Sustainable Geoenvironmental Engineering Practice - Sustainable Practices in Geoenvironmental Engineering - page 497

13.3. Energy will be required to separate the smaller particles from the coarse particles to
disperse them. Experience showed that cavitation is much more effective than water jet-
ting for the separation of particles. This may be because cavitation acts as a tensile force for
the detachment of particles (Fukue et al., 2012).
13.6.4 Technological Images
For vast surface areas and for vast volumes of contaminated soils, a primary objective for
remediation of the affected soils is to reduce the volume of contaminated soils. The same
holds for contaminated sediments. To achieve this we need to separate contaminated frac-
tions from the noncontaminated fractions. The schematic rendering of the elements of
the remediation system, developed by Aomi Construction, Japan (Figure 13.14) shows the
technology consisting of four types of activities: separation, segregation, iltration, and
dilution (when required). The technology has been successfully applied for removal of
organic matter and ine particles from the bottom sediments in Fukuyama Port, Japan
(Fukue et al., 2012). For soils contaminated with radioactive substances, a closed system
is required together with the proper monitoring system to ascertain complete removal of
health-threatening issues.
13.6.4.1 Demonstration Pilot Tests on Contaminated Sediments and Soils
The techniques used in the demonstration pilot tests on contaminated sediments are
instructive inasmuch as they serve to inform one on how the system shown in Figure 13.14
would perform with contaminated soils. In the pilot tests that used a prototype of the
system shown in Figure 13.15, the contaminated sediments were placed in the segregation
tank and for dispersion by water jets that induced cavitation (116 L/min). In the siphon
typed rod, smaller particles (less than 75 µm) were pumped in to the separation tank to
remove loating material from the pumped mud water. To separate loating material, a
0.5 mm mesh was used, as shown in Figure 13.15. The suspension with particles greater
than 10 µm was separated by the cyclone (120-250 L/min) and was moved into the tanks for
ine mud. The supernatant was reused for water jetting. These procedures were repeated
and the sediments in the segregation tank were segregated into very ine or ine mud by
sedimentation process in the ine mud tank.
The grain size distribution curves for the suspended solids at various stages are shown
in Figure 13.16. The original sample soil was silty sand. The sediment after cavitation treat-
ment was sand without a ine fraction. Suspensions at a low level in the cyclone contained
silt fractions with a little amount of clay fractions. The suspension at the top of the cyclone
consisted of clayey silt without sand and gravel fractions. Thus, the pumped suspension—
i.e., upper and lower suspensions in the cyclone—contained only clay and silt fractions.
Thus, ine and coarse fractions of the sampled soil were well separated by the cavitation
and the cyclone treatments.
The effects of cavitation and supersonic separation were examined independently in the
laboratory. For cesium-contaminated soils, the procedures for measuring 134 Cs and 137 Cs of
different samples are shown in Figure 13.17, where sample A is the original contaminated
soil and sample B is obtained from the sediments after the treatment by cavitation. The
sediments in the cavitation treatment tank were moved into the ultrasonic treatment tank.
Samples C to G were obtained from the sediments at different times (3, 6, 9, 12, and 15 min)
during the ultrasonic treatment. Sample H consists of ine fractions settled in the loccula-
tion tank following locculant addition and sample W was obtained from the solution in