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Potential and promises
The near-term opportunities for bio-processing can be summarized briefly as follows:
- the production of organic chemicals with the aid of big-catalysts, e.g. enzyme technology (fine chemicals, starch and cellulose, bio-polymers), fermentation products (ethanol, single cell protein, antibiotics, nitrogen fixation for fertilizers), and animal and plant cell cultures;
- the use of biomass for fuel and energy production;
- food production and processing;
- the production of industrial materials (e.g. vegetable oils, pulp, and paper) from biomass.
A few examples will help to put the situation in perspective.
Enzymic conversions, as a consequence of the potential advantages mentioned, are in an excellent position to contribute to a cleaner environment. The use of enzymes offers industry an opportunity to replace processes using aggressive chemicals with mild big-processes exhibiting minimal impact on the environment. The raw materials come from agriculture. Also the effluents are non-toxic, although they contain nitrogen, phosphorus, and organic matter. This leads to high amounts of wastes in the water. The major part of the spent dry matter is collected as a sludge and then spread on nearby farmland. The sludge consists of dead biomass, filter aid, nutrient surplus, and an insoluble residue.
In 1990, Novo Nordisk, a Danish pharmaceutical manufacturer, reused 500,000 m3 of sludge containing 5 per cent dry solids including 800 metric tons of nitrogen and 285 metric tons of phosphorus. The sludge instead acts as an efficient slow-releasing N-P fertilizer: more than 90 per cent of N is bound in organic matter, which means that the evaporation of ammonia is minimal. Figure 3.1 depicts the situation of this enzyme production plant, which fits nicely into an ecological cycle with agriculture (Falch 1991; Novo Nordisk 1993). The full-scale process, now in operation, is shown in the diagram.
Biological control agents (big-pesticides)
A big-pesticide is a living organism or a product derived from microorganisms or plant sources that kills the pest in order to sustain its own growth cycle. The characteristics of a big-pesticide are pest specificity, environmental stability, safety, and low cost. Bio-control agents, despite being new entrants in the field, have already made substantial contributions in preserving the fertility of the soil, maintaining an ecological balance, and preventing resurgence of pests. This has been achieved with little harm to non-target animals and plants and with few side-effects. The potential of big-toxins being active as insecticides, herbicides, and fungicides is basically known. However, widespread practical application is still in the wings, mainly owing to high costs.
Fig. 3.1 Closed-cycle technology in the Novo Nordisk enzyme production plant (Source: Falk 1991)
A good example of application is in India, where the big-pesticide market is around 100,000 tons per year, representing 3 per cent of the total market. Biologicals have a market share of 0.5 per cent of global chemical pesticides, as of 1995, while in the year 2000 a penetration rate of about 10 per cent is expected by some experts, out of a total global pesticide market of US$40-45 billion. At the moment the biotoxins produced from Bacillus thuringiensis (Bt) dominate, with nearly 70 per cent of the market.
Bio-pesticides can already substitute effectively for some chemical pesticides in agriculture (e.g. protection of cotton, sugar cane, oil seeds such as groundout, rapeseed) as well as floriculture and horticulture. They have uses too in public health (e.g. control of disease vectors of malaria, filariasis, and encephalitis with B. sphaericus and B. thuringiensis formulations). Bio-pesticides can be broadly classified into the following categories, indicating a broad diversity in species as well as in specific actions:
- predators pathogens
- neem oil
Commonly used predacious species are Cryplolaemus nontrouzuri, Chrysopa, Scymnus, Coccivera, and Nephus spp. against mealy bugs and Cerilocorus nigritus and Pharoscymnus houri against scale insects. Ladybird beetles are used to protect rice (against brown plant hopper), fruits such as citrus and grapes, and plantation crops such as coffee.
Pathogens (viral, fungal, bacterial)
Among the different entomopathogens, referred to as "biorational pesticides" as viral pathogens, the most important are the bacillo viruses. More than 10 types of such viruses have been isolated and extensively studied for their potential in pest management. Of these, nuclear polyhedrosis viruses (NPV) and granulosis virus (GV) are found to have good potential for pest control. The use of fungi to control pathogens that incite plant disease is another concept that has been in existence for some time. Insects infected with fungus exhibit general lethargy, slow growth, cessation of feeding, and changes in colour. The difference between fungi and other pathogens is that fungi do not have to be consumed by the insect to cause disease; instead they grow through the insect's skin. Many fungi are found to be pathogenic to a number of pests such as Metarhizium anisopilae, Beauveria brongniartii, Anopheles stephensi, and Trichoderma.
The most prominent bacteria in biological control are in the genus Bacillus, the group of Gram positive, rod-shaped bacterium. Bacillus thuringiensis (Bt) is the most widely known and researched aerobic spore-forming bacterium within this group for insecticides properties and is differentiated from other spore-forming bacilli by the presence of a parasporal body that is formed within the sporangium during sporogenesis. The parasporal body is a high molecular mass protein crystal that is referred to as crystalline protein delta-endotoxin. The insecticidal activity of B. thuringiensis products is based on the deltaendotoxin. Bacillus thuringiensis is primarily a pathogen of lepidopterous pests. Being a natural protein, Bt endotoxin is highly biodegradable. It is also degradable by ultraviolet radiation. As a result, it is environmentally safe, because it cannot leave behind any residues to contaminate the soil, water, or food. Naturally occurring Bt are spore forming bacteria. The spores are resistant to desiccation, high temperature, UV, and biodegradation.
The families Mermithidae, Steinernematidae, Romanomernis culicivoran, Goniazas nephantidis, Bracon brevicormis, Sturmiopsis inferens, and Trichogramma are of special importance as examples of insect parasitic forms.
Insects rely on a sense of smell and communicate with each other by releasing specific chemicals (odours) to indicate their selection of food plants, sites to lay eggs, location of prey, defence and offense, mate attraction, and courtship. These specific chemicals that deliver intra-specific communications between individuals of single species are called pheromones. Between 600 and 1,000 pheromones have been isolated, identified, and synthesized, many for insects.
Kairomones are compounds emitted by an insect to convey a behavioral response to a member of a different species. They carry an advantage to the receiver (e.g. compounds used by parasites to locate a host). They are utilized in conjunction with Trichogramma to improve their efficiency in parasitization.
Extracts of Neem seed provide various crops with resistance to insect pests. Neem oil contains several chemicals of which the most potent one, "Azadirachtin," interacts with the reproductive and digestive processes of insects. Neem oil acts in a number of subtle ways, especially as a repellent and anti-feedant. It also has a growth regulatory effect by disturbing the insect's metabolism during various phases of development.
Another interesting field of research is allelopathy, where the metabolic substances produced by one plant inhibit the growth of another plant. This can be regarded as a potential alternative to the use of chemical herbicides and the evolution of herbicide-resistant crops. Plants also offer quite innovative chances for new applications in the area of removal of heavy metals from the environment, e.g. "phytoremediation" (Salt et al. 1995), especially from soil, e.g. "phytoextraction" (Kumar et al. 1995), and from aqueous media, e.g. "rhizofiltration" (Dushenkov et al. 1995).
Bio-leaching of ores
Bio-leaching utilizes sulphur-loving bacteria that live in the ore itself. Examples include Thiabacillus ferroxidans, Thiobacillus thiooxidans, and Leptospirillum ferroxidans. When exposed to oxygen and carbon dioxide they obtain metabolic energy by reacting oxygen with sulphur, producing sulphuric acid as a metabolic waste. Compared with conventional heap leaching methods (using sulphuric acid recovered from ore roasting), big-leaching can offer real economic advantages. Typically the economic feasibility differs for several plants on several site-specific factors such as concentrations, leaching rates, and residence times. Bio-leaching is commercially applied for the recovery of copper and uranium in the United States and for gold in South Africa and Brazil. The main obstacle is the investment in conventional plants (TME1992).
The Biox(r) Genmin process for gold leaching involves the oxidation of a sulphitic concentrate slurry in a series of stirred tanks. Large volumes of compressed air are sparged into the tanks to fulfil the oxygen and carbon dioxide demand of the bacteria. A retention time of 3-5 days results in more than 90 per cent conversion of gold. The oxidized slurry then flows into a series of counter-current decantation thickeners to separate solids from acidic solutions. After neutralization to a pH of 11, cyanide is added and the gold is dissolved. Bio-oxidation currently offers real economic advantages over roasting and pressure oxidation for production plants with a capacity of less than 1,200 tons per day.
Denitrification of drinking water
In the denitrification of drinking water, denitrifying bacteria reduce nitrates and nitrites to harmless nitrogen gas and oxygen, which they use for metabolic purposes. A full-scale denitrifying plant is in operation in Austria, using a 2 m3 fixed-bed big-reactor system, operating with a natural population of microbes as denitrifiers. Because it is based on a naturally existing strain of bacteria, which accumulates during the start-up phase itself, sterile process operation is unnecessary. The process economics of denitrification are shown quantitatively in Table 3.1, which compares biological and physico-chemical approaches (Moser 1996).
Table 3.1 Process costs for the denitrification of drinking water, comparing biological and chemical paths
|Biological + ethanol||0.15-0.27||
Source: Moser (1996).
a: analyses; c: chemicals; m: maintenance; p: personal; w: waste removal.
Nowadays a large number of synthetic polymers are produced from petroleum derivatives because they are cheap, are available, can be prepared and processed easily, and are subject to few fluctuations of quality. Moreover, synthetic polymers offer a wider range of characteristics than natural polymers. However, genetic engineering offers at least the possibility of producing natural polymers with equivalent properties without the need for large-scale chemical processing.
There are two different ways to obtain polymeric materials from plants that are useful for engineering purposes:
1. making use of the original polymeric structure of the plant material by conserving most of it and chemically modifying only side chains;
2. degrading the plant material chemically, or having it degraded by animals or micro-organisms, and subsequently synthesizing new polymers by means of chemistry or biotechnology.
Quite a few classes of plant polymers can be used as engineering materials without degrading the polymer backbone. Cellulose is one.
The biosphere is abundant in cellulose, from timber, cotton, flax, and hemp. (Cellulose is the basis of rayon, cellophane, and celluloid.) Other natural polymers include natural rubber (a cis-polyisoprene), gutta-percha, lignin, polyphenols, and gums. Technologically useful polymers derived from animals also include proteins, such as wool, silk, leather, horn, gelatin, casein, chitin, and chitosan.
Some polymers with possible industrial application are produced by microorganisms. Biopolymers (e.g. polysaccharides), with properties and applications similar to those of plant gums, are secreted by certain bacteria and can be obtained by means of biotechnology. In the 1980s processes were developed to produce polyhydroxy-alkanoates (PHAs) as thermoplastics on an industrial scale. PHAs are polyesters that are produced by a great variety of micro-organisms as a cellular storage material. The most widespread type of PHA is PHB (polyhydroxybutyrate). However, its properties are not quite suitable to serve as a thermoplastic. This is why methods to produce similar substances with improved processing and application properties are sought.
As a result of these efforts a copolymer of polyhydroxybutyrate and polyhydroxyvalerate (PHB/V) has been developed, with properties very much like polypropylene. This biopolymer, called "biopol," is produced by ICI in Great Britain by a fermentation process using glucose and propionic acid as organic substrates. The latter is currently derived from mineral oil but there are also ways to produce it from renewable raw materials by biotechnological methods. Biopol is biodegradable and therefore can be used for packaging products for quick disposal. In Germany a shampoo bottle made of biopol is on the market. This may be only the beginning (Moser 1994; Braunegg and Lefebvre 1993).
Use of genetic engineering
"Modern biotechnology" consists of new techniques, based on recombinant DNA technology, monoclonal antibodies, hybridoma techniques, cell fusion, vector-initiated gene techniques, and novel methods of cell and tissue cultures, resulting in genetically engineered organisms (GEOs).
The complexity, as well as the costs of development, increase in the following sequence (Swaminathan 1992): biological nitrogen fixation, plant tissue culture, embryo transfer, monoclonal antibody production, plant protoplasm fusion, rDNA for disease diagnosis, biocontrol agents, animal vaccine development, rhizobia improvement, plants, animals. Regardless of the high costs, there is no debate over the question of whether or not developing countries should begin genetic species engineering. Even the poorest should be thinking about a "survival kit" based in modern techniques; for example, a country with root crops as a staple food should initiate a tissue culture laboratory to facilitate the importation of tissue cultures of virus-free clones developed abroad. This would also allow rapid propagation if the plants proved adaptable to local conditions and acceptable to local producers and consumers. Table 3.2 gives some examples of genetic engineering activities and their actual and potential benefits.
It is generally agreed that the potential use of genetic techniques is very promising. Their application can further promote sustainability by, e.g., diversification of agricultural, forest, and fishery production systems, supplementation of genetic resources, and development of life forms appropriate to formerly impossible agricultural situations. A major consequence is considered to be the reduction of economic risk, but environmental risk is also likely to be reduced.
Current technologies can modify a single gene or chromosome. Major future breakthroughs will require more complex transfers. For example, at least six gene modifications would be involved in transferring nitrogen-fixing ability to cereals. Longer-term progress thus depends on further advances in basic science, notably in such areas as genome mapping. Bio-engineering applications are still extremely limited. The potentials have barely begun to be exploited. They are currently being held in check by the need for still more research to identify more useful genes plus more research to avoid harmful effects and big-safety hazard.
To decide whether an activity is pro- or contra-nature, I have suggested a series of four eco-principles (Moser 1996):
Table 3.3 applies principle (1) to various types of biotechnology.
Indigenous technologies: Food and health care
Ancient knowledge is a source of inspiration for sustainable technology development. Meso-American cultures had wide technological activities resulting from the combination of cultural, biological, and ecological diversities (Lopez-Mungia et al. 1994). A famous example in agriculture comes from the Incas, who were able to grow cereals at an altitude of 4,000 m with extraordinarily high productivity (10 tons/ha), although modern techniques (with chemical fertilizers) yield only 4 tons/ha. This 3,000year-old "waru-waru" process is completely natural, having a renaissance in Bolivia under the name of "socca collos." The plants are grown on platforms 1 m in height, 4-10 m wide and 10-100 m long, made from soil dug from the canals. Water absorbs the sun's heat by day and radiates it back by night, protecting the crops against frost by creating a layer at +4°C. By capillary effects water ascends to the roots of the plants. Sediments from nitrogen-rich algae and plant and animal remains serve as fertilizer.
Table 3.2 GEO success stories
|Insect resistance||Immunity from boll- worm, caterpillars, corn borers, hornworms...||Cotton||Reduced pesticide costs, reduced crop losses (c. US$1.5 billion), increased yields|
|Disease resistance||Protection against tobacco mosaic virus, rice tungro virus, cucumber mosaic virus...||Tomato, rice, cucumber||Increased yield (25% for tomatoes)|
|Herbicide resistance||Tolerance for non- selective roundup herbicides||Sugar beet, maize, cotton, tobacco, potato||Less labour-intensive weeding needed|
|N-fixation||Stimulation of nodule- like structures in roots||Rice, wheat||Reduction in fertilizer costs|
|Drought resistance||Genes inserted from species growing in deserts, e.g. cacti||Wheat, corn, soybean et al.||~40% less water needed|
|Baking||Gene modification||Baker's yeast|
|Cold-tolerating microbes||Deletion of gene for ice-nucleation protein||Potato, straw- berry||~30% profit increase|
|Crop-ripening qualities||Antisense gene to block enzyme formation involved in softening/ ripening||Tomato||Increased solid content and longer shelf-life|
|Disease- attacking microbes||Seedling roots soaked in a solution of modified bacteria||Stone fruits, nuts, roses||Losses reduced at minor cost (~US$1/litre)|
|Insecticidal microbes||Modified Bacillus thuringiensis||Various||Replacement of chemical insecticides, reduced costs|
Table 3.3 Clarification big-processes and biotechnologies by degree of invasiveness
|Non or low invasive (wisdom or common-sense based)|
|Use of those natural strains of micro-organisms, plants, and animals widely available in classical biotechs for food and feed and waste treatment|
|Use of simple selection and mutation (natural screening methods)|
|Use of GEOs where proved to fulfil all eco-requirements/eco-principles Use of enzymes in fully biocompatible, aqueous systems|
|Medium invasive; based on classical natural and agro-sciences such as microbiology, biochemistry, cell biology, and engineering|
|Use of species cultivated in "modern biotech" laboratories (e.g. within the pharmaceutical industry and in plant and animal breeding) using modern mutation and selection methods (scientific screening)|
|Use of enzymes in non-biocompatible, non-aqueous media|
|Highly invasive; based on molecular biology and genetic engineering|
|Use of genetically modified organisms with modifications on the gene/genome level|
|Use of transgenic species; gene transfers on the level of "high biotech" (monoclonal antibodies, biocide-resistances) using, e.g., hybridoma techniques, cell fusion, vector-initiated gene technology|
When Europeans arrived, the Incas had domesticated between 60 and 80 edible plants after centuries of interaction with ecosystems and species. In addition, more than 600 non-cultivated plants with adequate nutritional value, 300 species of fish, and 101 species of insects were used as food. Although much of this knowledge has evidently been lost, some of it may be recoverable. Surely the effort would be worth while. Meanwhile, the simple fact that such knowledge did exist at one time constitutes a powerful argument for preserving biodiversity.
Indigenous technologies are also very rich sources for human health care (big-drugs). Some international firms have initiated joint ventures with tropical countries to identify active compounds from roots and plants (Girardet 1987). Table 3.4 lists some examples of products from indigenous processes.
Table 3.4 Products stemming from indigenous technologies
|Basic techniques in agriculture|
|Waru-waru: sophisticated nature-integrated agriculture in the Andes|
|Chinapas: the "floating gardens" in the lakes, i.e. artificial isles|
|Others described in "Codices Florentino"|
|Echinacea purpurea ("red sun heat"): antiseptic, antibiotic, antiviral|
|Sepherdia rotundifolia ("buffaloberry"): ointment against eye infections|
|Artemisia tridenta ("big sagebrush"): against rheumatism and colds|
|Ayurvedic medicine (India)|
|Cochinilla (coccus cacti L.), red pigment|
|Indigo from "xiuhquilitl" (indigofera sufruticosa), blue|
|(recombinant E. cold based industry in Mexico)|
|Orange ink from achiyotl (bixa oreyana)|
|Red ink from haematoxylum brasiletto|
|Xantophyles from flowers of cempazuchitl (tagetes erecta)|
|Chilli (annus capsicum)|
The growing need for fertilizers to enable a relatively fixed amount of arable land to support a growing human population is clear. Are chemical or biological fertilizers the best choice? A strong argument for replacing water-soluble chemical fertilizers such as urea, used in quantities up to 250 kg/ha, is that as much as about half of it goes directly into the groundwater and much of the remainder is lost to denitrifying bacteria. Bio-fertilizers such as Rhizobium can be applied in lesser amounts - as little as 0.5 kg/ha potentially resulting in reduced costs.
For example, one can imagine an interrelated system combining a big fertilization plant (Rhizobium) with a sugarcane plantation and ethanol production where the main mass fluxes are consumed internally within the three operations. Further products could be added (food and feed, biological control agents such as Bacillus thuringiensis, bio-polymers for packaging materials, industrial raw materials, etc.), as shown schematically in figure 3.2 (Moser 1996).
Fig. 3.2 Example of a technology mix utilizing agriculture-integrated bio-processing
It is known that in tropical countries there are a great number of plants that are able to live in symbiosis with nitrogen-fixing bacteria such as Rhizabium species (for leguminous plants) or associated symbiotics, e.g. Azosperillum for sugar cane. Genetic manipulation is possible, in the case of Rhizobium species, for further improvement. Some plants depend symbiotically on other microbes for nitrogen fixation. Recently it has been found that such microbes live not only in the roots but sometimes also on the surface of the plant (Doebereiner 1994). There are also non-symbiotic N-fixing bacteria (e.g. azobacter, cyanobacteria, blue and green algae). Research in this area is still at the earliest stages and the very fact that much of value remains to be learned constitutes a strong argument for preserving biodiversity.
Fig. 3.3 Hemp (cannabis saliva) as a typical renewable material for a diversity of applications
There is a renaissance of plant-derived bulk raw materials in the United States (Robbelen et al. 1991). In the past decade, technological advances have lowered the cost of producing high-quality products from plant matter, while environmental regulations have raised the cost of using petroleum-derived products. Another potential source of renewable materials is the large amount of waste organic material from agriculture and forestry, especially paper pulping, municipal solid wastes, and food processing. The total is nearly 350 million metric tons/year in the United States alone.
The potential of using plants as industrial raw materials, instead of crude oil, has been neglected up to now owing to the low cost of petroleum. Consequently petrochemicals are the primary source of several categories of industrial materials. In effect, oil has replaced plant-derived matter not only for most textiles but also for significant uses of glass, metals, wood, and even paper. As one example of the potential for increasing the use of plant matter, the case of hemp is illustrated in figure 3.3. Practically all products can, in principle, be produced from plant materials. The basic technologies exist; only cost considerations, and sometimes quality differences, are preventing introduction to the market. The full potential of plant materials for replacing petrochemicals is shown schematically in figure 3.4.
Fig. 3.4 Production paths from renewable raw materials to industrial products
Agro-based "industrial ecosystems"
An example of a possible interconnected but self-contained network of different activities to exploit plant-derived materials was shown in figure 3.2. There are other interesting possibilities for arranging a series of interconnected conversions, where each step uses the waste stream from the step before, with the final result that very little biomass is wasted.3 A second example (Paul) 1994) is the case of beer brewing, shown in figure 3.5, where the liquid waste stream is used as nutrient for fish farming for the production of proteins. An indirect advantage is that the production of 1 kg protein via fish needs only 30 per cent of the feed (in caloric terms) needed to obtain red meat from animals.
Fig. 3.5 "Zero emissions research initiative" applied in the beer brewing industry (Source: Pauli 1994)
Another good example of an integrated big-process is the use of "green juice" from grass and potatoes for the production of dried grass pellets and co-products such as lactic acid, amino acids, other fermentation products, biogas, and inorganic fertilizers (Kiel 1992). A further example of combining many kinds of specialized workshops or factories into a unified ecological complex is that of Aoxue Companie in Anyang/Henan province in China (Wang 1995). This began in 1988 as a simple cornstarch factory. This factory has been innovative in finding uses for wastes. Most of the original wastes are now utilized through "food-chain" adding successive processes to produce higher valued by-products. The range now includes flour, corn syrup, inositol, corn oil, corn wine, protein forage, and protein powder. Other interesting cases from "eco-villages" have been compiled (Swaminathan 1994, table 7).
Table 3.5 presents a pattern of different activities characteristic of some "eco-villages" in India and China.
Table 3.5 Main eco-technologies in China's "eco-villages"
|Biogas digester using wastes|
|High-efficiency production in agriculture|
|Edible mushroom production using crop and animal by-products|
|Fly pupae production|
|Chicken waste used as swine feed|
|Multi-layer fish culture|
|Raising of natural enemies of pests|
|Biological control of erosion|
|Biological wastewater treatment|
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