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Research topic: Environmental Biotechnology 3rd ICAB
154
ELECTRICITY GENERATION BY MEANS OF A MICROBIAL FUEL CELL FROM
WATERS TREATED BY CONSTRUCTED WETLAND
1Stoyan Groudev, 2Veneta Groudeva, 1Irena Spasova, 1Marija Nicolova, 1Plamen Georgiev,
2Mihail Iliev, 2Ralitsa Ilieva
1University of Mining and Geology “St Ivan Rilski”, Sofia Bulgaria
2University of Sofia”St Kliment Ohridski”, Sofia, Bulgaria
e-mail: Miliev1@biofac.uni-sofia.bg
Abstract
Acid drainage waters generated after rainfall in a heap consisting of low-grade mixed sulphide ores and
various mining wastes were subjected to treatment by means of a constructed passive system consisting of a
constructed wetland and two permeable barriers located in the wetland perpendicularly to the direction of
the water flow. The wetland was characterized by an abundant waters and emergent vegetation and diverse
microflora. Typha latifolia, Typha angustifolia, Paragmites australis, Scirpus lacustris as well as species of
the genera Juncus, Potamogeton, Eleocharis, Carex, Poa and several algae (mainly of Scenedesmus,
Pediastrum and Endorina) were present in the wetland. The wetland microflora consisting mainly of
various heterotrophic microorganisms including such well known for their ability to generate electricity by
menace of constructed two-section microbial fuel cells. The effluents from the wetland containing dissolved
biodegradable organic compounds were used as a feed stream to a constructed two-section microbial fuel
cell of this type. This stream was supplied to the bottom anodic section of the fuel cell and the effluents
passed through cathode section and continuous exited at the top. Air was injected during the treatment to
the cathodic section. Electricity with power within 28-325 mW/m2 was generated by this system using
different microorganisms, mainly sulphate-reducing (from the genera Desulfovibrio, Desulfobacter and
Desulfomonas) and iron-reducing (from the genera Shewanella and Geobacter) bacteria, as well as by
means of mixed cultures of various microorganisms.
Keywords: Water treatment, Microbial fuel cell, Bioelectricity
INTRODUCTION
The generation of acid drainage waters is one of the essential ecological problems in countries with
developed mining and mineral processing industries. The averting of this problem is usually
connected with several difficulties and costly decisions. In any case, the treatment of the acid waters
is unavoidable in most countries, at least. Such treatment can be performed by different methods but
is preferable to be connected with the recovery of the valuable components (mainly heavy metals)
dissolved in these waters (Groudev et al., 2009; Pozo-Antonio et al., 2014). Very useful in this respect
is the application of some microorganisms, mainly sulphate-reducing bacteria, able to precipitate the
dissolved heavy metals in the form of the relevant sulphides under alkaline, neutral or even slightly
acidic pH. Apart from this, the sulphate-reducing bacteria and some other anoxic heterotrophic
microorganisms such as the iron-reducing and various fermenting bacteria can be used for electricity
generation from such waters containing biodegradable organic compounds. The treatment of this type
is performed by means of microbial fuel cells with specific but various constructions.
MATERIALS AND METHODS
Materials
Acid drainage waters generated after rainfall in a heap consisting of low-grade mixed sulphide ores
and various mining wastes were subjected to treatment by means of a passive system consisting of a
constructed wetland and two permeable barriers. The wetland was constructed from reinforced
concrete into the ground and had a rectangular shape, 8.0 m long, 1.80 m wide and 0.80 m deep. The
bottom of the wetland was covered by a layer 0.35 m thick, consisting of a mixture of soil rich in
Research topic: Environmental Biotechnology 3rd ICAB
155
biodegradable organic compounds, plant compost, manure, crushed limestone and sand. Two
permeable barriers consisting of the mixture mentioned above and with size of 0.60 m height, 1.80 m
width and 0.90-0.60 m length (at the bottom and the top side, respectively) were constructed in the
wetland perpendicularly to the direction of the water flow.
The wetland was characterized by an abundant water and emergent vegetation and a diverse
microflora. Typha latifolia, Typha angustifolia, Phragmites australis, Scirpus lacustris as well as
species of the genera Juncus, Potamogeton, Eleocharis, Carex, Poe and several algae (mainly of the
genera Scenedesmus, Pediastrum and Eudorina) were present in the wetland.
Methods
The microbial fuel cell used in this study was a Plexiglas cylindrical column 80 cm high, with an
internal diameter of 12 cm. A perforated slab graphite-Mn4+ anode and graphite-Fe3+ cathode were
located in the bottom and in the top sections of the column, respectively. The two sections were
separated by a permeable barrier of 5 cm thickness consisting of a 2.5 cm layer of glass wool and a
2.5 cm layer of glass beads. The feed stream, i.e. the solution subjected to treatment, was supplied to
the bottom anodic section of the column and the effluents passed through the cathodic section and
continuously exited at the top. Air was injected during the treatment to the cathodic section.
The elemental analysis of the waters was performed by means of atomic absorption spectrometry and
inductively coupled plasma spectrometry. The isolation, identification and enumeration of
microorganisms was carried by classical physiological and biochemical tests (Karavaiko et al., 1988)
and by the molecular PCR methods (Sanz & Köchling, 2007; Escobar, 2008).
RESULTS
The presence of a large number of various water plants and a soil rich in biodegradable organic
compounds resulted in the creation of environment favorable for the growth and activity of a rich
microflora consisting mainly of various heterotrophic microorganisms (Table 1).
Table 1. Microflora of the polluted drainage waters and of the waters and sediments from the constructed
wetland
Microorganisms
Sources of the samples tested
Polluted
drainage
waters
Waters from the wetland
Sediments
from the
wetland
Cells/mL (g)
Aerobic heterotrophic bacteria
10 2-106
106-108
102-106
Cellulose-degrading microorganisms
0-102
103-106
101-104
Oligocarbofiles
102 -104
102-105
102-104
Nitrifying bacteria
0-102
101-104
0-102
Streptomyces
0-101
101-103
0-102
Fungi
0-103
102-104
101-103
Fe2+-oxidizing chemolithotrophs (at pH 2)
105 - 108
0 -103
0-102
S0-oxidizing chemolithotrophs (at pH 2)
104 -107
101-104
101-102
Fe2+-oxidizing heterotrophs (at pH 7)
0-101
101-102
0-102
S0-oxidizing heterotrophs (at pH 2)
0-102
101-103
0-102
Nitrogen-fixing bacteria
0-102
101-103
101-102
Anaerobic heterotrophic bacteria
0-102
102-107
103-108
Bacteria fermenting sugars
0-101
102-106
103-107
Sulphate-reducing bacteria
0-102
103-108
103-107
Denitrifying bacteria
0-101
102-106
103-106
Methanogenic bacteria
0
0 -102
101-104
Fe3+-reducing bacteria
0-101
102-104
102-105
Mn3+-reducing bacteria
0-101
101-103
101-104
This microflora performed an efficient purification of drainage waters from the former uranium
deposit Curilo containing radionuclides and various toxic elements, mainly heavy metals and arsenic
Research topic: Environmental Biotechnology 3rd ICAB
156
(Table 2). Moreover, some of these microorganisms were well known for their ability to generate
electricity by means of a constructed two-section microbial fuel cell (Spasova, 2014; Du, 2007).
Table 2. Composition of the drainage waters in the uranium deposit Curilo before and after their treatment
by means of a constructed wetland
Parameters
Before
treatment
After
treatment
Permissible levels
for waters used
in agriculture and/or
industry
Temperature, ºC
(+3.7) - (+21.7)
(+3.7 ) - (+21.5)
–
pH
1.90 -3.74
6.48 – 7.52
6-9
Total content of dissolved substances,
mg/l
530 - 2180
312 - 1544
1500
Solid substances, mg/l
25 - 145
14 - 114
100
Dissolved organic carbon, mg/l
0.5 - 4.1
17 - 82
20
Sulphates, mg/l
424 - 1522
295 - 1090
400
Uranium, mg/l
0.23 - 3.52
< 0.10
0.6
Radium, mg/l
0.05 - 0.45
< 0.05
0.15
Copper, mg/l
0.37 - 8.21
< 0.1 - < 0.5
0.5
Zinc, mg/l
0.95 - 14.3
< 0.5
10
Cadmium, mg/l
0.01 -0.14
< 0.01
0.02
Lead, mg/l
0.17 - 0.71
< 0.1
0.2
Nickel, mg/l
0.31 - 4.82
< 0.5
0.5
Cobalt, mg/l
0.21 - 4.40
< 0.5
0.5
Iron, mg/l
75 - 1241
< 1-15
5
Manganese, mg/l
0.97 - 51
< 0.5 - 4.2
0.8
Arsenic, mg/l
0.02 - 0.62
< 0.01 - < 0.1.1
0.2
Effluents from the wetland containing dissolved biodegradable organic compounds were used as a
feed stream to this fuel cell. This stream was supplied to the bottom anodic section of the fuel cell and
the effluents passed through cathodic section and continuously exited at the top. Air was injected
during the treatment to the cathodic section.
Electricity with power within 28-325 mW/m2 was generated by this system using different
microorganisms, mainly sulphate-reducing (from the genera Desulfovibrio, Desulfobacter and
Desulfomonas) and iron-reducing (from the genera Shewanella and Geobacter) bacteria, as well as by
means of mixed cultures of various microorganisms (Table 3).
Table 3. Electricity generation from the wetland effluents
by means of a microbial fuel cell
Parameters
Values
COD, mg O2/L.h
530-1590
Sulphate, mg/L
325-1070
pH
6.80-7.45
Eh, mV
(-215) – (-260)
Temperature, ºC
28-37
Voltage of the open circuit, mV
140-280
O2 dissolved in the cathodic section, mg/L
7.4-8.2
Power, mW/m2
28-325
Research topic: Environmental Biotechnology 3rd ICAB
157
DISCUSSION
It was found that the ability of some strains related to one and the same taxonomic species to generate
electricity was quite different. In most cases the higher generation of electricity was connected with
the higher rate of consumption of the organic substrates used as donors of electrons in the anoxic
section of the microbial fuel cell. It was found that the specific activities of the enzymes participating
in the degradation of the relevant organic substrates by these microorganisms usually were also
higher. However, the faster rate of electron removal from the organic donors used in this study was
not the only factor determining the level of electricity generation.
The microbial consumption of a portion of the electrons from the relevant microorganisms in the
anodic section of the fuel cell decreased to some extent the efficiency of electricity generation. For
that reason, the most effective electricity production was performed by means of microbial strains
characterized by relatively low efficiency of utilization of the electrons for their own needs, i.e. the
strains characterized by a low production of biomass under such conditions.
CONCLUSIONS
The results from this investigation revealed that the passive treatment of waters heavily polluted by
very toxic elements (uranium radium, several non-ferrous metals and arsenic) was real very efficient
way to clean such waters. Furthermore, the enrichment of these waters during the treatment with
dissolved organic substrates made the water effluents suitable for generation of electricity by means
of microbial fuel cells.
ACKNOWLEDGMENTS: The Bulgarian National Science Fund under project T02/2 supported this
study.
REFERENCES
Groudev, S. N., Spasova, I. I., Nikolova, M. V., 2009. “Treatment of acid drainage by means of
constructed wetlands”, Analele Universitati Targu Jiu, No 3, pp. 205-216.
Pozo-Antonio, S., Puente-Luna, I., Lagüela-Lopez, S., Veiga-Rios, M., 2014. “Techniques to correct
and prevent AMD: A review,” Universidad Nacional de Columbia, DYNA, 81 (184), 73-80.
Karavaiko, G. I., Rossi, G., Agate, A. D., Groudev, S. N., Avakyan, Z. A., 1988. “Biogeotechnology
of Metals. Manual”, GKNT Center for International Projects, Moscow.
Sanz, J. I., Köchling, T., 2007. “Molecular biology techniques used in waste water treatment
overview”, Process. Biochem., 42, 119-133.
Escobar, B., Bustos, K., Morales, G., Salazar, O., 2008. “Rapid and specific detection of
Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans by PCR”, Hydrometallurgy, 92, 102-
106.
Spasova, I., Nikolova, M. V., Georgiev, P. S., Groudev, S. N., 2014. “Mine waters cleaning connected
with electricity generation”, Annual of the University of Mining and Geology, Sofia, 57 (II) 137-139.
Du, Z., Li, H., Gu, T., 2007. “A state of the art review on microbial fuel cells: A promising
technology for wastewater treatment and bioenergy”, Biotechnology Advances, 25, 464-482.
