-
ELSEVIER FEMS Microbiology Reviews 16 (1995) 111-142
MICROBIOLOGY REVIEWS
Liquid and gaseous fuels from biotechnology: challenge and
opportunities
N. Kosaric *, J. Velikonja Department of Chemical and
Biochemical Engineering, University of Western Ontario, London,
Ont. N6A 5B9, Canada
Abstract
This paper presents challenging opportunities for production of
liquid and gaseous fuels by biotechnology. From the liquid fuels,
ethyl alcohol production has been widely researched and
implemented. The major obstacle for large scale production of
ethanol for fuel is the cost, whereby the substrate represents one
of the major cost components. Various scenarios will be presented
for a critical assessment of cost distribution for production of
ethanol from various substrates by conventional and high rate
processes. The paper also focuses on recent advances in the
research and application of biotechnological processes and methods
for the production of liquid transportation fuels other than
ethanol (other oxygenates; diesel fuel extenders and substitutes),
as well as gaseous fuels (biogas, methane, reformed syngas).
Potential uses of these biofuels are described, along with
environmental concerns which accompany them. Emphasis is also put
on microalgal lipids as diesel substitute and biogas/methane as a
renewable alternative to natural gas. The capturing and use of
landfill gases is also mentioned, as well as microbial coal
liquefaction. Described is also the construction and performance of
microbial fuel cells for the direct high-efficiency conversion of
chemical fuel energy to electricity. Bacterial carbon dioxide
recovery is briefly dealt with as an environmental issue associated
with the use of fossil energy.
Keywords: Fuels; Liquid fuels; Gaseous fuels; Biotechnology;
Ethanol; Biogas; Energy; Fermentation
Contents
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 111
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . 112
2. Fermentation ethanol for fuel . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . 116 2.1. The semi-continuous (modified fed-batch) process . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
118 2.2. Continuous process: internal yeast settling . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 119
3. Biotechnology in the production of 2,3-butanediol . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
121
* Corresponding author. Tel.: (+ 1-519) 661 2131; Fax: (+ 1-519)
661 3498
Federation of European Microbiological Societies. SSDI
0168-6445(94)00049-2
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112 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
4. Biotechnology in the production of liquid and gaseous fuels
from coal . . . . . . . . . . . . . . . . . . . . . . . . . . . .
127
5. Biotechnology in methane and biogas production . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . !
29
6. Biotechnology in diesel fuel and gasoline production from
microalgae . . . . . . . . . . . . . . . . . . . . . . . . . . . .
132
7. Biotechnology in the production of other oxygenated
alternative fuels and fuel extenders . . . . . . . . . . . . . . .
. . 135
8. Biotechnology in direct energy conversion: microbial fuel
cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. 137
References . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . 141
1. Introduction
The energy needs of the world today are esti- mated at close to
1021 joules per year, which amounts globally to about 20-30 TW
continuous power re- quirement (perhaps rising to 100 TW) [1]. This
equals a continuous average per capita consumption of about 4-6 kW,
which is very unevenly distributed among individual countries
(Table 1).
An estimated 2.5 1012 W, or only 20% from today's needs, would
cover the basic energy require- ments of the world population
(apart from physiolog- ical energy supplied by food), whereas the
remaining 80% are spent on the ever growing technological
activities and increasing life quality.
The obtainable energy on earth is available in different
renewable and non-renewable resources. An idealized representation
of power outputs from the renewable world resources and some
associated problems are given in Table 2. Most of the energy used
today comes from fossil fuels (Table 3).
There is a great discrepancy in production and consumption of
energy worldwide as shown in Fig. 1. The remaining reserves of oil,
estimated for the end of 1985, are presented in Fig. 2. One should
point out, however, that the reserves of the former USSR and China
may not be accurate and that much larger reserves are probably
available in these re- gions which have not been so far fully
evaluated.
The world consumption of commercially provided energy is shown
in Fig. 3, from which it is evident that coal, oil and natural gas
(non-renewable fossil fuels) represent almost 90% of the world
energy
consumption. Comparing these different energy sup- plies (Fig.
4), it is predicted that by the year 2060 the use of coal, natural
gas, nuclear, hydroelectric, and new sources of energy will
predominate, while petroleum supply will gradually diminish.
Another breakdown of these trends is shown in Fig. 6.
Another growing problem in terms of energy consumption
represents also the great imbalance of annual energy consumption
between north and south (Fig. 5) and between the industrialized and
develop- ing countries. The world population distribution (around
3:1 for developing vs. industrialized coun- tries) aggravates the
problem even more.
Both population and pollution problems are also associated with
energy use and distribution. The environmental impacts of these
tremendous amounts of various energy forms are given in Tables 4,5,
6, and 7 for oil natural gas coal, and nuclear power,
respectively.
The non-renewable energy resources (fossil fuels) are by far the
most exploited forms of energy today, as exemplified in Table 3. In
fact, the whole super- structure of the modern industrial society
is built upon oil which, at the present production rate, will be
exhausted in the next century with grave conse- quences of global
warming and environmental pollu- tion. Apart from having the
potential to affect and upset the climatic, geological and
biological equilib- rium in nature, its production and use directly
influ- ence all aspects of humanity. As shown in Fig. 6, the
production of liquid fuels from oil is expected to peak around
2015, with approximately the same amount produced by coal
liquefaction at that time.
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N. Kosaric, J. Velikonja / FEMS Microbiology Reciews 16 (1995)
111-142 113
Table l Per capita commercial energy usage (1988)
Country kV Country kW
Canada 9.0 Japan 3.6 United States 8.3 Italy 3.2 Saudi Arabia
7.0 Spain 2.3 Former E. Germany 6.8 Brazil ~ 1.4 Sweden 6.2 Mexico
a 1.2 Former W. Germany 5.1 China a 0.7 Former Soviet Union 4.9
Nigeria a 0.5 United Kingdom 4.0 India a 0.3
After Cole [1]. Countries with high consumption of traditional
fuels.
Another major peak of liquid fuel production is expected around
the year 2030, with a rapid decline to zero by 2090.
This projection into the not-so-far future does not reflect on
the odds of maintaining a steady growth of technology and economy,
keeping a reasonable qual- ity of life for those who would not want
to lose it, and possibly extending it to a larger part of the world
population, which will double in the same period-- mostly in
underdeveloped countries. The answer to that depends primarily on
three other issues: (i) development and worldwide
implementation
of viable technologies for industrial produc- tion, heating, and
transportation based on al- ternative (renewable) fuels and
feedstocks;
(ii) availability of sufficient quantities of renew- able energy
and feedstocks;
(iii) development and implementation of tech- nologies for the
reduction of environmental pollution and emission of CO 2.
Table 2 Maximum power outputs of renewable sources
Source Power/W Comments (assumed 100% land coverage)
Solar photovoltaic 1015
Solar photosynthetic biomass 9 1012 Aeolian 1 1015
Undular
Hydroelectric
Tidal Geothermal
Uncertain < 6 1012
Uncertain < 1012 < 7 1012 < 3 1013
7-10% conversion efficiency; REQUIRED, heavy duty storage system
and higher conversion efficiency Land coverage difficulties; visual
pollution Land coverage and harvesting: social problems REQUIRED:
heavy duty storage system Land coverage: technical and social
problems, visual pollution Useful near the sea; heaviest, most
expensive engineering
Restricted in global application
Restricted to tidal regions Restricted to specific areas Present
potential < 3 109 W Mid-ocean ridges: in very distant
perspective
Adapted from Cole [1].
Table 3 Worldwide reserves of fossil fuels (various sources)
Resources Total reserves proven + undiscovered
Volume equ. (109 bbl oil) Energy a (1018 j) %
Proven/recoverable reserves
Volume equ. (109 bbl oil) Energy a (1018 j) %
Oil 1 177 7 203 15.4 Heavy oil ~ 543 3323 7.1 Shale oil ~ 1066 6
524 13.9 Bitumen b 345 2 111 4.5 Coal c 3 175 19430 41.5 Natural
gas J 1 335 8 172 17.5 Total 7 641 46 763 99.9
703 4 303 11.1 450 2 752 7.1 1 066 6 524 16.8 345 2 111 5.4 3
175 19430 50.1 593 3 629 9.4 6 332 38 749 99.9
Based on a heating value of oil of 6.12 GJ/bbl (1 bbl = 42 US
gal = 159 1). b Heavy oil, shale oil and bitumen were given the
same heating value as oil. c Based on a metric-ton-of-coal
equivalent of 7 109 cal /t (29.3 GJ/t). d Based on an heating value
of 37.3 MJ /m 3 natural gas.
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114 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
~ Consurnption < ~ r'-I Domestic supply
~.o ~ ~ _~ e 3 ~ c "-. 2 ~ C ._
11 ".iT,
u~ 1.C ]
,J,
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N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 115
Hydroe lec t r i c 6.7 */0
~i i~. : . .~L-~ ~___.____N uc lear / - '~ . : : . . ' . : - . .
. . .%, 4G 0/,
Coal 30.7 *
Natural Gas
20.1 */0
Oil 37.9 */.
Fig. 3. World consumption of commercially provided energy
(source [46]).
and for internal-combustion engines (ICEs) which were being
studied so far as economically and tech- nologically promising
are:
Liquid fuels: (i) ethanol; (ii) other alcohols (e.g. butanol,
2,3-butanediol); (iii) short-chain aliphatic acids as precursors
(e.g.
acetic to valeric);
1o
.2 K
30(3 Cool
2OO
Natural gas
Nucleor 10(: New SOurCes
Petroleum Hydro elect r i
Non commerciQI energies
19~0 1980 2000 2020 2040 2060
Yeor
Fig. 4. Evolution of world energy supplies (From [47]).
(iv) other oxygenated solvents (e.g. ketones); (v) lipids
(fatty-acid triglycerides, other fatty-acid
esters). Gaseous fuels:
(i) methane; (ii) medium-heat content biogas;
(iii) hydrogen. Biotechnology also offers the possibility of
gener-
ating electricity by direct conversion of fuel energy in
microbial fuel cells.
Major alternative routes are presented below.
Table 4 Environmental impacts of oil
Energy activity
Environment Exploration Extraction, production, pro-
Transmission Use and disposal cessing
Atmosphere Emissions of hydro- Refinery emissions of SO 2, -
Emissions of SO2, CO 2, carbons as a result of HzS, CO2, NOx, and
hydro- and hydrocarbons a blowout carbons
Hydrosphere Blowouts and spills Blowouts and spills from
exploratory Brine and drilling chemicals wells at sea, leading
disposal Refinery effluents to oil contamination
Lithosphere Blowouts and spills Blowouts and spills Sludge
Pipeline construction and Used oil disposal on land disposal spills
Damage due to per-
mafrost Human im- Disruption of life Interference with fisheries
Interference with fish- Hydrocarbons and poly pact style eries or
land use Disrup- nuclear aromatic hydro-
tions of life style during carbons from combustion
construction
Tanker accidents, lead- ing to oil contamination
Groundwater contamina- tion by leaking tanks
From Runnalls and Mackay [53].
-
2. Fermentation ethanol for fuel
E O Or )
- - tO 13m
t : t- O
Fermentation of sugars by yeasts is one of the oldest practised
biotechnology processes. Major em- phasis in the past was to
produce potable alcohol in the form of beer and wine. More
recently, particu- larly in countries which lack petroleum but have
abundant sugar crops (e.g. Brazil with sugar cane), a large scale
fermentation industry for production of fuel alcohol has been
developed. Productivities of alternative batch and continuous
systems are shown in Table 8.
A typical process for production of ethanol in a batch mode, as
applied in Brazil, is the 'Melle- Boinot' process, presented in
Fig. 7. Two approaches are being practised by use of molasses or
sugar cane juice and the industrial yields are shown in Table 9.
Other raw materials for fuel alcohol production have also been
investigated, such as sugar beets, Jerusalem artichokes, cassava,
wood hydrolysates, starches, sweet sorghum, etc. A comprehensive
review on alcohol production, recovery, and biotechnology has been
presented by Kosaric and Duvnjak [2].
e-
~J Nor th 7.11
[ ] South 6.2e ~_271
5.44
4 .59
4
2 .73
97 1.10 60 74 "
1960 1980 2000 2020 2040 2060
Year
Fig. 5. Levels of energy consumption (From [47}).
300 o
u
200 .~
E
E
8 ~oo -
c c <
Concerning yeasts, Saccharomyces cerevis iae has been mainly
used. Of particular interest is also the use of flocculating
yeasts, such as Saccharomyces diastaticus, for fuel alcohol
production, as investi-
Q
u :3
"o o 1,. o.
1960
~ 2 Ill
%
I I I I I |
1980 2000 2020 2040 2010 2080
l 16 N. Kosaric, J. Velikonja / FEMS Microbiology Reuiews 16
(1995) 111 - 142
Calendar years
Fig. 6. Projected rate of world production of fossil fuels (From
[48]).
2100
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N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142
Table 5 Environmental impacts of natural gas
117
Energy activity
Environment Exploration Extraction, production, Transmission Use
and disposal processing
Atmosphere EmissionsofgasandH2S Gas plant emissions of -
Emissions of CO 2, during an accidental H2S, SO 2, and hydrocar-
NO~ blowout bons
Hydrosphere Blowouts Blowouts and drilling - - Disposal of
chemicals
Lithosphere - - Construction of pipeline - Damage due to per-
mafrost LNG accidents Disrup- tions of life style during
construction
Human impact - LNG accidents H 2 S emissions
From RunnaUs and Mackay [53].
Table 6 Environmental impacts of coal
Energy activity
Environment Exploration Extraction, production, processing
Transmission Use and disposal
Atmosphere - Emissions of SO 2 and PNAs - Emissions of CO2, NOx,
COz, from processing to gas or liquid and particulates fuel Coal
dust dispersal
Hydrosphere - Leaching of acids and metals - Thermal effects
Organic compounds formed with 'synfuels' Siltation
Lithosphere - Disruption from strip mining - Fly ash disposal
and subsidence Slag heaps
Human impact - Lung disease Mine safety - Exposure to emissions
from combustion and coke ovens
From Runnalls and Mackay [53].
Table 7 Environmental impacts of nuclear power
Energy activity
Environment Exploration Extraction, production, process-
Transmission Use and disposal ing
Atmosphere - Accidents Radon emissions from - - mine
railings
Hydrosphere - Accidents Leachate from mine - Thermal effects
tailings
Lithosphere - Accidents Tailings contamina- Transmission
Disposal of spent fuel and tion lines waste
Human impact - Accidents and mine-plant ex- Accidents during
Exposure to wastes Terror- plosive mining hazards fuel transport
ism
From Runnalls and Mackay [53].
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118 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
Table 8 Productivities of alternative batch and continuous
fermentation systems utilizing yeast
System C 2 H5 OH productivity (g1-1 h -1)
Continuous, vacuum recycle 80 Continuous, recycle 40 Batch,
recycle 15 Continuous, multi-stage 12 Continuous 5 Batch 2
Adapted from Vergara [54].
series of photographs which were taken in 10-s intervals after
the mixing was stopped (Fig. 8). This clearly illustrates a special
capability of this system as compared to processes where yeast has
to be concentrated by costly centrifuges for its return to the
fermentation broth.
Based on this property, two processes were devel- oped: a
semicontinuous (modified fed-batch) process and a continuous
process with internal cell recycle, without the need for use of any
mechanical settling devices, as is the case in other continuous
processes (e.g. 'Biostil l ' developed by Alfa Laval).
gated in our laboratory. This yeast has a high effi- ciency in
converting sugars to alcohol. Another ad- vantage is in its high
flocculating capability. The yeast produces very stable flocs
during growth which can rapidly settle if needed, but can also be
effi- ciently maintained in suspension when sufficient mixing is
applied. The settling is illustrated in the
2.1. The semi-continuous (modified fed-batch) pro- cess
The schematic of the operation of this process is presented in
Fig. 9. A conventional bioreactor (stirred tank reactor) is filled
with the medium, inoculated
HzSO~ _ ! Molasses or cane juice
[ ! Weighing and 1 Brix sterilizing I ~ adjustment .lt. to 22"1o
v/v
Preparahon of yeast
l Wort = [ I -I
Decanted wine
Recuperation of yeast
Fermentahon 1 Wine [ Decantation J
and
J ~1 centrifu~ation I t
Rechhed Alcohol 20/. v/v a lcoho l
L , Raw alcohol
Phleg Fusel _ ~ Stilla ~ oil
DISTILLATION RECTIFICATION
Benzene ,~r ' '
DEHYDRATION
Decantation 1
H~O Recycle
RECUPERATION OF BENZENE
Fig. 7. Typical process for the production of ethanol from sugar
cane (From [49]).
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N. Kosaric, J. Velikonja / FEMS Microbiology Reciews 16 (1995)
111-142
Table 9 Yields in production of ethanol from sugar cane
119
Alcohol, indirectly Alcohol, directly from molasses from sugar
cane
63 63 8.32 8.32 7.0 2.21 66.2 1 ~32 8.73 675 4 460 11.5 75 730 4
800
Sugar cane yield in 1.5-2-year cycle (south central region),
t/ha Average sucrose yield (13.2 wt %), t/ha Crystal sugar
production, t/ha Final molasses or cane juice production, t/ha
Fermentable sugar, molasses, or juice, t/ha Alcohol yield at 100%
global efficiency, kg/ha Alcohol yield at reasonable 85% global
efficiency, 1/ton of cane or in l/ha
From Lindeman and Rocchicciolo [55].
with about 10% of an inoculum (previously prepared in shake
flasks) and the fermentation is run to com- plete utilization of
the substrate sugars. At this time the mixer is stopped and the
yeast is allowed to rapidly settle, leaving a supernatant devoid of
yeast flocs. Some non-flocculating microorganisms may still be in
the upper zone at this time. As soon as the settling is complete
(to the desired level), the upper clear supernatant is withdrawn
and sent to distilla- tion, new medium is pumped into the same
vessel containing the settled yeast and the next fermentation
started under full mixing. As can be seen in Fig. 10, as soon as
the high biomass concentration in the bioreactor is achieved, the
subsequent fermentation times are considerably reduced down to
about 3 h from the initial 20 + h, as obtained in simple batch
experiments.
These fermentation cycles have been separately run in a dozen
other fermentations, for up to 10 consecutive runs without a
visible loss in ethanol productivity (Fig. 10).
There are a number of advantages of this process as compared to
simple batch fermentations and these can be summarized as
follows:
(i) High productivities are achieved. (ii) High biomass
concentration in the reactor is
maintained in the order of up to 50 g / l . The biomass
represents an excellent yeast by- product which can be easily
dewatered (in- cluding a simple settling operation) which would
considerably reduce its recovery cost. This biomass could be a rich
source of pro- tein and other nutrients for either human nutrition
or animal feed.
(iii) The operation is simple, requiring only a stirred tank and
storage vessels and pumps.
(iv) The yeast is being concentrated without the use of any
centrifuges or other mechanical concentration devices.
(v) While the feed broth must be sterilized (like for any other
fermentation process), the ac- tual fermentation run can be done
under non-sterile conditions. The fermentation time is short for
any interfering development of contaminating microorganisms
(bacteria and wild yeast), and if these do develop, they will
probably not flocculate and will thus be withdrawn from the
bioreactor at the end of each cycle in the spent broth.
(vi) Considerable reduction in the fermentation time to about 3
h from conventional 20 h in simple batch operation. Due to this
fact, much smaller reactors and equipment are needed, which reduces
the overall capital and investment costs.
(vii) The energy required to run the fermentation process is
only required for mixing and pumping of the liquid.
At the present time, there is no such process in commercial
operation. All runs were made in our pilot plant 10-1
fermenters.
2.2. Continuous process: internal yeast settling
The same flocculating yeast, S. diastaticus, al- lowed the
development of this continuous process. Its capability to rapidly
settle against an upflow of fluid allowed a development within the
reactor of a
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120 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
Mlxem' s topped, T ime : (I sec
A f te r I0 sec A f te r 20 sec
~ L ~" ~ ~
Af ter 3(I sec A f te r 4(I sec
A f ter 50 sec Aft.er 60 sec
Fig. 8. Settling of Saccharomyces diastaticus (From [49]).
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N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 121
OPERATE ST~L DP~W FILL
Fig. 9. Schematic diagram of the semi-continuous (modified fed-
batch) process (From [49]).
well mixed turbulent yeast zone and of a clear liquid zone at
the top. Depending on the mixing applied, the height of the top
clear zone can be regulated and maintained during the operation of
the bioreactor. The process is depicted schematically in Fig.
11.
Fermentation of fodder beet and Jerusalem arti- choke juices by
this yeast showed that a high con- centration of yeast (40-70 g/ l
) can be kept in the bioreactor at high dilution rates, and
therefore a high volumetric ethanol productivity of 40-50 g L- i h-
is achieved. Figs. 12 and 13, as well as Tables 10 and 11, show the
results of this system with the following advantages:
(i) High ethanol productivities at high dilution rates.
(ii) High ethanol yield at 96% of theoretical. (iii) No need for
external yeast recycling and for
cell concentration within the bioreactor. (iv) Simple bioreactor
configuration. (v) Easy maintenance of desired biomass con-
centration within the bioreactor. (vi) Improved economics and
energetics of the
system. (vii) Less capital investment due to elimination of
external cell recycling and concentration sys- tem.
No such system is at present operating commer- cially. Further
developments are under way to scale- up the process, modify and
optimize the bioreactor for this fermentation and demonstrate the
process on a large production facility.
The key to this process is the flocculating ability of the
selected yeast. This ability was never lost in our tests and the
flocculating stability must be main- tained in a large scale
installation. These tests are now under way in our
laboratories.
Two continuous processes, which are at the pilot plant
demonstration stage, can be compared to our process. These are the
Hoechst-Uhde process utiliz- ing another flocculating yeast which
apparently is sometimes washed out from the system (personal
communication) and which achieves a volumetric ethanol productivity
of about 16 g 1 -~ h J (as compared to 40-50 g 1-~ h-~ in our
system). The Hoechst-Uhde process incorporates an internal cell
setling and recycle system, which is also not required in our
process.
Another process for comparison is the Biostill continuous
process installed by Alfa-Laval in Brazil as a pilot plant
demonstration project producing 150000 I alcohol/day (Alfa-Laval
Report, 1983). The Biostill process claims: (i) High alcohol yield
because of low by-product
formation (mainly glycerol). (ii) Low stillage flow because of
low dilution
water requirements (see Fig. 14). (iii) Low manning cost because
of continuous
processing. (iv) Compact plant containing just one
fermenter.
A comparison of the Biostill with a conventional alcohol plant
in Sao Luiz (Brazil) using the same substrate is shown in Table
12.
A schematic representation of the Biostill process is given in
Fig. 15. As can be seen from the figure, the centrifuge represents
an integral part for cell concentration and recycling to the
fermenter.
Even though at the present time we do not possess the values for
all parameters required for a compari- son with the pilot plant
Biostill data, our process appears to be at least as efficient, but
is definitely cheaper as no external cell recycle is required.
3. Biotechnology in the production of 2,3- butanediol
Butanediol has a heating value of 114 MJ/kg [3], as compared to
ethanol (122 MJ/kg), and an equimolar mixture of the two (116
MJ/kg). How- ever, its price is not competitive with that of
fermen- tation or synthetic ethanol. Thus its main prospect in the
fuels industry is in the dehydration to MEK (methyl ethyl ketone or
2-butanone), which is much more suited as a fuel because of its
much lower
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122 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111 - 142
~r
r , l ( , j
r.~
I=~ 0..j
v l w
,j
- ~R~~, h ' =,0, , ,9 N
v l N
~n m
. i i / .n j ,~-
-~ j : ,,l~
(1_15) ' [OUeq;3 , j
(K.16) 'J~6ns
o L6
:= L~
a= ',O
o
o
-
N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 123
F o
X o
S 0
D o
0
-0 CLEAR ZONE +
MIX ING ZONE
! t -el--- VM ----~
t "- F r
e
X e
S e
P e
F =F o e
V " VOLUME OF SETTLING ZONE
V M VOLUI4E OF MIXING ZONE
= + V M V V s
F D : ~ DILUTION RATE
Fig. ] I. Schematic diagram of the continuous fermentation
process without external recycle (From [49]).
boiling point. Alternatively, condensation with MEK and
subsequent hydrogenation yield octane isomers for high-quality
aviation fuels.
2,3-Butanediol is another chemical whose produc- tion and
process development were stimulated by war. During World War II it
was needed for conver-
S o = 97.0 GL" Sugar in fermentor
= 40-50 GL" Biomass Concentration in fe rmentor
Ypts= 0 .49 GG "~
For all d i lut ion rates
o ~ GL"
Sugar concent ra t ion in fermentor
o~ GL"
Ethano l concent ra t ion in fe rmentor
PR GL" HR "I
Vo lumetr i c e thano l product i v i ty
aS.U.
/o of sugar ut i l i zed
o~ op ePRAS.U
10C 50-5C 10C
80- 4C-4C-BC
60. 30-3C .6(]
: / 40. 20- 2C ' 2C 20. 10- 1C ,20
~0 0 ~ O- 0 - ' - - " - ' "~"
o~2 o14 0.'6 o18 Fig. 12. Continuous fermentation of fodder beet
juice (From [49]).
i
1.0 D.~R "I
-
124 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
Table 10 Continuous fermentation of fodder beet juice with
Saccharomyces diastaticus
First fermentor Second fermentor
F o ] ) D S O S 1 P, Yp/~ Qp (mlh- (h - l ) (gl - l ) (g1-1) (gl
1) (g g- 1) (g I i h - ')
$2 P2 Yp/s Qp (g 1-]) (g 1-1) (gg 1) (g l - I h ~)
31.0 0,258 111.8 4.0 53.8 0.50 13.88 62.0 0.517 111.8 5.0 53.8
0.50 27.81 93.0 0.779 111.8 5,0 54.0 0.51 42.07 108.5 0.904 111.8
10.0 51.5 0.51 46.56 124.0 1.033 111.8 14.2 49.5 0.51 51.13
2.0 54.0 - - 2.0 43.0 - -
5.1 54.0 2.26 0.51 3.2 54.8 5.48 0.48
From Kosaric [49].
Table 11 Continuous fermentation of Jerusalem artichoke juice
with Saccharomyces diastaticus
First fermentor
F o D S o S 1 Pl Yp/s Qp (mlh I) (h- I ) (g l - I ) (g l - l )
(gl 1) (gg - l ) (g l - lh - J )
Second fermentor
$2 P2 Yp/s i) QP (gl 1) (gl J) (gg - (g1-1 h l)
15.5 0.129 161.0 36 61 0.49 7.9 31.0 - 0.258 161.0 51 54 0.49
13.9 46.5 0.387 161.0 47 56 0.49 21.7 62.0 0.517 161.0 52 55 0.49
28.4 108.5 0.904 164.0 64 49 0.49 44.3 132.5 1.162 164 72 38 0.41
44.1
28 65 0,50 0.5 27 66 0.50 3.1 39 60 0.46 1.5 39 60 0.49 2.6 44
59 0.50 9.0 46 51 0.50 15.1
From Kosaric [49].
sion into 1,3-butadiene, one of the building blocks of synthetic
rubber. It can occur in the form of two enantiomers: D - ( - ) , or
levo, and L- (+) , or dextro,
as well as an optically inactive meso-form. All are bacterial
products: pure D- ( - )-2,3-butanediol is pro- duced by Bacillus
polymyxa, whereas meso-2,3-
So: 1G1.0 GL" Total sugar in juice
: 50 -70 GL" B iomoss concent ra t ion in fe rmentor
Ypts: 0.49 GG "1 For all d i lu t ion ra tes
a g GL" Sugar concentration in fermentor
oP GL" Ethano l concent ra t ion in fermentor
PR GL "I HR "I Vo lumetr i c e thano l p roduct iv i ty
AS.U *t, 01 sugar ut i l ized
aS op ePR~S.U
12(
Bt3 4 8( A
4 . L , 1 /~/~ , , , , .
40 2C
0.2 0.4 0.6 0.8 1.O 1.2 -D. HR "1
Fig. 13. Continuous fermentation of Jerusalem artichoke juice
(not hydrolysed) (From [49]).
-
N. Kosaric, J. Velikonja / FEMS Microbiology Reciews 16 (1995)
111-142 125
16,
15
14
13
12
11
8
7
6
5
4
3
2
1
0
i - . . I . . . . . .%. . . . - i - . . . . . r . . . - .n . . .
. . - / - . - . - . r . - . - .1
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . .
. . . . . . . , . . . , . . . . . . - . . . . . - . - . . . . . . .
- . .o . .
iiiiliiiiiiii i iiiiiiiiiiiii: i iiiiiiiiiiiii i!
iiiiii!iiii!i!i iiiii!i i !i!i !i1i!iiiiii!i iiiiiiii!ii!
!i!i!iiiiiii!i!itiii
st i l
I I I I I 1 I
1 2 3 4 5 G 7
FIN
| |
8 9 10
Fig. 14. Ratios of stillage and ethanol volumes obtained at
differ- ent F/N conditions for conventional and biostill
fermentations (F, fermentable components; N, nonfermentable
components) (From [49]).
Table 12 Comparison of the biostill with a conventional plant at
Sao Luiz (Brazil) using the same substrate (Source: Alpha
Laval)
Parameter Biostill Conventional
Yield (% of theoretical) 94.5 87 Stillage (1/1 alcohol) 0.8 11
Manpower 3 7 Space requirement (m 2) 350 1350
butanediol is a product of Klebsiella pneumoniae (Aerobacter
aerogenes), which also produces some of the L - (+) isomer. There
are also other bacteria which synthesize mixtures of different
forms (e.g. Bacillus subtilis, Serratia marcescens, Aeromonas
(Pseudomonas) hydrophila), and also several yeasts, but they are
considered economically unimportant.
The use of various organisms and substrates as feedstocks is
shown in Tables 13, 14, and 15. Yields are not impressive, mostly
under 1 g l-~ h -=, with 8.2 g 1 = h - 1 (in the presence of 4.5
g/1 acetate) as the highest ever recorded [4]. One of the intrinsic
difficulties with product recovery is its high boiling point of
about 180C and high water affinity, for which alternatives to
distillation were being devel- oped, such as solvent extraction
(with ethyl acetate,
Conc. Feed
h,. . ! ........ n
llllllIlllll ~c
I~""""U I FERMENTER|
OOLER 4k T Yeast C ream, I
AIR 8 LO~,'ER I,,
CENTRIFUGE
,,~.r-i I
REGENERAT IVE HEAT EXCHANGER
d
AIcoho l
(q0-S0 t vvl
- - l-SECTION ~--" 1BEER ST ILL
Stillage
Fig. 15. Schematic of the biostill process (From [49]).
-
126 N. Kosaric, J. Velikonja /FEMS Microbiology Reviews 16
(1995) 111-142
Table 13 Batch fermentation of 2,3-butanediol: summary of data
for various bacterial strains and substrates
Substrate Organism Overall butanediol Overall butanediol
productivity (g 1-l h- l) yield (g/g substrate)
Glucose Aerobacter aerogenes NRRL B199 2.02 0.45 Glucose
Klebsiella pneumoniae NRRL B199 0.36 Xylose Klebsiella pneumoniae
NRRL B199 0.27 Xylose Klebsiella oxytoca ATCC 8724 1.35 0.36 Xylose
Bacillus polymyxa NRCC 9035 0.1 0.24 Mannose Klebsiella pneumoniae
AU- l-d3 0.64 0.30 Lactose Klebsiella pneumoniae NCIB 8017 0.06
0.24 Whey permeate Klebsiella pneumoniae 0.08 0.46 Hydrolysed whey
permeate KlebsieUa pneumoniae 0.14 0.39 Whey Klebsiella pneumoniae
ATCC 13882 0.38 Whey Bacillus polymyxa ATCC 1232 0.02 0.16 Starch
Aeromonas hydrophila NCIB 9240 0.17 0.2 Citrus waste Aerobacter
aerogenes 1.1 Xylan Bacillus polymyxa NRCC 9035 0.02 Wood
hemicellulose hydrolysate Klebsiella pneumoniae ATCC 8724 0.45
Agricultural residues Klebsiella pneumoniae ATCC 8724 Jerusalem
artichoke Bacillus polymyxa ATCC 12321 0.79 0.4
From Maddox [56].
ether, or n-butanol), membrane technologies, adsorp- tion, and
chemical recovery. None of these have as yet yielded commercially
applied solutions.
In situ conversion to MEK (boiling point 79.6C) by acid
catalysis would make recovery much easier and more efficient, but
decreased conversion rates in the complex broth await further
development.
The cost of 2,3-butanediol does not compare fa- vorably with
other fermentation products (Table 16), although several factors,
like the choice of raw mate- rials, could improve process
economics. Like with other fermentations for fuel production, the
combina- tion with waste utilization or with the elimination of
waste materials which present an environmental nui- sance, yield
improved overall performance. Thus, delignified water hyacinth was
recently studied as a potential substrate for 2,3-butanediol
fermentation [5], with similar results as those obtained for other
substrates. More encouraging results with this weed (1.4 g i-1 h-1
at 4 h hydraulic retention time) were obtained in continuous
operation with anaerobic fixed-film and UASBR reactors fed with
alkaline hydrolysate (19 g / l reducing sugars).
In conclusion, it can be stated that fermentations for
oxygenated fuels or fuel precursors other than ethanol will be
inevitably outcompeted by petro-
Table 14 Some intensified fermentation technologies for
2,3-butanediol: summary of data
Method Substrate Organism Butanediol productivity (g i -1 h-
l)
Continuous flow Sucrose Continuous flow Glucose Metabolistat
Lactose Continuous flow/carrageenan-immobi- Glucose lized cells
Continuous flow/alginate-immobilized Whey permeate cells Continuous
flow/cell recycle Whey permeate
Aerobacter aerogenes NCIB 8017 4.6 Klebsiella pneumoniae NRRL
B199 4.25 Enterobacter cloacae 0.03 Enterobacter aerogenes IAM
1133
0.75 Klebsiella pneumoniae NCIB 8017
2.3 Bacillus polymyxa 1.04
From Maddox [56].
-
N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 127
chemica ls as long as oil cont inues to be the chemica l
and energy foundat ion of the industr ial civi l ization.
In all l ikel ihood this s ituation wil l change dramati -
cal ly in the next century for we l l -known reasons, But
even then the future of such products and technolo- gies is
unclear, s ince the search for a l ternat ive fuels
goes many di f ferent ways and may ult imately pro-
v ide much better solut ions in the form of c leaner and
more eff ic ient energy carriers, such as hydrogen.
4. Biotechnology in the production of liquid and gaseous fuels
from coal
In terms of energy, coal represents 71.4% (161 000
EJ) of wor ld ' s fossil fuel reserves, as compared to
7500 EJ in crude oil (3.3%). The recoverable coal
contains 91.1% of energy and 93.9% carbon con-
tained in oil, gas and coal combined [6]. A truly
remarkable resource!
Table 15 Summary of 2,3-butanediol production from potential
substrates
Substrate a Initial Fermentation Yields (g/l) Butanediol
monosaccharide time (h)
g/ l % used Diol EtOH HAc g/g used g/g available g 1- J h i
Waste sulfite liquor 38.0 69.7 72 9.0 3.3 - 0.34 0.24 0.13
Citrus press juice 215.0 91.5 56 51.0 - - 0.26 0.24 0.91 Sugar beet
molasses 56.6 71.0 24 20.1 - - 0.50 0.36 0.84 Sugar beet pulp 11.0
78.0 11 2.4 1.6 - 0.28 0.21 0.21 Wood hydrolysate (la) 100.0 55.0
46 16.5 - - 0.30 0.17 0.34 Wood hydrolysate (lb) 100.0 93.0 3.1
35.5 - - 0.38 0.36 1.04 Wood hydrolysate (2) 12.1 95.0 NR c 6.0 3.8
2.1 0.52 d 0.50 o _ Wood hydrolysate (3) 9.7 100.0 24 0.2 0.5 3.8
0.02 d 0.02 o 0.01 Wood hydrolysate (4) 40.0 100.0 46 20.0 5.9 0.1
0.50 d 0.50 d 171.42
Adapted from Magee and Kosaric [57]. a Wood hydrolysate: (la)
southern red oak hydrolysate (Scholler process); (lb) same as la,
except for acclimatized culture; (2) steam-exploded aspen,
hemicellulose fraction, acid hydrolysis; (3) steam-exploded aspen,
hemicellulose fraction, enzyme hydrolysis; (4) steam-exploded
aspen, cellulose fraction, acid hydrolysis. b Average value. c Not
reported. o Conversion of HAc and uronic acids not considered.
Table 16 Selling prices for selected solvents
Solvent Selling price (1985 US$)
Methanol (synthesis, tank) Ethanol (fermentation, tank) Ethanol
(synthesis, 190 proof, tank) Ethanol (absolute, 200 proof, tank)
iso-Propanol (anhydrous, 99%, tank) n-Butanol (synthesis,
fermentation, tank) Acetone (tank) 2-Butanone (MEK) (tank)
1,3-Butanediol (tank) 1,4-Butanediol (tank) 2,3-Butanediol
(tank)
0.14-0.19/1 0.39-0.45/1 0.48-0.50/1 0.51-0.53/1 0.53/1 0.79/1
0.51/kg 0.79/kg 1.59/kg 1.76/kg 3.02/kg
Adapted from Magee and Kosaric [57]. Higher value estimated by
Magee and Kosaric (1987) for a 1.2 Mt/a production; lower value
estimated in Eur. Chem. News, June 4, 1984
for 180 Mt/a.
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128 N. Kosaric, J. Velikonja /FEMS Microbiology Reviews 16
(1995) 111-142
Table 17 Some coal-solubilizing microorganisms
Fungi (Basidiomycetes) Coriolus versicolor Phanerochaete
chrysosporium Poria placenta
Fungi (Hyphomycetes) Acremonium sp. Aspergillus spp.
Cunninghamella sp. Mucor spp. Paecilomyces spp. Penicillium spp.
Sporothrix sp.
Yeast-like fungi Candida sp.
Actinomycetes Streptomyces badius Streptomyces setonff
Streptomyces viridosporus
Eubaeteria Bacillus sp. Pseudomonas sp.
From Faison [6].
Under the term coal are classified many different products of
carbonization of ancient organic matter. The younger ones are
low-rank coals (lignites and subbituminous coals), whereas the
older ones are high-rank coals (bituminous coals and anthracite).
Coal constituents are organic compounds, inorganics (clays, quartz,
calcite, iron sulfides, etc.) and water. All of these vary
considerably in their amounts in coals. The organic part consists
of aromatic and aliphatic compounds, the latter being considerably
more abundant in lower rank coals. Oxygen is more abundant in
younger coals (60% in ether bonds and hydroxylic groups, 40% in
esters, carboxylic and carbonyl groups).
COAL
MIXED CULTURE No. 2 (PRIMARILY BACTERIA)
PRODUCTION OF L)OUIO FUELS
FUNGI OR ACTINOMYCETES
OAEREAcToR~ COAL SOLUBILIZATION ROBIC~)
t t METHANOl. CH4 ETHANOL (METHANE)
(PRIMARILY BACTERIA)
BIOGASIF ICAT ION
Fig. 16. Schematic of a two-stage process for the production of
fuel chemicals from coal (From [6]).
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N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 129
Some coals (mostly low-rank and in some cases bituminous coals)
have the potential to be solubilized by the action of
microorganisms [7]. There are sev- eral microorganisms, from
different taxa, for which a coal solubilization capability was
demonstrated (Ta- ble 17). Various kinds of oxidative (hydrogen
perox- ide, ozone, 8 M nitric acid/48 h, air/7 days/150C), as well
as non-oxidative pretreatments with surfac- tants (SDS), buffers
(Tris, Gly-Gly, phosphate) at alkaline pH, and acid extraction
(HCI) have shown to enhance microbial solubilization. It appears
that ligninolytic organisms more readily attack lignite (chemically
related to lignin) than non-ligninolytic organisms [8].
The product thus obtained is a dark, acidic, polar,
water-soluble liquid, consisting of polycondensated, oxidized
aromatics, some of them with molecular masses between 30 and 300
kDa [9]. Coal solubi- lizates of fungal and bacterial origin do not
differ markedly from one another.
Solubilized and non-solubilized lignite can be a potential
substrate for the microbial production of methane, alcohol and
fatty acids. It is unlikely that any organism will ever be able to
use all or most of the complex organic structure of coal. But a
two-stage process, similar to the one in Fig. 16, could be a
promising future technology. Some examples cited below illustrate
studies on laboratory coal solubiliza- tion.
Subbituminous, nitric-acid pretreated coal was partly (approx.
10%) solubilized by Paecilomyces TLi [10]. The medium, containing
2.5 g / l unfrac- tionated, solubilized coal as the sole C-source,
sub- jected to methanogenic fermentation by an accli- mated
culture, yielded 56% from predicted volume of biogas (approx. 25%
methane) after 100 days of incubation and a lag of 25 days. After
60 days, only carbon dioxide was produced, because of the exhaus-
tion of components which were metabolized into methane. Cultures
supplemented with CI. aceto- butylicum ATCC 824 (to break down
aromatics into low molecular mass oxygenates) caused an increase in
production.
Sheep rumen, sewage sludge and soil isolates were tested for
alcohol and acetate production [11]. After 10 days incubation of 1
ml solubilized lignite with sewage sludge isolates, the
concentration of ethanol was 0.072 g/ l , and that of acetic acid
0.83
g/1. With 10 ml solubilized lignite, the concentra- tions were
0.386 g/ ! and 0.642 g/ l , respectively. Two soil isolates gave
very little ethanol with 1% lignite, gradually disappearing at 48 h
of incubation, whereas acetate showed a peak of 1.16 g/1 at 48 h.
Another mixed culture from soil gave within 48 h an increase in
ethanol concentration of 0.35 g/ l and an acetate concentration of
0.40 g/I.
The above study, however, has shown that bacte- rial isolates
from coal environments were able to solubilize > 30% untreated
lignite in 28 h. Another very interesting finding was that small
quantities of cells (bacterial isolate LSC), grown on cheap sub-
strates (e.g. crushed barley hulls) and subsequently added to
pretreated lignite in water, brought about a 45% solubilization at
100C in only 10 min (90 g solubilized coal per liter).
Subbituminous coal solubilization with various oxidoreductases
in organic solvents and aqueous so- lutions under both aerobic and
anaerobic conditions was also studied [12], however without
convincing results.
From the above it may be concluded that research on coal
solubilization and subsequent fuel production is still in its
beginnings, although there is consider- able interest to convert
cheap, low-grade lignite into more valuable products like liquid
fuels or biogas. Accumulated data seem to indicate that a two-stage
aerobic/anaerobic process of solubilization and fuel production
would be most advantageous.
5. Biotechnology in methane and biogas produc- tion
Methane, the main constituent of natural gas and the principal
combustible component in biogas, has the highest molar heat of
combustion of all organic compounds: -890.31 kJ/mol (at 25C and
101.3 kPa). Enormous quantities are constantly being re- leased
into the atmosphere from geological sources (natural gas vents and
coal deposits), decaying or- ganic matter (lake and river
sediments, peat bogs, marshes), agricultural areas (paddy rice
fields), waste processing facilities (sewage treatment plants and
landfills), and from the digestive tracts of mammals (most notably
ruminants) and some insects. It is thought that microbially
produced methane world-
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130 N. Kosarie, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
Can run 2 horsepower engine for one hour
II !
Can run 300 litre refrigerator for 3 hours
Can illuminate mantle lamp ] equivalent to 60 walt
,~for about 7 hours
l %N~ Y Can cook 3 meals
for family of t, persons
One m 3 of biogas
(;an generate 1.25 kw electricity
Fig. 17. Possible applications of biogas (From [18]).
wide yields about 50 E J /a , whereas some 30 E J /a come from
geological sources. Besides carbon diox- ide, atmospheric methane
is a major greenhouse gas. Possible applications of biogas are
presented in Fig. 17.
Biogas is the final gaseous product of anaerobic degradation.
Almost all of it is methane (54-80%) and carbon dioxide (20-45%),
in a typical volume ratio of 3 /2 [13]. Other, usually minor,
constituents are hydrogen, molecular nitrogen, oxygen, hydrogen
sulfide, and carbon monoxide. The elemental compo- sition of
degradable biomass directly influences the
methane/carbon dioxide ratio, a fact reflected in the
Buswell-Mueller stoichiometric equation [14]:
( a b ) C.H~O b + n 4 2 H20
----.> - - _ _ q . - CO 2 + -- + -- _ _ CH 4 8 2 8 4
As with any other kind of fuel, methane produc- tion requires
cheap raw materials. Almost all biomass-based fuels must
necessarily come from the bioconversion of lignocellulosics, i.e.
the products of
Table 18 Raw materials for biogas production
Origin Type of waste
Agricultural wastes .Human wastes Animal wastes
Agriculture-based
Forestry wastes Aquatic wastes
Crop-related stubble, straw, spoiled fodders, weeds Excrements,
sewage sludge, refuse Cattle dung, pig, sheep, goat manure, poultry
litter; slaughterhouse, tannery, fishery, wood wastes Wastes from:
palm oil and rubber mills, sugar cane bagasse, tobacco manufacture,
breweries, distilleries, food, fruit and vegetable processing,
sugar and tapioca mills, tea and coffee plantations, textile and
jute mills, rice brans Twigs, barks, branches, leaves, dead trees,
plants Algae, weeds, water hyacinth, other aquatic plants
From Aziz [18].
-
N. Kosaric, J. Velikonja / FEMS Microbiology Reuiews 16 (I 995)
1 l 1-142 131
hydrolysis of its primary components: cellulose, hemicellulose
and, to a lesser extent, pectin. These are abundantly found in the
form of lignoceUulosic waste from silviculture, agriculture and
industry, as well as in municipal sewage sludge and municipal solid
waste. Lignin, a major constituent of wood (18-30% d.s.), is
considered to have no methanogenic potential, because its
decomposition rate is far too low. Useful waste materials are sum-
marized in Table 18. Methanogenic potentials of various classes of
precursor compounds are given in Table 19, as represented in
municipal solid waste.
Dedicated fuel crops present an enormous poten- tial for fuel
production, though they have a better potential for alcohol fuels,
as represented in Table 20.
Primary production of biomass through photosyn- thesis is
estimated at 172 billion tons per year (ap- prox. 2 /3 terrestrial
and 1/3 aquatic) [15], which is roughly one-tenth of the standing
biomass present on earth. In terms of energy, the annual biomass
produc- tion is estimated at 3.21 x 1021 J /a [16], assuming a
heating value of 18.6 GJ / t dry biomass. This is very close to the
actual world energy demand of today (see above). A decade ago it
was noted that biomass supplied about one-seventh of the world's
fuel, equivalent to 20 million barrels of oil per day, which
Table 19 Composition and methane potential of municipal
refuse
Chemical constituent Dry weight (%) Methane potential (%)
Cellulose 51.2 73.4 Hemicellulose 11.9 17.1 Protein 4.2 8.3
Lignin 15.2 0 Starch 0.5 O. 7 Pectin < 3.0 - Soluble sugars 0.35
0.5
From Barlaz [58].
was twice the Saudi Arabian oil production and equal to the
daily oil use in the USA [17].
Many developing countries, most notably China (9 million
digesters, serving some 35 million people in rural ares) and India
(over 70000 biogas plants producing annually an estimated 152
million tonnes of biogas, i.e. about 130-140 billion m 3, or some 3
EJ of energy) [18], have been successfully applying anaerobic
digestion of domestic and agricultural waste in small- to
medium-scale biogas generation.
Industrialized countries of the Western hemi- sphere have been
converting most of their agricul- tural waste into fuel ethanol
rather than into biogas, although dedicated fuel crops prevail as
raw materi- als. These nations traditionally continue to
generate
Table 20 World biomass potential for ethanol production
Source Mass(lO 9 t /a) Ethanol equivalents Oil equivalents
Energy (EJ) (109 1) (106 bbl)
Cane and beet molasses 38 11 69 0.23 Cane and beet juice - 5 31
0.11 Bagasse surplus to fuel 24 7.5 47 0.16 Grain, dedicated 23 8
50 0.17 Grain, low grade 80 27 170 0.57 B starch 116 52 327 1.10
Straw, chaff, stover 3 300 1000 6 290 21.20 Cassava, cull 2 1 6
0.02 Cassava, tops 45 14.4 90 0.31 Potato, cull 12 3.8 24 0.08
Jerusalem artichoke, tops 3 1 6 0.02 Forest logging residues + 360
125 786 2.65 non-commercial harvest Plantation forests 60 24 152
0.51 Municipal waste 250 37 232 0.78 Total 4 313 1316.7 8 280
27.91
From Wayman and Parekh [59]. (1 1 C2H5OH approx. 21.2 MJ).
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132 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
Table 21 Composition of municipal solid waste (1986)
Component Percent by wet weight
Paper, paperboard 41.0 Yard refuse 17.9 Food 7.9
Subtotal 66.8 Metals, ceramics 8.7 Glass 8.2 Textile, rubber,
leather, wood 8.1 Plastics 6.5 Inorganic (ash, rock), etc. 1.6
Subtotal 33.1
From Lewis [60].
waste (Table 21), with the highest methane potential for
cellulose, followed by hemicellulose and proteins (Table 19).
Potentially, landfilled refuse could generate 0.13 m 3 methane
per kg dry waste [20], but practically the production has ranged
from 1% to 52% of that value [21].
Sanitary landfills are slow but, due to their large dimensions,
quite productive biogas reactors. It was estimated that more than
825000 tonnes of coal equivalents per year were globally saved by
their methane production, with a tendency to increase further
[22].
most of the biogas from wastewater treatment and solid wastes.
The main reason for this lies in the fact that amounts of domestic
refuse and sewage present formidable waste management and
environmental problems, which can be alleviated by fuel produc-
tion. An estimated average of 1.64 kg MSW per person per day was
generated in the US in 1986 (Lewis, 1989). About 95% of the MSW in
the US was landfilled in 1984 [19].
Man-generated refuse represents an excellent feedstock for
methane/biogas generation by: (i) landfill gas collection; (ii)
anaerobic digestion of MSW in reactors.
It is estimated that more than two-thirds of MSW (on a wet
basis) consist of easily fermentable organic
6. Biotechnology in diesel fuel and gasoline pro- duction from
microalgae
Among the various possible fuels from biotech- nology research
and development, there is consider- able interest to tap the
high-density energy stored in lipids (35.6 MJ/ I for vegetable oil)
as possible alternatives for diesel (39.1 MJ/1) engines. Vehicles
(e.g. public transportation buses) are already testing vegetable
oils, but there is still some controversy over the environmental
benefits vs. risks. However, it will be a lasting endeavour of the
constructors of ICEs (internal combustion engines) to decrease pol-
lutant emission levels and improve fuel efficiency, environmental
safety and overall marketability of
Table 22 Lipid contents of selected microalgae
Species
Monalanthus salina Botryococcus braunii Outirococcus sp.
Scenedesmus obliquus Nannochloris sp. Dunaliella bardawil ( ~ D.
salina)
Navicula pelliculosa Radiosphaera negevensis Biddulphia aurita
Chlorella vulgaris Nitzschia palea Ochromonas dannica Chlorella
pyrenoidosa
Maximal lipid Species Maximal lipid content (% w/w) content (%
w/w) 72 Peridinium cincture 36 53-70 Neochloris oleabundans 35-54
50 Oocystis polymorpha 35 49 Chrysochromulina spp. 33-48 48
Scenedesmus acutus 26 47 Scenedesmus spp. 26
Chlorella minutissima 23 45 Prymnesium parvum 22-38 43 Navicula
pelliculosa 22-32 40 Scenedesmus dimorphus 16-40 40 Scotiella sp.
16-35 40 Ch lorella spp. 15-26 39-71 Euglena gracilis 14-20 36 (72)
Porphyridium cruentum 14 (22)
From Ratledge [36].
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N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 133
diesel engines, which currently use 17% of energy for
transportation purposes [23].
This chapter discusses the substrates, microorgan- isms and
biotechnological processes useful for fuel lipid production. A
relatively limited number of mi- croorganisms can accumulate large
amounts of stor- age lipids under specific growth conditions. Most
productive among them, and industrially the only important ones,
are some yeasts [24] and algae [25]. Yeasts, however, are less
favorable because for lipid production they must grow aerobically,
and that has a negative effect on substrate conversion yields. The
ability of microalgae and cyanobacteria to grow pho-
toautotrophically makes them far more interesting, since algae
cultivation can be directly coupled with carbon dioxide elimination
from power plant flue gas.
Microalgae accumulate up to 60% or more lipids (based on dry
biomass weight) intracellularly (Table 22), and these lipids,
predominantly triglycerides, can be transformed into low-sulfur
diesel substitutes [26]. The extracted triglycerides cannot be used
di- rectly for ICEs, but have to be either transesterified into
low-viscosity and low-melting point esters (e.g. methyl esters), or
catalytically converted into hydro- carbons as gasoline
substitutes. The potential advan- tages and usefulness of such
production seem to have escaped wider attention. Thus, in a review
on microalgae biotechnology from 1987 [27], there was no mention of
a fuel production potential of algae, although a price of (then)
US$ 0.4-0.6 per kg of algae with an average of 30% lipid content
was given for research-level production in unlined solar ponds and
a projected market of at least US$ 100 million.
Studies of extraction and transesterification of algal oils from
Chaetoceros muelleri and Mono- raphidium minutum show similarities
with the trans- esterification of vegetable oils, with the
difference that lipids from these algae had much higher free fatty
acid contents (about 25% FFA) than vegetable oils, and thus an
acid-catalysed reaction with strictly time-controlled duration was
recommended, along with 1-butanol as the most efficient extraction
sol- vent [28]. It was earlier postulated that transesterifi-
cation has the same economical potential as catalytic conversion,
if the by-product glycerol can be mar- keted [26].
Catalytic upgrading of pyrolysed microalgae lipids and whole
cells over medium-pore, shape-selective zeolite (HZSM-5) to a
high-octane, aromatic C-5 to C-10 gasoline was also studied
recently [29]. The studied algae were Chaetoceros muelleri var.
sub- salsum, Monoraphidium minutum, Navicula saprophila, and
Nannochloropsis sp. With the latter two algae at low partial
pressures 50-65% alkenes and 15-25% aromatics were obtained, with
almost no alkanes. Processing of whole algae cells, although highly
desirable because of high extraction costs (5-6 cents per liter oil
at 90% + extraction), gave ambiguous results due to high ash
content (10-50%). Additional research is needed for both
transesterifi- cation and the more promising catalytic
upgrading.
Outstanding among other algae is Botryococcus braunii strain B,
a fresh-water green alga isolated from the so-called 'Boghead Coal'
oil deposits. Rest- ing green cells of this alga produce traces of
hydro- carbons. Fast-growing green cells produce up to 17% of C-27,
C-29, and C-31 dienes, whereas brown resting cells accumulate
70-90% of their dry weight as predominantly two polyunsaturated
terpenoid hy- drocarbons, botryococcene and isobotryococcene (Fig.
18). Under laboratory growth conditions the hydrocarbon content is
lower (up to about 45%). Catalytic cracking of this hydrocarbon
produced 67% gasoline, 15% aviation turbine fuel, 15% diesel fuel
and 3% residual oil [30]. Due to low production rates of 0.12-0.15
g 1-1 d -1 (20-30% more after immo- bilization), that alga is still
not promising as potential fuel producer. This emphasizes the need
for genetic improvement of potential producer strains [31].
Microorganisms accumulate storage lipids when grown under
nutrient limitation. Idealized curves for
Botryococcene
Fig. 18. Structures of botryococcene and isobotryococcene (From
[501).
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134 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
"o ~ r- in medium~,
, , , , / | /C , pid 1% biomass /
0 10 20 30 40 50 60 70 Time (h)
Fig. 19. Idealized pattern of lipid accumulation in an
oleaginous microorganism grown in batch culture (From [36]).
batch and continuous growth are given in Figs. 19 and 20A. The
limiting nutrient is mostly nitrogen, but highly efficient diatoms
had also considerably increased lipid yields under conditions of
silicon deprivation, notwithstanding a concomitant decrease in
biomass yield. Thus for two diatoms, Hantzschia DI-60 [32] and
Cyclotella cryptica [33], the results shown in Table 23 have been
obtained.
The cultivation of algae for the production of cheap oils as
precursors for economically competi- tive fuels, must use
substrates and conditions other than those for food-grade and
specialty chemical production. They can be grown in open ponds, in
marine, brackish or waste water. Thus, algae from municipal sewage
treatment plants were reported to yield up to 50 g dry biomass per
m 2 per day [34]. It
has been estimated that a yield of 25 g m -2 d-~ is less than
10% of the theoretical maximum [35], and with oil contents of
25-50%, these algae would be much more efficient oil crops than
plant seed, with yields from 12.5 to 25 t ha-1 a-1 [36].
A readily available source of carbon dioxide for algae
cultivation is flue gases from power plants. An additional
advantage is the environmentally highly desirable concomitant
contribution to the elimination of waste carbon dioxide. A
conceptual scheme for such a process [37] is represented on Fig.
20B. Recent tests in such a pilot facility in Japan indicate that
an actual flue gas (10-12% carbon dioxide, 70-90 ppm sulfur and
nitrogen oxides) directly blown into the mechanically mixed
raceway-type pond did not adversely affect the growth and photo-
synthesis of Nannochloropsis sp. and Phaeodacty- lum sp. in
seawater. Results were comparable to those obtained with pure
carbon dioxide and with desulfurized flue gas: approximately 10 g m
-z d -~ at 400 Ly /d or half the value from laboratory tests. These
lower yields were attributed to changing illu- mination and
insufficient mixing. Although no at- tempt was made to determine
the lipid content of the algae, such an approach might be a
promising alter- native to algal lipid production.
In conclusion it can be said that in the long range algal lipid
production has a promising potential for fuel, especially diesel
fuel production since prices for such biodiesel have dropped from
between approx. US$ 4.49/1 and US$ 4.76/1 in the early 1980s to
about US$ 0.92/1 in 1992, with opportunities to lower them to US$
0.26/1 [38]. Taxes for carbon dioxide release could make these
fuels even more competitive.
Table 23 Changes of biomass and lipid yields of Hantzschia DI-60
and Cyclotella cryptica under nitrogen or silica deficiency at 20
and 30C
Organism Nitrogen sufficiency Nitrogen deficiency Silicon
sufficiency Silicon deficiency
AFDW a Total lipids Change Change AFDW a Total lipids Change
Change (g/I) (g/ l ) AFDF a (%) lipids (%) (g/ l ) (g/ l ) AFDF a
(%) lipids (%)
Hantzschia 20C 1.314 0.319 - 36 + 15 1.185 0.271 - 17 +48
DI-60
30C 1.582 0.468 - 29 + 28 1.264 0.334 - 16 + 41 Cyclotella 20C
1.114 0.181 - 16 + 120 1.161 0.222 - 16 +38 cryptica
30C 1.321 0.224 - 26 + 88 1.219 0.257 - 27 + 46
Adapted from Sriharan et al. [32,33]. a AFDW, ash-free dry
weight (measured after 5 -7 days of cultivation).
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N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 135
7. Biotechnology in the production of other oxy- genated
alternative fuels and fuel extenders
Butanol has a boiling point of 118C, a heat of combustion of
about 32 MJ/kg, and it is fully miscible with diesel fuel (a
microemulsion), where it acts as a co-solvent. For that reason it
may be interesting to know whether there is some real poten- tial
to produce it biotechnologically.
In 1915 Chaim Weizmann patented his process for the production
of acetone and butanol by fermen- tation of carbohydrates by
Clostridium aceto- butylicum. The interest for this fermentation in
the second year of World War I was enormous, since the british
military industry needed large quantities of acetone as a solvent
in the production of the explo- sive cordite. Scientific research,
although mostly of a serendipitous nature, can have far-reaching
conse-
E~
teck
A
E -t A ow
E2 .o .~_
~-~Biomass
" ~ ~ Nitrogen
. . . . . I ipi(! 1% I , i -m;L ' ; s )~N~l
/ n I I J ~ l
0-1 0-2 Dilution rate (h -I)
CO= Exhaust Gas COs II po., P,n, . i ' ,
Algal Growth Pond Water Recy'elo
Seawater. Nutrients
Nutrients Recycle
I i . l o-.,oo
Fig. 20. (A) Idealized pattern of lipid accumulation in an
oleaginous yeast grown in continuous culture (From [36]). (B)
Conceptual system of algae-based bioprocess for CO 2 removal (From
[51]).
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136 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
NAD + NADH + H + ~l ' CHz-CHOH-COOH I < ~ z j cH3_co_coo
H
Lactate Pyruvete
J
CHs-COOi.I e . - . ~ t, Acott, C.,-CO-CH -CO-CoA
Acetyl-P CoA Acetyl-CoA CoA Acetoaeetyl- CoA ATP ADP -i
Co.A ~ ~trrr ] -c ,a
CHs-CH0 CH3-CO-CHz-C00H Acetaldehyde Acetoecetate
Ethanol Acetone
FdHs e ) F~
Reactions in Clostri- dium acetobutylicum leading to the
formation of organic acids and solvents. 1, reactions of the
Embden-Meyerhof-Pamas path- way: 2, lactate dehydrosenase: 3,
p.vruvate: ferredoxin oxidore- ductase 4, ferredoxin: NAD *
oxidoreductase; 5, ferredoxin NADP" oxidoreductase; 6, hy-
drogenase; 7, phosphotransace- tylase: 8, acetate kinase: 9,
acetaldehyde dehydrogenase; 10, alcohol dehydrogenase: 11,
B-ketothiolase; 12, acetoacetyl- CoA: butyrate/acetate CoA
transferase; 13, acetoacetate de- carboxylase: 14, p-hydroxybuty-
ryl-CoA dehydrogenase: 15, crotonase; 16, butyryI-CoA de-
hydrogenase; 17, phosphotrans- butyry, lase; 18, butyrate kinase;
19, butyraldehyde dehydrogen- ase; 20, butanol dehydrogenase
l CH3-CHz-CH2-CH20H Butanol
CH3-CHz-CHz-COOH Butyl'ate I
Fig. 21. Biochemistry of the acetone-butanol-ethanol
fermentation (From [52]).
CH 3- CH z- CH z-CH0 Bu*.yraldehyde
t
2 ~ NADPH + H
NADP +
CHs-CHOH-CHz-CO-CoA - Hydroxybutyryl - CoA
t~HzO
CHs-CH=CH-C0-CoA Crotonyl- CoA
te~-- NADH + H + NAD
CHs-CHz-CHz-C0-CoA Butyryl - CoA
N A D ~ CoA
CH~-~-Iz-CHz-CO- 0 Butyryl-P
, e~ ADP ATP
-
N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 137
quences for human life, history, and even politics. In his 'War
Memoirs' David Lloyd George, who was Chairman of the Munitions of
the War Committee at the time, recounts that the Crown was so
grateful to Weizmann for acetone from the ABE process, that this
led to the famous Balfour Declaration, which enacted Palestine as
the Jewish national home [39].
However, since much cheaper feedstocks and more efficient
processes for acetone and butanol were later provided by
petrochemistry, the ABE fermentation went into obsolescence. Today
this well established technology is used in only a few places, most
notably in the Republic of South Africa, where again politics,
along with economic and climatic factors, have contributed to the
survival of the pro- cess. The interest for this fermentation has
never ceased and many improvements have been made since the gradual
disappearance of ABE fermentation after World War II.
The biochemistry of the process (Fig. 21) and its technological
features are well characterized [40,41].
The main advantage of this technology lies in the fact that
Clostridium acetobutylicum and C. beijer- inckii, the two principal
microorganisms, ferment not only hexoses but also pentoses from
hemicellulose, and can utilize a vast array of adequately
pretreated substrates.
The main drawbacks of ABE fermentations are: (i) low solvent
yields (30-35% by weight of
carbohydrate); (ii) low solvent concentration due to butanol
tox-
icity (usually 20-25 g/l); (iii) difficult and costly recovery
by distillation; (iv) phage sensitivity; (v) autolysin-induced
culture autolysis by the end
of the exponential phase; (vi) yield lowering due to ethanol
production.
Many of these problems have been partly solved by mutant
selection and genetic engineering of the commercial strains.
However, the economically most promising alternative to a cheaper
butanol as a diesel fuel extender seems to be in the improvement of
low-energy product recovery [42]. Anyhow, fermen- tation butanol is
not likely to outcompete petrochem- ical butanol in the near
future.
8. Biotechnology in direct energy conversion: mi- crobial fuel
cells
This chapter gives a brief description of specific and unique
processes of energy generation from fuels, rather than processes of
energy conservation in the form of fuels.
Oxidation A products "
Fuel ---'- -7
f
\
F .~ Load ~.
e e
Anode lCothod.
e
Reduced ~ oxidant Mediator
red)
e e
J Mediator (ox)
H + p
I
Oxldont
V Ion-exchange membrane
Fig. 22. Schematic diagram of a microbial fuel cell (From
[44]).
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138 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
Energy-rich chemical bonds of a fuel can be broken by the action
of oxidants. Thereby an overall redistribution of electric charge
between the partici- pating molecules of fuel and oxidant takes
place. The
fuel is being reduced, losing some of its internal energy in the
form of electrons. Simultaneously, the oxidant increases its
internal energy content by gain- ing the same electrons. The free
energy of the reac-
R,Nka ~ . ~ ~J t t t~ ~ . = i .~ ,M ptmr,wia, (~). ,,,.=i,,,.~
am~m,= .e.,w,lh (A.J
C a,., $1t~Ktutal formul,i Redox Incdillor (V) (lun)
C .#{,CHz- - I~~/N- -CH:C ,H , gena# viololcn -0.359 YEI
Cl %_._ ~
O==~:y~=N--~__~OH Z.e.~icmorot,l~'uotlnUot~e,,oI +0.217
cI N~ PIIENAZINES ~nazifl tho~ulphale +0.065
I CzH,
CH~ N.~ CH~
Hz N i NH: Sairanine-O -0 289 512 CH,)
SO~- PHENOTHIAZINES
(CHt)2N/~:~ O Alizm'in Brillian, Blue -0.173 641
OH
SOl ~ SOs-
CH,HN
N.N-dimet hyl-di~ulphonat cd iheonine +0+~"0 620
C:HsHN S 1~/ C:H,
Mclhylene Blue +0.011 f~l
New Methylene Blue -0.021 590
~ O ~.o~.++z,~,~ 0 13o s.o Fig. 23. Redox mediators and their
mid-point potentials (ETm) and maximum absorbance wavelengths (Area
x) (From [44]).
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N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 139
llzN NI4.,
fCH~)2N ..
C~H
( C I l O z N ~ 0 OH
HO, ,~N~O I~.soeurm
+0.064
Toluidlne BhJe-O +0.034
0.04"/ PHENOXAZINES
BliUilnl Cfesyl Blue
G:tll~'yanin +0.021
-o.~t
Fig. 23 (continued).
F/2
tion is negative, i.e. the reaction is spontaneous, and under
normal circumstances of fuel combustion, this free energy performs
volumetric work, causing the gaseous reaction products to expand.
If the process is rapid enough, or, in other words, operating with
a sufficient power output, we have the thermodynamic rationale of
internal combustion engines.
There are, however, other possible routes to chan- nel and use
the free energy liberated from fuels. This has been recognized as
early as 1839 by Growe and 1884 by Ostwald. Systems in which the
direct con- tact of fuel and oxidant molecules is prevented and the
electric charge transfer from fuel to oxidant is intercepted by a
galvanic element coupled to an external circuit are called fuel
cells. They are direct converters of chemical into electric energy,
operating much more efficiently than power plants. Theoreti- cally,
any organic or inorganic compound or a mix- ture can serve as a
fuel, provided it is oxidized by the appropriate organism. E.g. for
glucose:
C6H1206 q- 6H20 ~ 6CO 2 + 24e-+ 24H +
Conventional fuel cells must operate at high tem- peratures
and/or under extremes of pH if the neces- sary activation energy
for fuel oxidation at the anode is to be reached. The same can be
achieved much
more elegantly and at low temperatures by letting the redox
machinery of living cells, or isolated oxidore- ductases, do the
activation job and mediate in the transfer of electrons from fuel
to anode. This transfer can be direct, but for better coulombic
yields and a higher rate of charge transfer (higher currents) it is
necessary that the electron transfer be mediated by a reversible
redox couple. Since the power output of fuel cells is directly
proportional to the electromotive force of the cell, it is
desirable that the reduction potentials of the mediator molecule be
as low as possible. If live aerobic ceils are used, the mediator
molecule, apart from having long-term stability and being
water-soluble, has to be able to reversibly cross the cell membrane
and in its oxidized state to interact with the lowest-potential
points in the elec- tron transport chain (or at more than one
reaction site along it) [43].
The principle of operation of a microbial fuel cell is shown in
Fig. 22, along with examples of mediator molecules (Fig. 23). Both
are taken from Roller et al. [44].
An interesting microbial fuel cell design was de- scribed [45]
in which carbohydrates (simple sugars, starch) or hydrocarbons
(crude oil) were fed to a mixed culture of Proteus vulgaris,
Escherichia coli,
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140 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
CO2 H20
~ / SO4"
'~ bacteria ~ H* '~ S -o lyOz
02
CxHyOz (fuel) + trace elements
Fig. 24. Biochemical fuel cell with sulfate reduction (From
[45]).
Pseudomonas aeruginosa and Desulfovibrio desulfu- ricans in
0.1-0.5% sodium sulfate solution, solidi- fied as a bulky microbial
anode with clay or slate dispersions. Here the energy of the
organic molecules is coupled to sulfate reduction. The generated
sul- fide, a tertiary fuel, served as the anodic redox
mediator:
Biological reactions ( (CH20) is simplified carbo- hydrate
fuel):
2 < CH20 > +2H20 ~ 2CO 2 + 8H++ 8e-
SO42- + 8H++ 8e-~ $2-+ 4H20
Anode reaction:
S 2- + 4H20 ~ SO42- + 8H + 8e-
(and 8 /3S2- + 4H20 ~ 4/3S2032- + 8H++ 8e-
Cathode reaction:
20 2 + 8H++ 8e-~ 4H20
The principle of operation is shown in Fig. 24. This biochemical
fuel cell was shown to offer a
problem- and maintenance-free operation for 5 years.
Purified water
/Cathode~k
Anode Waste-water Slate materials Fig. 25. Construction of a
wastewater fuel cell with slate materials (From [45]).
It had a storage capacity of up to 0.2 A cm -2, and could
provide a current of 6 A /kg cell weight (1 h continuous load), or
15 A /kg (10 min continuously).
The same authors patented also a similarly built waste water
fuel cell, shown on Fig. 25. The waste elimination efficiency
achieved in short-period incu- bation, daily for 6 months, is
represented in Table 24.
The basic disadvantages of microbial fuel cells are their
generally low coulombic yields and low power outputs, attributed to
pH variation during operation and low fuel storage capacities. Many
more improvements, especially improvements of the electrode
materials and construction will be neces- sary, before biological
fuel cell production and use can be commercialized.
However, miniaturized versions of such systems, not meant as
power sources though in an advanced state of development and
marketed worldwide, con- stitute a large subgroup of
biosensors.
Table 24 Wastewater purification efficiency of a fuel cell Type
of wastewater TOC (mg/1) COD (mg/I) Incubation time (h) Degradation
(%)
Sewage works effluent 50 140 0.5 35 (fulvic acids) Effluent from
landfill 2 000 6 000 2 65-75
From Habermann and Pommer [45]. TOC, total organic carbon; COD,
chemical oxygen demand.
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N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16 (1995)
111-142 141
References
[1] Cole, G.H.A. (1992) Provision of the world's energy need.
Energy World 199, 15-19.
[2] Kosaric, N. and Duvnjak, Z. (1988) Ethanol. In: UUmann's
Encyclopedia of Industrial Chemistry, Vol. A9 (Lederberg, J., Ed.),
pp. 587-653. Academic Press, New York, NY.
[3] Flickinger, M.C. (1980) Current biological research in con-
version of cellulosic carbohydrates into liquid fuels: how far have
we come? Biotechnol. Bioeng. Symp. 22 (Suppl. 1, Ferment.: Sci.
Technol. Future), 27-48.
[4] Shazer, W.H. and Speckman, P.A. (1984) J. Dairy Sci. 67
(Suppl. 1), 50.
[5] Motwani, M., Seth, R., Daginawala, H.F. and Khanna, P.
(1993) Microbial production of 2,3-butanediol from water hyacinth.
Bioresource Technol. 44, 187-195.
[6] Faison, B.D. (1991) Biological coal conversions. CRC Crit.
Rev. Biotechnol. 11, 347-366.
[7] Cohen, M.S. and Gabrielle, P.O. (1982) Degradation of coal
by the fungi Polyporus oersicolor and Poria monticola. Appl.
Environ. MicrobioL 44, 23-27.
[8] Wondrack, L., Szanto, M. and Wood, W.A. (1989) Depoly-
merization of water soluble coal polymer from subbitumi- nous coal
and lignite by lignin peroxidase. Appl. Biochem. Biotechnol.
20/21,765-780.
[9] Scott, C.D., Strandberg, G.W. and Thewis, S.N. (1986)
Microbial solubilization of coal. Biotechnol. Prog. 2, 131-
139.
[10] Davison, B.H., Nicklaus, D.M., Misra, A., Lewis, S.N. and
Faison, B.D. (1990) Utilization of microbially solubilized coal:
preliminary studies on anaerobic conversion. Appl. Biochem.
Biotechnol. 24/25, 447-456.
[11] Ackerson, M.D., Johnson, N.L., Le, M., Clausen, E.C. and
Gaddy, J.L. (1990) Biosolubilization and liquid fuel produc- tion
from coal. Appl. Biochem Biotechnol. 24/25, 913-928.
[12] Scott, C.D., Woodward, C.A., Thompson, J.E. and Blank-
ship, S.L. (1990) Coal solubilization by enhanced enzyme activity
in organic solvents. Appl. Biochem. Biotechnol. 24/25, 799-814.
[13] Wheatley, B.I. (1980) The gaseous products of anaerobic
digestion - - biogas. In: Anaerobic Digestion (Stafford, D.A.,
Wheatley, B.I., Hughes, D.E., Eds.), pp. 415-428. Applied Science
Publishers, London.
[14] Buswell, A.M. and Mueller, H.F. (1952) Mechanisms of
methane fermentation. Ind. Eng. Chem. 44, 550-552.
[15] Szmant, H.H. (1986) Industrial Utilization of Renewable
Resources, Technomic Publishing Co., Thancaster, Basel.
[16] Whittaker, R.H. and Likens, G.E. (1975) The biosphere and
man. In: Primary Productivity of the Biosphere (Lieth, H. and
Whitaker, R.H., Eds.), pp. 305-328. Springer Verlag, New York,
NY.
[17] Zsuffa, L. (1982) The production of wood for energy. In:
Energy from Forest Biomass (Smith, W.R., Ed.), pp. 5-17. Academic
Press, New York, NY.
[18] Aziz, M.A. (1991) Biogas: an assessment of potentials,
tech- nologies and utilization in Asia. In: Energy and Environmen-
tal Progress. 1. Volume B: Solar Energy Applications, Bio-
conversion and Synfuels (Veziroglu, T.N., Ed.), pp. 419-439.
Nova Science Publishers, New York, NY.
[19] Carra, J.S. (1987) Design criteria for sanitary landfills:
the American concept. Proc. ISWA Symp. Process Technol. Environ.
Impact Sanit. Landfills, Cagliari, Sardinia, Italy, October 20-23.
Stanford, CA.
[20] Halvadakis, C.P. (1983) Landfill methanogenesis: literature
review and critique. Technical Report No. 271, Department of Civil
Engineering, Stanford University.
[21] Ham, R.K., Hekimian, K.K., Katten, S.L., Lockman, W.J.,
Lofy, R.J., McFaddin, D.E. and Daley, E.J. (1979) Recovery,
processing, and utilization of gas from sanitary landfills. EPA
Publication No. 600/2-79-001, Municipal Environmen- tal Research
Laboratory, Cincinnati, OH.
[22] Richards, K. (1988) Gas from waste makes growing contri-
bution to fuel supplies. Energy Man. 1, 25.
[23] American Solar Energy Society (1992) Economics of Solar
Energy Technologies, American Solar Energy Society, Boul- der,
CO.
[24] Rattray, J.B.M. (1988) Yeasts. In: Microbial Lipids. Vol. 1
(Ratledge, C. and Wilkinson, S.G., Eds.), pp. 555-697. Academic
Press, London.
[25] Wood, B.J.B. (1988) Lipids of algae and protozoa. In: Mi-
crobial Lipids Vol. 1 (Ratledge, C. and Wilkinson, S.G., Eds.), pp.
807-867. Academic Press, London.
[26] Neenan, B., Feinberg, D., Hill, A., Mclntosh, R. and Terry,
K. (1986) Fuels from Microalgae: Technology Status, Poten- tial,
and Research Requirements, Solar Energy Research Institute,
SERI/SP-231-2550, Golden, CO.
[27] Benemann, J.R., Tillet, D.M. and Weismann, J.C. (1987)
Microalgae biotechnology. Trends Biotechnol. 5, 47-53.
[28] Nagle, N. and Lemke, P. (1990) Production of methyl esther
fuel from microalgae. Appl. Biochem. Biotechnol. 24/25,
355-361.
[29] Milne, T.A., Evans, R.J. and Nagle, N. (1990) Catalytic
conversion of microalgae and vegetable oils to premium gasoline
with shape-selective zeolites. Biomass 21, 219-232.
[30] Hillen, L.W., Pollard, G., Wake, L.V. and White, N. (1982)
Hydrocracking of the oils of Botryococcus braunii to trans- port
fuels. Biotechnol. Bioeng. 24, 193-205.
[31] Dunahay, T.G., Jarvis, E.E., Zeiler, K.G., Roessler, P.G.
and Brown, L.M. (1992) Genetic engineering of microalgae for fuel
production. Appl. Biochem. Biotechnol. 34/35, 331- 339.
[32] Sriharan, S., Bagga, D. and Sriharan, T.P. (1990) Effects
of nutrients and temperature on lipid and fatty acid production in
the diatom Hantzschia DI-60. Appl. Biochem. Bioteehnol. 24/25,
309-316.
[33] Sriharan, S., Bagga, D. and Nawaz, M. (1991) The effects of
nutrients and temperature on biomass, growth, lipid produc- tion
and fatty acid composition of Cyclorella cryptica Reimann, Lewin,
and Guillard. Appl. Biochem. Biotechnol. 28/29, 317-326.
[34] Pearson, H.W. (1987) Algae associated with sewage treat-
ment. In: Microbial Technology in the Developing World (DaSilva,
E.J., Dommergues, Y.R., Nyns, E.J. and Ratledge, C., Eds.), pp.
260-288. Oxford University Press, Oxford.
[35] Shifrin, N.S. and Chisholm, S.W. (1980) In: Algal
Biomass
-
142 N. Kosaric, J. Velikonja / FEMS Microbiology Reviews 16
(1995) 111-142
(Shelef, G. and Soeder, C.J., Eds.), pp. 627-645. Elsevier/North
Holland, Amsterdam.
[36] Ratledge, C. (1989) Biotechnology of oils and fats. In:
Microbial Lipids, Vol. 2 (Ratledge, C. and Wilkinson, S.G., Eds.),
pp. 567-668. Academic Press, London.
[37] Negoro, M., Shioji, N., Miyamoto, K. and Miura, Y. (1991)
Growth of microalgae in high CO 2 gas and effects of SO x and NO x
. Appl. Biochem. Bioteehnol. 28/29, 877-886.
[38] Wyman, C.E. and Goodman, B.J. (1993) Biotechnology for
production of fuels, chemicals, and materials from biomass. Appl.
Biochem. Biotechnol. 39/40, 41-59.
[39] Litvinoff, B. (1982) The Essential Chaim Weizmann. The Man,
the Statesman, the Scientist. pp. 184-185. Weidenfeld and Nicolson,
London.
[40] Volesky, B. and Szczesny, T. (1983) Bacterial conversion of
pentose sugars to acetone and butanol. Adv. Biochem,
Eng./Biotechnol. 27, 101-118.
[41] Lovitt, R.W., Kim, B.H., Shen, G.J, and Zeikus, J.G. (1988)
Solvent production by microorganisms. CRC Crit. Rev. Biotechnol. 7,
106-186.
[42] Ennis, B.M., Gutierrez, N.A. and Maddox, I.S. (1986) The
acetone-butanol-ethanol fermentation: a current assessment. Proc.
Biochem. 21, 131-147.
[43] Allen, R.M. and Benetto, H.P. (1993) Microbial fuel cells:
electricity production from carbohydrates. Appl. Biochem.
Biotechnol. 39/40, 27-40.
[44] Roller, S.D., Benetto, H.P., Delaney, G.M., Mason, J.R.,
Stifling, J.L. and Thurston, C.F. (1984) Electron-transfer coupling
in microbial fuel cells: 1. Comparison of redox- mediator reduction
rates and respiratory rates of bacteria. J. Chem. Technol.
Biotechnol. 34B, 3-12.
[45] Habermann, W. and Pommer, E.H. (1991) Biological fuel cells
with sulphide storage capacity. Appl. Microbiol. Biotechnol. 35,
128-133.
[46] BP Statistical Review of World Energy (1986) British
Petroleum Company p.i.c., London.
[47] Frisch, J.R. (1986) Energy abundance: myth or reality?
Paper presented at the 13th Congress of the World Energy Confer-
ence, Cannes, France, October.
[48] Veziroglu, T.N. (1987) Int. J. Hydrogen Energy 12,
99-129.
[49] Kosaric, N. (1990) Development of short-residence time
ethanol fermentation processes. Proc. XIV Conf. Energy from Biomass
and Wastes, Lake Buena Vista, FL, January 29-February 2.
[50] Finnerty, W.R. (1989) Microbial lipid metabolism. In: Mi-
crobial Lipids. Vol. 2 (Ratledge, C. and Wilkinson, S.G., Eds.),
Academic Press, London, pp. 525-566.
[51] Negoro, M., Shioji, N., Ikuta, Y., Makita, T. and Uchiumi,
M. (1992) Growth characteristics of microalgae in high-con-
centration CO 2 gas, effects of culture medium trace compo- nents
and impurities thereof. Appl. Biochem. Biotechnol. 34/35,
681-692.
[52] Bahl, H. and Gottschalk, G. (1988) Microbial production of
butanol/acetone. In: Biotechnology. Vol. 6b (Rehm, H.J., Ed.), pp.
1-30. Verlag Chemic, Weinheim.
[53] Runnalls, O.J.C. and Mackay, D. (1989) Energy growth. In:
Environmental Science and Engineering (Henry, J.G. and Heinke, G.W.
Eds.), pp. 46-85. Prentice Hall, Englewood Cliffs, NJ.
[54] Vergara, W. (1980) Proe. IV Int. Symp. Alcohol Fuels
Technol. Sao Paolo, Brazil, October, p. 143.
[55] Lindeman, L.R. and Rocchicciolo, C. (1979) Ethanol in
Brazil: brief summary of the state of industry in 1977. Biotechnol.
Bioeng. 21, 1107-1119.
[56] Maddox, I.S. (1988) Microbial production of 2,3-butanediol.
In: Biotechnology. Vol. "19 (Rehm, H.J., Ed.), pp. 31-50. Verlag
Chemie, Weinheim.
[57] Magee, R.J. and Kosaric, N. (1987) The microbial produc-
tion of 2,3-butanediol. Adv. Appl. Microbiol. 32, 89-161.
[58] Barlaz, M.A., Ham, R.K. and Schaefer, D.M. (1990) Methane
production from municipal refuse: a review of enhancement
techniques and microbial dynamics. Crit. Rev. Environ. Con- trol
19, 557-584.
[59] Wayman, M. and Parekh, S.R. (1990) Crops that go on
forever. In: Biotechnology of Biomass Conversion: Fuels and
Chemicals from Renewable Resources. pp. 11-17. Prentice Hall,
Englewood Cliffs, NJ.
[60] Lewis, J. (1989) What's in the solid waste stream. EPA J.
15, 15.