Grantee Research Project Results

2005 Progress Report: A Novel Adsorption Technology for Small-Scale Treatment of Arsenic

EPA Grant Number: R831513
Title: 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: Pollution Prevention/Sustainable Development , Sustainable and Healthy Communities

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 C_effluent,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.

Figure 1. Medium Column Breakthrough Profile of Virgin and Iron GAC #’s 3, 4, and 6 at an Initial pH ~6.0

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 project

Supplemental 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,, Sustainable Industry/Business, RFA, Scientific Discipline, INTERNATIONAL COOPERATION, TREATMENT/CONTROL, Water, Environmental Chemistry, Arsenic, Drinking Water, New/Innovative technologies, Environmental Engineering, Environmental Monitoring, Technology, adsorption, detoxification, treatment, drinking water treatment facilities, green engineering, drinking water system, drinking water contaminants, drinking water treatment, other - risk assessment, analysis of inorganic methods, clean technologies, arsenic removal, drinking water distribution system

Progress and Final Reports:

Original Abstract

2004

Final