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21. – 23. 9. 2011, Brno, Czech Republic, EU
A REVIEW STUDY OF NANOFIBER TECHNOLOGY FOR WASTEWATER TREATMENT
Lucie KRIKLAVOVA
a
, Tomas LEDERER
b
a
TECHNICAL UNIVERSITY OF LIBEREC, Faculty of Mechatronics, Informatics and Interdisciplinary
Studies, Institute of Novel Technologies and Applied Informatics, Studentska 2, 461 17 Liberec,
Czech Republic, lucie.kriklavova@tul.cz
b
TECHNICAL UNIVERSITY OF LIBEREC, Centre for Nanomaterials, Advanced Technologies and
Innovations, Studentska 2, 461 17, Liberec, Czech Republic
Abstract
Nanotechnologies are increasingly applied in a wide spectrum of human activities. In this article we describe
several experiences with nanofiber technology in combination with biological removal of toxic xenobiotics in
the application of industrial wastewater treatment. Microbial biofilm formation can be greatly supported using
nanofiber structures, and the whole system provides stable and accelerated biodegradation. The main
purpose of the current work was to create a final design of the nanofiber carrier. The main aims of biomass
carrier were microorganism colonization, chemical and physical stability, surface morphology, maximum
surface area, density comparable to wastewater, and optimal size considering the technology used at the
wastewater treatment plant. The resulting structure of the nanofiber carrier was tested on several real
industrial wastewaters under different arrangements and different conditions. The following characteristics of
the nanofiber carriers were examined: cleaning efficiency of toxic compounds, stability of carrier and
nanofiber layer, rate of carrier ingrowths by relevant microorganisms, disintegration of nanofibers, sorption
properties and others. The results show the possibility of using nanotechnology for the treatment of
wastewater. Nanofiber carriers can be used even where other methods of treatment have failed.
Keywords: nanofiber technology, wastewater treatment, biomass carrier, immobilization of microorganisms
1. INTRODUCTION
Nanotechnology, the field dealing with dimensions in the order up to hundreds of nm, offers great potential
for the use of new materials for the treatment (cleaning and disinfection) of surface water, groundwater and
wastewater contaminated by toxic, organic and inorganic substances. The presence of various pollutants
has a large impact on the environment, public health and the economy. Most traditional techniques such as
extraction, adsorption and chemical oxidation are generally effective but often very expensive. The ability to
reduce toxic substances to safe levels effectively and at a reasonable cost is therefore very important. In this
respect, nanotechnologies can play an important role. Due to their unique active surface area, nanomaterials
can offer a wide range of applications such as catalytic membranes, nanosorbents, bioactive nanoparticles
and metal nanoparticles such as iron, silver, titanium oxides and many others.
This article describes the use of nanofibers in the biological treatment of industrial wastewater, where
primarily microorganisms on a biomass carrier are used. Wastewater tested during individual trials mainly
included monoaromatic substances (aniline, diphenyl guanidine, phenylurea, chloramine, phenols and
cresols). The system combining biological treatment supported by nanomaterials helps to intensify the whole
water treatment process. The main purpose of the present work is to create a biomass carrier possessing the
advantages of nanotechnology, while supporting as much cell colonization as possible. The result is the
production of fine fibers of different polymers, with diameters ranging from tens of nanometers to several
micrometers. With regard to the materials and finish used it is possible to create non-woven strips of
nanofibers with a high specific area, possessing extreme flexibility, formability and also high stability.
21. – 23. 9. 2011, Brno, Czech Republic, EU
2. THEORETICAL SECTION
Each biomass carrier must meet the basic parameters (microorganism colonization ability, chemical and
physical stability, surface morphology, maximum specific surface). The exceptional properties of nanofiber
carriers are primarily the large specific surface, high porosity and small pore size. Depending on the type of
polymer, nanofibers are durable, easily moldable and chemical resistant. The principal advantage of
nanofiber materials is their comparability with the dimensions of micro-organisms, the surface morphology
and biocompatibility, which allows for faster colonization of the nanofiber surface by the microorganisms.
Moreover, the carrier itself is not made of a “hard” polymer of a predetermined shape but it is flexible and
pliable stable fibrous polymer. An important advantage of the technology is the possibility of a bacterial
biofilm buildup not only on the surface of the carrier but also closer to its center (inside the carrier), where the
bacteria are much more protected against the toxic effects of the surrounding environment and shear forces
during hydraulic mixing. In addition, penetration of substrate and oxygen to the microorganisms is also
possible. High specific surface of the nanofiber layer allows to the bacteria great adhesiveness and as a
result it simplifies the immobilization of microorganisms, especially in the initial stages of colonization of the
surface carriers and also even during difficult emergency conditions (reducing the required regeneration
time). After a longer period of colonization the microbial biomass grows naturally on the places without the
nanofibers. This observation documents the assessment of biofilm growth on carriers during the first weeks.
Fig 1. The development of a biofilm on a nanofiber carrier (1st, 5th, 10th and 15th day)
3. EXPERIMENTAL SECTION
3.1. Production of nanofibers and technical potential
A new type of carrier was developed based on the decisive parameters using nanofiber materials as the
biomass carrier (mainly polyethylene, polypropylene, polyurethane and others). The basis is a nanofiber
layer obtained by electrospinning, which is applied using NANOSPIDER technology. The novel technology
(chaotically tangled fibers) is morphologically very remarkable because the spatial curves of the resulting
fibers increase the surface, which may end up being up to 1000 m
2
/g. The great advantage of this
technology is the ability to combine different polymers and thereby set the carrier density (density of approx.
900 kg/m
3
to 1200 kg/m
3
) based on the requirements of the specific application.
Fig 2. Different methods of nanolayer fixation (old and new approach), detail of the nanofibers
The final nanofiber yarn is composed of three parts. The basic fiber is Prolenvir CE polypropylene (660 dtex,
air shaped), the coating is made of Larithane 1083 polyurethane nanofibers (30 – 100 dtex, electrospinning,
21. – 23. 9. 2011, Brno, Czech Republic, EU
nanofiber diameter is approx. 260 nm), everything is double-wrapped in a protective polyethylene fiber (167
dtex, protecting against friction during processing and during subsequent application against disintegration of
nanofibers). The outline for the surface formations is made of polypropylene fibers (200 dtex). The specific
surface of the resulting formation with a PU value of the nanofiber of 100 dtex has at least 800 m
2
/m
3
(an
evaluation of the most suitable density nanofibrous layers is included in [4]).
The resulting yarn can be processed using textile technology in the form of bobble-type coils (for use in a
fluid bed) or as a surface structure (technology for interlacing with an embedded weft, for use in a fixed bed).
The first form is a carrier type called a "nano-bobble" (see Figure 3a), where the carrier flows together with
the activation mixture; the dimensions of the carrier are comparable to commercially available carriers. The
structure is completely arbitrary but preferably of a spherical shape, which minimizes costs primarily for
mixing. The second form is fixed in the tank and the activation mixture moves through the carrier in a form of
fixed knit fabrics (see Figure 3c). For mutually interwoven threads a technology of supporting frames has
been developed, which can be installed in an existing aeration tank as a removable module. Options include
a high variability mesh sieve, which can be adjusted depending on the treatment process or the properties of
the wastewater or the microbial population used (e.g. depending on the speed of growth of the
microorganisms).
Fig 3. a) Nanofiber carrier (nano-bobble), b) Technology of removable supporting frames, c) Detail of solid
nanofiber fabric
3.2. Sorption tests
Sorption tests were carried out as kinetic tests in sealable containers. The content of the carriers was 30% of
the bulk volume of the container; the remaining volume was filled with an aqueous solution of the model
contaminant (10 g/l aniline). The containers were then placed on a horizontal shaker, and evenly blended for
the given time. Finally, chemical oxygen demand in mg/l was measured as an indicator of sorption rates
using a cuvette test which is based on the use of the dichromate method.
3.3. Disintegration of nanofiber tests
Disintegration tests were carried out in 100 ml beakers filled with 80 ml of water, into which was immersed a
microscopic slide with wound nanofiber yarn. In order to recreate realistic wastewater treatment conditions,
the beaker was gently bubbled. Tests were conducted without a bacterial population. Fixation of the fibers on
the microscopic slide made it possible to observe the same place on the fiber throughout the experiment. An
aqueous medium was then monitored with the presence of the nanofibers. The water was filtered through a
membrane filter of 0.22 micron porosity. Although the fibers are small in diameter, they are very long so the
probability of the nanofibers passing through the filter is minimal. Images of the surface layers of the
nanofibers and the surface of the filter were subsequently taken using a fluorescence microscope.
3.4. Biofilm carrier rinse tests with water and CrSO4
Nanofiber textile fabric previously colonized by bacterial populations for approx. 7 months was used for this
test. The biofilm built up on the fiber was carefully washed off at intervals using water that was carefully
21. – 23. 9. 2011, Brno, Czech Republic, EU
sprayed through the carrier, or using chromo-sulfuric acid, in which the carrier remained with occasional
mixing. An optical microscope helped to evaluate both approaches.
3.5. Application of nanofiber biomass carriers under laboratory conditions
One example was the operation of biofilm model reactors with a capacity of 3 liters with real groundwater
containing phenols and cresols. Rhodococcus erythropolis was chosen as the bacterial population for
degradation of phenols at The Institute of Chemical Technology in Prague. The first reactor was filled with
the commercial carrier AnoxKaldnes. AnoxKaldnes is made of polyethylene with a specific surface
of 500 m
2
/m
3
(Veolia Water Solutions & Technologies). The second reactor was filled with nanofiber fabrics
fixed in place. The output parameters pH, ORP, dissolved oxygen, conductivity, turbidity of the solution and
chemical oxygen demand were monitored to evaluate the effectiveness of the degradation processes.
4. RESULTS AND DISCUSSION
4.1. Sorption tests
Microorganisms use organic compounds represented by the organic contaminants present as a source of
carbon and energy. It is much faster and easier if microorganisms have simpler access to these substances.
The appropriate sorption on the surface of the carrier can to some extent influence the rate of colonization of
the microorganisms. Adsorption of contaminants on the surface of the nanofibers increases their
accessibility; on the other hand it also increases the possible toxic effects of the contaminants. For example,
the sorption of aniline on nanofiber yarn with the greatest density of nanofiber cover is clearly higher, which
explains the lower rate of colonization for this type of cover. Conversely, for low and moderate cover (in the
graph marked 30 and 50 dtex) sorption to the surface is markedly lower. Colonizing microorganisms in the
case of a medium level of cover will find ideal conditions for colonization by the given percentage of cover,
while at the same time the cover is not
contaminated above the limit for the
toxic contaminant. The high degree of
sorption of toxic contaminants such as
aniline and particularly phenols and
cresols may interfere with (slow down)
the rate of initial colonization of the
surface of the microorganisms. For
toxic contaminants, there is clearly an
optimum adsorption concentration on
the carrier and the cover, which was
verified through the experiments.
Fig 4. Sorption for nanofibers and
commercial carriers
4.2. Disintegration of nanofiber tests
The objective of the test was to create conditions that may happen at wastewater treatment plants using
nanofiber technology during the initial phase, prior to colonization of bacterial populations. It is necessary to
monitor how the nanofibers can become loose before they are colonized. The result of the experiment is
100% stability of the nanofiber layers during the first week; during the second week the structure of the fibers
became damaged. The nanofibers aggregate to each other, thereby reducing the specific surface area. Only
a small number of fibers, mainly those that are not well fixed during production, escape into the surrounding.
The result of monitoring the surface of the membrane filter (after filtration of aqueous media) is a very small
amount of nanofibers (approximately 0.5% of the surface of the filter). This results in the possibility to use the
21. – 23. 9. 2011, Brno, Czech Republic, EU
nanofibers even for slowly growing microorganisms where the induction is slow and the possibility of release
is high. For real application it is necessary to rinse the nanofiber carrier and subsequently consider filtering
only if after the bioreactor there is no clarifier. The methodology for determining the disintegration of the
nanolayers is critical if the effluent from sewage may enter directly into natural waters, therefore this
approach will be further studied.
Fig 5. Detail of nanolayers prior to application and after the 7
th
and 15
th
day of bubbling in water
4.3. Biofilm carrier rinse tests with water and CrSO4
Rinsing with water (or chromo-sulfuric acid) is tested particularly for the possibility of reusing the carriers,
which is an indispensable aspect due to the price of the carriers. The water rinse test resulted in minimal
violation of the nanolayers but a high residual population of microorganisms remaining on the carrier. The
chromo-sulfuric acid rinse test (which is commonly used for determining the total biomass on the carrier)
showed that the nanolayers are damaged (there was a clumping of nanofibers), but the population on the
medium is completely eradicated. The nanofiber carrier can thus be used several times but under certain
conditions. Washing the biomass from the surface with water is not 100% effective, but it is economic and
sufficient for use in sewage treatment plants. On the contrary, the use of chromo-sulfuric acid is indeed
effective, but difficult in practice;
moreover its use destroys the
nanolayers and thus reduces the
specific surface area of the carrier.
Fig 6. Carrier rinse test with water or
chromo-sulfuric acid,
(microorganisms are shown by a
slightly yellow-brown color)
4.4. Application of nanofiber biomass carriers under laboratory conditions
Nanofiber carriers were successfully applied during the last few years under laboratory conditions as a
biomass carrier. Various different arrangements (bioreactors) were tested as well as various shapes and
groupings of carriers, and different bacterial populations for removing different kinds of pollution. Laboratory
results confirm the suitability of using fibers with nanolayers as carriers of bacterial populations. Their
application for wastewater treatment plants is still being verified in the laboratory, but it certainly brings great
benefits. The stability and surface of the active biofilm can be greater than for conventional carriers, which
also bring more effective removal of pollutants by biological methods using microorganisms.
The following images capture how the biofilm grows on the nanofiber carrier. The nanofibers form the
skeleton of the biofilm and hold it together but they allow penetration of nutrients and oxygen to the center of
the biofilm. The result is increased robustness of the active biofilm compared to standard technologies, while
maintaining the high activity of the whole complex and high biodegradation efficiency. In the laboratory
experiments, the stability of the complex was demonstrated even at high concentrations of contaminants and
high flow rates, where the bacterial population dispersed in water completely disappeared, but the biofilm on
21. – 23. 9. 2011, Brno, Czech Republic, EU
the nanofiber structures maintained its efficiency. This is documented by the following charts from the last
operation of the bioreactors verifying the treatment of groundwater with high phenol content.
Fig 7. Biofilm on a fixed carrier (laboratory experiment), detail of biofilm in wet and dry state
The output parameter of COD was nearly comparable for both technologies throughout the whole period.
The noticeable advantage of using nanofiber technology is under extreme conditions (temperature, flow,
salinity). There are no significant fluctuations in efficiency when using the nanofiber technology. In addition,
the initial colonization of carriers is faster (for colonization rate see [4]). Moreover we use less material
compared to commercial technologies but we can achieve higher specific surface area.
Fig 8. Input and output parameters for biological treatment using nano-fiber and commercial carrier
5. CONCLUSIONS
The results of the study using nanofiber technology for wastewater treatment are several variants of stable
and usable biomass carriers that meet the requirements for a carrier of a bacterial biofilm. Application of
nanotechnology in combination with biological methods brings distinct advantages. There are still several
contentious issues, such as disintegration of nanofibers and toxicity to higher organisms, which will be
further studied.
ACKNOWLEDGEMENTS
This project is realized under the state subsidy of the Czech Republic within the project 2B08062
AROMAGEN and the program of specific research no. 7824/115 supported by Ministry of Education.
LITERATURE
[1.] Wu J, Chen K, Chen C, Hwang J. Hydrodynamic Characteristics of Immobilized Cell Beads in a Liquid–Solid Fluidized-Bed
Bioreactor, 2003, Biotechnol Bioengng 83:583–594
[2.] Masák J, Čejková A, Siglová M, Kotrba D, Jirků V, Hron P. Biofilm formation: A tool increasing biodegradation activity. Proc.
Environmental Biotechnology 2002, Vol. III. Massey University Press, 2002, pp. 523-528.
[3.] Zbigniew L, Beyenal H. Fundamentals of biofilm research, 2007, CRC Press
[4.] Kriklavova, L, Lederer, T. The use of nanofiber carriers in biofilm reactor for the treatment of industrial wastewaters, 2010,
Nanocon 2010, 2nd International Conference, Czech Republic, Thomson Reuters Web of Knowledge, p. 165-170
