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Biomass plants

The comprehensive utilization of resources is Nature's strategy for using solar energy to keep the biosphere in balance. Planet Earth intercepts about 21000 MJ of solar energy per square meter and year, but the hydrological cycles and weather systems only leave about 4200 for heating the ecosystems and for running their internal water and mineral cycles. Half of this goes to photosynthesis, which is Nature's great engine for recycling and for genetic adaptation.

This engine utilizes the solar energy to produce biomass and oxygen from water and carbon dioxide, and it needs about a decade to recycle all living matter on the planet. This is in the order of 2000 billion tons, out of which perhaps 200 billion tons dry weight is plant biomass. Out of this man "borrows" about 1 % for his needs of fuel, food, fodder, fiber and building materials.

However, satisfying those needs also required the development of a variety of technologies which depend on a large-scale and capital intensive utilization of non-renewable mineral and fossil resources. This has produced an industrial society which favors specialization and centralization, but which also has a tendency to disregard the environ-mental, social and demographic side effects.

In many parts of the world the negative effects, like diffuse emissions, have now reached proportions which cause concern and raise questions about break-through "nature-oriented technologies" that could balance the undesirable consequences of specialization and centralisations. Obviously this calls for a quantum-jump in the agroindustrial utilization of biomass, both in terms of new crops and new processing technologies.

Different plants vary greatly in their photosynthic efficiency led by sugar cane which can reach more than 100 tons dry weight per ha and year (South Texas). Other examples are Durra 76 tons dw/ha/year (Puerto Rico), Eycalyptus 60 (California), Kenaf 49 (Florida),Water Hyacinth 39 (Florida) Sudan grass 38 (California), Sunflower 33 (Russia), Salix 30 (Sweden) and Alfalfa 20 (New Mexico), Polulus 20 (Pennsylvania) and Bamu 12 (South East Asia).

Just like grains, many of those crops are separated in a commercial product (sugar from sugar cane) and an agricultural residue (tops and bagasse in the case of sugarcane). Since utilization of plant resideus as fodder or as soil conditioner involves storage, transport and market-ing costs, they infringe on the core operations, so they often end up as in-house fuel or simply as a waste that needs to be treated. This is often neglected, which means that industries which upgrade biological resources, like sugar and starch (for instance the food-, beverage -and fermentation industries), are often regarded as notorious polluters. This often strikes bioengineers and ecologists as strange in view of the multiple uses which have been developed for such materials.

However, even in the case of the dominant and most complex component of biomass, the lignocellulose, the pulp-and paper industry has demonstrated the feasibility of water recycling and of recovering both process chemicals and the energy content of its waste streams. The problem is that this calls for very large and highly specialized facilities at the cross-roads of long transports routes both for inputs and outputs.

Towards a comprehensive utilization of plant materials

The challenge can thus be formulated:† can "Biorefineries" be de-signed which are scale-neutral, emission-free and energy-and water-saving, at the same time as they separate biomass in components that are all so commercially viable that they leave no waste. Biogas as a well-known ultimate destination for organic materials that can find no other uses is left out of this report.

With this reservation, the strategy must be based on a first separation in seeds, green material and residues. All three components then follow separate but partly intersecting processing lines.

The aim of this report is to concentrate attention on the four areas indicated in bold letters, and to do this in the context of a biorefinery aimed at drastically reduced emissions. It is suggested that this can be done by relying on a combination of steam separation and simple extraction processes. Considering the environmental and other constraints in developing countries, the use of mechanical and physical separation techniques (steam explosion, membrane filtration and supercritical extraction) has been seen as preferable to the use of potentially harmful organic solvents. Consequently only steam explosion will be discussed in any detail, since it can serve as a core technology to which many others can be added on.

a. Seeds

The global interest in vegetable oils is a good indicator of a growing interest in biomass in preparation for 1/ the inevitable depletion of fossil oil reserves (80-100 years), 2/ the possibility that biofuels become competitive when fossil oil prices go above 20 $US per barrel 3/ environmental pressures that call for carbon dioxide recycling, reduced emissions of sulphur dioxide and aromatic compounds, and also for safer handling.(sunflower oil's flashpoint is 215^oC, compared with 77^oC for diesel) and finally 4/political wishes to differentiate agri-culture in order to keep the farmers on the land.

Of course the growing of crops for energy is nothing new even in industrialized countries where, some decades ago, it was not unusual that 30 % of the total rural area was used to feed animals for work (horses, mules, cows). Now the area needed to produce enough ethanol or oil to move tractors and farm machines is 10 % (Biofuels, 1995) . In fact, it is not too difficult to visualize farms that are net exporters of energy ,provided that they use an appropriate mix of liquid biofuels and biogas and in addition support their crops with biological nitrogen fixation and biological insect control.

There are more than 300 plant species which produce vegetable oils that are normally contained in the seeds or fruits. The oil is pressed out after preheating, followed by solvent extraction of the expeller feed stuff, and this is then normally used as a protein fodder which helps to cover the processing cost. Deodorization and bleaching is not necessary for fuel applications which however might require transesterification into vegetable oil esters which then perform just like an ordinary diesel oil.

If the vegetable fuel would become a major bulk product the glycerol split off in this process might constitute a problem on the world market. This illustrates one of the many needs for industrial clustering which ZERI advocates. After all, the glycerol could find use for the synthesis of polyglycerols and† hydrophile centers of emulsifiers that might replace ethoxylates in non-ionic detergents and also for the synthesis of specific surfactants.

Rape and sunflower oil have been studied in considerable detail and "FAL Biosystemtechnik" has presented the following mass flow diagram for 1 hectare (Biofuels, 1995):

Fig.2

This means that almost half of the crop's energy (straw: 78,2 GJ/ha out of 56 GJ/ha) is plowed down in the field, begging the question if the value as soil conditioner outweighs the chemical value of the lignocellulose. Modern co-composting techniques for solid waste (Rondeco, 1995) ought to be a cheaper soilconditioner that a homogenous chemical feedstock such as straw.

Photosynthesis of course serves as a carbon sink which the greenhouse effect might force us to expand, for instance with the help of carbon dioxide taxes paying for global reforestation programs and for the opening of new areas for photosynthesis.

For thousands of years the fertility of the planet's coastlines have been destroyed by erosion. However, according to Carl Hodges (1993), the loss of land to the sea can now be reversed by the use of salt-tolerant plants. Dry coastal ecosystems should be regarded as a major natural resource and Hodges has estimated that there are actually over 50 million hectares of arid lands, suitable for halophyte farms, along the world's sea coasts. He has shown that this land could be used both for raw material production and as a very substantial carbon sink.

Plantations of the oil seed Salicornia would yield 20 tons ha/year of biomass above ground. The oil has many financially attractive uses, but only a third of the carbon in the soil can be expected to enter long term storage. Actually, out of 7,5 ton carbon stored per hectare 4,3 is returned to the atmosphere. If Man would like to exploit the capacity of arid lands to the hilt, not only for producing valuable biomass, but also as a carbon dioxide sink, he would obviously have to consider uses of straw that have a long turn-over time, for instance in the form of building materials. This has actually led the Biofocus Foundation to suggest trial runs on Salicornia straw, using the steam explosion technique that will be discussed later.

b. Green material

Leaf Protein Concentrate (LPC) has a well documented value as a protein-, vitamin- and iron source for children and it has a long history of application in poor countries. The protein is then often heat coagulated and filtered off for use as food, leaving a sugar-rich liquid which can serve as a fermentation substrate. The green juice can also be used, either directly, or after drying and pelletization, as an excellent feed for pigs, poultry, fish etc, notably because of its content of vitamins and proteins. In fact, such "health foods for animals" provides an attractive means to eliminate/reduce the use of antibiotics in intensive farming and to increase fertility.

In this paper LPC† will only be considered in the context of a comprehensive utilization of biomass, where high value components might help to support an overall zero-emission goal. This must of course take the lignocellulose residues into account, and it is in this context that the steam decompression method, developed by E.A.DeLong (the Tigney process) deserves special attention.

This method permits the utilization, not only of "throw-outs" such as straw and bagasse, but also the woody parts of green plants grown under conventional farming conditions after the green juice has been removed in a press and further upgraded for instance by fermentation. The possibility to integrate various products (such as yeast cells), into feeds for fish and other small animals (such as chicken and guineapigs) ought to be in the back of the mind of all scientists working on zero-emission recycling projects.

An economically interesting use of green juice is as a source of natural products including not only proteins, vitamins and minerals, but also aroma compounds, fine chemicals and human health-food constituents. The relative abundance and economic importance of a given component is then of course related to the plant selected. It is for instance possible to isolate pure fraction 1 protein (ribulose 1,5-diphosphate carboxylase) for medicinal and nutritious use, carotenoids and terpenoids for food colouring, flavors and health food, flavanoid glucosides for anti-inflammatoric use etc. In some instances the job.-creating capacity of such initiatives could be very great..

Still more rewarding, economically and scientifically, is the introduction of genes which make plants express selected proteins or other compounds of therapeutic interest. This can be performed in several ways, the most obvious one being the development of transgenic plants. Major advantages of using plants over classical fermentor procedures are that commonly encountered problems such as infections and growth retardation are circumvented and that scaling-up is notably easier.

Such studies, initiated by C. Enzell within a Swedish Tobacco Co project in 1988, were carried out by Professor Lars Rask (Cell Research, BMC, Uppsala University). He demonstrated, in colla- boration with a Swedish pharmaceutical company, that the tobacco plant can be altered genetically to express tPA (tissue plasminogen activator) in concentrations of 3-4 µg/g green leaf tissue. This compound, which is effective against thrombi and acute cardiac infarction, has a potential market which has been estimated to be around10¹⁰† SEK.

†It was also shown, by the group mentioned, working within the same project, that tobacco could also be transformed to express IGF-1 (insulin-like growth factor-1), a cell stimulating factor which fairly recently has been found to improve certain defects related to aging, i.e. to increase the lean body mass and the skin thickness, and to decrease the adipose tissue mass.

An alternative approach to that practiced in the studies mentioned, has been applied by Biosource Genetics, Vacaville, California, USA. Here tobacco mosaic virus is genetically trans-formed and used to infect regular tobacco growing in the field. The plant then expresses the protein selected.

The usefulness of this technique has been amply demonstrated in field studies, e.g. by isolation of the protein trichosantin (com-pound Q) from field-grown tobacco infected by the cloned virus. The potential of this approach for the production of human albumin has been considered by a group including representatives from Swedish companies and Biosource Genetics. Although all involved parties found the approach attractive, notably because the product would be completely safe from a HIV point of view, the project was not initiated since the production unit of the pharmaceutical company involved postponed the operation.

Another highly interesting compound, which could be produced in either of the above manners, is a bacteriolytic agent which has the potential of serving as a non-allergenic and anti-inflammatory drug. A remarkable spectrum of activities has been demonstrated in animal tests, and the potential of the substance to serve as an alternative to some antibiotics has made the Biofocus Foundation suggest that its production ought to be the target for a ZERI task-force, once the envisaged Biorefinery is in place. The fact that the structure is known , the gene is available and a close relative has been expressed in tobacco, makes this drug a very attractive candidate for a major effort coordinated by an interested leading expert in the field.

In conclusion it should be noted that tobacco has roughly the same climatological requirements as the coca bush, so a profitable competitive crop might have many advantages.