Engineered passive bioreactive barriers: risk-managing the

Engineered passive bioreactive barriers: risk-managing thelegacy of industrial soil and groundwater pollutionRobert M Kalin

Permeable reactive barriers are a technology that is one decade

old, with most full-scale applications based on abiotic

mechanisms. Though there is extensive literature on engineered

bioreactors, natural biodegradation potential, and in situ

remediation, it is only recently that engineered passive

bioreactive barrier technology is being considered at the

commercial scale to manage contaminated soil and groundwater

risks. Recent full-scale studies are providing the scientific

confidence in our understanding of coupled microbial (and

genetic), hydrogeologic, and geochemical processes in this

approach and have highlighted the need to further integrate

engineering and science tools.

AddressesEnvironmental Engineering Research Centre, School of Civil

Engineering, The Queen’s University of Belfast, Belfast BT9 5AG,

Northern Ireland, UK

e-mail: [email protected]

Current Opinion in Microbiology 2004, 7:227–238

This review comes from a themed issue on

Ecology and industrial microbiology

Edited by Elizabeth Wellington and Mike Larkin

Available online 10th May 2004

1369-5274/$ – see front matter

� 2004 Elsevier Ltd. All rights reserved.

DOI 10.1016/j.mib.2004.04.014

AbbreviationsMNA monitored natural attenuation

NA natural attenuation

PRB permeable reactive barrier

IntroductionThe development of our current societal infrastructure

and standard of living has produced a legacy of land and

groundwater that is contaminated with potentially harm-

ful inorganic and organic compounds. At the turn of the

new millennium much of the developed world turned its

attention to ‘sustainability’ where emphasis is now

placed on a balance between economic, social and envir-

onmental issues. This change in emphasis on integration

of the natural and anthropogenic environments is sum-

marized in the following two quoted mission statements:

‘We will be recognized as the leading source of knowledge

and skills required to create a sustainable natural and

built environment for the benefit of future generations’

�Institution of Civil Engineers (ICE) UK Vision Statement

‘Environmental Engineering is the integration of the

built environment within the natural environment using

science and engineering to meet the principles of social,

economic and environmental sustainability’ �Prof. RobertM. Kalin

There are three primary strategies used separately or in

conjunction to reduce or eliminate the risk of contami-

nants in soil and groundwater:

1. Destruction or alteration of contaminants.

2. Extraction or separation of contaminants from envir-

onmental media.

3. Immobilization of contaminants.

There is a variety of both in situ and ex situ treatment

technologies capable of contaminant destruction by alter-

ing the chemical structure including thermal, biological

and chemical treatment methods. Highly engineered

treatment technologies that are commonly used for

extraction and separation of contaminants from environ-

mental media include soil treatment by thermal de-

sorption, soil washing, solvent extraction, soil vapour

extraction and ground water treatment by either phase

separation, carbon adsorption, air stripping, ion exchange,

or by some combination of these technologies. Immobi-

lization technologies are generally only applied to soil-

based contamination and include stabilization, solidifica-

tion and containment technologies, such as placement in

a secure landfill or construction of cement-bentonite

slurry walls. However, the contaminants have not been

treated and it is now realized that no immobilization

technology is permanently effective.

To this end, it has been realized over the past three

decades of environmental remediation that it is not

possible to use engineering to completely degrade all

contaminants that have been released to the environ-

ment. Thus, the development of remediation technol-

ogies to degrade these compounds has moved from

strongly intensive in situ and ex situ treatments to com-

bined engineered and passive/natural approaches (treat-

ment train) that manage the risks associated with the

‘source’ of the contaminants, the ‘pathways’ of flux and

contaminant transport and impact on the ‘receptor’

which may either be human health related or additional

environmental impact.

One of the main obstacles to implementation of this

‘sustainable’ approach to dealing with contaminants in

soil and groundwater is the added costs, in time and

money, required to manage the risks of contaminants

www.sciencedirect.com Current Opinion in Microbiology 2004, 7:227–238

in the environment. As a generalisation, the dominant

ex situ method for dealing with contaminated soil has

involved digging up much of the contamination and

disposing it in landfills. However, both legislative pres-

sure and the increased costs of land-filling (both in the

UK, the EU and other countries) and a world-wide move

towards more sustainable remedial technologies are

prompting developers to consider alternative in situ andex situ methods of dealing with organic contaminants.

Alternative remediation technologies that permanently

destroy or detoxify contaminants are becoming common-

place in the USA, Australasia and European countries.

The complete degradation of man-made or xenobiotic

chemicals by microorganisms in the environment is uni-

versally considered to be beneficial. In particular, those

high priority pollutants of soils and groundwater’s that are

regarded as carcinogenic and toxic (EU Council Directive

2000/60/EC). The concept of ‘microbial infallibility’ with

respect to biodegradation has long been the assumption.

Indeed, Stanley Dagley concluded in his introduction to

the text ‘Microbial Degradation of Organic Compounds’ that

‘On thermodynamic grounds, no organic compound can

be excluded from serving as a possible energy source for

aerobic microorganisms’.

Some of the most promising alternative technologies are

based therefore on bioremediation [1–3]. When consid-

ered from an ‘engineering’ perspective, there are two

general approaches to microbial biodegradation i) those

that use engineered or inoculated microorganisms [4–6],

or ii) those that use natural microbial biodegrative poten-

tial [7–17,18�19�] in technologies such as bio-sparging,

bio-slurping and natural attenuation (NA) [20–22]. Of

these biological technologies, NA has received significant

attention. NA relies on the indigenous microbial popula-

tion and aquifer nutrients to biodegrade contaminants.

Monitored natural attenuation (MNA) can be used for

risk management and as a remediation method for con-

taminant plumes. The application of MNA can be limited

by nutrient availability and/or high risks associated with

contaminant movement, hence at some sites the potential

to use NA as a risk management strategy is poor and

intervention is necessary.

There is a plethora of publications in the literature that

describe microbial species, populations and mechanisms

for biotransformation of potentially hazardous com-

pounds, but many of these publications focus on a very

limited number of substrates. ‘Real’ sites may have many

hundreds or thousands of contaminants partitioned

between soil, water and vapour phases, and for which

bioremediation is expected to provide a successful reduc-

tion in risk. Engineering a sustainable bioremediation

solution depends on long-term microbial populations that

will biotransform a significant number of contaminant

substrates and metabolites as well as a superfluity of

natural carbon substrates. Other complicating factors

whereby natural degradative processes are limited

include nutrient availability, redox conditions, substrate

competition, bioavailability, toxicity and a combination of

geologic, geotechnical and hydrogeologic factors that

make the subsurface an immensely complex environ-

ment. An evolution of approach is needed which develops

a conceptual understanding of all elements and identifies

knowledge gaps. There is also a need for further devel-

opment/refinement of tools for site study that will provide

an understanding of the rate controlling mechanisms for

natural biodegradative processes [23–25].

In this review, I have chosen to write from the ‘engineer-

ing’ perspective and briefly touch upon a wide range of

both engineering and science issues that must be con-

sidered for implementation of passive bioreactive barrier

technology. This includes not only the microbiological

biotransformations, but also where the technology has

come from (including abiotic transformations), the wide

scope of issues that are needed to design the engineering

of a bioreactor that must operate with little or no main-

tenance for decades, and cost effective and rapid ways of

monitoring the ‘health’ of the system.

Engineered passive bioreactive barriersPermeable reactive barriers (PRBs) are a passive inter-

vention remediation technology [26–31] that have been

used for risk-management in even the most extreme

environments found on earth [32�,33�,34,35�,36��]. In

PRB systems contaminated groundwater passes through

an in situ reactive material that either biotically or abio-

tically degrades the contaminants. PRBs are unique

because they can be engineered to prevent contaminant

movement across site boundaries before risk receptors, or

simply to cut-off the source of a contaminant plume that

then dissipates via NA processes. By far the most success-

ful PRB technology to date is barriers of zero-valent iron

[37–43,44�,45�]. The laboratory, pilot scale and full-scale

experience, of which there are nearly 80 installations

world-wide, have been shown to abiotically degrade

chlorinated solvents such as trichloroethene and tetra-

chloroethene, trace metals and radionuclides, and inor-

ganic contaminants such as nitrate and sulphate/sulphide

[46–56]. Microorganisms have a greater scope for trans-

formation of a wide range of compounds and recent

studies are examining synergetic degradation between

abiotic zero-valent iron and biologic processes [57,58��].

There is a considerable research effort to continually find

new abiotic methods for destruction of contaminants

using passive techniques [59–61,62�,63]. PRBs using

activated carbon can remove many organic contaminants

from groundwater through sorption (non-destructive pro-

cess), but some compounds may not be removed, or if

inappropriately designed, the effect of ‘roll-up’ may end

in chromatographic effects that release concentrations of

228 Ecology and industrial microbiology

Current Opinion in Microbiology 2004, 7:227–238 www.sciencedirect.com

contaminants in higher concentration than was originally

observed [64–67,68�,69,70�,71�].

The recent advancement on this technology is to use

engineered passive bioreactors in situ to take advantage of

the potential for microbial biotransformation of poten-

tially hazardous compounds. Bioreactive ‘zones’ have

been engineered to change redox conditions or provide

substrates/nutrient that facilitate the natural biodegrada-

tive system [72–81]. Current biological reactive zones rely

on either dissolved nutrients or injected nutrients to

support the biodegradation of contaminants passing

through the ‘barrier’. Delivery of nutrients throughout

a barrier has been shown to be hydrologically difficult and

can add considerable expense to a remediation project.

Additionally, there is the potential that media must be

replenished periodically.

Given the complexity of the subsurface, passive bioreac-

tive barriers have applied the principles and knowledge

used in the biotransformation of potentially hazardous

compounds with bioreactor technology [82–89,90�]. Exsitu bioreactors have been used successfully for remedia-

tion of contaminated soil and groundwater for most com-

pounds of concern [91–103,104�,105,106��,107].

The engineering challenge was therefore to take existing

knowledge and expertise and apply it passively using only

the inertia of natural groundwater systems to transport a

flux through the bioreactive barrier, and design systems

capable of operation for years to decades with little or no

maintenance. The overall performance of a bioreactive

PRB must also balance the rate of contaminant degrada-

tion with the flux of contaminants entering the reactive

zone. Laboratory batch and column studies using real site

water and microbial populations can provide an estimate

of the rate of biotransformation [108–112,113�,114,115�,116,117�]. However, there are a large number of variables

that could be examined and it often takes significant

research to elucidate the major factor(s) that control

the occurrence and rate of biodegradation. Figure 1 pre-

sents a flow diagram of the decision making and design

process for implementation of a PRB. An integral part of

evaluation is laboratory and pilot scale experiments that

study, under site conditions, the operational windows for

in situ bioreactive barrier methods [118–121,122�] before

Figure 1

Current Opinion in Microbiology

Microbiology

Geochemistry

Microbiology

Geochemistry

Modelling

Evaluation

Evaluation

Risk assessmentSolution identification

Site investigation

HydrogeologyFlux

BiogeochemistryMicrobiology

Identificationof knowledge

gapPilot scaletrial studies

Design andimplementation

Engineering

Full scale PRBevaluation

Scale up todesigncriteria

Evaluation ofpilot scale

In situ passive remediation of contaminants in soil and groundwater (e.g. Permeable Reactive Barrier, PRB) must integrate the rate flux of

substrate transport or availability, rates of natural or enhanced biodegradation with evaluation of the temporal uncertainty in each of these parameters

to allow design and implementation. It will be essential that large complex genetic databases are easily available (at minimal cost) so that the

emerging array technology can reach its ultimate potential and provide rapid and detailed feedback for remediation science and technology.

Engineered passive bioreactive barriers: risk-managing the legacy of industrial soil and groundwater pollution Kalin 229


design and full-scale implementation of bioreactive PRB

systems [123–132,133��,134�,135��,136�]. One of the most

significant single-use sources of contaminated soil and

groundwater in the UK and Europe is former coal gasi-

fication sites. The long and complex history of these

activities has resulted in a wide range of compounds

in soil and groundwater that require risk-management.

There is a significant body of literature on the biotrans-

formation of many of these compounds [137,138�,139–

141], the use of ex situ bioreactor techniques [142–144]

and recent applications of pilot-scale to full-scale PRBs

for risk management of these sites [145–151]. Significant

collaborative research on full-scale engineered bioreac-

tive barrier systems at two UK Sites is on-going between

two research groups at the Queen’s University Belfast

(QUESTOR Centre and Environmental Engineering

Research Centre), Oxford University and the University

of Surrey, and two industrial partners, Second-Site

Property Holding Ltd, and Parsons Brinkerhoff.

Figure 2 shows the site and bioreactor layout for one

of the projects on Sequential REactive BARrier (SER-

EBAR) remediation of contaminated groundwater, the

results of this research has highlighted the need for

integration of science and engineering when imple-

menting this technology.

Of particular note is the difficulty for prediction of not

only how a bioactive barrier might adapt and function

over timescales that range from days to decades, but also

how to measure temporal changes in microbial popula-

tions. Figure 3 depicts a conceptual/hypothetical series of

changes in microbial ecology or genetic diversity over

time or resulting from shocks to the bioreactive barrier.

Chemical monitoring of the system provides confirmatory

cause/effect information on the end-result of biotransfor-

mation, or lack thereof, but can provide little predictive

Figure 2

AbioticAnaerobicAerobicSorptive

SEquencedREactiveBARrier(SEREBAR)


Site and design drawings of the engineered bioreactive barrier for project SEREBAR at a former coal gasification site in the UK combining site

groundwater flow and contaminant flux with abiotic, anaerobic biotransformation, aerobic biotransformation and abiotic sorption stages.



measure of the ‘health’ or ‘sustainability’ of the microbial

populations doing all the work.

There is a challenge to find cost effective and time

efficient ways to monitor these systems at the biofilm/

microbiological level. On-line automated measurement is

needed of toxicity, respiration, identification of metabo-

lites, and potentially, direct methods [152–161,162�]. The

increasing use of isotopes, either natural abundance or

labelled compounds provides direct evidence of substrate

Figure 3


Toxic event

Toxic event

0 5 10 15 20 25 30

Incr

easi

ng m

icro

bial

div

ersi

tyor

deg

rada

tion

pote

ntia

l

Time (months)

Biofilm strongly affected

Biofilm not affected

Adaptive Biofilm

Adaptive diversity

Increasing diversity

Declining diversity

Toxic event

Toxic event

In situ passive treatment of groundwater and soil is a process that takes months to decades and there is a lack of extant knowledge vis-a-vis the

long-term response of microbial biodegradation on these time scales. There are several potential changes in microbial biodegradative potential

over time, hypothetical variations shown here, which must be evaluated by the emerging body of research into this technology (e.g. the UK

BBSRC Link and CLAIRE project SEREBAR). Note: A toxic event may reflect an abrupt change in substrate, nutrients or concentration.

Table 1

Typical time frames for PRB implementation.

Task Timeframe

Technology selectionPreliminary site evaluation and risk assessment 1 to 12 weeks

Hydrogeologic study 4 to 26 weeks

Detailed biogeochemical site evaluation 4 to 12 weeksa

Choice of technology generally 4 to 26 weeks

PRB remediation validationHydrogeologic/contaminant flux modelling 2 to 12 weeks

Laboratory trials/kinetics of reactions 5 to 15 weeksa

Conceptual design 2 to 4 weeks

Pilot scale studies and conceptual design period generally 5 to 19 weeks

PRB tender and constructionEngineering design 2 to 4 weeks

Implementation/construction 10 to 26 weeks

Engineering design and implementation generally 14 to 30 weeks

PRB operationMonitoring and maintenance Years to decades

In general, is takes between 6 months and 1.5 years for implementation of passive PRB technology. aHowever, there is a limited window

of opportunity during which detailed microbial evaluation and results are able to provide specific design parameters. It is imperative that the

microbial genetics revolution develops a capability to provide detailed understanding of both site investigation soil and groundwater samples

and laboratory trials in a highly time efficient manner if this data are to be used in Engineering Design to its greatest potential.



utilization [162�,163–167,168�]. However, the greatest

potential lies with array techniques that elucidate large

amounts of genetic information on both expression and

potential of the microbial community [169–175,176��,177��]. The challenge will be providing a rapid, cost

effective routine and reliable monitoring application of

this technology. In particular, there is need to model the

short-term and long-term behavior of engineered passive

systems. A significant research effort is needed to couple

predictive modeling of microbial behavior [178,179,180�,181��,182��], microbial transport and establishment

within the bioreactor [182��,183–188,189��], the forma-

tion and behavior of the resulting biofilm [190–193]

within the predictive design and modeling of full-scale

PRB systems [194–201], and the response of bioremedia-

tion to changes in operational parameters [202–204].

A further challenge is to provide this information within a

‘typical’ project management time-line for an engineered

PRB system such that the information can play a crucial

role in the conceptual model, design and implementation.

Table 1 presents recent experience on the evaluation,

design and implementation of engineered bioreactive

PRBs and the associated time-scales for sites in the

UK. There is often only a matter of weeks during which

sample collection, microbial evaluation and substrate

utilization, and predictive study can take place. For

detailed design, the results of microbial investigation

must also be interpreted side-by-side with hydrogeologi-

cal, biogeochemical and engineering results. Without

readily available rapid and robust (inclusive and depend-

able) screening methods, there will continue to be a

limited ability for detailed microbiological study to pro-

vide predictive design input for full-scale engineering,

and thereby have the greatest benefit for implementation

and monitoring of novel ‘sustainable’ technology.

ConclusionsSustainability, economic, social and environmental,

requires implementation of contaminated land and

groundwater risk-management on decadal time scales.

Although significant scientific understanding of natural

bioattenuative processes has emerged, there is a current

lack of knowledge or engineering experience that allows

the accurate prediction of the long-term sustainability of

passive engineered bioremediation systems for soil and

groundwater. The challenge for the future is to use the

potential of emerging microbial genetic methods to pro-

vide a prediction of long-term changes in microbial biode-

gradative potential in combination with hydrogeological,

biogeochemical, geotechnical and engineering under-

standing for effective design and implementation.

AcknowledgementsThe author would like to acknowledge years of discussion and research withcollaborators at QUB and in the QUESTOR Centre, in particular MikeLarkin, at Oxford University, at the University of Surrey, in particularStephan Jefferis, and members of PRB-Net, in particular Robert Puls

of the US EPA. The research experience of the author has been supportedby the BBSRC, EPSRC, NERC, EA, and by industrial partners/collaborators,in particular the QUESTOR Industrial Board, Second-Site PropertyHoldings Ltd, Keller Ground Engineering, and EnvironmentalTechnologies (ETI).

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32.�

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33.�

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35.�

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36.��

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44.�

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45.�

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48. Puls RW, Paul CJ, Powell RM: The application of in situpermeable reactive (zero-valent iron) barrier technology for theremediation of chromate-contaminated groundwater: a fieldtest. Appl Geochem 1999, 14:989-1000.

49. Gupta N, Fox TC: Hydrogeologic modeling for permeablereactive barriers. J Hazard Mater 1999, 68:19-39.

50. Gavaskar R: Design and construction techniques for permeablereactive barriers. J Hazard Mater 1999, 68:41-71.

51. Eykholt GR, Elder CR, Benson CH: Effects of aquiferheterogeneity and reaction mechanism uncertainty on areactive barrier. J Hazard Mater 1999, 68:73-96.



http://www.prb-net.org

52. Vogan JL, Focht RM, Clark DK, Graham SL: Performanceevaluation of a permeable reactive barrier for remediation ofdissolved chlorinated solvents in groundwater. J Hazard Mater1999, 68:97-108.

53. Day SR, O’Hannesin SF, Marsden L: Geotechnical techniques forthe construction of reactive barriers. J Hazard Mater 1999,67:285-297.

54. Blowes DW, Ptacek CJ, Benner SG, McRae CWT, Bennett TA,Puls RW: Treatment of inorganic contaminants usingpermeable reactive barriers. J Contam Hydrol 2000, 1-2:123-137.

55. Morrison SJ, Metzler DR, Dwyer BP: Removal of As, Mn, Mo, Se,U, V and Zn from groundwater by zero-valent iron in apassive treatment cell: reaction progress modeling. J ContamHydrol 2002, 56:99-116.

56. Cantrell KJ, Kaplan DI: Zero-valent ion colloid emplacementin sand columns. J Environ Eng 1997, 123:499-505.

57. Gandhi S, Oh B-T, Schnoor JL, Alvarez PJJ: Degradation of TCE,Cr(VI), sulfate, and nitrate mixtures by granular iron in flow-through columns under different microbial conditions.Water Res 2002, 36:1973-1982.

58.��

Fernandez-Sanchez JM, Sawvel EJ, Alvarez PJJ: Effect of Fe0quantity on the efficiency of integrated microbial-Fe0treatment processes. Chemosphere 2004, 54:823-829.

This paper shows that there is likely to be a greater relationship betweenabiotic reactions of iron and microbial processes during removal ofchromium from groundwater than perhaps was previously considered.The results may also suggest that a better understanding of this inter-action may allow for a more ‘refined’ permeable reactive barrier design.

59. Chen X, Wright JV, Conca JL, Peurrung LM: Effects of pH on heavymetal sorption on mineral apatite. Env Sci and Technol 1997,31:624-631.

60. Fryar AE, Swartz FW: Modelling the removal of metals fromground water by a reactive barrier: experimental results.Water Resour Res 1994, 30:3455-3469.

61. Johnson JG, Odencrantz JE: Management of a hydrocarbonplume using a permeable ORC Barrier. Proceedings of the 4thInternational In Situ and On-Site Bioremediation Symposium 1997,4:215-220.

62.�

Centi G, Perathoner S: Remediation of water contaminationusing catalytic technologies. Appl Catal Environ 2003, 1-2:15-29.

This paper discusses how abiotic catalytic degradation could be used formethyl tertiary butyl ether and other contaminants, and interestinglysuggests that microbiological breakdown of residual compounds isexpected at the back end of the process.

63. Bill M, Schuth C, Barth JAC, Kalin RM: Carbon isotopefractionation during abiotic reductive dehalogenation oftrichloroethene (TCE). Chemosphere 2001, 44:1281-1286.

64. Smith CC, Anderson WF, Freewood RJ: Evaluation of shreddedtyre chips as sorption media for passive treatment walls.Eng Geol 2001, 1-4:253-261.

65. Lorbeer H, Starke S, Gozan M, Tiehm A, Werner P: Bioremediationof chlorobenzene-contaminated groundwater on granularactivated carbon barriers, water, air and soil pollution.Focus 2002, 2:183-193.

66. Czurda KA, Haus R: Reactive barriers with fly ash zeolites forin situ groundwater remediation. Appl Clay Sci 2002, 1-2:13-20.

67. Park J-B, Lee S-H, Lee J-W, Lee C-Y: Lab scale experiments forpermeable reactive barriers against contaminatedgroundwater with ammonium and heavy metals usingclinoptilolite (01-29B). J Hazard Mater 2002, 95:65-79.

68.�

Ake CL, Wiles MC, Huebner HJ, McDonald TJ, Cosgriff D,Richardson MB, Donnelly KC, Phillips TD: Porous organoclaycomposite for the sorption of polycyclic aromatichydrocarbons and pentachlorophenol from groundwater.Chemosphere 2003, 51:835-844.

The results of this paper suggest that organo-clays should be supportedon granular activated carbon and not alumino-silicate structures toincrease the efficiency of sorption. This seems intuitive, however asorgano-clays may be useful for maintaining microbial populations duringbioremediation, there is more work needed on the bioavailability ofcontaminants sorbed to these types of materials.

69. Gates WP: Crystalline swelling of organo-modified clays inethanol-water solutions. Appl Clay Sci 2004, in press.

70.�

Komnitsas K, Bartzas G, Paspaliaris I: Efficiency of limestone andred mud barriers: laboratory column studies. Miner Eng 2004,17:183-194.

This is another paper on new media for permeable reactive barriers,however not only do the authors use laboratory columns, but they alsouse geochemical models to provide a validation and predictive element tothe work.

71.�

Wan M-W, Petrisor IG, Lai H-T, Kim D, Yen TF: Copper adsorptionthrough chitosan immobilized on sand to demonstrate thefeasibility for in situ soil decontamination. Carbohydr Polym2004, 55:249-254.

This paper is representative of a body of literature in the civil and chemicalengineering field where by-products of food engineering (in this casechitin) are proposed for full-scale permeable reactive barrier (PRB) appli-cations. There is a need to bring this work together with microbialprocesses if the long-term sustainability of easily biodegradable materialis to be used for long-term sorption PRBs.

72. Rijnaarts HHM, Hesselink PGM, Doddema HJ: Activated in situbioscreens. In Contaminated Soil, vol 2. Edited by van den BrinkWJ et al. Kluwer Academic Publishers 1995:929-937.

73. James GA, Warwood BK, Cunningham AB, Sturman PJ, Hiebert R:Evaluation of subsurface biobarrier formation and persistence.Proceedings of the Tenth Annual Conference on Hazardous WasteResearch 1995:82-91. Hazardous Substance Research Centre,Manhattan.

74. Watanabe E: Starved bacteria investigated as bioremediationbarrier technology. Environ Sci Technol 1996, 30:332.

75. Hohener P, Hunkeler D, Hess A, Bregnard T, Zeyer J: Methodologyfor the evaluation of engineered in situ bioremediation: lessonsfrom a case study. J Microbiol Methods 1998, 32:179-192.

76. Brough MJ, Al-Tabbaa A, Martin RJ: Active biofilm barriersfor waste containment and bioremediation: laboratoryassessment. Proceedings of the 4th International In Situ andOn-Site Bioremediation Symposium 1997, 4:233-238.

77. Hunkeler D, Hohener P, Bernasconi S, Zeyer J: Engineered in situbioremediation of a petroleum hydrocarbon-contaminatedaquifer: assessment of mineralization based on alkalinity,inorganic carbon and stable carbon isotope balances.J Contam Hydrol 1999, 37:201-223.

78. Barbaro JR, Barker JF: Controlled field study on the use ofnitrate and oxygen for bioremediation of a gasoline sourcezone. Bioremediation J 2000, 4:259-270.

79. Hunkeler D, Hohener P, Zeyer J: Engineered and subsequentintrinsic in situ bioremediation of a diesel fuel contaminatedaquifer. J Contam Hydrol 2002, 59:231-245.

80. Fang Y, Hozalski RM, Clapp LW, Novak PJ, Semmens MJ:Passive dissolution of hydrogen gas into groundwater usinghollow-fiber membranes. Water Res 2002, 36:3533-3542.

81. Witt MlE, Klecka GM, Lutz EJ, Ei TA, Grosso NR, Chapelle FH:Natural attenuation of chlorinated solvents at Area 6, Dover AirForce Base: groundwater biogeochemistry. J Contam Hydrol2002, 57:61-80.

82. Jacobsen BN, Becher G, Jensen BK, Monarca S, Scholz-Muramatsu H, Struijs J: Fate prediction of specific organiccompounds in bioreactors. Water Sci Technol 1996, 33:289-296.

83. Shimomura T, Suda F, Uchiyama H, Yagi O: Biodegradation oftrichloroethylene by Methylocystis sp. strain M immobilizedin gel beads in a fluidized-bed bioreactor. Water Res 1997,31:2383-2386.

84. Hirl PJ, Irvine RL: Reductive dechlorination of perchloroethyleneusing anaerobic sequencing batch biofilm reactors (AnSBBR).Water Sci Technol 1997, 35:49-56.

85. Komatsu T, Shinmyo J, Momonoi K: Reductive transformation oftetrachloroethylene to ethylene and ethane by an anaerobicfilter. Water Sci Technol 1997, 36:125-132.

86. Daugulis J: Two-phase partitioning bioreactors: a newtechnology platform for destroying xenobiotics.Trends Biotechnol 2001, 19:457-462.



87. Elmidaoui MA, Tahaikt M, Chay L, Taky M, Elmghari M, Hafsi M:Selective nitrate removal by coupling electrodialysis and abioreactor. Desalination 2003, 153:389-397.

88. Mansell O, Schroeder ED: Hydrogenotrophic denitrificationin a microporous membrane bioreactor. Water Res 2002,36:4683-4690.

89. Kimura K, Nakamura M, Watanabe Y: Nitrate removal by acombination of elemental sulfur-based denitrification andmembrane filtration. Water Res 2002, 36:1758-1766.

90.�

Min B, Evans PJ, Chu AK, Logan BE: Perchlorate removal in sandand plastic media bioreactors. Water Res 2004, 38:47-60.

The bioreactor in this paper was inoculated with a specific strain andrelates to previous work done on both mixed and pure cultures. Theconcept represents a highly engineered approach to biodegradation ofcontaminants in water.

91. Pardieck L, Bouwer EJ, Stone AT: Hydrogen peroxide use toincrease oxidant capacity for in situ bioremediation ofcontaminated soils and aquifers: a review. J Contam Hydrol1992, 9:221-242.

92. Truax D, Britto R, Sherrard JH: Bench-scale studies ofreactor-based treatment of fuel-contaminated soils.Waste Management 1995, 15:351-357.

93. Wong JWC, Wan CK, Fang M: Pig manure as a co-compostingmaterial for biodegradation of PAH-contaminated soil.Environ Technol 2002, 23:15-26.

94. Saner M, Bollier D, Schneider K, Bachofen R: Mass transferimprovement of contaminants and nutrients in soil in a newtype of closed soil bioreactor. J Biotechnol 1996, 48:25-35.

95. Zappi ME, Rogers BA, Teeter CL: Bioslurry treatment of a soilcontaminated with low concentrations of total petroleumhydrocarbons. J Hazard Mater 1996, 46:1-12.

96. Cassidy DP, Irvine RL: Biological treatment of a soilcontaminated with diesel fuel using periodically operatedslurry and solid phase reactors. Water Sci Technol 1997,35:185-192.

97. Glaser JA: Utilization of slurry bioreactors for contaminatedsolids treatment – an overview. 4th International In Situ andOn-Site Bioremediation Symposium, New Orleans 1997,5:123-130.

98. Truax DD: Bench-scale studies of reactor-based treatment offuel-contaminated soils. Fuel Energy Abstr 1997, 38:47.

99. Steinle P, Stucki G, Bachofen R, Hanselmann KW: Alkaline soilextraction and subsequent mineralization of 2,6-dichlorophenol in a fixed-bed bioreactor. Bioremediation J 1999,3:223-232.

100. Wang Z: Application of biofilm kinetics to the sulfur/limepacked bed reactor for autotrophic denitrification ofgroundwater. Water Sci Technol 1998, 37:97-104.

101. Katsoyiannis A, Zouboulis H, Althoff H, Bartel H: As(III) removalfrom groundwaters using fixed-bed upflow bioreactors.Chemosphere 2002, 47:325-332.

102. Logan BE, LaPoint D: Treatment of perchlorate- and nitrate-contaminated groundwater in an autotrophic, gas phase,packed-bed bioreactor. Water Res 2002, 36:3647-3653.

103. Losi ME, Giblin T, Hosangadi V, Frankenberger WT Jr:Bioremediation of perchlorate-contaminated groundwaterusing a packed bed biological reactor. Bioremediation J 2002,6:97-103.

104.�

Nano G, Borroni NA, Rota R: Combined slurry and solid-phasebioremediation of diesel contaminated soils. J Hazard Mater2003, 100:79-94.

This paper shows the optimization required to gain the most efficientengineering approach. What is lacking is a combined understanding ofhow the processes of microbial biotransformation changed with differentparameters. There is a need for joined-up thinking between microbiolo-gists and engineers in this area.

105. Schoefs O, Dochain D, Perrier M, Samson R: Estimation of thehydrodynamic and biokinetic models of soil bioremediationprocesses. Chem Eng Res Des 2003, 81:1279-1288.

106.��

Troquet J, Larroche C, Dussap CG: Evidence for the occurrenceof an oxygen limitation during soil bioremediation bysolid-state fermentation. Biochem Eng J 2003, 2-3:103-112.

This paper presents detailed results of four fixed bed and one rotatingbioreactors, in particular there is detailed data on the influence of differentoperating variables on the biodegradation kinetics presented. This is thetype of study where it would interesting to compare changes to microbialpopulations at the molecular level concurrently.

107. Stembal T, Markic MO, Ribicic N, Briski F, Sipos L: Removal ofammonia, iron and manganese from Groundwaters of northernCroatia–pilot plant studies. Process Biochem 2004, in press.

108. Hess P, Hohener D, Hunkeler D, Zeyer J: Bioremediation of adiesel fuel contaminated aquifer: simulation studies inlaboratory aquifer columns. J Contam Hydrol 1996, 23:329-345.

109. Hunkeler D, Jorger D, Haberli K, Hohener P, Zeyer J: Petroleumhydrocarbon mineralization in anaerobic laboratory aquifercolumns. J Contam Hydrol 1998, 32:41-61.

110. Kao CM, Chen SC, Su MC: Laboratory column studies forevaluating a barrier system for providing oxygen and substratefor TCE biodegradation. Chemosphere 2001, 44:925-934.

111. Nyman L, Caccavo F Jr, Cunningham AB, Gerlach R:Biogeochemical elimination of chromium (VI) fromcontaminated water. Bioremediation J 2002, 6:39-55.

112. Rasmussen G, Fremmersvik G, Olsen RA: Treatment of creosote-contaminated groundwater in a peat/sand permeable barrier–acolumn study. J Hazard Mater 2002, 93:285-306.

113.�

Kao CM, Chen YL, Chen SC, Yeh TY, Wu WS: Enhanced PCEdechlorination by biobarrier systems under different redoxconditions. Water Res 2003, 37:4885-4894.

An example of using by-products from other processes (in this casesludge-cake) to provide substrates that enhance reductive dechlorinationof perchloroethylene.

114. Wang S, Jaffe PR, Li G, Wang SW, Rabitz HA: Simulatingbioremediation of uranium-contaminated aquifers; uncertaintyassessment of model parameters. J Contam Hydrol 2003,64:283-307.

115.�

Ma X, Novak PJ, Clapp LW, Semmens MJ, Hozalski RM:Evaluation of polyethylene hollow-fiber membranes forhydrogen delivery to support reductive dechlorination in asoil column. Water Res 2003, 37:2905-2918.

This application has potential for engineered reactive zones. The resultsof this research show that approximately 5% of the hydrogen is used forreductive dechlorination and the remainder supporting methanogens.

116. Kao CM, Chen SC, Wang JY, Chen YL, Lee SZ: Remediationof PCE-contaminated aquifer by an in situ two-layerbiobarrier: laboratory batch and column studies. Water Res2003, 37:27-38.

117.�

Moon HS, Ahn KH, Lee S, Nam K, Kim JY: Use of autotrophicsulfur-oxidizers to remove nitrate from bank filtrate in apermeable reactive barrier system. Environ Pollut 2004,129:499-507.

This is a very recent paper clearly showing how laboratory data canprovide engineering design information for permeable reactive barrierimplementation.

118. Wang LK, Kurylko L, Hrycyk O: Biological process forgroundwater and wastewater treatment. Biotechnol Adv 1996,14:616.

119. Cox CD, Nivens DE, Ripp S, Wong MM, Palumbo A, Burlage RS,Sayler GS: An intermediate-scale lysimeter facility forsubsurface bioremediation research. Bioremediation J 2000,4:69-79.

120. Hunter WJ: Use of vegetable oil in a pilot-scale denitrifyingbarrier. J Contam Hydrol 2001, 53:119-131.

121. Guerin TF, Horner S, McGovern T, Davey B: An application ofpermeable reactive barrier technology to petroleumhydrocarbon contaminated groundwater. Water Res 2002,36:15-24.

122.�

Ribeiro de Nardi R, Ribeiro M, Zaiat M, Foresti E: Anaerobicpacked-bed reactor for bioremediation of gasoline-contaminated aquifers. Process Biochem 2004, in press.



A chemical engineering paper that validates the application of a technol-ogy through laboratory analysis.

123. Environmental Biotechnology: Principles and Applications,Proceedings of the International Symposium on EnvironmentalBiotechnology, held at the University of Waterloo, Ontario,Canada, July 4-8, 1996, Edited by Moo-Young M, AndersonWA, Chakrabarty AM. Kluwer Academic Publishers;ISBN 0-7923-3877-4.

124. Edil TB, Kim JY, Park JK: Reactive barriers for containmentof organic compounds. Proc. Int. Symposium 3rd EnvironGeotechnol 1996, 1:523-532.

125. Warith M, Fernandes L, Gaudet N: Design of in situ microbial filterfor the remediation of naphthalene. Waste Management 1999,19:9-25.

126. Kao CM, Lei SE: Using a peat biobarrier to remediate PCE/TCEcontaminated aquifers. Water Res 2000, 34:835-845.

127. Benner SG, Gould WD, Blowes DW: Microbial populationsassociated with the generation and treatment of acid minedrainage. Chem Geol 2000, 169:435-448.

128. Kao CM, Chen SC, Liu JK: Development of a biobarrier for theremediation of PCE-contaminated aquifer. Chemosphere 2001,43:1071-1078.

129. Beeman RE, Bleckmann CA: Sequential anaerobic-aerobictreatment of an aquifer contaminated by halogenated organics:field results. J Contam Hydrol 2002, 57:147-159.

130. McGovern T, Guerin TF, Horner S, Davey B: Design,construction and operation of a funnel and gate in situpermeable reactive barrier for remediation of petroleumhydrocarbons in groundwater. Water Air Soil Pollut 2002,136:11-31.

131. Benner SG, Blowes DW, Ptacek CJ, Mayer KU: Rates of sulfatereduction and metal sulfide precipitation in a permeablereactive barrier. Appl Geochem 2002, 17:301-320.

132. Ferguson AS, Doherty R, Larkin MJ, Kalin RM, Irvine V,Ofterdinger US: Toxicity assessment of a former manufacturedgasplant. Bull Environ Contam Toxicol 2003, 71:21-30.

133.��

Amos PW, Younger PL: Substrate characterisation for asubsurface reactive barrier to treat colliery spoil leachate.Water Res 2003, 37:108-120.

A wonderful field demonstration of a bioreactive permeable reactivebarrier system.

134.�

Schipper LA, Barkle GF, Hadfield JC, Vojvodic-Vukovic M,Burgess CP: Hydraulic constraints on the performance of agroundwater denitrification wall for nitrate removal fromshallow groundwater. J Contam Hydrol 2004, 69:263-279.

This paper presents field validation of transport and rates of biodegrada-tion of nitrate.

135.��

Devlin JF, Katic D, Barker JF: In situ sequenced bioremediationof mixed contaminants in groundwater. J Contam Hydrol 2004,69:233-261.

All who are interested in sequential treatment steps during passivebioremediation should read this paper. This is an extensive publicationproviding the ‘whole’ picture for combined anaerobic/aerobic degrada-tion of mixed chlorinated hydrocarbons and benzene, toluene, ethylben-zene and the xylenes.

136.�

McGeough KL, Ferguson AS, Walsh KP, Larkin MJ, Ofterdinger US,Kalin RM: Laboratory-based feasibility trials of BTEXbiodegradation within a biological permeable reactive barrier.In In Situ and On-Site Bioremediation—2003. Proceedings of theSeventh International In Situ and On-Site BioremediationSymposium (Orlando, FL; June 2003). Edited by Magar VS,Kelley ME. Batelle Press; 2004.

A paper that shows how laboratory experiments are used to developdesign parameters for bioreactive barriers.

137. Keck J, Sims RC, Coover M, Park K, Symons B: Evidence forco-oxidation of polynuclear aromatic hydrocarbons in soil.Water Res 1989, 23:1467-1476.

138.�

Chang BV, Chang SW, Yuan SY: Anaerobic degradation ofpolycyclic aromatic hydrocarbons in sludge. Advancesin Environmental Research 2003, 7:623-628.

An interesting paper that shows, as expected, that sludge from a pet-rochemical water treatment plant is more adapted to polycyclic aromatichydrocarbon (PAH) degradation. However, the relative rates of reactionsfor the main PAHs were different when compared with municipal sludge.A good candidate for application of molecular techniques.

139. Allen CCR, Boyd DR, Kulakov LA, Larkin MJ, Reid KA, Sharma ND,Wilson K: Metabolism of naphthalene, 1-naphthol, indeneand indole in Rhodococcus sp NCIMB12038. Appl EnvironMicrobiol 1997, 63:151-155.

140. Ramsay JA, Li H, Brown RS, Ramsay BA: Naphthalene andanthracene mineralization linked to oxygen, nitrate, Fe(III) andsulphate reduction in a mixed microbial population.Biodegradation 2003, 14:321-329.

141. Wilson SC, Jones KC: Bioremediation of soil contaminated withpolynuclear aromatic hydrocarbons (PAHs): A review.Environ Pollut 1993, 81:229-249.

142. Miller KM, Suidan MT, Sorial GA, Khodadoust AP, Acheson CM,Brenner RC: Anaerobic treatment of soil wash fluids from awood preserving site. Water Sci Technol 1998, 38:63-72.

143. Koran KM, Suidan MT, Khodadoust AP, Sorial GA, Brenner RC:Effectiveness of an anaerobic granular activated carbonfluidized-bed bioreactor to treat soil wash fluids: a proposedstrategy for remediating PCP/PAH contaminated soils.Water Res 2001, 35:2363-2370.

144. Saponaro S, Bonomo L, Petruzzelli G, Romele L, Barbafieri M:Polycyclic aromatic hydrocarbons (PAHs) slurry phasebioremediation of a manufacturing gas plant (MGP). SiteAged Soil. Water Air Soil Pollut 2002, 135:219-236.

145. http://www.prb-net.qub.ac.uk/eerg/dissemination/wpm/index.htm.

146. Lee S, Cutright T: Bioremediation of polycyclic aromatichydrocarbon-contaminated soil. J Clean Prod 1995, 3:255.

147. Oesterholt FIHM, Pluim MP, de Vries PW: Groundwater treatmentat the former gas work remediation site ‘griftpark’ in Utrecht,the Netherlands. Results of the semi-permanent testing facility.Water Sci Technol 1997, 35:165-172.

148. Doherty R, Ofterdinger US, Yang Y, Dickson K, Kalin RM: Observedand modelled hydraulic aquifer response to slurry wallinstallation at the former Gasworks Site, Portadown (NorthernIreland, U.K.). In Advanced Groundwater Remediation: Active AndPassive Technologies. Edited by Simon FG, Meggyes T, McDonaldCM. Thomas Telford Press; 2001:Chapter 15.

149. Guerin TF: A pilot study for the selection of a bioreactor forremediation of groundwater from a coal tar contaminated site.J Hazard Mater 2002, 89:241-252.

150. Ferguson AS, Larkin MJ, Irvine V, McGeough KL, Ofterdinger US,Kalin RM: Characterization of indigenous microorganisms at aformer manufactured gas plant. In In Situ and On-SiteBioremediation—2003. Proceedings of the Seventh International InSitu and On-Site Bioremediation Symposium (Orlando, FL;June 2003). Edited by Magar VS, Kelley ME. Batelle Press; 2004.

151. Kalin RM, Doherty R: CIRIA remediation case study: permeablereactive barriers. In Non-Biological Methods For The AssessmentAnd Remediation Of Contaminated Land – Case Studies. Edited byBarr D, Bardos RP, Nathaniel CP. Classic House, London: CIRIAPress ISBN 0 86017 588 X; 2003:113-121.

152. Hund K, Traunspurger W: Ecotox-evaluation strategy for soilbioremediation exemplified for a PAH-contaminated site.Chemosphere 1994, 29:371-390.

153. Gersberg RM, Carroquino MJ, Fischer DE, Dawsey J:Biomonitoring of toxicity reduction during in situbioremediation of monoaromatic compounds in groundwater.Water Res 1995, 29:545-550.

154. Mandelbaum RT, Shati MR, Ronen D: In situ microcosms inaquifer bioremediation studies. FEMS Microbiol Rev 1997,20:489-502.

155. Balba MT, Al-Awadhi N, Al-Daher R: Bioremediation of oil-contaminated soil: microbiological methods for feasibilityassessment and field evaluation. J Microbiol Methods 1998,32:155-164.



http://www.prb-net.qub.ac.uk/eerg/dissemination/wpm/

http://index.htm

156. Franzmann PD, Zappia LR, Power TR, Davis GB, Patterson BM:Microbial mineralisation of benzene and characterisation ofmicrobial biomass in soil above hydrocarbon-contaminatedgroundwater. FEMS Microbiol Ecol 1999, 30:67-76.

157. Baker RJ, Baehr AL, Lahvis MA: Estimation of hydrocarbonbiodegradation rates in gasoline-contaminated sediment frommeasured respiration rates. J Contam Hydrol 2000, 41:175-192.

158. Kao CM, Chen SC, Liu JK, Wang YS: Application of microbialenumeration technique to evaluate the occurrence of naturalbioremediation. Water Res 2001, 35:1951-1960.

159. Namocatcat JA, Fang J, Barcelona MJ, Quibuyen ATO,Abrajano TA Jr: Trimethylbenzoic acids as metabolitesignatures in the biogeochemical evolution of an aquifercontaminated with jet fuel hydrocarbons. J Contam Hydrol 2003,67:177-194.

160. Chaineau CH, Yepremian C, Vidalie JF, Ducreux J, Ballerini D:Bioremediation of a crude oil-polluted soil: biodegradation,leaching and toxicity assessments. Water Air Soil Pollut 2003,144:419-440.

161. Bodour AA, Wang JM, Brusseau ML, Maier RM: Temporal changein culturable phenanthrene degraders in response to long-termexposure to phenanthrene in a soil column system.Environ Microbiol 2003, 5:888-895.

162.�

Lefaux S, Manceau A, Benguigui L, Campistron I, Laguerre A,Laulier M, Leignel V, Tremblin G: Continuous automatedmeasurement of carbon dioxide produced by microorganismsin aerobic conditions: application to proteic filmbiodegradation. Comptes Rendus Chimie 2004, in press.

This paper focuses on biodegradation of proteic films and presentsmonitoring that could be used for automated measure of respirationfor permeable reactive barriers. Another interesting point is that theresearch was undertaken in response to impending EU legislation.

163. Hall JA, Kalin RM, Larkin M, Allen C, Harper D: Variation in stablecarbon isotope fractionation during aerobic degradation ofPhenol and Benzoate by contaminant degrading bacteria.Org Geochem 1998, 30:801-811.

164. Hammer BT, Kelley CA, Coffin RB, Cifuentes LA, Mueller JG: 13Cvalues of polycyclic aromatic hydrocarbons collected from twocreosote-contaminated sites. Chem Geol 1998, 152:43-58.

165. Conrad ME, Templeton AS, Daley PF, Alvarez-Cohen L: Isotopicevidence for biological controls on migration of petroleumhydrocarbons. Org Geochem 1999, 8:843-859.

166. Richnow HH, Annweiler E, Koning M, Luth J-C, Stegmann R,Garms C, Francke W, Michaelis W: Tracing the transformationof labelled 13C phenanthrene in a soil bioreactor. Environ Pollut2000, 108:91-101.

167. Schroth MH, Kleikemper J, Bolliger C, Bernasconi SM, Zeyer J:In situ assessment of microbial sulfate reduction in apetroleum-contaminated aquifer using push-pull tests andstable sulfur isotope analyses. J Contam Hydrol 2001,51:179-195.

168.�

Bailey VL, McGill WB: Fate of 14C-labeled pyrene in a creosote-and octadecane in an oil-contaminated soil. Soil Biol Biochem2004, 34:423-433.

A paper that shows results using isotope labels to determine the long-termfate of carbon from contaminant substrates after biodegradative activity.

169. Muyzer G, DeWaal EC, Uilterlinden UAG: Profiling of complexmicrobial populations by denaturing gradient gelelectrophoresis analysis of polymerase chain reaction-amplified genes coding for 16srRNA. Appl Environ Microbiol1993, 59:695-700.

170. Murrell JC, McDonald IR, Bourne DG: Molecular methods for thestudy of methanotroph ecology. FEMS Microbiol Ecol 1998,27:103-114.

171. Brigmon RL, Franck MM, Bray JS, Scott DF, Lanclos KD,Fliermans CB: Direct immunofluorescence and enzyme-linkedimmunosorbent assays for evaluating organic contaminantdegrading bacteria. J Microbiol Methods 1998, 32:1-10.

172. Muyzer G, Smalla K: Applications of denaturing gradient gelelectrophoresis (DGGE) and temperature gradient gel

electrophoresis (TGGE) in microbial ecology. Antonie VanLeeuwenhoek 1998, 73:127-141.

173. Torsvik V, Daae FL, Sando RA, Øvrea UL: Novel techniques foranalysing microbial diversity in natural and perturbedenvironments. J Biotechnol 1998, 64:53-62.

174. Bundy JG, Paton GI, Campbell CD: Microbial communities indifferent soil types do not converge after diesel contamination.J Appl Microbiol 2002, 92:276-288.

175. Robertson WJ, Franzmann PD, Mee BJ: Indirectimmunofluorescence and FISH for enumerating contaminatedsite sulfate-reducers. Bioremediation J 2002, 6:25-38.

176.��

Mills DK, Fitzgerald K, Litchfield CID, Gillevet PM: A comparison ofDNA profiling techniques for monitoring nutrient impact onmicrobial community composition during bioremediation ofpetroleum-contaminated soils. J Microbiol Methods 2003,54:57-74.

This paper is a good recent example of how molecular techniques can beused to show changes in populations that result from different nutrientadditions over time.

177.��

Mesarch MB, Nakatsu CH, Nies L: Bench-scale and field-scaleevaluation of catechol 2,3-dioxygenase specific primers formonitoring BTX bioremediation. Water Res 2004, 38:1281-1288.

This is an important new paper which presents both lab and field-scaleresults for the application of molecular genetic techniques to monitorspecific enzyme activity

178. Kosson DS, Agnihotri GC, Ahlert RC: Modeling and simulation ofa soil-based microbial treatment process. J Hazard Mater 1987,14:191-211.

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180.�

Nakhla G: Biokinetic modelling of in situ bioremediation of BTXcompounds–impact of process variables and scale upimplications. Water Res 2003, 37:1296-1307.

The design of long-term bioreactive barriers will depend on an under-standing of the uncertainty applied to design criteria such as kinetics. Thispaper provides the reader with an additional parameter — that of variablegroundwater velocity.

181.��

Batstone DJ, Keller J, Blackall LL: The influence of substratekinetics on the microbial community structure in granularanaerobic biomass. Water Res 2004, 38:1390-1404.

The biofilm modeling and molecular results presented in this publicationneed to be linked to modeling of the full-scale processes seen in otherpapers. The approach of this work would be very useful for long-termprediction of biofilm stability if it were coupled to modeling of a bioreactiveengineered permeable reactive barrier system.

182.��

Thullner M, Schroth MH, Zeyer J, Kinzelbach W: Modeling ofa microbial growth experiment with bioclogging in atwo-dimensional saturated porous media flow field.J Contam Hydrol 2004, 70:37-62.

This is a very important new paper that has developed a model for long-term microbial biofilm formation within the modeling of fluid flow andcontaminant transport within a porous matrix.

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184. Rijnaarts HHM, Norde W, Bouwer EJ, Lyklema J, Zehnder AJB:Bacterial adhesion under static and dynamic conditions.Appl Environ Microbiol 1993, 59:3255-3265.

185. Strong-Gunderson JM, Palumbo AV: Laboratory studies identifya colloidal groundwater tracer: implications forbioremediation. FEMS Microbiol Lett 1997, 148:131-135.

186. Jewett DG, Logan BE, Arnold RG, Bales RC: Transport ofPseudomonas fluorescens strain P17 through quartz sandcolumns as a function of water content. J Contam Hydrol 1999,1-2:73-89.

187. Fuller ME, Mailloux BJ, Zhang P, Streger SH, Hall JA, Vainberg SN,Beavis AJ, Johnson WP, Onstott TC, DeFlaun MF: Field-scaleevaluation of CFDA/SE staining coupled with multipledetection methods for assessing the transport of bacteriain situ. FEMS Microbiol Ecol 2001, 37:55-66.



188. Ginn TR, Wood BD, Nelson KE, Scheibe TD, Murphy EM,Prabhakar Clement T: Processes in microbial transport in thenatural subsurface. Adv Water Resour 2002, 25:1017-1042.

189.��

Pote J, Ceccherini MT, Van VT, Rosselli W, Wildi W, Simonet P,Vogel TM: Fate and transport of antibiotic resistance genes insaturated soil columns. Eur J Soil Biol 2003, 39:65-71.

The authors of this paper rightly point out that not only do we need tounderstand the transport of microorganisms, but also the fate of thegenes that they carry. Though focused on antibiotic resistant genes, thereader should think laterally to transfer of genes for remediation andtoxicity resistance and perhaps the engineering needs to consider waysof enhancing gene transport and transfer.

190. Zhang W, Bouwer E, Wilson L, Durant N: Biotransformation ofaromatic hydrocarbons in subsurface biofilms. Water SciTechnol 1995, 31:1-14.

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192. Brough MJ, Al-Tabbaa AA, Martin RJ: In situ subsurfaceactive biofilm barriers. Research Developments article,Ground Engineering 1998, 31:32.

193. Ebihara T, Bishop PL: Biofilm structural forms utilized inbioremediation of organic compounds. Water Sci Technol 1999,39:203-210.

194. Thomas AO, Drury DM, Norris G, O’Hannesin SF, Vogan JL:The in situ treatment of trichloroethane-contaminatedgroundwater using a reactive barrier — results of laboratoryfeasibility studies and preliminary design considerations. InContaminated Soil, vol 2. Edited by van den Brink WJ et al.Kluwer Academic Publishers 1995:1083-1091.

195. Jefferis S, Norris GH, Thomas AO: Developments in permeableand low permeability barriers. Land Contam Reclam 1997,5:225-232.

196. Hayes JJ, Marcus DL: Design of a permeable reactive barrierin situ remediation system, vermont site. GeotechnicalSpecial Publication 1997, 71:56-67.

197. Teutcsh G, Tolksdorff J, Schad H: The design of in situ reactivewall systems — a combined hydraulical-geochemical-economical simulation study. Land Contam Reclam 1997,5:125-130.

198. Garon KP, Schultz DS, Landis RC: Modeling of plume captureby continuous, low-permeability barriers. Ground WaterMonitoring Res 1998, 3:82-87.

199. Jaffe PR, Taylor SW: Assessment of the potential for cloggingand its mitigation during in situ bioremediation. In BiologicalTreatment Of Hazardous Wastes. Edited by Lewandowski GA,DeFilippi LJ. John Wiley & Sons, Toronto; 1998:215-235.

200. United States Environmental Protection Agency: PermeableReactive Barrier Technologies for Contaminant Remediation.EPA/600/R-98/125; 1998.

201. Carey MA, Fretwell BA, Mosley NG, Smith JWN: Guidance onthe Design, Construction, Operation and Monitoring ofPermeable Reactive Barriers. Environment Agency England andWales; 2002.

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203. Vandevivere P, Baveye P: Saturated hydraulic conductivityreduction caused by aerobic bacteria in sand columns.Soil Sci Soc Am J 1992, 56:1-13.

204. Kastner JR, Domingo JS, Denham M, Molina M, Brigmon R:Effect of chemical oxidation on subsurface microbiology andtrichloroethene (TCE) biodegradation. Bioremediation J 2000,4:219-236.



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