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Deposited colloid (mg , colloid/g, sand). Relative Concentration (C/C 0 ). Relative Concentration (C/C 0 ). Relative Concentration (C/C 0 ). Relative Concentration (C/C 0 ). Saitama University. Relative Concentration. 1L of ARW. 26.3cm, 26.9 cm. - PowerPoint PPT Presentation
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1Graduate School of Science and Engineering, Saitama University, JAPAN ([email protected]) 2Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, DENMARK
Mobilization and Deposition of Variably Charged Soil Colloids in Saturated Porous Media
Anu Sharma1, Chamindu Deepagoda T.K.K.2, Ken Kawamoto1, Per Moldrup2, Toshiko Komatsu1
ABSTRACT
Understanding colloid mobilization and retention in subsurface is important for predicting colloid-facilitated transport of contaminants and developing remedial strategies. The behavior and transport of colloids in varying physical and chemical conditions is yet to be fully understood. This study investigated transport behavior of water dispersible colloids (WDC) with different surface charges, extracted from volcanic ash soil (VAS) from Nishi-Tokyo, Japan and Red-yellow soil (RYS) from Okinawa, Japan. WDC solutions containing colloids with diameter <1µm were applied at water-saturated flow through 10cm-column packed with 0.1-0.5mm Toyoura sand or 0.42-0.85mm (Narita sand) size fraction under different colloid concentrations, flow rates and pH conditions. The colloidal solutions were characterized from the measurement of turbidity, zeta potential, and particle size distribution. 0.001M NaBr was used as a conservative tracer and the pH was adjusted using 0.1M HCl. Mechanisms of colloid transport and retention were studied by measuring colloid effluent concentration, deposition profile, and particle size distribution.
The results showed solution concentration of WDC had minimum effects on transport and deposition for RYS-WDC, however low flow rate caused more reversible entrapment of WDC compared to high flow rate condition. The breakthrough and breakdown curves, deposition profile and particle size distribution measurements clearly indicated additional effects of low solution pH in stronger colloid retainment, especially for VAS-WDC.
Porous MediaToyoura sandNarita sand
MATERIALS
Water Dispersible Colloids (WDC)WDC extracted from two types of soils from Japan Volcanic ash soil ( VAS-WDC) from
Nishi-Tokyo Red yellow soil (RYS-WDC) from
Okinawa
Properties of porous media
Selected properties for eluent and colloidal solution
Effect of pH
Effect of pH is evident from breakthrough curves of WDCs at natural pH and low pH (Fig 2), deposition profile and particle size distribution (Fig 3).
Comparison of porous media
COLUMN EXPERIMENTS
RESULTS AND DISCUSSIONS
Experimental Procedure The collected effluents were analyzed for
• Turbidity• pH• Electrical conductivity• Particle size distribution • Tracer (bromide) concentration
After column experiments• The column was dissected into 1cm sections• Deposited colloid concentration was measured
Experimental conditions and Mass balance results
Solution Application
SUMMARY OF RESULTS
For the same amount of colloid applied (~160mg/L), Toyoura sand irreversibly retained more water dispersible colloids (40%) than Narita sand (10%) (Fig 4). The particle size of Toyoura sand is much smaller than that of Narita sand and therefore, the WDC likely to get deposited in the saturated sand. (Fig. 5)
Saitama University
Porous media
Average diameter, d50 (mm)
Particle density ρs
(g/cm3)
Dry bulk density ρd (g/cm3)
Saturated hydraulic conductivity (Ks) cm/hr
Porosity, ϵ
Toyoura Sand
0.18 2.64 1.58 78.1 0.4
Narita Sand
0.64 2.6 1.56 27.76 0.4
Soil +
ARW
26.3cm, 26.9 cm
Shake 24 hrs,
25oC
Let it stand 20 hrs,
25oC
Filtration 1μm
Soil (125g of VAS) or (10g of RYS)
1L of ARW
Solution pH EC (mS/m)
Turbidity (NTU)
Concentration of CS (mg/L)
ζ potential at natural pH (mV)
ARW 6.5~ 6.8 2.1~2.3 0 -
VAS-WDC 6.5~7.0 2.5~5.8 7.2~10.1 4.8~7.1 -12~-14
RYS-WDC 7.5~8.0 5.5~8.0 126~131 88.7~99.2 -18~-20
ARW3PVs
Colloidal Solution10PVs
ARW7PVs
The colloid characterization results for VAS-WDC showed significant change in colloidal stability and zeta potential with change in pH indicating VAS-WDC as pH dependent surface charge dominant WDC, while a less significant change was observed in case of RYS-WDC suggesting it as permanent surface charge dominant WDC. The particle size distributions also indicate VAS-WDC as less stable WDC resulting in coagulation within short time than RYS-WDC.
Red Yellow Soil WDC
Fig. 1 Breakthrough and breakdown curves showing the effect of concentration and flow rate for RYS-WDC.
Fig. 2. Breakthrough and breakdown curves for (A) RYS-WDC and (B) VAS-WDC at low concentration and high flow rate with natural and low pH conditions .
Pore VolumesPore Volumes
(A) RYS-WDC (B) VAS-WDC
LC_HF LC_HF
CS_Natural pH CS_Low pH
Fraction collector
Computer
Data logger
Pressure transducer Nylon
Mesh 105 µm
ARW +CS, Br-
L=10cmdia = 4.91cm
ARW
Extraction procedure for water dispersible colloids
Particle size of RYS-WDC tends to become bigger at low pH resulting in coagulation/aggregation. (Fig. 4 and right table).
Pore volume
µ(µm)
HF_ HC Natural pH
σ(µm)
µ(µm)
HF_HC Low pH
σ(µm)
6 0.42 0.30 083 0.44
10 0.40 0.30 0.59 0.42
14 0.39 0.30 0.59 0.30
Mean particle size of RYS-WDC at high flow rate, high concentration , both at natural pH and low pH condition.
Artificial Rain Water (ARW)
0.085mM NaCl + 0.015 mM CaCl2
Nishi-Tokyo (Tokyo) Pasture / Agricultural land
Volcanic ash soil (Tachikawa loam)
Nakijinson (Okinawa) Hilly site Red-yellow soil (Kunigami mahji)
Soil sampling sites
WDC concentration had little effect, while the effect of flow rate was evident in RYS-WDC. At high flow rate condition, the water dispersible colloids seemed to be deposited irreversibly indicating similar
kinetics for both high concentration and low concentration of RYS-WDC (Fig. 1(A)) Low flow rate (10 times higher residence time) and high concentration of RYS-WDC caused reversible attachment
and release of colloids, apart from irreversible attachment (Fig. 1(B)). Thus, the colloid breakthrough and breakdown curves showed that the overall kinetics of RYS-WDC is flow
dependent than concentration dependent.
ASA-CSSA-SSSA2009 International annual Meeting
November 1-5, 2009, Pittsburgh, PA
Fig. 3. Particle size distribution for RYS-WDC at high flow, high concentration and low pH condition.
Particle size (µm)
Time (hrs)
RY
S-W
DC
Stability of WDC at different pHζ Potential as function of pH at 0, 48 hours
pH
Time (hrs)
VA
S-W
DC
pH
Particle size distribution at 0, 48 hours
Particle size (µm)
Particle size (µm)
Pore VolumesHC_HF LC_HF
Pore Volumes
HF_HC LF_HCBromide
(A) Effect of concentration (B) Effect of flow rate
HF: High flow rate; LF: low flow rate; HC: High concentration; LC: Low concentration; LpH: Low pH; NM: Not measured
Effect of pH
VAS-WDC is a pH dependent surface charge dominant WDC. With decrease in pH, the VAS-WDC becomes less negatively charged and therefore deposited on the porous media resulting in higher deposition and lower colloid recovery (Fig 2).
Fig. 4 Comparison of WDC (RYS and VAS) and porous media (Narita and Toyoura sand)
Fig. 5 Pore size distribution of Toyoura and Narita sand.
RYS-Br-
Pore Volumes
RYS-WDC VAS- Br-VAS-WDC
VAS-WDC & Toyoura sand
RYS-WDC & Narita sand
Pore diameter, d cm)
Toyoura Narita
Acknowledgements: This research was partially supported by a grant from the Research Management Bureau, Saitama University and the grant-in-aid for Young Scientists (A) (No 18686039) from the Japanese Ministry of Education, Science, Sports, and Culture (Monbukagakusho) and grant from Japan Interaction in Science and Technology Foundation (JIST Foundation).
Experimental Conditions Mass balance results
Porous media WDC Condition Flow
RateDarcy Flux (cm/min)
Concentration (mg/L)
Average Flow rate (cm3/min)
Turbidity (NTU) pH Residence
time (min)
Eluted fraction (Me)
Deposited fraction (Ms)
Total fraction (Mt)
LF_HC 0.06 245.63 1.05 396.00 6.2-6.9 70 0.86 0.15 1.01
LF_LC 0.06 33.72 1.16 44.68 5.7-6.6 70 0.51 0.40 0.91
HF_HC 0.53 151.28 9.98 244.00 6.4-6.9 7 0.94 0.28 1.22
HF_LC 0.55 20.00 10.42 32.25 6.2-6.7 7 0.88 0.76 1.64
HF_HC_LpH 0.57 238.58 10.69 384.80 4.6-5.8 7 0.62 0.39 1.01
HF_LC_LpH 0.56 25.78 10.60 41.58 4.9-5.9 7 0.68 0.48 1.16
HF_LC_LpH 0.56 22.24 10.52 4.6 4.6-5.3 7 NM NM NM
HF_HC_LpH 0.56 550 10.54 43.78 4.7-5.8 7 NM NM NM
HF_HC 0.57 567.00 10.79 44.99 7 NM NM NM
HF_LC 0.57 167.00 10.79 15.99 7 NM NM NM
LF_HC 0.16 575.00 3.03 45.57 30 NM NM NM
LF_LC 0.12 159.74 2.27 15.47 30 NM NM NM
NaritaSand
Toyoura Sand
RYS
VAS
Low
High
Low
Natural
Low
Natural