scale. Extreme conditions inside bubble 
enable to generate sonochemical effect and 
sonophysical effect. Generally sonochemical effects 
are used for the removal of organic pollutants in 
homogeneous aqueous phase while sonophysical 
effects are employed for the surface cleaning and 
micro-mixing such as emulsification in 
heterogeneous system [1-5]. 
In soil-washing process, desorption of the organic 
or inorganic pollutants from the contaminated soil 
is the key step. Conventionally, water or water with 
surfactants is added as solvent and then mechanical 
mixing for washing is applied. Basically this typical 
washing process can remove pollutants only from 
the soil particle surface. However residual 
pollutants strongly adsorbed on the surface or 
pollutants entrenched inside pore require more 
mixing intensity, mixing time, or washing solvent. 
Sonophysical effects induced by ultrasound 
irradiation can enhance the mass transfer from the 
solid phase to liquid phase by violent action 
including micro-jet, micro-streaming, and shock 
wave, therefore the removal efficiency can be 
increased significantly by ultrasound [6, 7]. 
The purpose of this study was to esimate removal 
efficiency for mechanical soil washing, ultrasonic 
soil washing, and ultrasonic and mechanical soil 
washing process and to optimize the energy 
consumption in ultrasonic and mechanical soil 
washing processes. 
2. Experimental Methods 
Fig. 1 shows a schematic of the experimental 
set-up. The pentagon-shape sonoreactor consisted 
of a stainless steel reactor and five ultrasonic 
transducer modules (Mirae Ultrasonic Tech.) which 
was placed on each side wall. Each transducer 
module contained three lead zirconate titanate  
------------------------------------------------------------ 
hyeong@korea.ac.kr
(PZT) transducers (Tamura) which could produce 
four frequencies of 35, 72, 110, and 170 kHz. The 
ultrasound of one of four frequencies was irradiated 
from five side walls and concentrated at the center 
of the reactor. A 400 mL pyrex vessel containing 
target materials was placed at the upper position of 
the sonoreactor. The reactor was filled with 5 L of 
tap water and the water temperature was maintained 
at 25 ± 2  using recirculation cooling system. 
Fig. 1 Schematic of sonoreactor for soil washing 
processes.
The electric input power for the whole sonoreactor 
was measured by a multi-meter (M-4660M, 
METEX). The water temperature in the vessel was 
measured for calorimetry during ultrasound 
irradiation using a thermometer (DTM-318, Tecpel) 
and effective ultrasonic power in the vessel was 
obtained using following equation:  
( / ) pUltrasonic Power dT dt c M�    (1) 
where /dT dt  was rate of temperature increase in 
the solution, 
pc was heat capacity of solution 
(water), M was mass of solution 
Joomunsin sand commercially available in Korea 
was sieved to the particle size of 0.24~2 mm. The 
sieved soil was contaminated with diesel and then 
aged over 15 days in the dark vessel at room 
temperature. The initial concentration of diesel in 
the soil was 20,000 mg/kg.  
－ 145 －
Proceedings of Symposium on Ultrasonic Electronics, Vol. 30 (2009) pp. 145-146 
18-20 November, 20091P4-30
For all experimental sets the soil-water ratio was 
1:3 (a 10 g of soil was used) and mechanical mixing 
using agitator with Teflon blade was applied at the 
speed of 50 and 100 rpm. The electric power 
consumed by agitator was measured using the 
multi-meter. After 1 min washing process the 
residual diesel concentration in terms of total 
petroleum hydrocarbons (TPH) was measured 
according to the Korean standard method for soil 
pollution. The slurry sample in the vessel was 
dehydrated using anhydrous sodium sulfate and 
then residual diesel was extracted from the soil 
using dichloromethane under ultrasonic irradiation 
for 10 min. The extraction solution was filtered by 
disposable syringe filter and injected into a gas 
chromatography (Agilent Technologies 6890N) 
equipped with a flame ionization detector and a 
DB-TPH column (30m × 0.32mm × 0.25 mm). 
3. Results and Discussion 
Fig. 2 shows removal efficiency of diesel 
from contaminated soil for ultrasonic soil washing 
and ultrasonic/mechanical soil washing under 
various conditions. Low removal efficiencies were 
obtained in ultrasonic soil washing while relatively 
high removal efficiencies were observed in 
ultrasonic and mechanical soil washing. High 
removal efficiency in ultrasonic and mechanical soil 
washing was resulted from physical effects such as 
micro-jet and micro-streaming induced by 
ultrasonic cavitation. These sonophysical effects 
could enhance mass transfer of diesel from soil to 
aqueous phase and enable to remove the pollutant 
inside the pore which hardly desorbed by 
mechanical mixing. 
Fig. 2 Removal efficiency under ultrasonic and 
ultrasonic/mechanical soil washing conditions.
Fig. 3 shows the removal efficiency for electric 
energy consumption under various conditions. The 
mixing speed was 50 and 100 rpm and electric 
energy consumptions for 50 and 100 rpm were 2.00 
and 2.70 W, respectively. In ultrasonic and 
mechanical soil washing increase of energy for 
mechanical mixing resulted in about 6 % increase 
of removal efficiency at ultrasonic energy of 0.84 
W while at ultrasonic energy of 1.59 W increase of 
mechanical mixing did not make any significant 
increase.
Fig. 3 Removal efficiency for electric energy 
consumption under ultrasonic and ultrasonic/mechanical 
soil washing processes. 
Acknowledgment 
This work was supported by the Korea Research 
Foundation Grant funded by the Korean 
Government (MOEHRD) (KRF-2008-313- 
D00576). 
References 
1. Y.G. Adewuyi: Ind. Eng. Chem. Res. 40 (2001) 
4681. 
2. L.H. Thompson, L.K. Doraiswamy: Ind. Eng. 
Chem. Res. 38 (1999) 1215. 
3. M. Lim, S. Kim, Y. Kim, J. Khim: Ultrason. 
Sonochem. 14 (2007) 93. 
4. Y. Kim, J. Park, S. Kim, J. Khim: Jpn. J. Appl. 
Phys. 46 (2007) 4912. 
5. M. Lim, Y. Son, J. Yang, J. Khim: Jpn. J. Appl. 
Phys. 47 (2008) 4123. 
6. T.J. Mason, J.P. Lorimer: Applied Sono 
chemistry-The Uses of Power Ultrasound in 
Chemistry and Processing, Wiley-VCH Verlag 
GmbH, Weinheim, 2002. 
7. G. Dermont, M. Bergeron, G. Mercier, M. 
Richer-Lafleche: J. Hazard. Mater. 152 (2008) 1. 
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Analysis of Energy Consumption in Ultrasonic Soil Washing Processes for the Diesel-Contaminated Soil

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Analysis of Energy Consumption in Ultrasonic Soil Washing Processes for the Diesel-Contaminated Soil

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