ASTM D6586-03(2008)
(Practice)Standard Practice for the Prediction of Contaminant Adsorption On GAC In Aqueous Systems Using Rapid Small-Scale Column Tests
Standard Practice for the Prediction of Contaminant Adsorption On GAC In Aqueous Systems Using Rapid Small-Scale Column Tests
SIGNIFICANCE AND USE
Granular activated carbon (GAC) is commonly used to remove contaminants from water. However if not used properly, GAC can not only be expensive but can at times be ineffective. The development of engineering data for the design of full-scale adsorbers often requires time-consuming and expensive pilot plant studies. This rapid standard practice has been developed to predict adsorption in large-scale adsorbers based upon results from small column testing. In contrast to pilot plant studies, the small-scale column test presented in this practice does not allow for a running evaluation of factors that may affect GAC performance over time. Such factors may include, for example, an increased removal of target compounds by bacterial colonizing GAC or long term fouling of GAC caused by inorganic compounds or background organic matter . Nevertheless, this practice offers more relevant operational data than isotherm testing without the principal drawbacks of pilot plant studies, namely time and expense; and unlike pilot plant studies, small scale studies can be performed in a laboratory using water sampled from a remote location.
This practice known as the rapid small-scale column test (RSSCT) uses empty bed contact time (EBCT) and hydraulic loading to describe the adsorption process. Mean carbon particle diameter is used to scale RSSCT results to predict the performance of a full-scale adsorber.
This practice can be used to compare the effectiveness of different activated carbons for the removal of contaminants from a common water stream.
SCOPE
1.1 This practice covers a test method for the evaluation of granular activated carbon (GAC) for the adsorption of soluble pollutants from water. This practice can be used to estimate the operating capacities of virgin and reactivated granular activated carbons. The results obtained from the small-scale column testing can be used to predict the adsorption of target compounds on GAC in a large column or full scale adsorber application.
1.2 This practice can be applied to all types of water including synthetically contaminated water (prepared by spiking high purity water with selected contaminants), potable waters, industrial waste waters, sanitary wastes and effluent waters.
1.3 This practice is useful for the determination of breakthrough curves for specific contaminants in water, the determination of the lengths of the adsorbates mass transfer zones (MTZ) and the prediction of GAC usage rates for larger scale adsorbers.
1.4 The following safety caveat applies to the procedure section, Section 10, of this practice: This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D6586 − 03(Reapproved 2008)
Standard Practice for
the Prediction of Contaminant Adsorption On GAC In
Aqueous Systems Using Rapid Small-Scale Column Tests
This standard is issued under the fixed designation D6586; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D2854Test Method for Apparent Density of Activated
Carbon
1.1 This practice covers a test method for the evaluation of
D2867Test Methods for Moisture in Activated Carbon
granular activated carbon (GAC) for the adsorption of soluble
D2862Test Method for Particle Size Distribution of Granu-
pollutantsfromwater.Thispracticecanbeusedtoestimatethe
lar Activated Carbon
operating capacities of virgin and reactivated granular acti-
vated carbons. The results obtained from the small-scale
3. Terminology
column testing can be used to predict the adsorption of target
compounds on GAC in a large column or full scale adsorber
3.1 Definitions:
application.
3.1.1 For definitions of terms in this practice relating to
1.2 This practice can be applied to all types of water
activated carbon, refer to Terminology D2652.
including synthetically contaminated water (prepared by spik-
3.1.2 For definitions of terms in this practice relating to
ing high purity water with selected contaminants), potable
water, refer to Terminology D1129.
waters, industrial waste waters, sanitary wastes and effluent
waters.
4. Summary of Practice
1.3 This practice is useful for the determination of break-
4.1 This practice consists of a method for the rapid deter-
through curves for specific contaminants in water, the deter-
mination of breakthrough curves and the prediction of GAC
mination of the lengths of the adsorbates mass transfer zones
(MTZ) and the prediction of GAC usage rates for larger scale usage rates for the removal of soluble contaminants from
adsorbers. water.Thisisaccomplishedbypassingthecontaminatedwater
at a constant controlled rate down flow through a bed of a
1.4 The following safety caveat applies to the procedure
specially sized granular activated carbon until predetermined
section, Section 10, of this practice:This standard does not
levels of breakthrough have occurred.
purport to address all of the safety concerns, if any, associated
with its use. It is the responsibility of the user of this standard
4.2 When the assumption is made that conditions of con-
to establish appropriate safety and health practices and
stant diffusivity exist within the GAC column, the break-
determine the applicability of regulatory limitations prior to
through data obtained from the column test can be used to
use.
estimate the size and operational conditions for a full-scale
carbon adsorber.
2. Referenced Documents
2.1 ASTM Standards:
5. Significance and Use
D1129Terminology Relating to Water
D1193Specification for Reagent Water
5.1 Granular activated carbon (GAC) is commonly used to
D2652Terminology Relating to Activated Carbon
remove contaminants from water. However if not used
properly, GAC can not only be expensive but can at times be
1 ineffective.Thedevelopmentofengineeringdataforthedesign
This practice is under the jurisdiction of ASTM Committee D28 on Activated
Carbon and is the direct responsibility of Subcommittee D28.02 on Liquid Phase
of full-scale adsorbers often requires time-consuming and
Evaluation.
expensive pilot plant studies. This rapid standard practice has
Current edition approved Aug. 1, 2008. Published September 2008. Originally
been developed to predict adsorption in large-scale adsorbers
approved in 2000. Last previous edition approved in 2003 as D6586–03. DOI:
10.1520/D6586-03R08.
based upon results from small column testing. In contrast to
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
pilotplantstudies,thesmall-scalecolumntestpresentedinthis
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
practice does not allow for a running evaluation of factors that
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. may affect GAC performance over time. Such factors may
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6586 − 03 (2008)
include, for example, an increased removal of target com- and large-column tests, respectively.The condition of constant
pounds by bacterial colonizing GAC or long term fouling of diffusivity also requires the Reynolds numbers for the RSSCT
GAC caused by inorganic compounds or background organic and the large-column be equal. This means the following
matter . Nevertheless, this practice offers more relevant opera- equation must also be satisfied:
tional data than isotherm testing without the principal draw-
V R
sc lc
5 (2)
backs of pilot plant studies, namely time and expense; and
V R
lc rc
unlike pilot plant studies, small scale studies can be performed
where: V and V are the hydraulic loadings in the RSSCT
in a laboratory using water sampled from a remote location. sc lc
and large columns, respectively. Based upon the above
5.2 Thispracticeknownastherapidsmall-scalecolumntest
equations, the operating conditions for the RSSCT can be
(RSSCT) uses empty bed contact time (EBCT) and hydraulic
selected to precisely simulate the desired (specified) operating
loading to describe the adsorption process. Mean carbon
conditions for a full-scale adsorber.
particle diameter is used to scale RSSCT results to predict the
NOTE 1—There is an important issue relating to RSSCT design using
performance of a full-scale adsorber.
Equation 2 . Sometimes using leads to a design with a high head loss,
5.3 This practice can be used to compare the effectiveness
which increases dramatically with operating time, as the GAC is crushed
of different activated carbons for the removal of contaminants by a large pressure drop across the RSSCT. This may be avoided by
loweringthesuperficialvelocityaslongasdispersiondoesnotbecomethe
from a common water stream.
dominant transport mechanism and intraparticle mass transfer is limiting
theadsorptionrate.ThePecletnumberbasedondiametercanbeestimated
6. Summary of Practice
from the following equation :
6.1 The development of the RSSCT is based on the
Pe 50.334 for160#Re·Sc#40,000
d
When the velocity is reduced below what is given in EquationA, axial
dispersed-flow pore surface diffusion model (DFPSDM)
dispersion,whichiscausedbymoleculardiffusion,canbemoreimportant
(Crittenden, et al ) which takes into account many of the
intheRSSCTthaninthefullscaleprocess.Consequently,EquationAcan
mechanisms that are known to occur in fixed-bed adsorption.
be used to check whether dispersion becomes important as the velocity of
The following mechanisms, which cause the breakthrough
the RSSCT is reduced in an effort to reduce the head loss. Typical Sc
curves for an adsorber to spread out and create the mass values for SOCs is ~ 2000; consequently, the Re for the RSSCT must be
kept greater than ~0.1 and the Pe must be kept above 50 for the length of
transfer zone are included in the DFPSDM: external mass-
the mass transfer zone.
transfer resistance or film transfer, axial mixing due to disper-
NOTE2—Empty-bedcontacttime(EBCT)isdefinedasthebedvolume
sion and the internal mass-transfer resistances of pore and
(in liters) divided by the water flow rate in liters/minute. For example if a
surface diffusion.
full scale adsorber holds 20 000 Lof activated carbon and the water flow
rate is 2500 L/min, the EBCT would be equal to 20 000/2500 or 8.0 min.
6.2 To simulate full-scale performance, the amount of
6.3 The assumption that conditions of constant diffusivity
spreading in the breakthrough curve relative to column depth
existwithintheGACcolumndoesnotapplytoallwatersorall
must be identical for the RSSCT and the full-scale column. To
targetcompounds.Forexamplethisassumptiondoesnotapply
achieve this, the relative contributions of the mechanisms that
for the decolorization of water and the adsorption of large
cause most of the spreading are matched by maintaining
molecules, such as humic and fulvic acids. It is recommended
similarity as the GAC process is scaled. Studies have shown
thatatleastoneRSSCTpilot-columncomparisonbeconducted
that matching of the spreading of the breakthrough curve can
to aid in selecting the RSSCT design variables for a given
beachievedbyequatingthedimensionlessgroupsinPFPSDM
water matrix (Crittenden, et al ). A detailed comparison be-
(Plug Flow Pore Surface Diffusion Model). Under the condi-
tween the constant diffusivity and proportional diffusivity
tions that intraparticle diffusivities are assumed to be indepen-
approaches and their respective domains of application is
dent of the carbon particle radius, i.e. the condition of constant
beyond the scope of this practice.
diffusivity, the following equation describes the relationship
between the small and large columns:
6.4 GAC bed volume and preparation methods are impor-
tant design parameters for the RSSCT. The GAC bed volume
EBCT R t
sc sc sc
5 5 (1)
S D
usedwilldeterminetherequiredwaterpumpingrateandaffect
EBCT R t
lc lc lc
theamountofwaterneededtocompletethetest.Theminimum
where:EBCT andEBCT aretheempty-bedcontacttimes
sc lc
column diameter needed to avoid channeling should be 50
forthesmall-column(RSSCT)andthelarge-column(full-scale
particlediameters.Forthe10-mmdiametercolumncommonly
adsorber), respectively; R and R are the radii of the carbon
sc lc
used in RSSCT systems, a 60 by 80 mesh carbon should be
particlesusedinthesmallandlargecolumns,respectively;and
used. Proper GAC sampling (Practice E300) and preparation
t and t are the elapsed times required to conduct the small-
sc lc
(grinding, classification and washing) are required for repro-
ducible results.
Owen,D.M.,Chowdhury,Z.K.,Summers,R.S.,Hooper,S.M.,andSolarik,G.,
6.5 Based upon the water feed rate to the column, the time
“Determination of Technology and Costs for GAC Treatment Using the ICR
required to reach the desired breakpoint and the weight of
Methodology,”AWWAGAC&MembraneWorkshop,March1996,Cincinnati,OH.
Knappe,D.,Snoeyink,V.,Roche,P.,Prados,M.andBourbigot,M.,“TheEffect
of Preloading on RSSCT Predictions of Atrazine Removal By GAC Adsorbers”, Crittenden, J. C., Berrigan, J. K., Jr., Hand, D. W., and Lykins, B. W., Jr.
Water Research, Vol. 31, No. 11, 1997, pp. 2899-2909. "Design of rapid fixed-bed adsorption tests for non-constant diffusivities," Journal
Crittenden, J. C., Berrigan, J. K., Jr., and Hand, D. W., "Design of rapid of Environmental Engineering, Vol. 113, No. 2, pp. 243-259, 1987.
small-scale adsorption tests for a constant surface diffusivity," Journal Water Fried, J. J., Groundwater Pollution. Elsevier Scientific, Amsterdam, The
Pollution Control Federation, Vol. 58, No. 4, pp. 312-319, 1986. Netherlands, 1975.
D6586 − 03 (2008)
carbon used, GAC usage rates for treating the water can be 8.1.2 GAC Support—Acolumn of fine glass wool installed
calculated. Breakthrough curves for each contaminant being to give a flat surface across the diameter of the column can be
monitored during the column test can also be generated. used for support of the GAC column.Alternatively the carbon
bed can be supported on a 100-mesh stainless steel screen
placed between two short sleeves made from ⁄2 in. PTFE
7. Interferences
tubing (see Fig. 2).The sleeves should be sized to fit tightly in
7.1 Insoluble materials such as oils and greases, suspended
the column to prevent any fluid from flowing between the
solids, and emulsions will interfere with the adsorption of
sleeves and the column wall.
soluble materials by the GAC. Suspended solids in the column
8.1.3 Feed Pumps—A liquid metering pump capable of
feed can lead to increased pressure drop and interfere with the
maintaining a steady flow rate of 6 0.05 mL/min at a column
operation of the column. These materials must be removed by
back pressure of up to 100 psig should be used. To prevent
suitable means before the water being treated is introduced to
over-pressurization of the column system in the event of
the column.
column plugging during operation, the pump should be set up
7.2 Air bubbles can interfere with water flow through the
with a bypass loop that allows the discharge from the pump to
column and lead to misleading results. A means for removing
beventedbacktothepumpinletthroughanadjustablepressure
air bubbles that are introduced into the system with the feed
relief device. The column inlet pressure and water flow rate
water should be incorporated to prevent these problems from
should be monitored and recorded throughout the run.
occurring.
8.1.4 Water Filtration—Afilter to remove suspended solids
that may be present in the water should be installed after the
8. RSSCT Test Apparatus
metering pump. A 47-mm inline filter housing with a 1.5 µm
8.1 The RSSCT test apparatus should be constructed of glassmicro-fiberfilterhasbeenfoundtobeadequatetoremove
glass, PTFE and/or stainless steel, to minimize the adsorption suspended solids that may prematurely plug the carbon bed.
Care must be exercised to ensure organic contaminants in the
of organic compounds. The apparatus shown in diagram form
in Fig. 1 consists of a metering pump, inlet filter, pressure and water being treated are not removed by the filter paper.
flow indicators, up to three columns operating in series and 8.1.5 Feed Water Containment—The feed water should be
means for water sample collection and analysis. maintained at the same temperatures as the carbon columns. If
8.1.1 Glass columns, vertically supported, 10.5 6 0.5 mm the feed water contains volatile organic compounds (VOCs),
inside diameter and approximately 35 cm in length with special care must be taken to prevent their loss during the test.
threaded joints at both ends are most commonly used. For short duration column tests where a relatively small
Threaded PTFE end caps with seats for neoprene o-ring seals amount of water is to be treated, the feed water can be stored
andtubingconnectorsshouldbeprovidedatthetopandbottom under zero head space conditions in pillow shaped bags
of the column for the admission and discharge of water. For manufactured from PTFE or similar material (typically used
operation at other than room temperature, a means for heating forthecollectionofgassamples).Gassamplingbagsupto100
or cooling the columns and the water being treated should be Lin volume can be conveniently used if properly supported. If
established. larger
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation:D6586–00 Designation:D6586–03 (Reapproved 2008)
Standard Practice for
the Prediction of Contaminant Adsorption On GAC In
Aqueous Systems Using Rapid Small-Scale Column Tests
This standard is issued under the fixed designation D 6586; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice covers a test method for the evaluation of granular activated carbon (GAC) for the adsorption of soluble
pollutants from water. This practice can be used to estimate the operating capacities of virgin and reactivated granular activated
carbons. The results obtained from the small-scale column testing can be used to predict the adsorption of target compounds on
GAC in a large column or full scale adsorber application.
1.2 This practice can be applied to all types of water including synthetically contaminated water (prepared by spiking high
purity water with selected contaminants), potable waters, industrial waste waters, sanitary wastes and effluent waters.
1.3 This practice is useful for the determination of breakthrough curves for specific contaminants in water, the determination
of the lengths of the adsorbates mass transfer zones (MTZ) and the prediction of GAC usage rates for larger scale adsorbers.
1.4 The following safety caveat applies to the procedure section, Section 10, of this practice: This standard does not purport
to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish
appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D 1129 Terminology Relating to Water
D 1193 Specifications for Reagent Water
D 2652 Terminology Relating to Activated Carbon
D 2854 Test Method for Apparent Density of Activated Carbon
D 2867Test Method Moisture Content of Activated Carbon Test Methods for Moisture in Activated Carbon
D 2862 Test Method for Particle Size Distribution of Granular Activated Carbon
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms in this practice relating to activated carbon, refer to Terminology D 2652.
3.1.2 For definitions of terms in this practice relating to water, refer to Terminology D 1129.
4. Summary of Practice
4.1 This practice consists of a method for the rapid determination of breakthrough curves and the prediction of GAC usage rates
for the removal of soluble contaminants from water. This is accomplished by passing the contaminated water at a constant
controlled rate down flow through a bed of a specially sized granular activated carbon until predetermined levels of breakthrough
have occurred.
4.2 When the assumption is made that conditions of constant diffusivity exist within the GAC column, the breakthrough data
obtained from the column test can be used to estimate the size and operational conditions for a full-scale carbon adsorber.
5. Significance and Use
5.1 Granular activated carbon (GAC) is commonly used to remove contaminants from water. However if not used properly,
GAC can not only be expensive but can at times be ineffective. The development of engineering data for the design of full-scale
This practice is under the jurisdiction of ASTM Committee D-28 on Activated Carbon and is the direct responsibility of Subcommittee D28. 02 on Liquid PHase
Evaluation.
Current edition approved Sept. 10, 2000. Published November 2000.
ThispracticeisunderthejurisdictionofASTMCommitteeD28onActivatedCarbonandisthedirectresponsibilityofSubcommitteeD28.02onLiquidPhaseEvaluation.
Current edition approved Aug. 1, 2008. Published September 2008. Originally approved in 2000. Last previous edition approved in 2003 as D 6586–03.
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
, Vol 11.01.volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6586–03 (2008)
adsorbers often requires time-consuming and expensive pilot plant studies. This rapid standard practice has been developed to
predict adsorption in large-scale adsorbers based upon results from small column testing. In contrast to pilot plant studies, the
small-scale column test presented in this practice does not allow for a running evaluation of factors that may affect GAC
performance over time. Such factors may include, for example, an increased removal of target compounds by bacterial colonizing
3 4
GAC or long term fouling of GAC caused by inorganic compounds or background organic matter . Nevertheless, this practice
offers more relevant operational data than isotherm testing without the principal drawbacks of pilot plant studies, namely time and
expense; and unlike pilot plant studies, small scale studies can be performed in a laboratory using water sampled from a remote
location.
5.2 This practice known as the rapid small-scale column test (RSSCT) uses empty bed contact time (EBCT) and hydraulic
loading to describe the adsorption process. Mean carbon particle diameter is used to scale RSSCT results to predict the
performance of a full-scale adsorber.
5.3 This practice can be used to compare the effectiveness of different activated carbons for the removal of contaminants from
a common water stream.
6. Summary of Practice
6.1 The development of the RSSCTis based on the dispersed-flow pore surface diffusion model (DFPSDM) (Crittenden, et al )
which takes into account many of the mechanisms that are known to occur in fixed-bed adsorption. The following mechanisms,
which cause the breakthrough curves for an adsorber to spread out and create the mass transfer zone are included in the DFPSDM:
external mass-transfer resistance or film transfer, axial mixing due to dispersion and the internal mass-transfer resistances of pore
and surface diffusion.
6.2 To simulate full-scale performance, the amount of spreading in the breakthrough curve relative to column depth must be
identical for the RSSCT and the full-scale column. To achieve this, the relative contributions of the mechanisms that cause most
6 5
of the spreading are matched by maintaining similarity as the GAC process is scaled. Crittenden et. al. Studies have shown that
matching of the spreading of the breakthrough curve can be achieved by assuming equating the dimensionless groups in PFPSDM
(Plug Flow Pore Surface Diffusion Model). Under the conditions that intraparticle diffusivities are assumed to be independent of
the carbon particle radius, i.e. the condition of constant diffusivity. Under these conditions of constant diffusivity, the following
equation describes the relationship between the small and large columns:
EBCT |R | t
sc sc sc
5 5 (1)
EBCT |R | t
lc lc lc
EBCT R t
sc sc sc
5 5 (1)
S D
EBCT R t
lc lc lc
where: EBCT and EBCT are the empty-bed contact times for the small-column (RSSCT) and the large-column (full-scale
sc lc
adsorber), respectively; R and R are the radii of the carbon particles used in the small and large columns, respectively; and t
sc lc sc
and t are the elapsed times required to conduct the small- and large-column tests, respectively. The condition of constant
lc
diffusivity also requires the Reynolds numbers for the RSSCT and the large-column be equal. This means the following equation
must also be satisfied:
V R
sc lc
5 (2)
V R
lc rc
where: V and V are the hydraulic loadings in the RSSCT and large columns, respectively. Based upon the above equations,
sc lc
the operating conditions for the RSSCT can be selected to precisely simulate the desired (specified) operating conditions for a
full-scale adsorber.
NOTE1—Empty-bed contact time (EBCT) is defined as the volume (in liters) of carbon in the adsorber bed divided by the water flow rate in
litres/minute. For example if a full scale adsorber holds 20 000 L of activated carbon and the water flow rate is 2500 L/min, the EBCT would be equal
to 20 000/2500 or 8.0 min.
6.3The assumption that conditions of constant diffusivity exist within the GAC column does not apply to all waters or all target
compounds.Forexamplethisassumptiondoesnotapplyforthedecolorizationofwaterandtheadsorptionoflargemolecules,such
Annual Book of ASTM Standards, Vol 15.01.
Owen, D.M., Chowdhury, Z.K., Summers, R.S., Hooper, S.M., and Solarik, G., “Determination of Technology and Costs for GAC Treatment Using the ICR
Methodology,” AWWA GAC & Membrane Workshop, March 1996, Cincinnati, OH.
Owen, D.M., Chowdhury, Z.K., Summers, R.S., Hooper, S.M., and Solarik, G., “Determination of Technology and Costs for GAC Treatment Using the ICR
Methodology” AWWA GAC & Membrane Workshop, March 1996, Cincinnati, OH.
Knappe, D., Snoeyink, V., Roche, P., Prados, M. and Bourbigot, M., “The Effect of Preloading on RSSCT Predictions ofAtrazine Removal By GACAdsorbers”, Water
Research, Vol. 31, No. 11, 1997, pp. 2899-2909.
Knappe, D., Snoeyink, V., Roche, P., Prados, M. and Bourbigot, M., “The Effect of Preloading on RSSCT Predictions ofAtrazine Removal By GACAdsorbers”, Water
Research, Vol 31, No. 11, 1997, pp. 2899-2909.
Crittenden, J. C., Berrigan, J. K., Jr., and Hand, D. W., 9Design of rapid small-scale adsorption tests for a constant surface diffusivity,9 Journal Water Pollution Control
Federation, Vol. 58, No. 4, pp. 312-319, 1986.
D6586–03 (2008)
as humic acids. It is recommended that at least one RSSCT pilot-column comparison be conducted to aid in selecting the RSSCT
design variables for a given water matrix (Crittenden, et al 1—There is an important issue relating to RSSCT design using
Equation 2 . Sometimes using 2 leads to a design with a high head loss, which increases dramatically with operating time, as the
GAC is crushed by a large pressure drop across the RSSCT. This may be avoided by lowering the superficial velocity as long as
dispersion does not become the dominant transport mechanism and intraparticle mass transfer is limiting the adsorption rate. The
Peclet number based on diameter can be estimated from the following equation :
Pe 5 0.334 for 160 # Re · Sc # 40,000
d
When the velocity is reduced below what is given in Equation A, axial dispersion, which is caused by molecular diffusion, can be more important in
the RSSCT than in the full scale process. Consequently, Equation A can be used to check whether dispersion becomes important as the velocity of the
RSSCT is reduced in an effort to reduce the head loss. Typical Sc values for SOCs is ~ 2000; consequently, the Re for the RSSCT must be kept greater
than ~0.1 and the Pe must be kept above 50 for the length of the mass transfer zone.
NOTE 2—Empty-bed contact time (EBCT) is defined as the bed volume (in liters) divided by the water flow rate in liters/minute. For example if a full
scale adsorber holds 20 000 L of activated carbon and the water flow rate is 2500 L/min, the EBCT would be equal to 20 000/2500 or 8.0 min.
6.3 The assumption that conditions of constant diffusivity exist within the GAC column does not apply to all waters or all target
compounds.Forexamplethisassumptiondoesnotapplyforthedecolorizationofwaterandtheadsorptionoflargemolecules,such
as humic and fulvic acids. It is recommended that at least one RSSCT pilot-column comparison be conducted to aid in selecting
the RSSCT design variables for a given water matrix (Crittenden, et al ). A detailed comparison between the constant diffusivity
and proportional diffusivity approaches and their respective domains of application is beyond the scope of this practice.
6.4 GAC bed volume and preparation methods are important design parameters for the RSSCT.The GAC bed volume used will
determine the required water pumping rate and affect the amount of water needed to complete the test. The minimum column
diameter needed to avoid channeling and to minimize column head loss should be 50 particle diameters. For the 10-mm diameter
column commonly used in RSSCT systems, a 60 by 80 mesh carbon should be used. Proper GAC sampling (Practice E 300) and
preparation (grinding, classification and washing) are required for reproducible results.
6.5 Based upon the water feed rate to the column, the time required to reach the desired breakpoint and the weight of carbon
used, GAC usage rates for treating the water can be calculated. Breakthrough curves for each contaminant being monitored during
the column test can also be generated.
7. Interferences
7.1 Insoluble materials such as oils and greases, suspended solids, and emulsions will interfere with the adsorption of soluble
materials by the GAC. Suspended solids in the column feed can lead to increased pressure drop and interfere with the operation
of the column. These materials must be removed by suitable means before the water being treated is introduced to the column.
7.2 Air bubbles can interfere with water flow through the column and lead to misleading results. A means for removing air
bubbles that are introduced into the system with the feed water should be incorporated to prevent these problems from occurring.
8. RSSCT Test Apparatus
8.1 TheRSSCTtestapparatusshouldbeconstructedofglass,PTFEand/orstainlesssteel,tominimizetheadsorptionoforganic
compounds. The apparatus shown in diagram form in Fig. 1 consists of a metering pump, inlet filter, pressure and flow indicators,
up to three columns operating in series and means for water sample collection and analysis.
8.1.1 Glass columns, vertically supported, 10.5 6 0.5 mm inside diameter and approximately 35 cm in length with threaded
joints at both ends are most commonly used. Threaded PTFE end caps with seats for neoprene o-ring seals and tubing connectors
should be provided at the top and bottom of the column for the admission and discharge of water. For operation at other than room
temperature, a means for heating or cooling the columns and the water being treated should be established.
8.1.2 GAC Support—Acolumn of fine glass wool installed to give a flat surface across the diameter of the column can be used
forsupportoftheGACcolumn.Alternativelythecarbonbedcanbesupportedona100-mesh
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