Technology Demonstration of a Thermal Desorption-UV Photolysis

Apr 24, 1987 - 1 International Technology Corporation, 312 Directors Drive, Knoxville, ... 3 Waste Technology Programs, EG&G Idaho, Idaho Falls, ID 83...
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Chapter 26

Technology Demonstration of a Thermal Desorption-UV Photolysis Process for Decontaminating Soils Containing Herbicide Orange Downloaded by NORTH CAROLINA STATE UNIV on August 25, 2013 | http://pubs.acs.org Publication Date: April 24, 1987 | doi: 10.1021/bk-1987-0338.ch026

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R. Helsel , E . Alperin , T. Geisler , A. Groen , R. Fox , T. L . Stoddart , and H. D. Williams 3

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International Technology Corporation, 312 Directors Drive, Knoxville, T N 37923 Headquarters, Air Force Engineering Services Center, Research & Development Directorate, Environics Division, Environmental Engineering Branch, Tyndall Air Force Base, F L 32403 Waste Technology Programs, EG&G Idaho, Idaho Falls, ID 83415

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Laboratory and field testing determined the effectiveness of a new decontamination process for soils containing 2,4-D/2,4,5-T and traces of dioxin. The process employs three primary operations - thermal desorption to volatilize the contaminants, condensation and absorption of the contaminants in a solvent, and photochemical decomposition of the contaminants. Bench-scale experiments established the relationship between desorption conditions (time and temperature) and treatment efficiency. Laboratory tests using a batch photochemical reactor defined the kinetics of 2,3,7,8-TCDD disappearance. A pilot-scale system was assembled to process up to 100 pounds per hour of soil. Tests were conducted at two sites to evaluate treatment performance and develop scale-up information. Soil was successfully decontaminated to less than 1 ng/g 2,3,7,8-TCDD at temperatures above 460°C.

As p a r t o f a major program b e i n g conducted by the U.S. A i r Force t o r e s t o r e t o normal use s e v e r a l Department o f Defense s i t e s where s o i l s have been contaminated w i t h low l e v e l s o f H e r b i c i d e Orange (HO), I n t e r n a t i o n a l Technology C o r p o r a t i o n ( I T ) , under s u b c o n t r a c t to EG&G Idaho, has been c o n d u c t i n g a p r o j e c t i n v o l v i n g l a b o r a t o r y b e n c h - s c a l e and f i e l d p i l o t - s c a l e t e s t s t o demonstrate a new s o i l t r e a t m e n t p r o c e s s - t h e r m a l desorption/UV p h o t o l y s i s (TD/UV). The i n t e n t o f t h e d e m o n s t r a t i o n was t o reduce t h e combined t e t r a - , p e n t a - , and h e x a - c h l o r i n a t e d d i b e n z o d i o x i n (CDD) and f u r a n (CDF) congeners, which o r i g i n a t e d from the HO, t o l e s s than 1 ng/g, which represented the a n t i c i p a t e d s o i l clean-up c r i t e r i a . Treatment s h o u l d a l s o e f f e c t i v e l y remove the p r i m a r y HO c o n s t i t u e n t s , 2,4-D 0097-6156/87/0338-0319$06.00/0 © 1987 American Chemical Society

In Solving Hazardous Waste Problems; Exner, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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and 2 , 4 , 5 - T . Two s i t e s were i n c l u d e d i n t h e f i e l d demonstration p r o j e c t f o r t h e TD/UV p r o c e s s , each having s u b s t a n t i a l l y d i f f e r e n t types o f s o i l b u t r e a s o n a b l y s i m i l a r c o n c e n t r a t i o n s o f t h e HO constituents. T e s t i n g a t the Naval C o n s t r u c t i o n B a t t a l l i o n Center (NCBC) a t G u l f p o r t , M i s s i s s i p p i was conducted by IT d u r i n g May 1985; t e s t i n g a t Johnston I s l a n d ( J I ) i n t h e P a c i f i c Ocean o c c u r r e d i n J u l y 1 9 8 6 . Based on t h e r e s u l t s o f these f i e l d p i l o t demonstrat i o n s , an e n g i n e e r i n g and c o s t e v a l u a t i o n i s being performed f o r a p p l y i n g TD/UV technology u s i n g l a r g e , m o b i l e systems f o r these two s i t e s o r o t h e r s i t e s h a v i n g s i m i l a r contaminated s o i l problems. T h i s paper d e s c r i b e s t h e t e c h n o l o g y , h i g h l i g h t s t h e r e s u l t s o f t h e i n i t i a l l a b o r a t o r y t e s t phase, and summarizes t h e f i e l d demonstration results. Process

Description

The thermal d e s o r p t i o n / U V p h o t o l y s i s process developed by IT a c c o m p l i s h e s s u b s t a n t i a l volume r e d u c t i o n and t o x i c i t y r e d u c t i o n by c o n c e n t r a t i n g t h e hazardous c o n s t i t u e n t s c o n t a i n e d i n t h e s o i l i n t o a s m a l l volume which i s e a s i e r t o t r e a t than l a r g e q u a n t i t i e s o f soil. The p r o c e s s i n c o r p o r a t e s t h r e e s t e p s : Desorption

- heating the s o i l t o v o l a t i l i z e the organic contaminants Scrubbing - c o l l e c t i n g the v o l a t i l i z e d organics i n a suitable solvent P h o t o l y s i s - c o n v e r t i n g t h e contaminants t o r e l a t i v e l y non-hazardous r e s i d u e s through p h o t o c h e m i c a l reactions. A s c h e m a t i c b l o c k - f l o w diagram i s presented as F i g u r e 1. Contaminated s o i l i s passed c o n t i n u o u s l y through an i n d i r e c t l y heated desorber which can be one o f many types o f c o n v e n t i o n a l equipment a p p l i c a b l e f o r thermal p r o c e s s i n g o f s o l i d s . The t r e a t ment performance o f t h e desorber i s c o n t r o l l e d by t h e r e s i d e n c e time and temperature o f t h e s o i l . Treatment r e q u i r e m e n t s ( i . e . , o p e r a t i n g c o n d i t i o n s ) a r e determined by t h e v o l a t i l i t y o f t h e s o i l c o n t a m i n a n t s and t h e r e q u i r e d contaminant removal e f f i c i e n c y ( f i n a l versus i n i t i a l c o n c e n t r a t i o n ) . The o f f - g a s l e a v i n g t h e desorber c o n t a i n s o r g a n i c vapors, water vapor o r i g i n a t i n g as i n i t i a l soil moisture, and s m a l l q u a n t i t i e s o f a i r which e n t e r w i t h t h e s o i l . Scrubbing using a h i g h b o i l i n g hydrocarbon s o l v e n t i s used t o t r e a t t h e o f f - g a s t o remove t h e o r g a n i c c o n t a m i n a n t s and water vapor by c o o l i n g , condens a t i o n , and a b s o r p t i o n . P a r t i c u l a t e s ( e . g . , f i n e s o i l ) which may be e n t r a i n e d by t h e o f f - g a s a r e a l s o c o l l e c t e d by t h e s c r u b b i n g solvent. Scrubbed o f f - g a s i s passed through a c o n v e n t i o n a l emiss i o n c o n t r o l system, such as carbon a d s o r p t i o n , t o ensure t h a t no o r g a n i c contaminants o r s o l v e n t vapors a r e r e l e a s e d . Scrubber s o l v e n t i s r e c i r c u l a t e d t o t h e scrubber a f t e r being processed through a system o f phase s e p a r a t i o n , f i l t r a t i o n , and c o o l i n g . Condensed w a t e r , which i s i m m i s c i b l e w i t h t h e s o l v e n t , i s s e p a r a t e d and e i t h e r d i r e c t l y t r e a t e d u s i n g c o n v e n t i o n a l t e c h n i q u e s , such a s f i l t r a t i o n and carbon a d s o r p t i o n , o r d i s c h a r g e d t o an e x i s t i n g

In Solving Hazardous Waste Problems; Exner, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

Downloaded by NORTH CAROLINA STATE UNIV on August 25, 2013 | http://pubs.acs.org Publication Date: April 24, 1987 | doi: 10.1021/bk-1987-0338.ch026

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Thermal Desorption-UV Photolysis Process

Thermal d e s o r p t i o n / U V p h o t o l y s i s p r o c e s s c o n c e p t .

In Solving Hazardous Waste Problems; Exner, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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wastewater treatment f a c i l i t y . F i l t e r e d s o l i d s are r e c y c l e d t o the desorber o r packaged as process waste f o r o f f - s i t e d i s p o s a l , depending on the r e l a t i v e q u a n t i t y and c o m p o s i t i o n . A s m a l l p o r t i o n o f t h e r e c i r c u l a t e d s o l v e n t stream i s d i v e r t e d t o a UV p h o t o l y s i s system t o t r e a t ( d e t o x i f y ) and remove the o r g a n i c c o n t a m i n a n t s , w i t h t h e t r e a t e d s o l v e n t purge r e c y c l e d to t h e s c r u b b i n g system. The e q u i l i b r i u m c o n c e n t r a t i o n o f t h e contaminants i n t h e scrubber s o l v e n t i s maintained as h i g h as p r a c t i c a l t o m i n i m i z e the purge stream and a f f o r d h i g h e r p h o t o l y s i s r e a c t i o n r a t e s , thereby d e c r e a s i n g the s i z e o f the p h o t o l y s i s treatment system. The c o n c e n t r a t i o n l i m i t a t i o n i s dependent on t h e s o l u b i l i t y p r o p e r t i e s and p a r t i a l p r e s s u r e o f the contaminants i n the s o l v e n t , and t h e r e s u l t a n t e f f e c t on scrubber e f f i c i e n c y and emission p o t e n t i a l . The p h o t o l y s i s system c o n t a i n s a s p e c i a l l y designed f l o w r e a c t o r which s u b j e c t s the c o n t a m i n a n t - l a d e n s o l v e n t to UV r a d i a t i o n t o induce m o l e c u l a r d e c o m p o s i t i o n . High i n t e n s i t y mercury vapor lamps produce a band o f wavelengths, some o f which match the a b s o r p t i o n energy o f the s p e c i f i c o r g a n i c m o l e c u l e s b e i n g treated. C o o l i n g i s p r o v i d e d t o the r e a c t o r t o remove the thermal o u t p u t o f t h e lamp. The p h o t o l y z e d s o l v e n t i s t r e a t e d by u s i n g s e l e c t e d c o n v e n t i o n a l p h y s i c a l o r thermal s e p a r a t i o n processes, such as d i s t i l l a t i o n , t o remove t h e r e a c t i o n product residue. A l t e r n a t i v e l y , a purge o f the p h o t o l y z e d s o l v e n t can be d i s c a r d e d as waste t o c o n t r o l t h e l e v e l s o f r e a c t i o n p r o d u c t s i n the r e c i r c u l a t e d s o l v e n t system. Other c o n f i g u r a t i o n s o f treatment processes u s i n g thermal d e s o r p t i o n as t h e primary s e p a r a t i o n technique can be a p p l i e d t o organically contaminated soils. Alternative physical/chemical processes can be used t o t r e a t t h e desorber o f f - g a s and t h e contaminants. To a c h i e v e complete contaminant d e s t r u c t i o n , t h e o f f - g a s can be t r e a t e d by u s i n g c o n v e n t i o n a l fume i n c i n e r a t i o n o r o t h e r thermal treatment technology. The c h o i c e o f t h e type o f desorber and o f f - g a s treatment system depends on the c o n c e n t r a t i o n and p r o p e r t i e s o f the c h e m i c a l c o n t a m i n a n t s , s o i l c h a r a c t e r i s t i c s , q u a n t i t y o f contaminated m a t e r i a l , s i t e c h a r a c t e r i s t i c s , a v a i l a b i l i t y o f o f f - s i t e d i s p o s a l , and r e g u l a t o r y and r e l a t e d r e q u i r e m e n t s . Laboratory

T e s t i n g and R e s u l t s - Thermal

Desorption

Thermal d e s o r p t i o n i s a p h y s i c a l separation process, although chemical t r a n s f o r m a t i o n o f t h e o r g a n i c contaminants may occur depending on t h e thermal s t a b i l i t y and the o p e r a t i n g temperatures r e q u i r e d t o a c h i e v e adequate d e c o n t a m i n a t i o n efficiency. Thermal d e s o r p t i o n has been used o n l y i n a l i m i t e d number o f cases (1-4) for treating contaminated soil, and these a p p l i c a t i o n s have i n v o l v e d r e l a t i v e l y v o l a t i l e o r g a n i c compounds, such as s o l v e n t s . Because o f t h e extremely low v o l a t i l i t y o f CCD and CDFs, t h e development o f b a s i c t r e a t a b i l i t y data was e s s e n t i a l t o c o n f i r m t h a t 1 ng/g l e v e l s i n s o i l c o u l d be a c h i e v e d and t h a t the r e q u i r e d desorption c o n d i t i o n s were p r a c t i c a l , considering the design f e a t u r e s and o p e r a t i n g r a t e s o f equipment a v a i l a b l e f o r p e r f o r m i n g such treatment. D e s o r p t i o n t r e a t a b i l i t y t e s t i n g was conducted on samples o f contaminated s o i l from t h r e e HO contaminated s i t e s - NCBC, J I , and

In Solving Hazardous Waste Problems; Exner, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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E g l i n A i r Force Base. The g o a l s o f the t e s t e f f o r t were t o e v a l u a t e the e f f e c t o f time and temperature on 2,3,7,8-TCDD removal e f f i c i e n c y and t o e s t a b l i s h the importance o f s o i l t y p e . The samples were s e l e c t e d by the A i r Force based on r e s u l t s o f s i t e surveys to y i e l d high contamination l e v e l s i n order to i n v e s t i g a t e a broad range o f t r e a t a b i l i t y . T h i s t e s t i n g was an e x t e n s i o n o f e a r l i e r t e s t i n g performed f o r the EPA on two d i o x i n - c o n t a m i n a t e d s o i l samples from M i s s o u r i t o s u p p o r t EPA's mobile i n c i n e r a t o r t r i a l burn i n 1985 ( 5 ) . A f t e r each s o i l sample was blended, a i r d r i e d , and screened (2 mm s i e v e opening) t r i p l i c a t e a l i q u o t s were taken and a n a l y z e d f o r 2,3,7,8-TCDD, CDD and CDF congeners, and 2,4-D and 2,4,5-T. The t h r e e prepared s o i l s had 2,3,7,8-TCDD l e v e l s g r e a t e r than 100 ng/g and 2,4-D/2,4,5-T l e v e l s o f about 1000 yg/g. The J I s o i l had s i g n i f i c a n t c o n c e n t r a t i o n s o f hepta and o c t a CDD compared w i t h the o t h e r two samples. In a d d i t i o n , s e l e c t e d p h y s i c a l and c h e m i c a l p r o p e r t i e s p r e s e n t e d i n T a b l e I , were measured (6). The EPA t e s t program (5) had i n d i c a t e d t h a t s o i l p r o p e r t i e s had o n l y a minor i n f l u e n c e on removal e f f i c i e n c i e s f o r 2,3,7,8-TCDD. Table I .

P h y s i c a l - C h e m i c a l A n a l y s i s o f Prepared S o i l Samples Used f o r L a b o r a t o r y Thermal D e s o r p t i o n T e s t s

Parameter PH C o n d u c t i v i t y (millimhos/cm) O r g a n i c matter ( p e r c e n t ) C a t i o n exchange c a p a c i t y milliequivalents/100g) O i l and grease c o n t e n t (grams/100g) S u r f a c e a r e a (m /g) Particle size distribution (percent) Medium sand F i n e sand Silt C l a y (