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Page 1: Anaerobic treatment of soil wash fluids from a wood preserving site

e Pergamon

PH: S0273-1223(98)OO608-8

Wat Sci. T~ch. Vol. 38. No.7. pp. 63-72.1998.1AWQ

Il) 1998Published by Elsevier SCIence LId.Printed in Oreal Britain. All rights reserved

0273-1223198 S19'00 + 0'00

ANAEROBIC TREATMENT OF SOILWASH FLUIDS FROM A WOODPRESERVING SITE

K. M. Miller*, M. T. Suidan*, G. A. Sorial*,A. P. Khodadoust*, C. M. Acheson** and R. C. Brenner**

... Department ofCivil and Environmental Engineering, University ofCincinnati, 741Baldwin Hall, Cincinnati. OH 45221-0071. USA...... U.S. Environmental Protection Agency National Risk Management ResearchLaboratory. 26 W. Martin Luther King Drive. Cincinnati. OH 45268. USA

ABSTRACf

An integrated system has been developed to remediate soils contaminated with pentachlorophenol (PCP) andpolycyclic aromatic hydrocarbons (PAHs) . This system involves the coupl ing of two treatment technologies.soil solvent washing and anaerob ic biotreatment of the extract. Specifically. this study evaluated theeffectiveness of the granular activated carbon (GAC) fluidized-bed reactor to treat a synthetic waste streamof pcp and four PAHs (naphthalene. acenaphthene. pyrene, and benzo(b)f1uoranthene) under anaerobicconditions. This waste stream was intended to simulate the wash fluids from a soil washing process treatingsoils from a wood preserving site. The reactor achieved a removal efficiency of greater than 99.8% for pcpwith conversion to its dechlorination intermediates ranging from 47% to 77'10. Effluent, carbon extraction,and isotherm data also indicate that naphthalene and acenaphthene were removed from the liquid phase withefficiencies of 86% and 93%, respectively. Effluent levels of pyrene and benzo(b)f1uoranthene wereextremely low due to the adsorptive capacity of GAC for these compounds. Experimen tal evidence does notsuggest that these compounds were chemically transformed within the reactor . © 1998 Publ ished by ElsevierScience Ltd . All rights reserved

KEYWORDS

Activated carbon; anaerobic; fluidized-bed ; PAHs; PCP.

INTRODUCTION

Sites contaminated with wood preserving or wood treating contaminants are common throughout the UnitedStates. Soils at these sites may be contaminated with pentachlorophenol (PCP), polycyclic aromatichYdrocarbons (PAHs) and other hydrocarbons, and heavy metals such as copper, chromium, or arsenic.Many former wood preserving sites and PCP manufacturing sites are now classified as RCRA (ResourceConservation and Recovery Act) and Superfund sites (Superfund Record of Decision, 1986. 1987, 1989).Removal of PCP from soils contaminated with more than 1 ppm (l mg PCPlkg soil) is mandated throughCERCLA (Comprehensive Environmental Response, Compensation. and Liability Act).

63

Page 2: Anaerobic treatment of soil wash fluids from a wood preserving site

64 K. M.MILLER et al.

An integrated system has been developed to remediate soils contaminated with PCP and PAHs. This systeminvolves the coupling of two treatment technologies, soil solvent washing and anaerobic biodegradation ofthe extract. Khodadoust et al. (1994) developed a soil washing procedure for the removal of PCP from soilusing a 50% ethanoUwater solution. The wash fluid from this procedure could be fed to a biologicaltreatment process. Specifically, this study evaluated the effectiveness of a granular activated carbon (GAC)fluidized-bed reactor to treat a synthetic waste stream of PCP and PAHs under anaerobic conditions. Thiswaste stream was intended to simulate the wash fluids from a soil washing process treating soils from awood preserving site. In order to have a representative waste stream, four PAHs were selected from thosecompounds commonly found in contaminated soils at wood preserving sites. A 2-, 3-,4- and 5-ring PAHwere chosen: naphthalene, acenaphthene, pyrene, and benzo(b)fluoranthene, respectively.

Numerous researchers have shown that PCP can be effectively degraded under anaerobic conditions(Wagner et al., 1993; Wilson et al., 1995). PCP is degraded anaerobically through reductive dechlorinationof the phenolic ring. Previous studies by Wagner et al. (1993) and Wilson et al. (1995) have demonstratedthat PCP can be degraded anaerobically in a GAC fluidized-bed reactor even at low empty bed contact times(EBCTs). Equimolar conversion of PCP to monochlorophenol (MCP) was achieved at an EBCT as low as1.16 hr, and mineralization may occur under these conditions (Wilson et al., 1995).

In contamination associated with wood treating wastes, PCP may be accompanied by PAHs or aliphatichydrocarbons. While PAHs are known to degrade under aerobic conditions (Dyksterhouse et al., 1995;Madsen et al., 1996; Zappi et al., 1996), these compounds are typically recalcitrant to anaerobic treatment.Studies suggest that some 2- and 3-ring PAHs can be degraded anaerobically (Bregnard et al., 1996; Coateset al., 1996; Langenhoff et al., 1996), but there is no evidence to indicate that PAHs with more than threerings can be degraded under anaerobic conditions. Naphthalene has been shown to degrade under sulfatereducing conditions (Coates et al., 1996; Langenhoff et al., 1996) and under denitrifying conditions(Bregnard et al., 1996). While these studies indicate that anaerobic degradation of some PAHs is possible,little is known about the degradation pathways.

The purpose of this study is to evaluate the performance of a GAC fluidized-bed reactor system in treating amixed waste stream of PCP and PAHs under anaerobic conditions. Performance will be evaluated based oncontaminant levels in the effluent and periodic GAC extraction.

METHODS

Anaerobic GAC reactor

A schematic diagram of the anaerobic fluidized-bed reactor system used in this study is shown in Figure I.The reactor system includes a water jacketed main column with recycle loop, an influent header, an effluentheader, a feed system, and an effluent and gas collection system. The main column of the reactor is aPlexiglas tube with an inner diameter of 10.2 em, a length of 96.5 em, and a total volume of II L includingthe recycle loop. The reactor temperature is maintained at 35°C by circulating water from a constanttemperature water bath through the outer jacket of the column. The reactor was initially charged with I kg of16 x 20 U.S. Mesh F400 GAC (Calgon Corporation, Pittsburgh, PA) and was seeded with a methanogenicculture from a similar anaerobic GAC fluidized-bed reactor treating a synthetic pollutant stream of PCP.Auidization of the GAC bed, to 30% by volume based on original carbon volume, is accomplished byrecirculation of the effluent at a recycle ratio of 200: I. A side arm to the reactor extends into the column at alevel below the effluent recycle line to allow for carbon replacement, if necessary. The influent header ispacked with 1.5 and 0.6 em glass marbles to uniformly distribute the flow across the GAC bed and toprevent GAC from entering the recycle line. The effluent header contains an effluent sampling port and agas collection port.

The feed system consisted of a synthetic organic waste stream, a nutrient feed solution, and an inorganicbuffer solution. These solutions were fed separately to prevent biological growth external to the reactor, and

Page 3: Anaerobic treatment of soil wash fluids from a wood preserving site

Anaerobic treatment of soil wash fluids 65

were introduced into the suction side of the recycle line. The synthetic organic waste stream consisted of amixture of PCP (99%, Aldr ich Chem ical Company, Milwaukee, WI), naphthalene (99+%, Aldrich Chem icalCompany), acenaphthene (99%, Aldrich Chem ical Company), pyrene (99%, Aldr ich Chemical Company),benzo(b)f1uoranthene (99%, Radian Corporation), and ethanol ( 100%, USP Grade, Midwe st Grain Product s,Weston , MO). Influent concentrations of these compounds are listed in Table 1. This solution was fed intothe recycle line using a Model 11 high precision syringe infusion pump (Harvard Apparatus, Inc. , SouthNatick, MA) with a lO-mL fixed needle syringe (Hamilton Company, Reno , NV) via 1/16-in . A316 stainlesssteel tubing. The nutrient feed solution provided the essenti al salts and vitamins necessary to maintainmicrob ial growth (Fox et al. , 1984). The inorganic buffer solution contained sodium carbonate, sodiumsulfide, and the balance of the ethanol not fed via syringe. Nutrient and buffer so lutions were fed into therecycle line using constant-speed pumps controlled through a programmable timer.

Elllucnt Header

Elllucnl • If

RecirculatineW Oller ltnth

Influent Header

-{' ] fiO'_C-:> Meter

[. . -1 nS,d c Ann

:.--( ~ Ell1ucnl Samf'lin~ Pnr1

~

Organic Feed

,... 0~ Nuuienl Feed

, {-DlIullcr Feed

_ ~lu id ilcd fiA t:

c:J Marhlc I'ad....... Valve

Figure I. Schematic diagram of the anaerobic GAC fluidized-bed reactor.

Table I . Influent pollutant concentrations

System operation

PCPNaphthaleneAcenaphthenePyreneBenzo(b)fluorantheneEthanol

Concentration, mg/L100.035.011.06.00.5

690 .0

The reactor system was initially operated at a flow rate of 6 Lid and an EBCT of 9.3 hr. After severalhundred days of stable operation, the organic mass loading rate and the hydraulic loading rate to the reactorwere increase d in 10% increments every 4 days until the loading rates were doubled . Once reactorperformance stabilized, the loading rates were again doubled . At day 640, a buffer feed pump failed and thereactor experienced an operational disturb ance due to a sudden pH shock. For a period of time follo wing thepH shock, the reactor was operated as a batch system. During this phase, the reactor was periodically flushedwith effluent from the reactor used to initially seed this reactor. This period lasted from day 640-705, anddata collected during that time are omitted from this discussion. Once reactor performance was stable, feedto the reactor was resumed at the initial loading rates. After about 80 days, the loading rates were increasedin two stages as before until the desired EBCT of 2.32 hr was achieved. This EBCT was determined to beoptimal by Wil son et al. (1995) based on PCP conversion to Mep and stable operation in a similar anaerobi c

Page 4: Anaerobic treatment of soil wash fluids from a wood preserving site

66 K. M. MILLER et al.

GAC fluidized-bed system. The reactor in this study underwent seven phases of operation, eachcorresponding to a different EBCf, and the operating conditions for each phase are listed in Table 2.

Table 2. Operating parameters

Phase of OperationI and V II and VI III and VIII IV

Days ofOperation I: 0-43 II: 435-472 III: 472-640 IV: 640-705V: 705-785 VI: 785-950 VII: 950-1035

Flow Rate, Ud 6.0 12.0 24.0 batch / flushEBCT, hr 9.3 4.65 2.32 0/2.32Organic Loading, g/d

PCP 0.6 1.2 2.4 0Naphthalene 0.21 0.42 0.84 0Acenaphthene 0.066 0.132 0.264 0Pyrene 0.036 0.072 0.144 0Benzo(b)fluoranthene 0.003 0.006 0.009 0Ethanol 4.28 8.33 16.66 0

Analytical methods

The reactor was monitored daily for effluent pH, total gas volume production, buffer and nutrient feed rates,and syringe feed rate. The pH was measured offline using an Orion Model 720A pH meter (Orion ResearchCo., Boston, MA). Gas volume production was measured using a wet tip gas meter (Environmental andWater Research Engineering, Nashville, TN). Weekly effluent samples were analyzed for chemical oxygendemand (COD), gas composition, chlorides, volatile fatty acids (VFAs), alcohols, and concentrations ofPCP, PCP dechlorination intermediates, and the four feed PAHs. Effluent COD was determined using theHach low range digestion vials (0-150 mg/L) and a Hach COD reactor Model 45600 (Hach Co., Loveland,CO). The digested vials were measured for percent transmittance using a Bausch and Lomb Spectronic 70Spectrophotometer (Bausch and Lomb, U.S.A.). Effluent gas samples were analyzed using a HewlettPackard 5890 Series II Gas Chromatograph (GC) (Hewlett Packard, Palo Alto, CA) equipped with a thermalconductivity detector to determine the percent carbon dioxide, oxygen, nitrogen, and methane in the productgas. Chloride ion concentration was measured using an Orion Model 9617BN chloride selective electrode.VFA and alcohol concentrations were determined using a Hewlett Packard 5890 Series II GC (HewlettPackard, Palo Alto, CA) equipped with a flame ionization detector (FID).

Effluent concentrations were determined by extracting the compounds into a solvent using a 5:1 sample-to­solvent ratio and injecting the extract into the GC. The solvents used for extraction contained an internalstandard to ensure uniformity of extraction efficiency and injection volume. Effluent PCP, PCPdechlorination products, and PARs were quantified using a Hewlett Packard 5890 Series II GC (HewlettPackard, Palo Alto, CA) equipped with either an electron capture detector (ECD) or a flame ionizationdetector (FID). A DB-5 Megabore column (J and W Scientific, Folsom, CA) was used to achieve separationof PCP and the tetra-, tri- and dichlorophenol species, which were then quantified using an ECD. Thesolvent used for this procedure was toluene with 2,4,6-tribromophenol (TBP) as an internal standard. Fordetermination of MCP and phenol concentrations, samples were extracted with ether containing o-creosol,and the extract was analyzed using a DB-I Megabore column (J and W Scientific, Folsom, CA) with an FID.PAH quantification was accomplished through extraction into hexane containing 2,4,6-TBP and analysisusing a DB-5 Megabore column (J and W Scientific, Folsom, CA) with an FID. Pyrene andbenzo(b)fluoranthene concentrations were extremely low in the effluent, and samples had to be concentratedto be detected by GC-FID. The same sample-to-solvent ratio was used as stated above, and the extract wasthen concentrated 14 times. The solvent used for this procedure was ether with 2,4,6-TBP as an internalstandard.

Page 5: Anaerobic treatment of soil wash fluids from a wood preserving site

Anaerobic treatment of soil wash fluids

Carbon extractions were performed periodically using the procedure outlined by Fox et at. (1984).

Isotherm studies

67

To determine the predicted adsorption capacity of GAC for naphthalene and acenaphthene, GAC adsorptionisotherm experiments were conducted for these compounds. The experiments were performed underanaerobic conditions at 35°C. For each compound, the isotherm studies were run at two different initialsolution concentrations: 15 and 25 mglL for naphthalene and 2.5 and 1.5 mgIL for acenaphthene. For eachof the four solutions, ten 250-ml bottles containing different carbon weights were filled with the PAHsolution, leaving no head space remaining to ensure anaerobic conditions. Two blanks containing no carbonwere also filled with the PAH solution to serve as controls. The bottles were tumbled for 2 weeks and thenanalyzed for aqueous concentrations of PAH. The concentration of PAH on the carbon, q, was calculatedfrom the measured aqueous concentration and plotted against the aqueous concentration, Ce, to obtain anadsorption isotherm curve. Carbon extractions were performed to determine the extraction efficiency relativeto the calculated values.

RESULTS AND DISCUSSION

The molar effluent concentrations of PCP and its chlorinated phenolic intermediates throughout each phaseof operation are presented in Figure 2. The molar influent concentration of PCP was 0.376 mmollLthroughout the study with the exception of Phase IV. This value is represented by the dotted line. During thefirst four phases, MCPs were the predominant intermediates measured in the effluent at levels approximatelyone order of magnitude above that of dichlorophenol (DCP) and phenol. Para-chlorophenol (4-CP) andmeta-chlorophenol (3-CP) were the primary MCP species present, with 4-CP dominating throughout most ofthe study. During Phase V, MCP and phenol concentrations rose sharply and phenol surpassed MCP as thepredominant intermediate. Phenol is typically degraded readily, and its presence in the effluent suggests thatthe system may have been experiencing stress of some kind.

1.·1 .

lnOuml l"C"l'• F.ffiuntt lorpo Effi"mt T~ac hkw~ft'Ols

OJ F.ffiumt rfKhlomrhntnl,a Em.... llKhI ..oph...oh• Em"mt MnnochkwClf'h~.

.. Em uC'nl I'hft'W)!

"..

III V

•o

VII

Days

Figure 2. Effluent chlorophenol concentrations.

Throughout the first three phases of operation, the reactor achieved greater than 99.9% removal of PCP.After the pH shock and recovery in Phase IV, removal efficiencies averaged 99.8% for the last three phasesof operation. This performance is similar to the performance reported by Wilson et al. (1995) using a similaranaerobic fluidized GAC reactor treating a waste stream containing PCP and ethanol. However, Wilson etal. (1995) report a near equimolar conversion of PCP to MCP, while in this study, the molar sum of allmeasured intermediates accounts for between 47% and 77% of the influent molar concentration of PCPduring the final three phases of this study. The difference between measured intermediates and influent PCPmay be accounted for by PCP mineralization or conversion to intermediates that are not quantified.

Page 6: Anaerobic treatment of soil wash fluids from a wood preserving site

68 K. M.MILLER et at.

Carbon extractions were performed to determine if adsorption could explain the difference between influentPCP and effluent phenolic concentrations. As shown in Figure 3, the mass of MCP and intermediatesadsorbed to the carbon decreases with reactor operating time, and thus, carbon adsorption cannot explain theobserved difference.

: e D

. ... .

o 0

I'CI'o Tnta(hlnrnr lwnols 0

Tnchlornrhm o l.rltchkw'o~enoll

• M""n<h!'1I'0rhC'n<lI. 0• I"mnl ~ 0~-~~-~ . ~-~._~//-~~~

I Joo \00 4 • I

...·...

,..,

,.-D

Days

Figure 3. Carbon extraction for chlorophenols.

In Figure 4, the cumulative moles of PCP fed to the reactor are compared to the moles of PCP and measuredintermediates exiting the reactor. The difference between the cumulative influent and the cumulativechlorophenols in the effluent represents the amount that is either adsorbed on the carbon, mineralized orexiting as another intermediate. The difference between these two values is depicted in Figure 5 as the linelabeled Chlorophenol Removed. The amount of total chlorophenols adsorbed on the carbon at discrete pointsthroughout the study is also shown in Figure 5. This value is the upper limit of adsorbed amounts becauseloss of carbon mass within the reactor due to attrition and sample removal were not considered here. Thedifference between the chlorophenols removed and the chlorophenols on the carbon is the molar equivalentof PCP that may have been mineralized or exited the reactor as another chemical species.

"oo !'" . ~ _ _.••.~ ..~_ .•' _ '~ " '_~''-''

. OOO ! - ~I~~"" I" Trl" 1)("" ~tcl " """"'/I~ 1\00 t • forI' • Tc<"P ' Tf'P • nrr· trr 1

~ 1'('1" l rCl" lei' · Df' (''C '000 t I'cr · Tc:orr · Tel ' i[ 1~ f • :~:: : •TtC r i~ 1 ! 1;; [ :..!l " 00 I 1

~ ' ~I L - - Ic_• • •~. ~ . . .. . . ~ . ~__ .....~. . ...~u .. .. _ • .'lo 300 .tOO 500 eoo " NX)

Days

Figurc.j Cumulauve mole balance for chlorophenols

.."OO t"··· ... · · ......"..·• • · • • · · ....... · · ·· -.p- ·-. ....... ......··/· .. ........ ·· ·-..- · ·.......... 14OOO ! - C hloforhmn l Rnno 'Vf'd I

~ ' '00I · n'o' ''l' h",ol on 0 "('

~ -t j~ I'OO! i~ I I ~J.~ 1\00 t ;

1 ' OOO ! IU \00 . • • j

• • 1o ....-"" __... .....~ .._ -........... :_~• • •~ 6- ......__• .. . ~....J, 200~ Sl)l!OO IIOJ goo ,

DlIYs

Figure 5. Comparison of cumulative chlorophenols removed from liquid phase to amounts adsorbed on GAC.

Page 7: Anaerobic treatment of soil wash fluids from a wood preserving site

Anaerobic treatment of soil wash fluids 69

Figure 6 shows the effluent concentrations of naphthalene, acenaphthene, pyrene, and benzo(b)f1uoranthene.During the first 400 days of operation. concentrations of all PAHs remained extremely low in the effluentdue to the strong affinity of GAC for PAHs. Throughout the entire study, levels of pyrene andbenzo(b)fluoranthene remained at a nearly constant level at or near the detection limit of the GC. By the endof the first phase, naphthalene was present in the effluent, and these concentrations continued to increaseuntil the end of phase III when the reactor experienced the pH shock. The concentration of naphthalene inthe effluent at the time of the shock was 3.8 mg/L, By the end of phase III, acenaphthene had similarlybegun an increasing trend in the effluent. During the recovery period after the pH shock, these trendsreturned until effluent concentration s of both naphthalene and acenaphthene were approximately 5 and 0.8mgIL, respectively. These concentrations represent removal efficiencies of 86% for naphthalene and 93% foracenaphthene . Carbon extraction data confirm that these compounds were not accumulating on the GAC(Figure 7).

'c+1Influent Nanhthalent:

Days

Figure 6. Effluent PAH concentrations.

I : n ~ UI v VI VII

000

0 s •0~

. · :0 0 · . · S' p '. 0: 0 ..· .,

[. 0,

0 0 ·1 0

0 ·0 0

00 9:.

[

. . . ,· · , · . .. 0 ,

,· Naphthalene:e Accnaphl.hene

· Pyr",.

· BcnZD(b)1luoranlhene,...o 100 100 )00 400 see 000 800 900 10011

Days

Figure 7. PAH concentrations on GAC.

Ic+'

,..]

f It+

d 1<'0

.~Ei I~ . t

co!! , .. 1u

1c+1

The cumulative mass of naphthalene, acenaphthene, pyrene, and benzo(b)f1uoranthene fed to the reactor andthe cumulative mass of these compounds leaving the reactor over the course of operation are shown inFigure 8. The difference between the cumulative influent PAHs and the cumulative effluent PAHs representsthe mass that is either adsorbed on the carbon or degraded . The difference between these two values isdepicted in Figure 9 as the lines indicating PAH removal. The mass of each PAH adsorbed on the carbon atdiscrete points throughout the study is also shown. The difference between PAH removal lines and the PAHmass remaining on the carbon is the mass of material which may have been degraded or converted to anunmeasured intermediate. From Figure 9, this difference is sizable for naphthalene and may suggest thatbiodegradation or biotransformation is occurring within the reactor. However, for acenaphthene, the mass

Page 8: Anaerobic treatment of soil wash fluids from a wood preserving site

70 K. M. MILLERet al.

removed from the liquid is comparable to the mass adsorbed on the carbon, and therefore, it does not appearthat acenaphthene is undergoing any chemical changes within the reactor.

./-­...... --»-?" --":::::...-..:::-'::::-'--'

- Influent Naphthalene- - Influent Acenephthene

. Influent Pyrene.. Influent Bcn2t>(b)f1uoranthene

• EffiuentNaphthaleneo Effiuent Accnaphthene• EffluentPyrencV Effluent Benzo(b )fluoranthc:ne

100 200 300 400 SOO 600 800 900 1000

Days

Figure 8. Cumulative mass balance for PAHs.

,..,OIle

13."

~ ,..,.,..s"e" ,..,u

•. ..,..• • 0 0 _- 0

• ...----- Q-"o III _~ ..__ ..- ..

fl¥rt~:.··~···+~·: q-

- Naphthalene Removed- - Acenaphthene Removed

PyreneRemoved....... Bc:nzo{b)fiuoranthene Removed

• Naphthaleneon OACo Acenaphthenc on GAC.. PyrcneonOACV Benzo(b)fluoranthene on GAC

100 200 300 400 SOO 600 800 900 1000

Days

Figure 9. Comparison of cumulative PAH mass removed from liquid phase to mass adsorbed on GAC.

Freundlich puamcters:

K "" 203.0S ±6.5n:E0.21 ±0.01

J- 10'

0.001 0,010 0.100 1.000 10.000

Ce (mgIL)

Figure 10. Naphthalene isotherm.

In order to determine if naphthalene was being degraded in the system, a GAC adsorption isotherm studywas performed, and from these data, a predicted breakthrough curve was generated. The breakthrough curverepresents the predicted effluent concentrations for naphthalene assuming no other compounds arecompeting for adsorption on the GAC and no biological activity is occurring within the system. Theisotherm and predicted breakthrough curves for naphthalene are presented in Figures 10 and 11,respectively. For the first 520 days, the observed effluent naphthalene concentrations followed the predictedbreakthrough curve closely. After day 520, the actual effluent concentration remained much lower than thepredicted breakthrough curve. This discrepancy indicates that naphthalene was being removed by some

Page 9: Anaerobic treatment of soil wash fluids from a wood preserving site

Anaerobic treatment of soil wash fluids 71

mechanism other than adsorption alone, such as biological activity within the reactor and on the GAC, ortransformation of naphthalene to other compounds.

A similar isotherm study was performed for acenaphthene, and a predicted breakthrough curve wasgenerated. The effluent concentrations of acenaphthene followed the predicted breakthrough curve for thefirst 640 days. After day 640, observed effluent concentrations of acenaphthene were higher than thepredicted breakthrough curve. Since the breakthrough curve ignores the effect of competitive adsorption, itrepresents the lower limit for predicted effluent breakthrough. Thus, this study indicates that carbonadsorption was the primary means of removal for acenaphthene.

16

14

~ 12e.f 1:8 6C8 4

- Predicted Breakthrough Curveo EffiuenlConcentration

.o.

)100 200 300 400 SOO 600 800 900 1000

Days

Figure II. Naphthalene breakthrough curve.

Effluent concentrations of pyrene and benzo(b)fluoranthene remained extremely low in the effluent due tothe adsorptive capacity of GAC for these compounds. There is no evidence to suggest that these compoundswere undergoing any transformations within the reactor.

CONCLUSIONS

An anaerobic GAC fluidized-bed reactor was used to treat a waste stream containing PCP and four PAHs.The reactor achieved a removal efficiency of greater than 99.8% for PCP with conversion to its measuredintermediates ranging from 47% to 77%. Effluent, carbon extraction, and isotherm data indicate that 86% ofthe naphthalene fed to the reactor was removed. Carbon adsorption does not account for the total amount ofnaphthalene removed, indicating that additional removal was being achieved through biodegradation orother transformations of the parent compound. Acenaphthene was removed primarily through carbonadsorption with a removal efficiency of 93%. Experimental data do not provide evidence to suggest thatpyrene and benzo(b)fluoranthene were undergoing any chemical transformation within the reactor.However, since after 1000 days of operation there was no evidence of these compounds in the effluent, theirremoval from the influent wastewater stream could be achieved through periodic carbon replacement.

REFERENCES

Bregnard, T., Hoehener, P.• Haener, A. and Zeyer, J. (1996). Degradation of weathered diesel fuel by microorganisms from acontaminated aquifer in aerobic and anaerobic microcosms. Environmental Toxicology and Chemistry, 15(3),299-307.

Coates. 1.. Anderson. R. and Lovley, D. (1996). Oxidation of polycyclic aromatic hydrocarbons under sulfate-reducing conditions.Applied Environmental Microbiology, 62(3), 1099-1101.

Dyksterhouse, S.• Gray. J.• Herwig. R.• Lara. J. and Staley. J. (1995). Cycloclasticus pugetti gen. nov., sp. nov., an aromatichydrocarbon-degrading bacterium from marine sediments. International Journal of Systematic Bacteriology, 45( I), 116­123.

Khodadoust, A.. Wagner. J .• Suidan, M. and Safferman, S. (1994). Solvent washing of PCP contaminated soils with anaerobictreatment of wash fluids. Water Environment Research. 66(5), 692-697.

Langenhoff, A.. Zehnder, A. and Schraa, G. (1996). Behaviour of toluene. benzene and naphthalene under anaerobic conditions insediment columns. Biodegradation.7(3), 267-274.

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72 K. M. MILLERet al.

Madsen. E.• Man. C. and Bilotta. S. (1996). Oxygen limitationsand aging as explanationsfor the field persistence of naphthalenein coal tar-contaminated surface sediment.Environmental Toxicology and Chemistry. 15(11). 1876-1882.

Wagner. J.• Khodadoust, A., Suidan, M. and Safferrnan, S. (1993). Treatment of pcp containing wastewater using anaerobicfluidized-bed GAC bioreactors. In: Proceedings of the /993 Water Environment Federation Conference. WaterEnvironmentFederation.Los Angeles.

Wilson. G.• Khodadoust, A.• Suidan, M.• Acheson. C. and Brenner, R. (1995). Anaerobic/aerobic biodegradation ofpentachlorophenol using GAC fluidized bed bioreactors: optimizationof the empty bed contact time. In: Proceedings oftM /995 WaterEnvironment Federation Conference. Water EnvironmentFederation.Los Angeles.

Zappi, M.• Rogers. B., Teeter, C., Gunnison, D. and Bajpai, R. (1996). Bioslurry treatment of a soil contaminated with lowconcentrationsof total petroleum hydrocarbons. Journalof Hazardous Materials, 46(I), 1-12.