Memorandum 45
Submission from Plymouth Marine Laboratory
BIOFUELS: PHOTOSYNTHETIC MICROBES AND SUSTAINABLE
ENERGY
"PHOTOSYNTHETIC MICROBES HAVE UNTAPPED
POTENTIAL TO HELP SOLVE THE GLOBAL ENERGY CHALLENGE."[151]
1. EXECUTIVE
SUMMARY
Photosynthetic microbes, encompassing both microalgae
and photosynthetic bacteria, are the most efficient users of the
sun's energy and present enormous opportunities to produce bioenergy.
As unique chemical factories they yield up to 40 times more biomass
per unit area compared to land plants. Photosynthetic microbes
have the potential to produce biofuel (biodiesel and biogas) and
to reduce energy consumption and greenhouse gas (GHG) emissions
in the sewage, solid waste, power and manufacturing industries.
Close to market applications recommended for
development include, the production of biogas and reduction in
energy consumption associated with Primary Industries. Under intense
International investigation is the capture of waste CO2
emissions and production of biodiesel. Central to the deployment
of these applications is the large scale cultivation of the microbes
using photobioreactor[152]
(PBR) and photosynthetic biofilm (PSB) technologies. The UK has
a strong research base in aquatic microbial bioscience and biotechnology
although it now lags behind US and European effort to develop
bioenergy technologies. We recommend research aimed at harnessing
the capabilities of this untapped resource. Here we welcome the
opportunity to provide evidence on the following applications:
Photosynthetic bacteria
— High quality pipeline biogas: photosynthetic
bacteria can be used to purify low quality biogas from Primary
Industries (eg sewage treatment, landfill, feed lots, food waste
and municipal solid organic waste) to produce pipeline quality
gas for network distribution.
— Biohydrogen: Ligno-cellulose can
be used as a feedstock for photosynthetic bacteria to produce
biohydrogen.
Microalgae
— Biogas. Microalgae grown using waste
CO2 emissions can be subsequently anaerobically digested
to produce biogas.
— Biodiesel: Molecular and genetic
engineering of microalgal species high in lipids, grown using
waste CO2 emissions have potential as an economically
viable route to biodiesel.
— Biogas: Microalgae can reduce energy
consumption in secondary and tertiary sewage treatment and resultant
biomass can be converted to biogas.
2. RECOMMENDATIONS
— Biochemical, genetic, metabolic and
ecological research aimed at harnessing the capabilities of photosynthetic
and other microbial systems.
— Investment in development of platform
PBR and PSB technologies including establishment of pilot and
demonstration facilities.
— Facilitate International collaboration
in areas with ideal climatic conditions (eg Ghana).
3. INTRODUCTION
Photosynthetic microbes (microalgae and photosynthetic
bacteria) have the potential to produce biofuel (biodiesel and
biogas) and reduce energy consumption and greenhouse gas (GHG)
emissions in the sewage, solid waste, power and manufacturing
industries. Here we provide background evidence on using photosynthetic
microbes for bioenergy.
Figure 1
SUMMARISES THE BROAD POTENTIAL OF PHOTOSYNTHETIC
MICROBES IN BIOENERGY PRODUCTION
As summarised in Figure 1 (refer to respectively
labelled paragraphs), photosynthetic microbial consortia can be
used to produce:
A. High quality pipeline biogas Conventionally
derived biogas from bacterial anaerobic digestion is of low calorific
value. Photosynthetic microbes can be used to convert this poor
quality biogas to pipeline quality biogas by removing CO2
and H2S and replacing with hydrogen (Table 1). The total biogas
potential for the UK equates to 6m T/y of oil equivalent and conversion
of raw biogas to pipeline quality gas could double this energy
value to around 12m T/y oil equivalent.[153]
By combining cultured strains and natural isolates, robust anaerobic
photosynthetic bacteria consortia capable of cleaning and upgrading
biogas from a wide range of sources including landfill, sewage
sludge digestion, abattoir and farm waste digestion, and municipal
solid waste digestion can be achieved.
|
| Component | Sewage Biogas
| Landfill Biogas |
Natural Gas | Enhanced Biogas (estimated)
|
|
| Energy content (MJ/M3) | 21
| 21 | 37
| 40 |
| Methane | 55-75
| 54 | 95
| 80 |
| Carbon dioxide | 25-45
| 42 | 0.7
| Trace |
| Carbon monoxide | 0-0,3
| 0-0.1 | Trace
| 0 |
| Hydrogen | 0-3
| 0-1 | Trace
| 18 |
| Hydrogen sulfide | 0.1-0.5
| 0.1-1 | Trace
| 0 |
| Chlorine (total CI) | Trace
| 22 mg/ m3 | 0
| Trace |
|
Table 1: Calorific values and compositions of biogas compared
to natural gas.[154]
B. Biogas production and reduction in energy consumption
in sewage treatment. The energy required to treat sewage is high
and the water industry is the fourth most energy intensive sector
in the UK. Further tightening of water quality standards suggests
energy costs will increase.[155]
Over 10 billion litres of sewage are produced every day in England
and Wales and it takes approximately 6.34 gigawatt hours of energy
to treat this volume of sewage, almost 1% of the average daily
electricity consumption of England and Wales. In total, the water
industry used 7,700 GWh of energy in its operations during 2005-06,
and emitted over four million tonnes of greenhouse gases, 1% of
total UK greenhouse gas emissions.[156]
We estimate that 50-70% of the existing UK sewage treatment plants
could be retrofitted with photosynthetic biofilm (PSB) technology,
where the main constraint on the remaining sites would be availability
of suitable land area for installation. Photosynthetically derived
oxygen from microalgal consortia could replace energy intensive
activated sludge processes (Figure 2). Resultant biomass can be
anaerobically digested producing raw biogas which can then be
upgraded as above.
Figure 2: Basic biological processes in wastewater treatment,
illustrating the benefits of algal/bacteria consortia
C. Biogas production from microalgae grown on waste CO2
emissions. GHG emissions from power stations can be reduced by
fixing CO2 using an autoflocculating microalgal consortia
grown in photobioreactors (Figure 3). Resultant biomass can be
anaerobically digested where the biogas is upgraded by a photosynthetic
bacterial community to produce methane and hydrogen biofuel. Practical
applications of microalgae biofixation of CO2 and biofuel
production in wastewater treatment could lead the way to future
applications, such as in the coproduction of biofertisers, higher
value co-products (i.e biopolymers and animal feed) and possibly
in the future to stand alone, dedicated, biofuel production systems
endowed with a much larger global potential.
Figure 3: Power station emission conversion into biofuel
diagram
D. Biodiesel from microalgae. Molecular and genetic engineering
of selected microalgal species for high lipid content needs research
to provide economically viable biodiesel. Microalgae biosynthesise
a wide range of commercially interesting bioenergy byproducts
such as fats, oils, sugars and functional bioactive compounds.
Many species are rich in lipids and hydrocarbons suitable for
direct use as high-energy liquid biofuels, at levels exceeding
those present in terrestrial plants, and also have potential as
substitutes for the refinery products of fossil fuels. Hardly
surprising considering that the majority of petroleum is believed
to originate from microalgae. One species, Botryococcus braunii,
in particular, has been widely studied.[157]
The yield of oil from microalgae is predicted to be up to 100
times greater then land based crops at 7,500-24,000 litres of
oil per acre per year compared to rapeseed and palmoil at 738
and 3,690 litres of oil per acre per year respectively. There
is now renewed widespread International effort on developing microalgal
based biodiesel although the UK is not currently part of this
effort. The National Renewable Energy Laboratory (NREL) funded
by the U.S. Department of Energy's Office of Fuels Development
has recently reinstated research in this area.[158]
E. Biohydrogen from lignocellulose feedstocks. Because
lignin is perhaps the second most abundant carbon polymer on Earth
and thus a renewable resource, it is a candidate substrate for
biofuel production, the most desirable of which is hydrogen. Of
the enzymes responsible for hydrogen production, hydrogenase requires
no ATP for activity but are reversible, thereby limiting hydrogen
accumulation. Nitrogenase, the enzyme responsible for reduction
of dinitrogen gas, also produces hydrogen but is very energy intensive.
However, the nitrogenase reaction is essentially irreversible
allowing pressurization of the hydrogen produced (Figure 4)..
The advantage in photosynthetic bacteria is that they can obtain
the energy necessary for hydrogen production through photosynthesis
driven by the "free" supply of sunlight.
Figure 4: The metabolic pathway leading to biohydrogen production
in photosynthetic bacteria.
4. FEASIBILITY, COSTS
AND TIMESCALES
The technologies described in this document are capable of
being retrofitted to existing infrastructure. We outline here
our predicted timescales and feasibility.
Table 2: (PML predictions)
|
| Bioenergy Route
| Feasibility
% |
Cost | Timescale
| Reliability
%
| Carbon footprint |
|
| 1 | Biogas Upgrade
| 85 | Low/Medium
| 2-5 | 75
| Low |
| 2 | Low energy sewage treatment
| 95 | Low
| 2-5 | 95
| Low |
| 3 | Power station flue gas to biogas
| 85 | Medium
| 2-5 | 75
| Low/Medium |
| 4 | Power station flue gas to biodiesel
| 70 | Medium/High
| 7-10 | 55
| Medium |
| 5 | Biogydrogen from ligno cellulose
| 60 | Medium/High
| 8-10 | 50
| Medium |
|
5. RECOMMENDATIONS FOR
ACTION
5.1 Basic research
There is clear strategic vision on bioenergy in Europe and
the United States, with considerable resource investments at the
bioscience end of the R&D spectrum. During the 1990s the UK
was at the forefront of bioenergy development from photosynthetic
microbes, but now UK R&D activities lag behind international
leaders in this field. The UK has a strong research base in microbial
bioscience and biotechnology and this should be utilised to provide
maximum benefit within the international bioenergy market sector.
Photosynthetic microbes can and will make a significant contribution
towards satisfying the global need for clean, alternative energy
sources. There is an urgent need for research aimed at harnessing
the capabilities of photosynthetic and other microbial systems.
The US Department of Energy has issued a call for Bioenergy Centers
to develop microbial-based strategies that generate alternative
energy sources from biomass, sunlight and other renewable resources.
In addition, the European Science Foundation is considering a
major funding initiative to support bio-inspired solar energy
strategies. These programmes and private sector initiatives represent
an exciting beginning to a long-term concerted effort to develop
clean microbial solutions to the world's energy challenge.
The continued development and improvement of these microbial
"biorefineries" will require significant additional
biochemical, genetic, metabolic and ecological insights into the
relevant microorganisms. It is essential to acquire a systems-level
understanding of energy capture and its transformation in order
to direct the reaction products into pathways that produce alternative
fuels or sequester greenhouse gases with increased efficiency.
Additional research is required to ascertain whether communities
of photosynthetic and non-photosynthetic bacteria could be tapped
to provide clean energy or replace fossil-fuel-derived feedstocks.
It will also be necessary to find economically viable biorefinery
options, optimize the processes involved, and scale-up the systems.
For algal biodiesel to become a more competitive option, metabolic
and genetic engineering and strain selection for lipid production
is required. Stable consortia, are essential to success and we
recommend a multidisciplinary and systems biology approach is
needed to develop, characterise and optimise microbial consortia.
5.2 Platform technology
PBRs and PSBs as a platform technologies have wide reaching
potential in bioenergy, CO2 mitigation and in high
value bioactives. Future developments in molecular and cellular
engineering of photosynthetic organisms will be implemented in
PBR and PSB platform technology. Therefore it is important to
invest in the PBR and PSB engineering and necessary IP to guarantee
the UK's dominance in the international biofuel market. In addition
to providing funding on fundamental R&D, Government should
also fund pilot and demonstration plants.
5.3 National gas network
The feasibility of using purified biogas in national gas
grid network needs to be fully assessed. For example; how will
the presence of low levels hydrogen in enhanced biogas affect
the network and final combustion devices?
5.4 International Cooperation
Ghana possesses the one of the best climates on Earth for
biofuel production from photosynthetic microbes, where warm night
time temperatures and high insolation will reduce the need for
PBR insulation and therefore capital costs. By combining the expertise
of UK algae biotechnologists and Ghanaian engineers, Ghana could
become a net exporter of Biofuels to the rest of the World and
provide a demonstration platform for Greenhouse Gas reducing technologies.
A joint project, whilst producing a sustainable replacement for
fossil fuels, will also benefit local sanitation, water supply
and ultimately poverty through job creation.
Several US and European groups are already planning PBR installations
in Ghana for biofuel production, so the UK Government should build
upon the existing close relationship with The Honourable President
John Kufuor's regime and the Ghanaian people, to ensure that superior
UK PBR and PSB technology can be implemented accordingly.
6. BACKGROUND INFORMATION
6.1 Solar Energy
Photosynthetic microorganisms can capture solar energy, a
free, abundant and under-used energy source. The amount of solar
energy that strikes the Earth every hour (4.3 1020 Joules) is
approximately equal to the total amount of energy that is consumed
on the planet every year (4.1 1020 Joules). Therefore, capturing
even a small fraction of the available solar energy could make
a significant contribution to global energy needs. Photosynthesis
plays a central role in all bioenergy production. It drives the
first step in the conversion of sunlight into chemical energy
and is therefore ultimately responsible for the production of
feedstocks required for all biofuel synthesis.
Land-based bioenergy crops create serious economic and environmental
concerns, which include the sequestering of huge areas of arable
land or ecologically sensitive regions (such as rain forests)
for their growth, the introduction of competition to food production,
and a concomitant increase in the price of staple food. In contrast,
aquatic-based large-scale photosynthetic microbes culturing facilities
can be sited on any land, including waste or industrial sites.
Photosynthetic microbes use sunlight far more efficiently than
soil based crops, with potential aerial productivities approaching
120T/ha/y, compared to 15T/ha/y for Miscanthus.
6.2 Microbial communities
There are billions of microorganisms populating every niche
of the Earth, many of which have untapped potential to help solve
the global energy challenge. To grow in unusual environments,
microorganisms have evolved unique metabolic strategies to extract
energy from nutrients and sunlight to generate various potentially
useful by-products. In many cases, these microorganisms function
cooperatively in communities and consortia where their concerted
activities perform functions that would not be possible in the
absence of their partners.
Consortia often contain diverse communities containing multiple
strains of microbes. This has a number of benefits. Firstly, diverse
communities tend to be more stable over long time periods. This
is particularly important in bio-treatment processes, which generally
operate in a continuous flow mode, frequently under unsteady state
conditions and involve multiple elemental (biogeochemical) cycles.
The value of using diverse microbial consortia is highlighted
in the sewage industry where consortia consisting of bacteria,
protozoa and fungi are applied in activated sludge for wastewater
treatment and in anaerobic digestion for high strength organic
feedstocks.
The largest group of microscopic photosynthetic microbes
are the microalgae. Microalgae have many advantages for cultivation
as renewable energy crops over land based crops in the production
of bioenergy; they have faster growth rates; they can be cultivated
in poor quality or nutrient loaded wastewater and under difficult
agro-climatic conditions; they require less land space and there
is no fertiliser run-off; they can uptake toxic metals like chromium,
cadmium and arsenic; by virtue of their relatively small sizes,
they can be easily chemically treated and they contain no sulphur,
are non-toxic and highly biodegradable. Costs associated with
the harvesting and transportation of microalgae are relatively
low, in comparison with those of other biomass materials from
higher plants.
The oldest group of photosynthetic microbes are the anoxygenic
photosynthetic bacteria which comprise a large and heterogeneous
group of organisms, brought together primarily because they all
use light as an energy source in the absence of oxygen. These
bacteria are mainly anaerobic organisms, and require a reduced
compound as electron donor, such as H2S and simple organic molecules.
Photosynthetic bacteria also produce hydrogen from organic compounds
by an anaerobic light-dependent electron transfer process. Organic
acids derived from either anaerobic digestion or fermentative
hydrolysis or digestion[159]
of organic waste/biomass provide ideal feedstocks for hydrogen
production.
6.3 Harvesting
Concentrating biomass for biofuel production is energy intensive.
Therefore it is important to develop robust microbial consortia
that have the ability to autoflocculate. Microorganisms can be
present in bio-treatment processes as discreetly dispersed cells,
as flocs, or as biofilms. The latter two are by far the most common
and both flocs and films can be considered as matrices of naturally
immobilised cells. More importantly, autoflocculation and biofilm
growth provide a low energy means of harvesting the biomass from
a liquid bulk. In the context of biofuels, low energy biomass
harvesting is a fundamental prerequisite.
6.4 Photobioreactor (PBR)
A PBR is a system that efficiently grows photosynthetic microbes,
which are then used in various commercial applications. By providing
efficient exposure to light, optimal temperatures, and pH levels,
photobioreactors make viable the commercial production of algae.
Figure 5: 5000 litre Biocoil PBR designed & constructed
in UK by S. Skill (1993)[160],[161]
During the 1980s, Professors John Pirt and David Hall of
Kings College, London, were the early pioneers of photobioreactors
and up until the late 1990s, the UK lead the world in PBR design
and development.[162]
PML now have the expertise[163]
and infrastructure to reinstate the UK at the forefront of this
field.
6.5 Photosynthetic Biofilms
PSB systems are a relatively new technology for the growth
of photosynthetic microbes and treatment of wastewater.[164],[165]
They are inexpensive to construct utilising waste transparent
plastic (PET: Polyethylene terephthalate) as the primary biofilm
support matrix. PSB systems are capable of removing nutrients,
heavy metals and hormone disrupting chemicals from wastewater
in a low cost, single stage process, where the resultant biomass
can be easily recovered and converted into biofuels.
7. PML AND IT'S
RELEVANT AREA
OF EXPERTISE
Plymouth Marine Laboratory (PML) is a Natural Environment
Research Council (NERC) Collaborative Centre. As an internationally
recognised interdisciplinary centre, PML is mission driven delivering
a valuable, integrated approach to solving problems and providing
solutions concerning the complexity of marine ecosystems and the
unique bioresources they contain. PML is uniquely qualified to
research and advise on many of the issues that form the debate
on global change and sustainability in marine systems.
PML has a strong core expertise in microbial chemistry, physiology
and molecular biology (algae, viruses and bacteria). Key to the
development of bioenergy within the UK, PML has world leading
expertise in growing photosynthetic microbes on the large scale
using Photobioreactor (PBR) Technology. Current research using
PBR technology at PML is working towards the replacement of petroleum
based products with a renewable resource and using CO2
from flue gas to promote growth and reduce CO2 emissions.
The PBR technology PML is developing within these projects is
directly applicable to large scale production of photosynthetic
microbes for biofuels and biogas production. PML have a long term
aim, building on core expertise, to build a centre of excellence
in photosynthetic microbe biotechnology encompassing bioactives,
biofuels, bioremediation and CO2 capture technology.
July 2007
151
Donohue & Cogdell (2006). Nature Reviews Microbiology 4,
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152
House of Commons Upper Waiting Hall: Photobioreactor Demonstration:
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153
www.nsca.org.uk/assets/biogas_as_transport_fuel_june06.pdf Back
154
www.nsca.org.uk/assets/biogas_as_transport_fuel_june06.pdf Back
155
Parliamentary Office of Science and Technology, Postnote No.
282 April 2007 Back
156
www.defra.gov.uk/corporate/ministers/speeches/ian-pearson/ip070426.htm Back
157
Banerjee, B, Sharma, Chisti Y, Banjeree UC. 2002: Critical reviews
in Biotechnology 22(3) 245-279. Back
158
http://www.nrel.gov/docs/fy06osti/40352.pdf Back
159
Patent: Robinson & Skill, Means for Continuous Digestion
of Organic Matter. US5637219 (1997) Back
160
National Geographic, March 1994 Back
161
New Scientist-Blooming Sewage, 2 October 1993 Back
162
Skill & Robinson (1991), Department of the Environment Select
Committee. Evidence submission. Back
163
Patent: Skill & Robinson (2002), Photoreaction. US6370815 Back
164
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