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    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





    Permeable reactive barrier


    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 8.0, the biodegradation efficiency of MTBE is the maximum and approximately48.9%. 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

    0mg/L, was pumped into this system at a flow rate of 500mL/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


    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 2227404705.

    E-mail address: (X.-G. Li).

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

  • 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 gasolines 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 pHmight 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

    6.58.5. 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 23mm 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 l