Available at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/watres

Laboratory column study for remediation ofMTBE-contaminated groundwater using a biologicaltwo-layer permeable barrier

She-Jiang Liua, Bin Jianga,b, Guo-Qiang Huanga,b, Xin-Gang Lia,b,�

aSchool of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR ChinabNational Engineering Research Centre for Distillation Technology, Tianjin University, Tianjin 300072, PR China

a r t i c l e i n f o

Article history:

Received 15 February 2006

Received in revised form

26 June 2006

Accepted 16 July 2006

Available online 7 September 2006

Keywords:

MTBE

Remediation

Groundwater

Permeable reactive barrier

Biodegradation

A B S T R A C T

In this study, an in situ biological two-layer permeable reactive barrier system consisting of

an oxygen-releasing material layer followed by a biodegradation layer was designed to

evaluate the remediation effectiveness of MTBE-contaminated groundwater. The first layer

containing calcium peroxide (CaO2) and other inorganic salts is to provide oxygen and

nutrients for the immobilized microbes in the second layer in order to keep them in aerobic

condition and maintain their normal metabolism. Furthermore, inorganic salts such as

potassium dihydrogen phosphate (KH2PO4) and ammonium sulphate ((NH4)2SO4) can also

decrease the high pH caused by the alkali salt degraded from CaO2. The second layer using

granular expanded perlite as microbial carrier is able to biodegrade MTBE entering the

barrier system. Batch experiments were conducted to identify the appropriate components

of oxygen-releasing materials and the optimum pH value for the biodegradation of MTBE.

At pH ¼ 8.0, the biodegradation efficiency of MTBE is the maximum and approximately

48.9%. A laboratory-scale experiment using two continuous upflow stainless-steel columns

was then performed to evaluate the feasibility of this designed system. The fist column was

filled with oxygen-releasing materials at certain ratio by weight. The second column was

filled with expanded perlite granules immobilizing MTBE-degrading microbial consortium.

Simulated MTBE-contaminated groundwater, in which dissolved oxygen (DO) content was

0 mg/L, was pumped into this system at a flow rate of 500 mL/d. Samples from the second

column were analyzed for MTBE and its major degradation byproduct. Results showed that

MTBE could be removed, and its metabolic intermediate, tert-butyl alcohol (TBA), could also

be further degraded in this passive system.

& 2006 Elsevier Ltd. All rights reserved.

1. Introduction

As an alternative to traditional pump-and-treat and dig-and-

treat methods for the remediation of contaminated ground-

water, permeable reactive barrier is a relatively new in situ

technology, and is attracting increased attention (Borden

et al., 1997; Rasmussen et al., 2002; Wilkin et al., 2003; Carsten

et al., 2004). The barriers are installed perpendicular to the

direction of groundwater flow within aquifers. As the ground-

water passes the barriers under natural hydraulic gradients,

the contaminants are scavenged or degraded from the water

by chemical, physical or biological action. The barriers also

ARTICLE IN PRESS

0043-1354/$ - see front matter & 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.watres.2006.07.015

�Corresponding author. School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China.Tel.: +86 22 27890628x8019; fax: +86 22 27404705.

E-mail address: lxg@tju.edu.cn (X.-G. Li).

WAT E R R E S E A R C H 4 0 ( 2 0 0 6 ) 3 4 0 1 – 3 4 0 8

prevent groundwater contaminants from migrating to un-

contaminated aquifers, which may be difficult to locate and

remedy. The main advantage of permeable reactive barrier

is the lower cost. Once installed, the barriers do not need

above-ground facilities or energy inputs, and they can take

advantage of the in situ groundwater flow to bring the

contaminants in contact with the reactive materials.

Methyl tert-butyl ether (MTBE) is the most commonly used

as fuel oxygenate that can enhance the gasoline’s octane

rating and improve the combustion efficiency of gasoline. In

spite of its relatively recent usage, MTBE has become the

second most common contaminant detected in the urban

groundwater which gives to the water both an unpleasant

taste and odour, and poses a significant health threat

(Squillace et al., 1996; Caprino and Togna, 1998; Kharoune

et al., 2001). In recent years, many methods for treatment of

MTBE have been proposed including carbon adsorption (Shih

et al., 2003), advanced oxidation technologies (AOTs) such as

UV/H2O2, UV/O3, Fenton reaction, H2O2/O3, TiO2 photocata-

lysis, sonolysis, and radiolysis. Although MTBE can be

removed effectively from contaminated water system using

above methods, most of these technologies are limited in

factual application for the remediation of the contaminated

subsurface. Furthermore, the major disadvantage of these

physical, chemical treatment methods is the potential for

forming byproducts with higher toxicity than the original

contaminant (Graham et al., 2004; Zang and Faronood, 2005;

Bergendahl and Thies, 2004; Safarzadeh-Amiri, 2001; Barreto

et al., 1995; Kang and Hoffmann, 1998; Hsieh et al., 2004).

Microcosm studies demonstrated that MTBE, tert-butyl alco-

hol (TBA) that is currently widely accepted as metabolic

intermediate or dead-end product of MTBE, may be biode-

gradable with special bacterial strains or natural isolates

under aerobic conditions (Fortin and Deshusses, 1999; Deeb

and Alvarez-Cohen, 2000; Prince, 2000; Fayolle et al., 2001;

Bradley et al., 2002; Sedran et al., 2002). However, MTBE

degradation was highly variable under different environmen-

tal conditions (Bradley et al., 2001). For the evaluation of MTBE

biodegradation, TBA instead of MTBE got even more concern

due to its higher toxicity (Schmidt et al., 2004). Besides, the

microbes using MTBE as sole source of carbon and energy

under aerobic conditions grow slowly with low yields of

biomass and are sometimes unstable. As a result, a viable

bioremediation process for MTBE has not been fully devel-

oped so far.

In generally, dissolved oxygen (DO) content is very poor

within the plum pore and mid-plume areas in the contami-

nated groundwater, which cannot maintain aerobic biode-

gradation of some organic contaminants. Several researchers

have developed an oxygen-releasing compound such as

calcium peroxide (CaO2) to passively increase DO in the

subsurface (Cassidy and Irvine, 1999; Arienzo, 2000; Kao et al.,

2001). CaO2, besides oxygen, releases Ca(OH)2 causing a

significant rise in pH of solution. Laboratory study showed

that high pH might inhibit microbial activity and decrease the

removal efficiency of contaminants (Kao et al., 2003). Ritter

and Scarborough (1995) illuminated that pH of environment

helping for microbial growth should be keep in the range of

6.5–8.5. But now, few researchers focus their attention on the

regulation of pH caused by the oxygen-releasing compound.

To this disadvantage influence of high pH, it mainly depends

on microbial adaptive ability and buffer capability of field soil

to deal. This is inevitable to prolong period and increase cost

of remediation.

As microbial carrier, granular expanded perlite with about

particle size of 2–3 mm was obtained from Tianjin Sanhua

Corporation Ltd., whose chemical composition (wt%) was as

follows: SiO2, 72.93; Al2O3, 12.90; TiO2, 0.05; CaO, 0.76; MgO,

0.16; Fe2O3, 0.53; FeO, 0.18; K2O, 5.3; Na2O, 2.57; MnO, 0.06; H2O,

4.56. The following reasons make it good candidate for this

study: (1) the surface of expanded perlite is porous and

coarse, which helps microbe to adsorb and immobilize; (2) as

a kind of silicate minerals, expanded perlite does not bring

any new contaminant into groundwater when it is placed in

the barriers and (3) expanded perlite is relatively inexpensive.

Based on the above discussions, we designed a biological

two-layer permeable reactive barrier system containing

oxygen-releasing material and biodegradation layers to

evaluate the remediation effectiveness of MTBE-contami-

nated groundwater. Oxygen-releasing materials and ex-

panded perlite granules with immobilized microbes can be

filled in remediation wells or permeable trenches. The

schematic diagram of this passive system is shown in Fig. 1.

The principle of this work was to design a passive

treatment system to bioremediate groundwater contami-

nated by MTBE. In this study, batch experiments were

conducted to identify the components of oxygen-releasing

materials, which could continuously release oxygen and

regulate the high pH caused by CaO2. In addition, the

biodegradation efficiency of MTBE under different pH value

conditions was also studied. A column experiment was then

performed to evaluate the feasibility and potential of this

passive barrier system for biodegradation of MTBE.

2. Materials and methods

2.1. Experimental microbes’ collection, enrichment andacclimation

The original experimental microbes were collected from the

soil located 35–45 cm deep at Dagang Oil Field in Tianjin city,

China. Under aerobic condition (pumping air at 30 mL/min

into the medium), microbes were enriched and acclimated in

ARTICLE IN PRESS

Spill Site

Clay

GroundwaterFlow Direction Oxygen

Oxygen-releasingMaterial Layer

Water Table

UncontaminatedGroundwater

Biodegradation Layer

Nutrients

Fig. 1 – Schematic diagram of the designed biological barrier

system.

WAT E R R E S E A R C H 4 0 ( 2 0 0 6 ) 3 4 0 1 – 3 4 0 83402

a biochemical culture bottle at room temperature for 2

months. The components of liquid mineral salts medium

were as follows (units are in mg/L of water): ammonium

sulphate ((NH4)2SO4), 1000; potassium dihydrogen phosphate

(KH2PO4), 500; K2HPO4, 500; MgSO4 � 7H2O, 30; Fe2(SO4)3, 30;

MnSO4 �H2O, 40; ZnSO4 �H2O, 50; CaCl2, 10. Glucose was used

as sole carbon source in the initial period of 0–15 days. During

15–30 days, the quantity of glucose decreased gradually from

2000 to 0 mg/L, and the quantity of MTBE increased from 0 to

2000 mg/L. After 30 days, MTBE was used as the sole carbon

source for the microbial growth. The suspension of accli-

mated microbe was used for the next experiments.

2.2. Batch experiments

2.2.1. Study on the pH controlTechnical CaO2 used in this study was purchased from Tianjin

Chilong Chemical Engineering Co. Ltd., whose main impurity

was about 50% of Ca(OH)2 by weight. KH2PO4 and (NH4)2SO4

were obtained from Tianjin Chemical Reagent Company,

whose purities were more than 99%. CaO2 releases oxygen

upon contact with water according to the following overall

reaction:

2CaO2 þ 2H2O! O2 þ 2CaðOHÞ2. (1)

During the oxygen-releasing process of CaO2, Ca(OH)2produced can result in a significant rise in pH of solution

that may decrease enzymatic activity of microbes. Therefore,

in this study, the pH was effectively regulated by using

(NH4)2SO4 and KH2PO4, which are usually used as nutrient

components in the medium. The appropriate mol ratio of

nitrogen (N) and phosphorus (P) is very important for

microbial growth in view of microbial metabolism. According

to the concentrations of N and P in the above medium, the

study on the pH control was carried out in an enclosed reactor

under the condition of fixing mol ratio of N:P at 2.6. Reactive

mixtures were obtained by taking 90 mg of CaO2, adding 90,

135, 180, 225, 270 mg of KH2PO4 and calculated weights of

(NH4)2SO4 based on that of KH2PO4, respectively. The reaction

was initiated by adding 200 mL of sterile deionized water

saturated by sparging nitrogen, which made the DO content

reduce to zero. All above experiments were conducted in a

reciprocal shaker at constant temperature (20 1C) and rotate

speed (130 r/min). A PHS-3C pH meter was used to online

monitor the pH changes.

2.2.2. Effects of pH on the biodegradation efficiency of MTBEThe biodegradation experiments were performed in five

600 mL enclosed reactors containing 200 mL of the mineral

salts medium described above with the pH value at 6.5, 7.5,

8.0, 8.5, 9.5, respectively, and MTBE (about 130 mg/L) as sole

source of carbon and energy. Air was sparged into the

medium before adding MTBE using an air pump for 10 min

in order to increase the DO content. The reactors were then

enclosed when 20 mL of the suspension of acclimated

microbe was inoculated, respectively. The five reactors, once

inoculated, were placed in a reciprocal shaker (130 r/min) at

20 1C. In this study, the control experiments were also

conducted with abiotic microbes. The liquid concentrations

of MTBE in the reactors were measured at the beginning and

end of the experiments. By calculating the degradation

efficiency of MTBE, the optimum pH value for the biodegrada-

tion can be determined. In addition, CO2 concentrations in

the headspace of reactors were also analyzed at the end of

experiments.

2.3. Microbial immobilization

The laboratory column of 100 cm length and 5 cm internal

diameter made of stainless steel was homogeneously packed

with the expended perlite granules. They have hardly

chemical adsorptive capacity for MTBE and TBA (data not

shown). At the same time, the suspension of acclimated

microbe was injected in this column to submerse the perlite.

Column feed solution consisting of MTBE (2000 mg/L) and

above mineral salts medium was pumped into the column by

using a peristaltic pump at a flow rate of 1.5 L/d for

maintaining the microbial metabolism and permitting the

development of microbial film on the surface of expended

perlite granules. In order to ensure this system aerobic

condition, air was introduced at 30 mL/min into the feed

solution before entering this column. The DO levels in the

effluent, the concentrations of MTBE in the influent and

effluent were measured respectively every 2–3 days. The

whole process of microbial immobilization lasted 25 days.

2.4. Column experiment

A laboratory-scale barrier system was designed using two

continuous upflow stainless-steel columns. The first oxygen-

releasing material column (100 cm length and 5 cm internal

diameter) was filled with the mixture of oxygen-releasing

materials prepared by blending CaO2, KH2PO4, (NH4)2SO4,

sand, trace elements at a ratio of 0.10:0.20:0.26:0.40:0.04 by

weight. Among the mixture, the ratio of CaO2, (NH4)2SO4,

KH2PO4 and trace elements which included MgSO4 � 7H2O,

Fe2(SO4)3, MnSO4 �H2O, ZnSO4 �H2O, CaCl2 was obtained from

the results of pH control experiment and the components of

mineral salts medium described above. CaO2 was used as

oxygen source for the aerobic microbes, (NH4)2SO4 and

KH2PO4 were used to provide nutrients for in situ nutrient

supplement and lower the pH caused by CaO2, trace elements

were used to provide necessary elements for the microbial

growth, and the sterile quartz sand (about 1 mm of grain size)

was used to increase the permeability of the mixture, which

may make groundwater flow easy to pass the barriers. The

column that had immobilized microbes described above was

used as the biodegradation column, which was equipped with

19 sampling ports positioned every 5 cm. These ports were

numbered 1–19 from the bottom to top of this column. In this

study, nos. 3, 7, 11, 15 and 19 were monitored for the changes

of MTBE concentration versus time. In addition, as an

appropriate parameter to assess the success of remediation

effort (Schmidt et al., 2004), TBA was also monitored during

the period of column experiment. Simulated MTBE-contami-

nated groundwater with 0 mg/L of DO content was continu-

ously pumped into the oxygen-releasing material column

with an upflow mode by peristaltic pump at a certain flow

rate. After the solution passed through it, designated hour 0,

the biodegradation column was connected to the first

ARTICLE IN PRESS

WAT E R R E S E A R C H 40 (2006) 3401– 3408 3403

column, and the flow rate of this system was adjusted to

500 mL/d. It is emphasized here that the feed solution

consisting of MTBE and mineral salts medium in the

biodegradation column was replaced by deionized water

before connecting it to the oxygen-releasing material column.

Fig. 2 presents the schematic diagram showing the laboratory

biological two-layer permeable reactive barrier system.

Residence time of the water in a duplicate column filled

with the same weight of expended perlite granules was

determined at the flow rate of 500 mL/d. Before the experi-

ment started, the column was filled with deionized water, but

not the suspension of acclimated microbe. The residence

time was determined by pumping a chloride tracer (sodium

chloride in water) through the column, and measuring

conductivity of effluent samples until breakthrough. Based

on the breakthrough curve, the residence time was found to

be 80 h in this case.

2.5. Analytic method

The column system was operated for about 800 h at room

temperature (�25 1C). The pH and DO values in the influent

and effluent of biodegradation column were respectively

determined with a PHS-3C pH meter and a portable DO meter

(Model JPB-607). The concentrations of liquid MTBE, TBA and

gas CO2 were analyzed by injecting 2 mL of liquid and 1 mL gas

into an gas chromatograph (PE AutoSystem XL, USA)

equipped with flame ionization detection (FID) and thermal

conductivity detection (TCD) using gastight syringes. N2

(1 mL/min) was used as the carrier gas for FID, and H2

(30 mL/min) was used as the carrier gas for TCD. Injection

and detector temperatures of FID were 230 and 300 1C

respectively. Injection and detector temperatures of TCD

were 150 and 150 1C, respectively. Other conditions were as

follows: oven temperature, 105 1C; air flow rate, 460 mL/min;

H2 flow rate, 48 mL/min; split ratio, 1:1. Prior the injection of

the liquid sample, the biomass was removed from the sample

using 0.22mm pore size polyethersulfone filter.

3. Results and discussions

3.1. Batch experiments

3.1.1. Effects of (NH4)2SO4 and KH2PO4 on pH of solutionAccording to chemical reaction equation, 1 mol KH2PO4 can

completely neutralize 1 mol Ca(OH)2 produced by CaO2 in

theory. In addition, (NH4)2SO4 can also provide a few H+ ions

produced by the hydrolyzation of NH4+ to react with hydroxy

ions in the solution. The ionization equilibrium of KH2PO4

and hydrolyzation equation of NH4+ were illuminated as

follows:

KH2PO4 ! KþþH2PO�4 ,

H2PO�4 Ð HPO2�4 þHþ;

HPO2�4 Ð PO3�

4 þHþ,

NHþ4þH2OÐ NH3 �H2OþHþ.

As seen from Fig. 3, Ca(OH)2 degraded from CaO2 caused the

pH to increase rapidly from 6.4 to 12.1 within short time that

might make most of microbes difficult to survive. Compared

with that of blank solution, the mixture of (NH4)2SO4 and

KH2PO4 contributed to decreasing the pH, and this action was

more obvious as the adding weight of the mixture increased.

With the presence of (NH4)2SO4, the pH was still alkali when

the mol ratio (g) of KH2PO4 (0.45 g/L) and pure CaO2 converted

from the technical was about 1. The main reason was that the

technical CaO2 contained about 50 (wt%) of Ca(OH)2 impurity,

which consumed a great number of H+ ions iodized from

KH2PO4 and hydrolyzed from NH4+. That is, (NH4)2SO4 and

KH2PO4 added were not enough to react with all alkali

substances in the solution. When the change of g was from

2 (KH2PO4, 0.90 g/L) to 3 (KH2PO4, 1.35 g/L), the mixture could

regulate the pH value to the range of 6.5–8.5. At the same

time, the pH slowly ascended because alkali substance

ARTICLE IN PRESS

Fig. 2 – Schematic diagram of the column experimental set-

up.

6

7

8

9

10

11

12

13

0 2 64 8 10 12 14 16 18

Time (d)

pH

0g/L0.45g/L0.675g/L0.90g/L1.125g/L1.35g/L

Fig. 3 – Effects of different adding weights of (NH4)2SO4 and

KH2PO4 on pH of solution (KH2PO4: ~, 0 g/L; ’, 0.45 g/L; m,

0.675 g/L; � , 0.90 g/L; W, 1.125 g/L; J, 1.35 g/L).

WAT E R R E S E A R C H 4 0 ( 2 0 0 6 ) 3 4 0 1 – 3 4 0 83404

contained in the system was neutralized from the beginning

of experiment.

3.1.2. Effects of the pH on the biodegradation efficiency ofMTBEMicrobial degradation is the process of enzymatic catalytic

reaction. The concentration of H+ ions in the solution has

obvious effect on the microbial enzymatic activity, and causes

the significant difference in the biodegradation efficiency.

Fig. 4 presents the effect of pH on the degradation efficiency

of MTBE. The degradation experiment was operated for about

200 h. As the pH increased from 6.5 to 8.0, the biodegradation

efficiency of MTBE increased from 37.1% to 48.9%, while the

efficiency decreased with the further increase of the pH. It

showed that the optimum pH value for the biodegradation of

MTBE should be 8.0 in this study. TBA was detected as

degradation byproduct of MTBE. In addition, CO2 was not

detected by analyzing gas components of the headspace of

enclosed reactor at the end of experiment. It indicated that

MTBE could not be completely mineralized under this

experimental condition.

According to the results of batch experiments, we chose the

weight ratio of CaO2 (0.45 g/L), KH2PO4 (0.90 g/L), (NH4)2SO4

(1.17 g/L) at 1.0:2.0:2.6 as the basic components of oxygen-

releasing materials in the column experiment, which may

keep the pH value of effluent of oxygen-releasing material

column in the optimum range for the biodegradation of

MTBE. Besides, above concentrations of (NH4)2SO4 and

KH2PO4 are about the same as that of nitrogen and

phosphorus in the medium. It means that they may not

cause new pollution in field application except for maintain-

ing microbial normal metabolism.

3.2. Microbial immobilization

Microbial immobilization was determined by measuring DO

levels in the effluent, and the concentrations of MTBE in the

influent and effluent throughout 25 days. In the beginning of

this operational phase (0–3 days), the effluent was slight

yellow because a few of microbes were washed out. But with

the time passing, the effluent became gradually clear

indicating that the microbes had been adsorbed on the

expanded perlite granules. During the whole process of

microbial immobilization, DO levels in the effluent were in

the range of 2.3–3.0 mg/L, and the concentrations of MTBE in

the effluent remained below the influent (data not shown). As

described above, it indicated that there was formation of

microbial film on the carriers, and the attached microbe could

maintain the aerobic metabolism using MTBE as sole source

of carbon and energy under this experimental condition.

3.3. Column experiment

In the column experiment, the samples of biodegradation

column influent and specified sampling ports were collected

and analyzed for pH, DO, MTBE and TBA. Fig. 5 presents the

variations in pH values in the biodegradation column influent

and effluent. The pH values in the biodegradation column

influent varied from 9.1 to 8.1 during the early operational

period, which were beyond the optimum value for the

biodegradation of MTBE, and then slowly closed to 8.0 after

400 h. Due to the gradual replacement of deionized water by

alkali solution from the oxygen-releasing material column,

the observed pH values in the biodegradation column effluent

rapidly increased from 6.4 to 8.3 before about 100 h, and then

dropped to 8.0–8.3 after this period. Although the high pH in

the early operational period might have influence on the

degradation of MTBE, it should not be a concern in the

field application because of the buffer capacity of field soil

located between the oxygen-releasing material layer and

biodegradation layer.

Fig. 6 presents the DO levels in the biodegradation column

influent and effluent. According to the equation (1), equili-

brium shifted to the right swiftly because DO of simulated

MTBE-contaminated groundwater entering this barrier sys-

tem was zero. As a result, released oxygen concentration

from the oxygen-releasing material in the biodegradation

column influent went up to 21 mg/L in the beginning of

ARTICLE IN PRESS

0.3

0.35

0.4

0.45

0.5

0.55

6 6.5 7.5 8.5 9.57 8 9 10

pH

Deg

rada

tion

effic

ienc

y

Fig. 4 – Effects of pH on the biodegradation efficiency of

MTBE.

6

6.5

7

7.5

8

8.5

9

9.5

0 100 200 300 400 500 600 700 800

Time (h)

pH

the influent

the effluent

Fig. 5 – Variations in pH values in the biodegradation

column influent and effluent (~, the influent; m, the

effluent).

WAT E R R E S E A R C H 40 (2006) 3401– 3408 3405

column experiment, and then slowly dropped to 11 mg/L

before the end of the experiment. The observed DO values in

the biodegradation column effluent kept in the range of

5.1–8.6 indicating that this passive system was under aerobic

condition during the whole operational period. Compared

with the DO levels in the influent, the decrease in DO

measurements in the effluent also indicated that aerobic

biodegradation had occurred in the biodegradation column.

The concentrations of MTBE and its degradation byproduct

(TBA) versus time in the specified sampling ports are shown

in Figs. 7a and b, respectively. Before the column experiment

started, concentrations of MTBE in each specified sampling

port remained below the detection limit. For no. 19, concen-

tration of MTBE was first detected on hour 182, which is

beyond the 80 h of residence time. It suggested that the

occurrence of biodegradation in the column caused

the significant lag period. The phenomenon was similar to

the observed from each specified sampling port. Concentra-

tions of MTBE gradually increased, reached a quasi-steady

state and remained constant. MTBE was not further degraded

after this period. TBA was first detected in specified sampling

ports from hour 44 to 95, and significant accumulation was

found during the early operational period. In this period, TBA

could not be utilized and degraded as the source of carbon.

This result could be explained on the basis that the

immobilized microbes in the biodegradation column were

not adapted to metabolize TBA because they were acclimated

in the medium containing MTBE. The microbes require a

period of time to adapt to new environment and synthesize

inducible enzymes degrading TBA. After the lag phase,

concentrations of TBA in each specified sampling port started

to decrease respectively. It indicated that the biodegradation

of MTBE and TBA as the sources of carbon could occur in this

passive system.

The average MTBE removal efficiencies between the influ-

ent and specified sampling ports (nos. 3, 7, 11, 15 and 19) in

the biodegradation column were about 16.3%, 22.1%, 33.3%,

41.1% and 50%, respectively. Based on the observed reaction

trends, complete MTBE and its byproduct (TBA) removal in

this designed barrier system is possible as long as sufficient

reaction time or extended reaction distance is provided.

4. Conclusions

As nutrient components of the medium, the mixture of

KH2PO4 and (NH4)2SO4 at a certain ratio can be used as buffer

ARTICLE IN PRESS

the influent, MTBE

no. 3, MTBE

no. 7, MTBE

no. 11, MTBE

no. 3, TBA

no. 7, TBA

no. 11, TBA

0

20

40

60

80

100

120

140

160

180

0 100 200 300 400 500 600 700 800

Time (h)

Con

cent

ratio

n (m

g/L)

(a)

the influent, MTBE

no. 15, MTBE

no. 19, MTBE

no. 15, TBA

no. 19, TBA

0 100 200 300 400 500 600 700 800

Time(h)

0

20

40

60

80

100

120

140

160

180

Con

cent

ratio

n(m

g/L)

(b)

Fig. 7 – Concentrations of MTBE and its degradation byproduct (TBA) in the influent and specified sampling ports. (a) �, the

influent; ’, no. 3, MTBE; m, no. 7, MTBE; ~, no. 11, MTBE; &, no. 3, TBA; W, no. 7, TBA; B, no. 11, TBA (b) �, the influent; ’,

no. 15, MTBE; m, no. 19, MTBE; &, no. 15, TBA; B, no. 19, TBA.

4

7

10

13

16

19

22

0 100 200 300 400 500 600 700 800

Time (h)

DO

(m

g/L)

the influent

the effluent

Fig. 6 – DO levels in the biodegradation column influent and

effluent (~, the influent; m, the effluent).

WAT E R R E S E A R C H 4 0 ( 2 0 0 6 ) 3 4 0 1 – 3 4 0 83406

reagents to control the regulation of pH caused by CaO2. In

this study, the technical CaO2 used as oxygen source

contained about 50% of Ca(OH)2 impurity, as a result, 1 mol

KH2PO4 could not completely neutralize 1 mol pure CaO2

converted from the technical even with the presence of

(NH4)2SO4. When the mol ratio of KH2PO4 and pure CaO2

converted from the technical was from 2 to 3, the mixture

could regulate the pH value from 12.1 to the range of 6.5–8.5.

The experimental results of MTBE biodegradation imply that

microbial activity is influenced by the concentration of H+

ions in the solution. Under this experimental condition,

the optimum pH value for the microbial degradation of

MTBE is 8.0.

A biological two-layer permeable reactive barrier system

was designed to bioremediate MTBE-contaminated ground-

water. Based on the results from the batch experiments, the

designed oxygen-releasing materials might be prepared easily

by blending CaO2, KH2PO4, (NH4)2SO4, sand and trace ele-

ments, which could release significant amount of oxygen and

control appropriate pH value. Although the pH in the early

operational period was beyond the desirable value, it might be

further decreased in the field application due to the buffer

capacity of natural soil located between the oxygen-releasing

material layer and biodegradation layer. In the passive

system, occurrence of aerobic degradation can be verified by

the consumption of MTBE, the decrease in DO levels in the

biodegradation column effluent compared to the influent. As

the MTBE byproduct, the transient accumulation of TBA in

the early operational period could be attributed to the

recalcitrance of the acclimated microbe used in the experi-

ment to new organic compound. After the lag phase, TBA

started to be biodegraded. Besides, the appropriate replace-

ment of the oxygen-releasing materials is necessary when

they are exhausted.

Although MTBE removal efficiency (�50%) is relatively low

during 800 h of operational period, the proposed barrier

system has the potential to improve its performance by using

obligate aerobic microbe to replace the microbe used in this

experiment, or adjusting other operational parameters such

as reaction time or reaction distance. Results from this study

will be useful in designing a permeable reactive barrier

system for field remediation of MTBE-contaminated ground-

water.

Acknowledegments

This work was supported by the National Natural Science

Foundation of PR China under Grant no. 20276048. Many

thanks to Lin Zhu for her laboratory work on this project. The

part work was conducted at Peiyang Distillation Company

Limited, Tianjin Economic and Technological Development

Area, PR China.

R E F E R E N C E S

Arienzo, M., 2000. Degradation of 2,4,6-trinitrotoluene in waterand soil slurry utilizing a calcium peroxide compound.Chemosphere 40, 331–337.

Barreto, R.D., Gray, K.A., Anders, K., 1995. Photocatalytic degrada-tion of methyl tert-butyl ether in TiO2 slurries a proposedreaction scheme. Water Res. 29, 1243–1248.

Bergendahl, J.A., Thies, T.P., 2004. Fenton’s oxidation of MTBE withzero-valent iron. Water Res. 38, 327–334.

Borden, R.C., Goin, R.T., Kao, C.M., 1997. Control of BTEXmigration using a biologically enhanced permeable barrier.Ground Water Monit. Remediat. 17, 70–80.

Bradley, P.M., Landmeyer, J.E., Chapelle, F.H., 2001. Widespreadpotential for microbial MTBE degradation in surface-watersediments. Environ. Sci. Technol. 35, 658–662.

Bradley, P.M., Landmeyer, J.E., Chapelle, F.H., 2002. TBA biodegra-dation in surface-water sediments under aerobic and anae-robic conditions. Environ. Sci. Technol. 36, 4087–4090.

Caprino, L., Togna, G.I., 1998. Potential health effects of gasolineand its constituents: a review of current literature (1990–1997)on toxicological data. Environ. Health Perspect. 106, 115–125.

Carsten, V., Albin, A., Helmut, L., Doreen, H., Lothar, W., Wolfgang,B., 2004. Bioremediation of chlorobenzene-contaminatedground water in an in situ reactor mediated by hydrogenperoxide. J. Contam. Hydrol. 68, 121–141.

Cassidy, D.P., Irvine, R.L., 1999. Use of calcium peroxide to provideoxygen for contaminant biodegradation in saturated soil.J. Hazard. Mater. 69, 25–39.

Deeb, R.A., Alvarez-Cohen, L., 2000. Aerobic biotransformation ofgasoline aromatics in multicomponent mixtures. Bioremediat.J. 4, 171–179.

Fayolle, F., Vandecasteele, J.P., Monot, F., 2001. Microbial degrada-tion and fate in the environment of methyl tert-butyl etherand related fuel oxygenates. Applied Microbiology and Bio-technology 56 (34), 339–349.

Fortin, N.Y., Deshusses, M.A., 1999. Treatment of methyl tertbutylether vapor in biotrickling filters. 1. Reactor startup, steady-state performance, and culture characteristics. Environ. Sci.Technol. 33, 2980–2986.

Graham, J.L., Striebich, R., Patterson, C.L., Krishnan, E.R., Haught,R.C., 2004. MTBE oxidation byproducts from the treatment ofsurface waters by ozonation and UV-ozonation. Chemosphere54, 1011–1016.

Hsieh, L.L., Lin, Y.L., Wu, C.H., 2004. Degradation of MTBE in diluteaqueous solution by gamma radiolysis. Water Res. 38,3627–3633.

Kang, J.W., Hoffmann, M.R., 1998. Kinetics and mechanism of thesonolytic destruction of methyl tert-butyl ether by ultrasonicirradiation in the presence of ozone. Environ. Sci. Technol. 32,3194–3199.

Kao, C.M., Chen, S.C., Su, M.C., 2001. Laboratory column studiesfor evaluating a barrier system for providing oxygen andsubstrate for TCE biodegradation. Chemosphere 44, 925–934.

Kao, C.M., Chen, S.C., Wang, J.Y., Chen, L.Y., Lee, S.Z., 2003.Remediation of PCE-contaminated aquifer by an in situ two-layer biobarrier: laboratory batch and column studies. WaterRes. 37, 27–38.

Kharoune, M., Pauss, A., Lebeault, J.M., 2001. Aerobic biodegrada-tion of an oxygenates mixture: ETBE, MTBE and TAME in anupflow fixed-bed reactor. Water Res. 35, 1665–1674.

Prince, R.C., 2000. Biodegradation of methyl tertiary-butyl ether(MTBE) and other fuel oxygenates. Critical Reviews in Micro-biology 26 (3), 163–178.

Rasmussen, G., Fremmersvik, G., Olsen, R.A., 2002. Treatment ofcreosote-contaminated groundwater in a peat/sand perme-able barrier—a column study. J. Hazard. Mater. B 93, 285–306.

Ritter, W.F., Scarborough, R.W., 1995. Review of bioremediation ofcontaminated soils and groundwater. J. Environ. Sci. HealthA 30 (2), 333–357.

Safarzadeh-Amiri, A., 2001. O3/H2O2 Treatment of methyltert-butyl ether (MTBE) in contaminated waters. Water Res. 35,3706–3714.

ARTICLE IN PRESS

WAT E R R E S E A R C H 40 (2006) 3401– 3408 3407

Schmidt, T.C., Schirmer, M., Weiß, H., Stefan, B., Haderlein, S.B.,2004. Microbial degradation of methyl tert-butyl ether andtert-butyl alcohol in the subsurface. J. Contam. Hydrol. 70,173–203.

Sedran, M.A., Pruden, A., Wilson, G.J., Suidan, M.T., Venosa, A.D.,2002. Effect of BTEX on degradation of MTBE and TBA bymixed bacterial consortium. J. Environ. Eng.—ASCE 128 (9),830–835.

Shih, T.C., Wang, P.M., Suffet, M., 2003. Evaluation of granularactivated carbon technology for the removal of methyl tertiarybutyl ether (MTBE) from drinking water. Water Res. 37,375–385.

Squillace, P.J., Zogorski, J.S., Wilbur, W.G., Price, C.V., 1996.Preliminary assessment of the occurrence and possiblesources of MTBE in groundwater in the United States,1993–1994. Environ. Sci. Technol. 30, 1721–1730.

Wilkin, R.T., Puls, R.W., Sewell, G.W., 2003. Long-term perfor-mance of permeable reactive barriers using zero-valent iron:geochemical and microbiological effects. Ground Water 41 (4),493–503.

Zang, Y.J., Faronood, R., 2005. Effects of hydrogen peroxideconcentration and ultraviolet light intensity on methyl tert-butyl ether degradation kinetics. Chem. Eng. Sci. 60,1641–1648.

ARTICLE IN PRESS

WAT E R R E S E A R C H 4 0 ( 2 0 0 6 ) 3 4 0 1 – 3 4 0 83408