Grantee Research Project Results
2005 Progress Report: A Novel Adsorption Technology for Small-Scale Treatment of Arsenic
EPA Grant Number: R831513Title: A Novel Adsorption Technology for Small-Scale Treatment of Arsenic
Investigators: Assaf-Anid, Nada M. , Duby, Paul F.
Institution: Columbia University in the City of New York
EPA Project Officer: Richards, April
Project Period: December 15, 2003 through December 14, 2004 (Extended to April 30, 2006)
Project Period Covered by this Report: December 15, 2004 through December 14, 2005
Project Amount: $49,794
RFA: Technology for a Sustainable Environment (2003) RFA Text | Recipients Lists
Research Category: Sustainable and Healthy Communities , Pollution Prevention/Sustainable Development
Objective:
Surface modified activated carbons hold promise as effective sorbents in arsenic (As) removal systems because they can be tailored to remove inorganic and organic As species, as well as other ions present in water, simultaneously. The objective of this research project is to explore the feasibility of three novel iron-impregnated granular activated carbon (GAC) materials for the treatment of both inorganic and organic As by adsorption. The rapid small-scale column test, which has been proven to simulate full-scale adsorbers adequately, was employed. The column breakthrough effluent concentration Ceffluent,b was equal to the allowable concentration of 10 ppb total As. This research project studied As adsorption in groundwater from the U.S. Environmental Protection Agency (EPA) Superfund site in Vineland, New Jersey, as well as in laboratory water spiked with a mixture of As(III) as Na3AsO3, As(V) as As2O5xH2O, and dimethylarsinic acid (also known as cacodylic acid or DMA; C2H7AsO2ˉ), at the 150-500 ppb levels. The influence of sulfate and pH on As displacement also was studied to evaluate sorbent selectivity.
Progress Summary:
Removals below 10 ppb were achieved in both the laboratory and at the EPA Superfund site in Vineland, New Jersey. The capacity of virgin GAC was determined to be approximately 0.1 mg/g for total As; this capacity was enhanced 100-fold after coating with iron (see Table 1 showing adsorbent characteristics) and reached 9.9 mg As/g Fe-GAC depending on treatment method and percent iron. The results indicate that iron-coated GAC is a promising adsorbent for the removal of inorganic and organic As species. Results also show that As adsorption on iron-coated GAC is not affected by the presence of natural organic matter or sulfate.
Table 1. Adsorbent Characteristics (the three iron-impregnated GACs were produced through three different heat treatments)
Adsorbent |
SBET |
Vt |
Pore Volume Distribution (cm3/g) |
pHpzc |
Iron Cont |
|||||
(m2/g) |
(cm3/g) |
<1 nm |
<2 nm |
<3 nm |
<5 nm |
<10 nm |
<100 nm |
(%) |
||
Virgin GAC HD 3000 |
686 |
0.712 |
0.134 |
0.176 |
0.203 |
0.243 |
0.327 |
0.535 |
5.3 |
0.1 |
Fe-GAC HD 3000 # 3 |
767 |
0.724 |
0.158 |
0.202 |
0.223 |
0.261 |
0.311 |
0.456 |
6.8 |
3.6 |
Fe-GAC HD 3000 # 4 |
646 |
0.649 |
0.119 |
0.161 |
0.185 |
0.228 |
0.290 |
0.453 |
6.8 |
11.6 |
Fe-GAC HD 3000 # 6 |
653 |
0.696 |
0.117 |
0.164 |
0.192 |
0.247 |
0.330 |
0.558 |
6.3 |
8.3 |
Medium Column Laboratory Experiments
For medium-sized column studies using GAC, as well as each of the Fe-GAC types (#’s 3, 4, and 6), a saturation curve was developed over 40 hours. Approximately 170 ppb of mixed As was prepared at a pH of about 6.0 and sent upward through four medium-sized columns packed with each media at a flow rate of approximately 1 mL/min. As expected, the virgin GAC reached saturation early, about 4 hours into the run. Fe-GAC # 3 was the second best adsorbent, lasting approximately 14 hours before exhaustion. Fe-GAC # 4 performed the best, reached breakthrough at approximately 8 hours, and did not reach complete saturation at the end of the experiment (at 61 hours). Fe-GAC # 6 was the second best, still not reaching saturation at the end of the 61-hour run but reaching breakthrough after only 4 hours. The capacity of the virgin GAC was consistent with the capacity obtained from the small-sized column studies at 0.1 mg As/g GAC. The capacities of Fe-GAC #3, #4, and # 6 were 1.6, 9.9, and 6.8 mg As/g Fe-GAC, respectively. Based on these results, Fe-GAC # 4 is approximately 100 times better than virgin GAC at capturing As. This is a significant increase in capacity. The graph and tabular results are shown in Figure 1 and Table 2, respectively.
Table 2. Medium Column Virgin and Iron GAC #’s 3, 4, and 6 Properties
Adsorbent: |
Virgin GAC |
Fe-GAC # 3 |
Fe-GAC # 4 |
Fe-GAC # 6 |
|
Adsorbent Volume |
1.556 |
1.556 |
1.556 |
1.556 |
mL |
Adsorbent Weight |
0.700 |
0.700 |
0.700 |
0.700 |
g |
Particle Density |
454 |
454 |
454 |
454 |
g/L |
Bulk Density (dry GAC) |
450 |
450 |
450 |
450 |
g/L |
Porosity |
0.01 |
0.01 |
0.01 |
0.01 |
|
Adsorbent Cost per Lb |
- |
- |
- |
- |
dollars |
Mesh Size |
100-140 |
100-140 |
100-140 |
100-140 |
|
Particle Diameter |
0.149-0.105 |
0.149-0.105 |
0.149-0.105 |
0.149-0.105 |
mm |
Adsorbent (BET) Specific Surface Area |
1000 |
1000 |
1000 |
1000 |
m2/g |
Flow Rate |
1.0 |
1.0 |
1.0 |
1.0 |
mL/min |
Adsorber Diameter |
0.0078 |
0.0078 |
0.0078 |
0.0078 |
m |
Adsorber Height |
0.300 |
0.300 |
0.300 |
0.300 |
m |
EBCT |
1.56 |
1.56 |
1.56 |
1.56 |
min |
Adsorber Cross-sectional Area |
0.0000478 |
0.0000478 |
0.0000478 |
0.0000478 |
m2 |
Adsorber Cross-sectional Area |
0.478 |
0.478 |
0.478 |
0.478 |
cm2 |
Superficial Velocity |
0.000349 |
0.000349 |
0.000349 |
0.000349 |
m/s |
Superficial Velocity |
1.256 |
1.256 |
1.256 |
1.256 |
m/h |
Adsorbent Height |
0.033 |
0.033 |
0.033 |
0.033 |
m |
Time at End of Experiment |
48 |
48 |
48 |
48 |
h |
Throughput Volume at End of Exp. |
2.9 |
2.9 |
2.9 |
2.9 |
L |
Number of Bed Volumes at End of Experiment |
1851 |
1851 |
1851 |
1851 |
|
Throughput Time at Saturation |
3.0 |
12.0 |
7.0 |
35.0 |
h |
Throughput Volume at Saturation |
0.18 |
0.72 |
0.42 |
2.10 |
L |
Number of Bed Volumes at Saturation |
116 |
463 |
270 |
1350 |
|
Particle Diameter to Inside Diameter Ratio |
0.0160 |
0.0160 |
0.0160 |
0.0160 |
|
Bed Length to Inside Diameter Ratio |
38 |
38 |
38 |
38 |
Figures 2 and 3 illustrate the breakthrough curves for total As and for each individual As species. The results show clearly that sulfate has no effect on total As adsorption at an approximate pH of 6.0 and that the Fe-GAC is much better at removing As(V) than DMA and As(III).
Figure 2. Medium Column Experiment Using all GAC Types With Sulfate at pH ~5.8
Figure 3. Medium Column Speciation of Virgin GAC With Sulfate at pH ~7.5
Medium Column Field Experiments
A field experiment was performed at the EPA Superfund site in Vineland, New Jersey, where activated alumina (AA), ferric hydroxide (Fe(OH)3), GAC, and Fe-GAC media were tested simultaneously for As removal from contaminated groundwater. During this field test, the best adsorbent was ferric hydroxide. It should be noted that Fe-GAC performed poorly; however, it was prepared using a procedure different than that used for the Fe-GAC #’s 3, 4, and 6 described earlier in this report.
Figure 4. Field Plot of Various Media at pH ~6.0 Put Date
Conclusions
The insight gained from this research will be important in risk predictions and performance considerations of this and other As adsorption technologies. The fixed bed technology used is a configuration that is well suited for small drinking water systems and for central use in homes or at the tap. Most importantly, the breakthrough curves measured in this study will be identical to those in the desired scaled-up systems (i.e., identical number of bed volumes at breakthrough), and they reflect possible interactions that can occur in those systems.
Future Activities:
The investigators did not report any future activities.
Journal Articles:
No journal articles submitted with this report: View all 6 publications for this projectSupplemental Keywords:
inorganic arsenic (III), As(III), inorganic arsenic (V), As(V), organic arsenic, dimethylarsinic acid, cacodylic acid, DMA, small filter, fixed bed adsorber, natural organic matter removal, iron-impregnated GAC, arsenic treatment, drinking water treatment, adsorption, pollutants/toxics, activated carbons, analysis of inorganic methods, arsenic removal, clean technologies, detoxification, drinking water system, drinking water contaminants, drinking water distribution system, drinking water treatment, drinking water treatment facilities, green engineering, groundwater,, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Water, TREATMENT/CONTROL, Sustainable Industry/Business, Environmental Chemistry, Arsenic, Technology, Environmental Monitoring, New/Innovative technologies, Drinking Water, Environmental Engineering, drinking water treatment facilities, clean technologies, detoxification, green engineering, other - risk assessment, arsenic removal, adsorption, drinking water distribution system, treatment, analysis of inorganic methods, activated carbons, drinking water contaminants, drinking water treatmentProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.