Proceedings of the First International Conference on Self Healing Materials
18-20 April 2007, Noordwijk aan Zee, The Netherlands
V.M. van Beek et al.
BIOSEALING, A NATURAL SEALING MECHANISM
THAT LOCATES AND REPAIRS LEAKS
V.M. van Beek*, D. den Hamer, J.W.M. Lambert, M.N. Latil and W.H. van der Zon
* GeoDelft
Stieltjesweg 2, 2628 CK Delft
The Netherlands
Tel: 0031 (0) 15 2693528
e-mail: V.M.vanBeek@GeoDelft.nl
In civil-engineering projects, leakage problems can origin from deficiencies in water-retaining constructions or
in natural layers. These problems result in higher drainage costs, damage to the surrounding areas as a result of
settlements, inflow of undesired salty or polluted ground water or loss of water from reservoirs. Even if the leaks
can be located with traditional techniques, it is often difficult to seal them because of the poor accessibility of the
leak or the high costs involved. In addition, it is also desirable to solve these problems in an environmentallyfriendly and sustainable way.
In order to self-heal leaks in civil engineering applications, a novel approach based on stimulating of naturally
present bacteria in the subsurface has been investigated. This stimulation involves injection of a nutrient solution
in the surrounding area of the leak. As the nutrients mix with the ground water flow they are automatically
transported to the leak resulting in an increase in bacterial activity at the leak location. This increased biological
activity in the vicinity of the leak results in a sustainable mechanical blockage within several weeks. The
clogging is caused by a combination of bacterial activity and converging streamlines towards the leak.
Laboratory studies were initiated to demonstrate the efficiency of this process and successful clogging was
obtained within several weeks after the injection of nutrients. The tests were conducted under a lot of different
conditions in sand-filled PVC columns which contained simulated leak in a water retaining layer (a disc with a
hole in its center) and a realistical water flow to simulate a leaking construction pit. Several weeks after the
injection of nutrients, a significant clogging at the location of the disk was observed.
In addition to laboratory tests, field-scale trials were also conducted at the Maasvlakte in the port area of
Rotterdam, and a practical scale test was performed along a newly constructed aqueduct beneath the
Haarlemmermeer ring canal in the Netherlands. Both tests were successful. Biosealing is a promising selfhealing technology to reduce leakage in civil engineering applications. The technique is simple, makes use of
naturally present microorganisms in the soil and is self-regulating for leak detection and reduction.
1
Introduction
In civil-engineering projects, damage to water retaining constructions or natural non-porous
layers can result in leakage problems within a construction site. These problems result in
higher drainage costs, damage to the surrounding areas as a result of settlements, inflow of
undesired salty ground water or loss of water from reservoirs. The leak is often difficult to
locate, which makes treatment difficult, costly and delaying. Once the location is known, the
treatment may consist of chemical injections close to the leak. All these factors imply
additional costs in the project as well as delay in time.
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© Springer 2007
Proceedings of the First International Conference on Self Healing Materials
18-20 April 2007, Noordwijk aan Zee, The Netherlands
V.M. van Beek et al.
In a preliminary feasibility study solutions for the locating as well as sealing of the leak were
investigated and clogging by means of feeding bacteria that are naturally present in the
subsurface appeared to be most promising.
In this research it is attempted to clog a leak in the subsurface by means of feeding bacteria
that are initially present in the subsurface with a substrate. A laboratory study was executed to
prove the mechanism at small scale, followed by a field experiment to test the method at a
realistic scale.
The purpose of the research was to test whether the injection of substrate leads to significant
clogging of a leak. Furthermore it is attempted to gain insight into the processes which
contribute to the clogging effect.
2
Clogging mechanisms
Clogging is a well-known and extensively studied subject in literature. Clogging is often
encountered as an unwanted process in injection or extraction wells in ground water. Research
in this area has lead to the statement of various clogging mechanisms that may occur
depending on the situation. Although in this research this proces is not an unwanted sideeffect, it is believed that the same mechanisms that are important in clogging wells may play a
role in the clogging of leaks, as performed in this research.
Several causes of decrease of permeability in soils are named by Baveye et al. (1998). These
involve the presence of suspended particles, swelling and dispersion of clay particles in the
soil and several biological causes, like the accumulation of metabolic byproducts, the
entrapment of gases and the precipitation of iron sulfides.
In this research the presence of suspended particles is also initiated by the injection of the
substrate, as the substrate itself contains small particles.
The swelling and dispersion of clay particles may be caused by a change in electrolyte
concentration. Although this is considered to be a chemical process, this change may be
induced by the degradation of organic material by bacteria. Due to the fermentation process
acid is formed and the availability of H+-ions causes instability of clay particles, as binding
ions in clay (Mg2+, Fe2+ and Al3+) are exchanged by the abundant H+-ions. A change of
environment may result in renewed stabilization of the particles.
Dispersion of clay particles may also be caused by the addition of the substrate itself. The
substrate is a highly conducting fluid. As salt flushes trough the soil pore volume it binds to
clay particles exchanging with binding ions in clay. The sodium causes instability of the clay
particles resulting in mobilization of clay colloids.
When stimulated, most bacteria excrete slimy or gummy materials on their surfaces, so called
exopolymers. The production of this material may temporarely block the pores in the soil.
Several processes exist, related to bacterial activity, by which gas is formed. Gas which is
trapped in the pores results in a reduction of the permeability.
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© Springer 2007
Proceedings of the First International Conference on Self Healing Materials
18-20 April 2007, Noordwijk aan Zee, The Netherlands
V.M. van Beek et al.
Proceeding bacterial activity causes a sulphate reducing environment. By this time ferri (Fe3+)
is reduced into Ferro (Fe2+), which can react with sulfide into iron sulfide (FeS).
The above-named processes may interact with eachother. A combination of several processes
may lead to permanent clogging whereas separate processes do not.
3
Laboratory experiments
Laboratory experiments were initiated to test the hypothesis that feeding of bacteria may
result in clogging of a leak. Many experiments have been performed from which one of them
has been chosen as an example (GeoDelft, 2006). Perspex columns (Ø 7.85 cm x 50.56 cm
length) were filled with sand and a disk with a centered hole (Ø 1.2 cm) was placed in the
column to simulate a leak. A constant hydraulic head difference over the column has been
applied, causing a constant upward flow of water in the column.
The columns were operated under environmental conditions comparable to subsurface
conditions, concerning exposure to sunlight, ambient temperature and complete saturated
conditions. The set up is located in a controlled temperature room, set at 12 ± 1°C. The
columns were rapped in dark plastic bags to prevent income of sunlight during reading of
measurements. A natural sand species is chosen to resemble both chemical and biological
properties in a field situation.
Monitoring consists of measuring the flow through the columns as well as the pressure heads
at various locations in the columns. Using these parameters the dimensionless clogging factor
can be calculated: the ratio of the current and initial hydraulic resistance between two
piezometers. The environmental parameters that have been monitored are conductivity, pH,
temperature, oxygen concentration and redox potential.
The used substrate is Nutrolase, which is a protamylasse, a wasteproduct of processed
potatoes, which is supplied by the AVEBE concern. Nutrolase is injected into the column
after dilution. The column clearly shows a severe increase in clogging factor within two and a
half weeks after the injection of Nutrolase solution. During the same time, a Blanco column
has been monitored without nutrition.
The clogging factor has been calculated over the disk en shows a maximum of 460 after 60
days. The clogging appears to concentrate at the location of the hole, as clogging factors
calculated for other parts of the column are considerably smaller. The clogging in the Blanco
column is insignificant.
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© Springer 2007
Proceedings of the First International Conference on Self Healing Materials
18-20 April 2007, Noordwijk aan Zee, The Netherlands
V.M. van Beek et al.
Clogging factor
500
450
400
Clogging factor [-]
350
300
250
Feeding period of 8.5 h
1600 ml diluted (1:80)
Nutrolase with particles
200
150
100
50
0
0
20
40
60
80
100
120
140
160
180
200
Time [days]
Column nutrition
Blanco Column
Clogging factor in the column with nutrition and the blanco column
Observations during demobilization do not show any evidence of gas formation or iron
sulfide. Redox measurements during the test confirm that the formation of iron sulfides has
not been possible, as conditions have not been sulfate-reducing.
4
Field experiments
To upscale the laboratory experiments to a realistic situation, a field experiment has been
perfomed [GeoDelft, 2004]. The purpose of the field experiment was to reduce the flow in a
known leak with at least a factor 5, to prove that BioSealing is applicable at field scale, and to
gain insight in the clogging processes.
A leakage has been simulated by burying three 20ft sea containers vertically in the subsurface
at a location on the Maasvlakte nearby Rotterdam. All three of the containers had holes in
different shapes. The shapes varied from an elongated crack to several small circular holes
(0.08m) or one big hole (0.25m). A constant head difference caused flow through the leak. To
simulate a building pit situation in and outside the container, the hydraulic head difference
was maintained at 3 m.
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© Springer 2007
Proceedings of the First International Conference on Self Healing Materials
18-20 April 2007, Noordwijk aan Zee, The Netherlands
V.M. van Beek et al.
Burying of the sea containers
The nutrients were injected directly into the subsurface by using a packer which is placed in a
tube à manchette (a vertically placed perforated pipe). The space around the tube à manchette
was filled with gravel to prevent clogging directly around the tube. The tubes were placed at
2.5 to 5 m distance from the leak. Each leak was surrounded by three tubes à manchette to
ensure the substrate to reach the leak.
During the injection of Nutrolase towards the first container (container 2) it was found that the
optimal concentration of Nutrolase was a dilution of 1:40 and continous injection of 15 l/day.
Monitoring consisted of measuring flow, hydraulic heads in the subsurface around the sea
container and various environmental parameters. From the observations the clogging factor
was calculated in time.
A large circular hole of 0.25 m in diameter has been created in the bottom of container 2.
Container 2 was the first container to be injected and no clogging has been achieved after the
single shot which was initially planned. After this period the schedule has been changed to
continuous injection of 15 l/day. The clogging factor increased then to a maximum of 30. No
clogging was observed in the nearby buried container 3, which was kept as a blanco until that
time.
Clogging factor container 2
C [-]
100
10
1
16 February
2004
1 March 2004 15 March 2004 29 March 2004
12 April 2004
26 April 2004
10 May 2004
date
Clogging factor container 2
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© Springer 2007
Proceedings of the First International Conference on Self Healing Materials
18-20 April 2007, Noordwijk aan Zee, The Netherlands
V.M. van Beek et al.
6 smaller circular holes were made in container 3. Container 3 was the second container to be
injected with nutrition. The injection was continuous at a rate of 15l/day. Monitoring has
taken place during 66 days from the first injection after which a clogging factor was reached
of 3.6. At that time the test had to be interrupted, although the clogging factor was still
increasing.
blanco
Clogging factor container 3
injection
C [-]
10
1
16
February
2004
1 March 15 March 29 March
2004
2004
2004
12 April
2004
26 April
2004
10 May
2004
24 May
2004
7 June
2004
21 June
2004
5 July
2004
19 July
2004
date
Clogging factor container 3
An elongated crack, 1m long and a decreasing width of 0.1 to 0m, has been made in the
bottom of container 1. After 57 days of injection the clogging factor was 7.3. The factor was
still increasing at the time the test was interrupted.
Clogging factor container 1
C [-]
10
1
17 May 2004
31 May 2004
14 June 2004
28 June 2004
12 July 2004
26 July 2004
date
Clogging factor container 1
After the experiment visual observations were executed to obtain information about the
clogging materials. After removal of the containers, a black colouring of the sand was
observed at locations between injection and leak, with increasing black colour in the direction
of leakage. Acidification of the black precipitate results in the formation of H2S, indicating
that the observed black colouring is iron sulfide.
The presence of iron sulfides is confirmed with ESEM/EDAX techniques. The iron sulfide
seems not to be totally blocking the pores, but is rather present as a layer around the sand
grains.
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© Springer 2007
Proceedings of the First International Conference on Self Healing Materials
18-20 April 2007, Noordwijk aan Zee, The Netherlands
5
V.M. van Beek et al.
Discussion
Both the field experiment and the laboratory experiment have shown that the injection of
diluted Nutrolase results in sealing of the leak.
The process of clogging can not be completely retrieved from the performed experiments. It is
unknown what the influence of the precipitation of iron sulfide on the clogging process. The
circumstances in the laboratory were aerobic, preventing the formation of iron sulfide. The
laboratory conditions were therefore not equal to subsurface conditions.
Gas formation is unlikely, as this has not been observed in the experiment. The other
processes, dispersion of clay particles and formation of metabolic by-products may be
combined in the process of BioSealing.
Based on all the experiments performed on BioSealing processes the hypothesis on the
clogging mechanism for BioSealing is as follows:
1. hydrocarbons (such as sugars and/or peptides) are decomposed under anaerobic
conditions. During this fermentation organic acids are formed.
2. The formed acids initiate an erosion of the natural particles in the soil, such as
feldspar. The particles formed, are so small that they can migrate through the pores of
the sand.
3. Further decomposition yields into the formation of biomass on that specific spot where
the most nutrients are available (there where the flow is high, thus in the surrounding
and inside the leak).
4. This biomass captures the eroded particles.
5. As a result of the presence of multi valent ions, such as calcium, iron and/or
magnesium a flocculation of the captured particles will occur. This results in a “lump”
of clay-like particles inside the pores of the sandgrains.
6
Conclusions
The process of BioSealing is successful in the field and in the laboratory. BioSealing proves
to be a clean and sustainable technique, whereby bacteria are stimulated which are intially
present in the subsurface, which is most active at the location of the leak. BioSealing can
therefore be considered suitable for locating and repairing leaks in practice.
Further research needs to be performed to gain insight in the exact process of clogging.
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© Springer 2007
Proceedings of the First International Conference on Self Healing Materials
18-20 April 2007, Noordwijk aan Zee, The Netherlands
V.M. van Beek et al.
REFERENCES
1.
2.
3.
4.
5.
[Baveye et al., 1998] Environmental impact and Mechanisms of the Biological Clogging of saturated
soils and aquifer materials, Crit.Rev. in Environmental Science and Technology, 28(2); 123-191 (1998)
[GeoDelft, 2003] Extensieve herstelmethoden, Factual report invloed omgevingsfactoren, GeoDelft
rap.no. CO-406290.0032 (2003)
[GeoDelft, 2004] BioSealing Veldexperiment, GeoDelft rap.nr. CO-406290.0051
Extensieve herstelmethoden van waterremmende constructies, field experiment, graduation report by V.
Veenbergen, Januari 2004
[GeoDelft, 2006] BioSealing laboratory experiments, GeoDelft rap. no. CO-421180.0004 (2006) (draft)
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© Springer 2007