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PlantPower

Living plants in microbial fuel cells for clean,

renewable, sustainable, efficient, in-situ

bioenergy production

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Colophon

This booklet presents the highlights of the FP7 PlantPower project. In this Future

Emerging Technology project, living plants in microbial fuel cells were

investigated for clean, renewable, sustainable, efficient, in-situ bioenergy

production. The content of this booklet is based on peer reviewed publications.

Period: 01/01/2009 - 31/12/2012

Project coordinators: Bert Hamelers & David Strik

Project details &reports: cordis.europa.eu/projects/226532

Website: www.plantpower.eu

Contact: David Strik

Email: david.strik@wur.nl

Acknowledgements: This research received funding from the European Community

Seventh Framework Programme FP7/2007-2013 under grant agreement no.226532.

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Index

Colophon 2

Index 3

Preface 4

Concept of Plant-MFC 5

Summary 6

Research highlights 9

Researchers involved in PlantPower 31

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Preface

The plant microbial fuel cell (Plant-MFC) has the potential to become a large-scale

electricity generating technology when implemented in wetlands. Such a system

can produce in-situ electricity without harvesting the plants, 24 hours per day. In

the Plant-MFC living plants provide organic matter to electrochemically active

micro-organisms that generate electrons harvested by the fuel cell. It is expected

that the Plant-MFC technology can cover 20% of Europe’s primary future

electricity need. The Plant-MFC produces in-situ renewable electricity. The system

can likely operate in a clean, sustainable, and efficient manner.

The objective of this project was: “To explore new areas of science & technology

needed to realize the novel, clean, renewable, sustainable, efficient Plant

Microbial Fuel Cell as a future bioenergy source in Europe”.

This booklet presents the highlights of the FP7 PlantPower project.

David Strik.

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Concept of Plant-MFC

Living plants in microbial fuel cells might be

integrated in wetlands to create large-scale green

power plants. How does that work?

Plants photosynthesize organic matter using solar

energy. A significant part of this organic matter is

released into the soil. There electrochemically

active micro-organisms break down the organic

matter producing electrons which are transported

to the anode of the fuel cell. The energy rich

electrons flow through a load to the cathode to

generate 24 hours per day electricity.

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Summary

POWER: The PlantPower consortium developed high-tech and sediment Plant-MFC

systems. The maximum electricity output improved 16 times up to 1.1 W/m2

projected growth area.

PLANTS: Especially grasses stay healthy and effective in Plant-MFCs.

FUEL: The fuel of the Plant-MFC consists of rhizodeposits like exudates and dead

roots.

BIOANODE-RHIZOSPHERE: Rhizodeposits are converted within a vigorous anode-

rhizosphere typically consisting of cellulosic degrading an electrochemically

active bacteria. Still there is significant microbial competition for rhizodeposits.

Rhizodeposition depends strongly on plant species, roots-architecture and likely

the microbial composition. Especially small carbohydrates released by plant roots

can be effective degraded into electrons at Coulombic efficiencies up to 70%.

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TECHNOLOGY: A flat-plate Plant-MFC was designed with a low internal resistance

of 0.1 Ω.m2

which can allow power outputs reaching the theoretical maximum of

3.2 W/m2

. Nowadays 0.2 W/m2

long term-output and maximum 1.1 W/m2

is reached.

GROWTH MEDIUM: A new effective plant growth medium was developed.

MODELING: Based on model and experimental results we conclude that power

output (at lab conditions) is likely limited by fuel availability, proton transport,

anode surface area and low (20%) long term Coulombic efficiency due to microbial

competition and oxygen. Notably, improvement is possible.

BIOCATHODE: By integrating novel biocathodes into a flat-plate Plant-MFC, we

were able to develop a complete biological sustainable system.

PROTOTYPES: A stacked Plant-MFC showed that upscale and energy harvest is

possible for e.g. sensor applications. Other interesting added value Plant-MFC

applications developed are; the constructed wetland Plant-MFC and Green

Electricity Roof.

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FEASIBILITY: Several Plant-MFC

applications seem economical

feasible. In case the added value

is primary electricity production,

e.g. the case in natural wetlands,

still significant costs reduction

and/or power output increase is

necessary. An early LCA study

revealed promising steps to

develop a technology which

generates electricity from a new

source greener than the current

electricity supply.

Grasses

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Grasses like plant-MFCs

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The environment in the anode of

a Plant-MFC is harsh for plants

as compared to regular growing

substrates. The permanent

waterlogging of the system, but

also interactions of the artificial

substrate (usually graphite

granules) with the plants can

cause inhibiting effects on plant-

growth and thus prevent a

healthy development of the

plants. In order to improve plant

growth - and especially root

exudation (i.e. the release of

organic carbon from the roots to

the soil), we investigated a

variety of plant species that are

known to be waterlogging

tolerant, because the adaptation

to waterlogging is of course a

prerequisite for surviving MFC

conditions. The following three

species appeared to grow without

any severe loss of vigour under

MFC-conditions: Phalaris

arundinacea (“Reed

Canarygrass”, native to Central

Europe), Glyceria maxima (“Reed

Mannagrass”, native to Central

Europe) and Oryza sativa (Asian

Rice, cultivated across the world).

Plant-Microbial fuel cells planted

with these species generated

comparatively high amounts of

power and produced even high

amounts of biomass that could be

harvested frequently. All these

plants are grasses and therefore

future works should keep the

focus on grasses or at least

related species as suitable plants

for plant-MFCs.

Plant-Soil

Interaction

Group, IBG-2,

Forschungs-

zentrum Jülich,

Germany

’Where ever

you go in the

world, it is

quite likely that

a grass is

already there

as well’

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ding for high exudation!

Improving crop species for the

Plant-MFC through breeding

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Root exudation is the limiting

factor for electricity production

by high-tech Plant-MFC's. In

our research, we focused on

the potential of tomato, a

horticultural model species, for

the high-tech Plant-MFC. The

first important result was that

micro-organisms in the

rhizosphere break down the

most common exudates in a

matter of hours. Therefore we

developed a sterile test

system with which genetic

variation in root exudation of

organic acids could be studied

quantitatively. Exudation of

commercial and wild tomato

varieties was compared and

significant genetic variation

was shown. Under the used

sterile conditions there was a

factor 3-6x difference in root

exudation of organic acids

(malate, citrate, oxalate,

acetate) between the highest

and the lowest exuding tomato

variety, depending on the

exudate species. In general

we can say that commercial

tomato genotypes exude less

than their wild relatives.

Besides this genetic variation

in exudation, there is also a

large genetic variation in root

morphology between these

same tomato varieties.

These results show

that there is a large potential

to breed for increased root

exudation. This could lead to

much higher electricity

production in the high-tech

Plant-MFC.

’Apparently,

man has

unintentionally

bred certain

crop species to

have low

exudation!’

René Kuijken MSc

PhD Student

Wageningen UR

13 Fuel:exudates & dead roots

Artificial root Plant-MFC

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Isabelle Collignon, Influence of exudate type and oxygen on power output and current density of a MFC. BSc

Thesis, Wageningen University/Fachhochschule Trier, 2012

Steinbusch K.J.J., Strik D.P.B.T.B., Hamelers H.V.M. Coulombic efficiency in a PMFC, effect of exudates type and

concentration, and oxygen. Comm.Appl.Biol.Sci. 76/2 2011.

The energy recovery of the

PMFC is important since it

tells you how efficient

electricity is produced from the

supplied fuel. The energy

recovery depends on the

Voltage efficiency (determined

by the internal resistances)

and the Coulombic efficiency

(CE). The CE is the

percentage of available fuel

(as electron) which is

converted in electricity.

Our research revealed that

the Plant-MFC is fuelled by

rhizodeposits consisting of

organic compounds

released by living roots

(exudates) as well as dead

root parts.

Plant Microbial Fuel Cells

were developed including an

artificial root to examine

different exudates and the

effect of oxygen as alternative

electron acceptor (Steinbusch,

2011). Coulombic efficiencies

up to 60-70% were reached

using citrate. Also dead roots

were supplied to a MFC and

appeared to be an attractive

substrate for the electro-

chemical active micro-

organisms (Collignion, 2012).

Here the Coulombic efficiency

was 15%.

Interestingly, these results do

match with microbial

community analysis and

model work.

‘The best time

to plant a tree

was 20 years

ago. The next

best time is

now’

Kirsten

Steinbusch Phd

Postdoc

Wageningen

University

15 Grasses like plant-MFCs

We’ve got the power –

Electrochemically active

bacteria in plant microbial

fuel cells

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Timmers R.A.*, Rothballer M.*, Strik D.P.B.T.B., Engel M., Schulz S., Schloter M., Hartmann A., Hamelers B.,

and Buisman C. (2012). Microbial community structure elucidates performance of Glyceria maxima plant

microbial fuel cell. Appl. Microbiol. Biotechnol. 94(2): 537-548 *These authors contributed equally to this work

The plant-MFC is a technology in which living plant roots provide electron donors via rhizodeposition to a mixed microbial community to generate electricity in a microbial fuel cell. Analysis and localisation of the microbial community is necessary for gaining insight into the competition for electron donors in a Plant-MFC.

In our study (Timmers, Rothballer et al. 2012) we characterised the anode-rhizosphere bacterial community of a Glyceria maxima (Reed Mannagrass) Plant-MFC. Electrochemically active bacteria (EAB), namely Geobacter sulfurreducens (see picture: cells in magenta colonizing a graphite fibre), were located on the root surfaces, but they were more abundant colonizing the graphite

granular electrode. Anaerobic cellulolytic bacteria dominated the area where most of the EAB were found, indicating that the current was probably generated via the hydrolysis of cellulose. When optimising electricity generation in a Plant-MFC, the focus should be on root biomass production and effective hydrolysis of the biomass.

Due to the presence of oxygen and nitrate, short chain fatty acid-utilising denitrifiers were the major competitors for the electron donors, whereas acetate-utilising methanogens played a minor role. Via inoculation of EABs and cellulose degraders at Plant-MFC start-up these beneficial bacteria can receive a competitive advantage towards the undesired denitrifiers.

Dr. Michael Rothballer,

Research Associate

Tina Sieper, Postdoc

Helmholtz Zentrum

München, Germany

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1) Arends, J. B. A. et al. Suitability of granular carbon as an anode material for sediment microbial fuel cells. J. Soils Sediments 12, 1197-1206, (2012).

Arends, J. B. A. & Verstraete, W. 100 years of microbial electricity production: three concepts for the future. Microbial Biotechnology 5, 333-346, (2012).

Guimarães, B. C. M. et al. Microbial services and their management: recent progresses in soil bioremediation technology. Appl. Soil Ecol. 46, 157-167 (2010).

Wetlands are a large source of

methane (CH4, a greenhouse

gas 25 times as strong as

CO2) release to the

atmosphere. CH4 is produced

under conditions comparable

to current generation at a

microbial anode. To

understand the interaction

between the methanogenic

metabolism and the current

generation in waterlogged

sediments, several lab scale

studies were set up.

First it was determined that

conductive granular carbon

mixed in a 2:3 volume ratio in

the sediment yielded the best

current production1.

Secondly, current generating

metabolism was able to

compete with methanogenic

metabolism only when the soil

organic carbon content was

low. However, when

interrupting the electrical

circuit or when an excess of

organic carbon was present,

methanogenic metabolism

was dominant.

Overall, current generation

with plant-MFCs is an

interesting option to control

CH4 emissions but needs to

be applied in combination with

other mitigation strategies to

be successful and

economically viable.

Jan Arends MSc.

PhD. Student

Ghent University

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Improvement of electrodes by

surface modification

Carb

on

electrod

e

Bacteria

Modifier

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L. Lapinsonnière, M. Picot, F. Barrière, ChemSusChem, 2012, 5, 995-1005.

M. Picot, L. Lapinsonnière, M. Rothballer, F.Barrière, Biosensors and Bioelectronics, 2011, 28, 181-188.

M. Picot, I. Nicolas, C. Poriel, J. Rault-Berthelot, F. Barrière, Electrochemistry communications, 2012, 20, 167-170.

Scientific reference 2

Scientific reference 3

Context

Electrode materials are

supports for biocatalyst growth

and connection. In that

context, the optimization of the

electrode surface is on critical

importance in order to

optimize the biofilm

performances.

Aims of the study

Our goal was to study the

effect of modifying the

electrode surface (by cathodic

reduction of different

diazonium salts). Thus,

different new properties have

been brought on the surfaces,

such the presence of positive

or negative charges. The

effect of the presence of these

new properties on the

performances of the system

has been investigated.

Results

- The presence of positive

charges on the surface led to

better performances than the

unmodified surfaces (probably

because of electrostatic

interactions with the

negatively charged bacteria

surfaces)

- The degree of modification

(thickness of the modifier) was

on critical importance in order

to get optimized performances

’Surface modification can be an efficient tool to optimize the biofilm connection’

Matthieu Picot

PhD, University of

Rennes 1, under

the supervision of

Dr. Frédéric

Barrière

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Study on sustainable biocathodes

O2

O2

H2O

Cathode

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D. Strik, M. Picot, F. Barrière, C. Buisman, Electroanalysis, 2012, 24, DOI: 10.1002/elan.201200358.

M. Picot, D. Strik, F. Barrière, Bioelectrochemistry, 2013, Submitted.

Context

Oxygen represents the more

suitable electron acceptor in a

Plant-MFC. Indeed, it is

naturally present in the air and

it possesses a high

thermodynamical potential.

However, its use in Plant-

MFCs implies the use of

catalysts. Among the catalysts

which have been considered,

microorganisms represent an

interesting option.

Aims of the study

Our goal was to develop and

to study an oxygen reducing

microbial biocathode.

Particularly, we have been

interested in studying the

effect of changing pH and

temperature values on the

biocathode performances.

Results

- Best performances were

obtained at low pH (~5) and

high temperature (31°C)

- Oxygen reducing biocathode

showed good stability when

facing short pH and

temperature variations

(several hours)

‘Micro-

organisms may

act as efficient

catalysts for O2

reduction’

Matthieu Picot

PhD, University of

Rennes 1, under

the supervision of

Dr. Frédéric

Barrière

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Environmental Technology

Electron Flow in PElectron Flow in P--MFC (high tech)MFC (high tech)Photosynthesis

Living Root

Oxic Rhizosphere

Dead Root

Anoxic Rhizosphere

Cathode

LoadC-bound e

Cation

Electron

CH4

O2

Modelling creates insights

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Modelling the plant microbial fuel cell. Hamelers HV, Timmers RA, Steinbusch KJ, Strik DP. Commun Agric

Appl Biol Sci. 2011;76(2):93-5.

Strik DP, Timmers RA, Helder M, Steinbusch KJ, Hamelers HV, Buisman CJ. Microbial solar cells: applying

photosynthetic and electrochemically active organisms. Trends in Biotechnology 2011 Jan;29(1)

The performance of the Plant-MFC is determined by the interplay of a number of processes like photosynthesis, root growth, rhizodeposition, oxygen leakage, hydrolysis, methanogenesis, electrogenesis, matter transport, electron transport and oxygen reduction, to name some of the most important. The electrons are transported towards the roots, where part of the electrons are respired, part is used for production of new roots and part end up as exudates or dead biomass.

The developed plant-MFC model simulates the flow of electrons that are available from the organic matter that is produced during photosynthesis. This model was coupled to an

equivalent circuit MFC model to show the actual power output.

The model showed that long Plant-MFC start-up times can be due to the time needed to create dead roots. Also it was revealed that application of bacterial inoculum is most effective when the inoculation takes place at the start of the experiment. Next, it was clearly shown that oxygen release by living roots can consume a large part of the available fuel.

New insights were used for new experiments and explanations of our results. Still, the electricity production is much more dynamic than we can explain….

’The P-MFC will

be a success if

we find the

right added

benefits’

Dr.ir. Bert

Hamelers

Associate Prof.

Wageningen

University

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Designing

effective

and

applicable

Plant-MFCs

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Marjolein Helder, Design criteria for the Plant-Microbial Fuel Cell: Electricity generation with living plants –

from lab to application, PhD thesis, Wageningen University, Wageningen, The Netherlands (2012)

Strik, D.P.B.T.B., Timmers, R.A., Helder, M., Steinbusch, K.J.J., Hamelers, H.V.M., Buisman, C.J.N.,

Microbial solar cells: Applying photosynthetic and electrochemically active organisms 2011 Trends in

Biotechnology 29 (1), pp. 41-49

Stichting Dienst

Landbouwkundig

Onderzoek

Power output of the Plant-MFC

depends on the plant

performance and the internal

resistances of the system. By

developing a flat-porous plate

system, internal resistances were

reduced. By applying a new plant

growth medium the power output

improved several times.

By technological,

environmental and

economic analysis, the

design criteria for the Plant-

Microbial Fuel Cell are set.

Several Plant-MFC

applications are promising.

The PlantPower concept is

proven for sensors, LEDs and

green roofs. The next step is

to develop systems for large

scale application.

‘Electricity generation with

living plants - from lab to

application’

Marjolein Helder,

Phd.

Wageningen

University

David Strik,

Assistant Prof.

Wageningen

University

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Pilot of Green Electricity Roof

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David P.B.T.B. Strik, M. Helder, H.V.M. Hamelers, Cees J.N. Buisman. Pilot study of Green Electricity Roof:

applying plant microbial fuel cells for electricity, storm water storage capacity biodiversity, energy savings

and aesthetical value. Comm. Appl. Biol. Sci. 77/2, 2012

www.plant-e.com

Plant-e is the spin-off company of

the FP7 PlantPower project.

In collaboration with Wageningen University and other partners a first scaled-up Plant-MFC was developed.

By integrating the Plant-MFC into a green roof one establishes a new technology which has the potential to combine advantages of green roofs with electricity production. In the summer of 2011 an 16m2 pilot site of a Green Electricity Roof was established at the rooftop of the Netherlands Institute of Ecology building. Scale-up was investigated by means of long term performance, harvesting electricity, and determination of benefits of the technology.

Cell phones can be charged and thousands of people have experienced electricity from living plants. Green electricity roofs are promising!

Marjolein Helder PhD, CEO

Plant-e

David Strik

Assistant Prof Wageningen

University/CSO Plant-e ‘To make the

world a greener

place’

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Outlook

Extensive progress has been made in understanding the Plant-MFC. The Plant-

MFC has now a performance that matches the net performance of current crop

based electricity systems. The knowledge of this project is disseminated world-

wide and a spin-off company is building follow-up projects to exploit our

developments. Still, further fundamental research, technological integration,

wetlands selection and demonstration in real wetlands is needed to show the

full PlantPower electricity potential. After a first full scale implementation a

complete environmental and economic performance analyses can be made to

prove the potential impact of PlantPower.

Follow PlantPower at

http://www.facebook.com/PlantMicrobialFuelCell

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Project partners

Wageningen University www.wageningenur.nl/ete

Forschungszentrum Jülich GmbH www.fz-juelich.de/ibg/ibg-2

Ghent Univerisity http://www.labmet.ugent.be

Stichting Dienst Landbouwkundig Onderzoek www.wageningenur.nl/nl/Expertises-

Dienstverlening/Onderzoeksinstituten/wageningen-ur-glastuinbouw.htm

MAST Carbon Technology Ltd www.mastcarbon.com

Eisenhuth GmbH KG www.eisenhuth.de

Maris Projects B.V. www.maris-projects.nl

Monsanto Holland B.V. www.monsanto.com

Helmholtz Zentrum Munchen Deutschesforschungszentrum Fur Gesundheit Und Umwelt GmbH

www.helmholtz-muenchen.de

Université de Rennes 1 www.scienceschimiques.univ-rennes1.fr/equipes/macse

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Researchers involved in PlantPower