Directory UMM :Data Elmu:jurnal:E:Environmental Management and Health:Vol10.Issue1.1999:

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Enviro nme ntal Manage me nt

Department of Civil and Materials Engineering, University of Illinois, Chic ago, USA

Robin Semer

Jeffrey A. Adams

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Krishna R. Reddy, Robin Semer and Jeffrey A. Adams

Air flo w o ptimizatio n and surfac tant e nhanc e me nt to re me diate to lue ne -c o ntaminate d saturate d so ils using air sparging

Enviro nme ntal Manage me nt and He alth

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sp a r gin g fi eld sy st em s b a sed on sit e-sp ecific d a t a (Red dy a n d Zh ou , 1996). Add it ion a lly, d a t a fr om a ir sp a r gin g fi eld sy st em s cu r r en t ly in op er a t ion w ill b e u sed t o va lid a t e a n d im p r ove t h e m od el.

Du r in g t h e u se of a ir s p a r gin g, con t a m in a -t ion ei-t h er in con -t a c-t w i-t h or in -t h e v icin i-t y of a n a ir p a ss a gew ay is vola t ilized a n d r em oved w h ile con t a m in a t ion d is t a n t fr om t h e p a ss in g a ir m oves t ow a r d t h e a ir ch a n n els t h r ou gh d iffu sion . Diffu s ion is oft en a r a t e-lim it in g p r ocess ; r em ed ia t ion of con t a m in a n t t r a p p ed in s oil p or es or in t h e in t er s t ices of clay occu r s ver y slow ly. Wh ile t h e m a jor it y of t h e con t a m in a n t m a ss is r em oved r ela t ively q u ick ly t h r ou gh vola t iliza t ion , a s y m p t ot ic levels a r e r ea ch ed w h en r es id u a l con t a m i-n a i-n t r em ova l b ecom es d iffu s ioi-n -d e p ei-n d ei-n t . T h e r em ova l of r es id u a l con t a m in a t ion oft en t a k es s ign ifi ca n t ly lon ger t h a n t h e r em ova l of t h e in it ia l bu lk con t a m in a t ion . In cr ea sed d is s olu t ion of t h e r es id u a l or ga n ic com p ou n d wou ld a cceler a t e t h e r em ed ia t ion p r ocess con s id er a b ly by m ob ilizin g t h e con t a m in a n t a n d a llow in g it t o in t er a ct w it h t h e fl ow in g a ir m or e q u ick ly. T h e u s e of s u r fa ct a n t foa m s a s a n a ir s p a r gin g en h a n cem en t t ech n iq u e

m ay s ign ifi ca n t ly in cr ea se t h e m ob ilit y of r esid u a l con t a m in a n t s, a llow in g for m or e efficien t r em ova l.

Th is pa per pr esen ts th e r esu lts of la bor a tor y exper im en ts wh ich in vestiga ted th e effective-n ess of a ir spa r gieffective-n g ieffective-n r em ovieffective-n g tolu eeffective-n e fr om differ en t types of sa tu r a ted soils. On edim en -sion a l colu m n exper im en ts wer e con du cted u sin g two differ en t types of soil, a fi n e gr avel a n d a m ediu m to fi n e sa n d, u n der differ en t in jected a ir fl ow con dition s. Th e effect of su r fa cta n t foa m in jection cou pled w ith a ir spa r gin g on con ta m in a n t r em ova l efficien cy h a s a lso been eva lu a ted in th is pa per.

Experimental program

M aterials

Two d iffer en t soil t y p es w er e u sed in t h is r esea r ch : a fi n e gr avel, a n d a m ed iu m t o fi n e Ot t aw a sa n d . La b or a t or y t est s w er e fi r st p er for m ed on t h ese soils t o d et er m in e t h eir in d ex a n d en gin eer in g p r op er t ies. T h ese t est s in clu d ed gr a in s ize a n a ly sis, sp ecifi c gr av it y, m in im u m a n d m a xim u m d en s it ies, a n d h yd r a u lic con d u ct iv it y. T h e t est r esu lt s for

Figure 1

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1 0 / 1 [1 9 9 9 ] 5 2 –6 3

t h es e t wo s oils a r e su m m a r ized in Ta ble I. T h e gr a in s ize d ist r ibu t ion for t h e t wo s oils is sh ow n in F igu r e 2. Tolu en e, a m a jor

con s t it u en t of ga solin e a n d ot h er p et r oleu m p r od u ct s, w a s s elect ed a s t h e r e p r es en t a t ive VOC for t h is in ves t iga t ion a n d is r ou t in ely u s ed a s a n in d ica t or of or ga n ic con t a m in a t ion in gr ou n dw a t er a t fi eld s it es. T h e p r op er -t ies of -t olu en e a r e sh ow n in Ta ble II.

Two differ en t su r fa cta n ts wer e u sed to gen -er a te foa m s in th is stu dy, sodiu m dodecyl su l-fa te (SDS) a n d w itcon ol SN 70. E a ch of th ese

su r fa cta n ts is r ela tively in expen sive a n d is com m er cia lly ava ila ble. Th ese su r fa cta n ts wer e selected beca u se th ey possess low su r fa ce ten sion , low specific gr avity, good deter gen cy a n d solu biliza tion , a n d low soil disper sion . Addition a lly, both su r fa cta n ts a r e biode gr a d-a ble. Th e pr oper ties of th ese su r fd-a ctd-a n ts d-a r e su m m a r ized in Ta ble III. Wh ile SDS is a n ion ic, w itcon ol SN70 is n on -ion ic; th er efor e, th eir u se in th e stu dy a llow s for th e investiga tion of th e su ita bility of two differ en t gr ou ps of su r fa c-ta n ts. Ca tion ic su r fa cc-ta n ts wer e n ot u sed in th is stu dy beca u se su ch su r fa cta n ts h ave been sh ow n to r eta r d con ta m in a n t r em ova l (Abdu l, 1990; Cla r k e et a l., 1993).

Table II

Phys ic al and c he mic al parame te rs fo r to lue ne (Clarke e t al., 1 9 9 3 )

Molec ular Formula C₇H₈

Aromaticity Yes

M olecular weight 9 2 .1 3

Color/ form Colorless liquid

Boiling point, °C 1 1 1

M elting point, °C –9 5

Density, g/ cm3 0 .8 6 6 1

Aqueous solubility, mg/ L 5 1 5

Vapor pressure, mm Hg 4 0 (at 3 1 .8 °C)

Vapor density (air=1) 3 .1 4

Log K_ow(Octonol water coefficient) 1 .8 3 – 2 .9 4

Log K_oc(Soil/ water distribution coefficient referenced to soil

organic content) 1 .1 2 – 3 .2 8

K_H, Pa·m3/ mol (Henry’s Law Coefficient) 6 8 0

Figure 2

Grain s ize dis tributio n o f s o ils us e d in this s tudy

Table I

Charac te ris tic s o f s o ils us e d in e xpe rime nts

Property Sand Gravel

Unified soil classification,

ASTM D 2487 SP GP

Effective particle size, D₁₀,

ASTM D 422 0 .1 8 2 .3 5

Coefficient of uniformity,

C_c*, ASTM D 422 2 .1 2 .0

Coefficient of curvature,

C_u*, ASTM D 422 1 .0 1 .1

Specfic gravity, G_sASTM D 854 2 .6 7 –

M inimum dry density (g/ cm3),

ASTM D 4254 1 .5 6 1 .6 2

M aximum dry density (g/ cm3),

ASTM D 4253 1 .8 5 1 .9 0

Hydraulic conductivity (cm/ s),

ASTM D 2434 1 .9 7 x 1 0–2 _{1 .6 0}

Note:

*_{= C}

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Experimental set-up

A on ed im en sion a l a ir s p a r gin g colu m n a p p a -r a t u s w a s u t ilized d u -r in g t h e in ves t iga t ion . A sch em a t ic of t h e t es t a p p a r a t u s is s h ow n in F igu r e 3. T h e p lexigla s colu m n , m ea s u r in g 93 cm in h eigh t w it h a n in s id e d ia m et er of 8.7 cm , w a s u s ed t o con t a in t h e t es t s oil. Seven sa m p lin g p or t s w er e loca t ed a t d is t a n ces of 9cm , 19cm , 29cm , 39cm , 49cm , 45cm , a n d 59cm , r es p ect ively, fr om t h e b a se of t h e colu m n . T h ese loca t ion s a r e d es ign a t ed a s p or t s 1 t h r ou gh 7, r esp ect ively. T h e p or t s con s is t ed of a s e p t a a n d b r a s s s leeves h eld in p la ce w it h Tefl on fi t t in gs. T h e t op a n d b ot t om of t h e colu m n w er e sea led w it h p lexigla s cover s. E a ch cover fea t u r ed a gr oove h old in g a r u bb er Or in g in p la ce, p r ov id in g a n a ir -t igh -t s ea l b e-t w een -t h e cover a n d -t h e colu m n .

Six m a ch in e s cr ew s w er e u sed t o con n ect t h e cover s t o t h e colu m n .

T h e b ot t om cover is p r ov id ed w it h t wo on e-w ay in let q u ick con n ect or s. T h e fi r st in let e-w a s u sed for a ir in ject ion in t o t h e soil colu m n . T h e in let led t o a st a r -sh a p ed gr id of h oles t h a t a ssu r ed a u n ifor m d ist r ibu t ion of in ject ed a ir. T h e secon d in let ser ved t wo p u r p oses. F ir st , it w a s u sed t o in ject con t a m in a n t solu t ion in t o t h e soil colu m n . Aft er t h is w a s a ccom p lish ed , t h e con t a m in a n t sou r ce w a s d iscon n ect ed , a n d a feed lin e lea d in g t o a clea n w a t er r eser -voir w a s con n ect ed in it s p la ce. T h e r eser -voir w a s u sed t o m a in t a in a con st a n t h ea d w it h in t h e colu m n d u r in g t est in g.

Bot h t h e clea n w a t er r eser voir a n d a con t a m in a n t r eser voir w er e p la ced so a s t o m a in -t a in -t h e a p p r op r ia -t e h yd r a u lic h ea d in -t h e colu m n . T h e clea n w a t er r eser voir con t a in ed a level r e gu la t or a n d w a s con n ect ed t o a t a p. T h is sy st em a llow ed a d esir ed , con st a n t w a t er level t o b e m a in t a in ed in t h e r eser voir t h r ou gh ou t t h e t est in g. T h e w a t er r eser voir w a s con n ect ed t o t h e colu m n b ot t om cover u sin g Tefl on t u b in g. A ch eck va lve w a s p r ov id ed t o a ssu r e u n id ir ect ion a l fl ow fr om t h e r es er voir t o t h e colu m n . An ot h er va lve for fl ow sh u t -off w a s p r ov id ed . T h e con t a m i-n a i-n t r eser voir, w h ich h a d a t wo-lit er ca p a cit y, w a s a lso con n ect ed u s in g Tefl on t u b in g t o t h e colu m n b ot t om cover.

Th e con t r olled in ject ion of clea n a ir in t o t h e colu m n w a s a ccom plish ed t h r ou gh t h e u se of a n a ir sou r ce (com pr essed a ir ), a r e gu la t or, a pr essu r e ga u ge a n d a fl ow m et er a s sh ow n in

Table III

Pro pe rtie s o f s urfac tants us e d

Surfactant SDS Witconol SN70

Chemical Name sodium lauryl sulfate ethoxylated alc ohol

Ave. molecular weight 2 8 8 3 9 2

Form powder liquid

Specific gravity 0 .4 0 0 .9 8

Solubility in water 1 0 % in water moderately at 2 5 °C

Vapor pressure (mm Hg at 25°C) negligible <1

pH of 1 per cent solution 8 -1 0 6 -7

Critical micelle concentration 0 .2 3 1 wt% (2 .3 1 g/ l) 0 .5 0 0 wt% (5 g/ l)

Biodegradable yes yes

Net charge anionic nonionic

Figure 3

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1 0 / 1 [1 9 9 9 ] 5 2 –6 3

t olu en e con cen t r a t ion s in ea ch p or t w er e n or m a lized w it h t h e in it ia l t olu en e con cen -t r a -t ion d e-t ec-t ed a -t -t h a -t p or -t a n d p lo-t -t ed . T h r ou gh v isu a l ob s er va t ion , it w a s d et er -m in ed t h a t a ir t r aveled p r ed o-m in a n t ly in t h e for m of bu bbles d ist r ibu t ed even ly t h r ou gh -ou t t h e s oil cr os s-sect ion . Wit h in cr ea sin g a ir fl ow r a t e, t h e a ct iv it y of t h es e bu bbles s ign ifi -ca n t ly in cr ea sed .

T h e n or m a lized con cen t r a t ion p r ofi les in F igu r es 4(a ) t h r ou gh 4(c) sh ow t h a t com p let e t olu en e r em ova l w a s a ch ieved in a ll t h r ee t es t s. Com p let e r em ova l w a s a ccom p lis h ed in 390 m in u t es u sin g a n a ir fl ow r a t e of 380 m l/ m in ; in 140 m in u t es a t a n a ir fl ow r a t e of 960m l/ m in ; a n d in 80 m in u t es a t a n a ir fl ow

r a t e of 2,225 m l/ m in . T h ese r esu lt s sh ow t h a t in cr ea sin g a ir fl ow r a t es led t o fa st er con t a m -in a n t r em ova l. T h e con cen t r a t ion p r ofi les sh ow n in F igu r es 4(a ) t h r ou gh 4(c) w er e u sed t o ca lcu la t e t h e p er cen t t olu en e r em a in in g in t h e soil a t d iffer en t t im es; t h ese va lu es w er e p lot t ed a s s h ow n in F igu r e 5. T h e r esu lt s in F igu r e 5 clea r ly d em on st r a t e t h e effect of in ject ed a ir fl ow r a t e on t h e con t a m in a n t r em ova l. Ra p id in it ia l con t a m in a n t r em ova l w a s follow ed by slow er r em ova l r a t es d u r in g t h e u se of t h e low est fl ow r a t e. At h igh er a ir fl ow r a t es, r a p id in it ia l con t a m in a n t r em ova l a lso occu r r ed , bu t t h e r em a in in g con t a m i-n a i-n t w a s r em oved sligh t ly fa st er t h a i-n d u r ii-n g low est a ir fl ow r a t e u s a ge. How ever, t h e

Table IV

Summary o f o ne -dime ns io nal air s parging te s t c o nditio ns

Initial Initial Injected air Injected air

density concentration flow rate entry pressure

Test Soil (g/ cm3₎ _(ppm) _{(ml/ min)} _(kPa) _Surfactant

1 Gravel 1 .6 2 2 5 0 3 8 0 6 .9 NA

2 Gravel 1 .6 2 2 5 0 9 6 0 6 .9 NA

3 Gravel 1 .6 2 2 5 0 2 ,2 2 5 6 .9 NA

4 Sand 1 .6 2 2 5 0 2 ,2 2 5 6 .9 NA

5 Sand 1 .5 8 5 0 9 6 0 6 .9 NA

6 Sand 1 .5 8 5 0 3 8 0 9 .7 –1 2 .4 SDS

7 Sand 1 .5 8 5 0 3 8 0 8 .3 –9 .7 Witc onol SN7 0

Notes:

NA = Not applic able

1

0 .9

0 .8

0 .7

0 .6

0 .5

0 .4

0 .3

0 .2

0 .1

0

0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0

TIME (MINUTES)

N

O

R

M

A

L

IZ

E

D

T

O

L

U

E

N

E

C

O

N

C

E

N

T

R

A

T

IO

N

C

/

C

o

PORT 1 PORT 2 PORT 3 PORT 4 PORT 5 PORT 6 PORT 7 GRAVEL

INJECTION AIR FLOW RATE = 3 8 0 ml/ min.

(a) Figure 4 a

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n u m b er of ch a n n els wer e for m ed . Th e con t a m in a n t t h a t w a s p r esen t in t h e v icin -it y of t h ese ch a n n els w a s r em oved q u ick ly ; h owever, t h e con t a m in a n t in r e gion s u n t ou ch ed by ch a n n els h a d t o d iffu se t ow a r d t h e ch a n n els in or d er t o b e r em oved . Th is d iffu sion -con t r olled

r em ova l a llowed r esid u a l con t a m in a t ion t o p er sist w it h r em ova l occu r r in g ver y slow ly. 4 Su r fa ct a n t foa m in ject ion a t ver y low a ir

fl ow r a t es w a s fou n d t o a cceler a t e t h e bu lk con t a m in a n t r em ova l; h ow ever, t h e t ot a l r em ova l of t h e con t a m in a n t w a s d ifficu lt t o a ch ieve u s in g su r fa ct a n t foa m s. SDS w a s fou n d t o b e a m or e effect ive su r fa ct a n t t h a n w it con ol SN 70. Su r fa ct a n t en h a n ce-m en t ce-m ay b e a v ia ble op t ion for ob t a in in g sign ifi ca n t r em ova l efficien cies w h en h igh fl ow r a t es a r e n ot p os s ible d u e t o sit e geol-ogy or ot h er s it e-sp ecifi c con d it ion s. 5 Over a ll, b a sed on t h e exp er im en t s of t h is

st u dy, a ir sp a r gin g h a s s h ow n t o b e effi-cien t in r em ov in g VOCs fr om s a t u r a t ed soils. H igh r a t es of r em ova l ca n b e

a ch ieved fr om h igh ly p er m ea ble s oils su ch a s gr avels w it h low fl ow r a t es ; h ow ever, in soils w it h r ela t ively low er p er m ea b ilit y su ch a s sa n d s, h igh er fl ow r a t es a r e r eq u ir ed t o r em ove con t a m in a t ion . In sa n dy s oils, t h e u s e of low a ir fl ow r a t es m ay r es u lt in lin ger in g r es id u a l con t a m i-n a t ioi-n , evei-n w it h t h e u s e of s u r fa ct a i-n t s.

References and further reading

Abdu l, A.S., Gibson , T.L., a n d Ra i, D.N. (1990),

“Selection of su r fa cta n ts for th e r em ova l of petr oleu m pr odu cts fr om sh a llow sa n dy a qu ifer s”, Grou n d Wa ter, Vol. 28 No. 6, pp. 920-6. Ar d it o, C.P. a n d Billin gs, J .F. (1990), “Alt er n a t ive

r em ed ia t ion st r a t e gies : t h e s u b s u r fa ce vola t iliza t ion a n d ven t ila t ion s y s t em ”, Pr oceed in gs of th e Con feren ce on Petr oleu m H yd r oca r b on s a n d Orga n ic Ch em ica ls in Gr ou n d w a ter: Prev en tion , Detection , a n d

R estora tion , N a t ion a l Wa t er Well As socia t ion ,

Du blin , OH , p p. 281-96.

Cla r k e, A.N., Om a , K.H ., Me geh ee, M.M. a n d

Wilson , D.J . (1993), “Soil clea n -u p by su r fa c-t a n c-t w a sh in g. II. Des ign a n d eva lu a c-t ion of c-t h e

com p on en t s of t h e p ilot -sca le su r fa ct a n t

r ecycle s y s t em ”, S ep a ra tion S cien ce a n d T ech -n ology, Vol. 28 N o. 13, p p. 2103-35.

J i, W., Da h m a n i, A., Ah lfeld , D., Lin , J .D. a n d H ill,

E . (1993), “La b or a t or y s t u dy of a ir sp a r gin g: a ir fl ow v isu a liza t ion ”, Gr ou n d Wa ter M on

i-tor in g R ev iew , p p. 115-26.

J oh n s on , R.L., J oh n s on , P.C., McWh or t er, D.B.,

H in ch ee, R.E ., a n d Good m a n , I. (1993), “An

over v iew of in sit u a ir sp a r gin g”, Gr ou n d Wa ter M on itor in g R ev iew , p p. 127-35.

Leon a r d , W.C., a n d Br ow n , R.A. (1992), “Air sp a r g-in g: a n op t im a l solu t ion ”, Pr oceed g-in gs of th e

Con feren ce on th e Petr oleu m H yd r oca r b on s

a n d Orga n ic Ch em ica ls in Gr ou n d w a ter: Pre-v en tion , Detection a n d R estora tion , H ou s t on ,

TX, p p. 69-71.

N a t ion a l Res ea r ch Cou n cil (1994), “Alt er n a t ives for gr ou n d s w a t er clea n u p ”, N a t ion a l Aca d

-em y P r es s, Wa sh in gt on , DC.

Red dy, K.R. a n d Zh ou , J . (1996), “F in it e elem en t

m od elin g of a ir sp a r gin g for gr ou n dw a t er

r em ed ia t ion ”, Pr oceed in gs of th e S econ d In ter n a tion a l Con g ress on E n v ir on m en ta l

Geotech n ics, Kyot o, J a p a n , N ovem b er. Red dy, K.R., Kosgi, S. a n d Zh ou , J . (1995), “A

r ev iew of in s it u a ir sp a r gin g for t h e r em ed ia

-t ion of VOC-con -t a m in a -t ed sa -t u r a -t ed soils a n d gr ou n dw a t er ”, H a z a rd ou s Wa ste a n d H a z

-a rd ou s M -a ter i-a ls, Vol. 12 N o. 2, p p. 97-118.

Sebb a , F. (1989), “N ovel se p a r a t ion s u sin g a p h r on s ”, S u r fa cta n t S cien ce S er ies on S u r fa