UNCONVENTIONAL BIOMASS PRODUCTION Chapter 4.— UNCONVENTIONAL BIOMASS PRODUCTION

Chapter 4 UNCONVENTIONAL BIOMASS PRODUCTION Chapter 4.— UNCONVENTIONAL BIOMASS PRODUCTION

Page Introduction ...... 91 TABLES Genetics ...... 91 Page Crop Yields .*...... 92 36. Optimistic Future Average Crop Yields for Unconventional land-Based Crops...... 95 Plants Under Large-Scale Production ...... 94 Lignocellulose Crops ...... 95 37. incomplete List of Candidate Vegetable Oil and Hydrocarbon Crops . . . . . 96 Unconventional Bioenergy Crops ...... 95 Starch and Sugar Crops ...... 97 38. Optimistic Cost Estimates for General Aspects ...... 97 Unconventional Crops...... 97 Aquiculture ...... 98 Mariculture ● ..********...... *.***** 101 Other Unconventional Approaches ...... 105 Multiple Cropping ...... 105 Chemical Inoculation...... 105 Energy Farms ...... 105 FIGURE Biophotolysis...... 106 Inducing Nitrogen Fixation in Plants ...... 107 Page Greenhouses ...... 108 13. Macrocystis Pyrifera ...... 102 Chapter 4 UNCONVENTIONAL BIOMASS PRODUCTION

Introduction

A number of unconventional approaches to istics, however, can aid in comparing the vari- biomass energy production have been pro- ous possible types of energy crops. posed. Several nontraditional crops that pro- The general aspects of farming, plant duce vegetable oils, hydrocarbons, and other growth, and the efficiency of photosynthesis chemicals or cellulosic material are under in- are considered in chapter 3. Since future crop vestigation. Both freshwater and saltwater yields will depend on these factors and on the plants are being considered, and various other development of hybrids for energy production, approaches to biomass fuel production are the possibilities for genetic improvements are being examined. A common feature to all of considered here. Following this, crop yields these approaches is that the full potential of and various unconventional bioenergy crops individual plants proposed as fuel-producers and approaches to farming them are discussed. cannot be fully assessed without further R&D. A description of some general plant character-

Genetics

There are two major areas of genetics. The characteristics into specialized cells such as first, which plant breeders have used most ef- the ability to produce insulin,1 and 3) improve- fectively to date is the classical Mendelian ap- ments in photosynthetic efficiency, plant proach (introduced by Gregor Mendel in the growth, and crop yields. The complexity of the 19th century). It involves selecting and cross- tasks increases greatly as one goes from 1) to breeding those plants with desired characteris- 3), as described below. tics (e.g., biomass yield, grain yield, pest resistance). The process is continued through The first type involves subjecting single cells each succeeding generation until a hybrid, or to chemicals or radiation that cause mutations in the celIs’ genes. The way these mutations oc- particularly favorable strain, is isolated. cur is not well understood and the effects are Strains with unique and desirable properties are often crossbred to produce hybrids that generally unpredictable. The result is to in- outperform the parents. Hybrid corn is an ex- crease the diversity of cell types over what oc- ample. This technique is limited, however, by curs naturally; and in favorable cases one may produce a cell that performs a particular func- the variability of characteristics that exist tion “better” than naturally occurring cells. naturally in plants or mutations that occur This method has been applied successfully to spontaneously during breeding. One can isolate the best, but one cannot produce better the production of antibiotics, in biological 2 and in increasing the than nature provides. conversion processes, tolerance of plants to certain diseases; but it is The second approach to genetics, molecular generally a “hit and miss” proposition. genetics, is a recent development that involves manipulating the genetic code more or less directly. Three types of potential advances from molecular genetics can be distinguished: 1 ) im- ‘A Elrich, et al , Science, VOI 196, p, 1313, 1977 provements in the efficiency or rate of biologi- ‘For example, see G H E inert and R. Katzen, “Chemicals From Biomass by Improved Enzyme Technology, ” presented at cal conversion processes (e.g., fermentation, the Biomass as a Non-Fossi/ tue/ Source, ACS/CSJ Joint Chemical anaerobic digestion), 2) introducing specific Congress, Honolulu, Hawall, April 1979

91 92 ● Vol. n-Energy From Biological Processes

The second type involves identifying the Some additional near- to mid-term advances genes responsible for a particular function in are likely in the area of biological conversion one cell and transferring these genes to anoth- processes and with gene transfers in the area er cell. This transfer does not always require a of synthesizing high-value chemicals, like in- detailed knowledge of how the gene produces sulin, that would be either impractical or im- the desired characteristic. One can draw from possible to synthesize by other means. The the pool of naturally occurring characteristics, complexity of plant growth and photosynthet- but the conceptual link between the gene and ic efficiency, however, reduces the chances of the characteristic must be relatively direct. improving ‘these characteristics in plants through molecular genetics in the near future. The third type probably would involve alter- Although the possibility cannot be precluded ing a complex set of interdependent processes that a scientist will alter a crucial process in in the plant. Although some plant physiologists plant growth despite the lack of knowledge, believe that some improvements in photosyn- there are few grounds for predicting that this thetic yield can be achieved by suppressing will occur before the fundamental biochemi- processes like photorespiration (a type of plant cal processes involved in plant growth and respiration that occurs only in the presence of photosynthesis and the way that environmen- light), this belief is highly controversial among tal factors limit them are better understood. specialists in the field. It is generally believed There is a great deal of controversy surround- that the processes involved in plant growth ing this subject, but most arguments— both and photosynthesis and their relation to specif- pro and con– are based on intuition rather ic genes are too subtle and poorly understood than demonstrated fact. at present to know what biochemical processes should or can be altered to improve plant growth and crop yields.

Crop Yields

Current knowledge and theories of plant cropland. Furthermore, since cropland that growth do not enable one to predict the crop could be devoted to energy crops is generally of yields that can be achieved with unconven- poorer quality than average cropland, using this tional crops. Nevertheless, because of the im- as a basis for estimates may be overstating the portance of biomass yields in determining the potential. economics of production, it is important to have an idea of the approximate magnitude of A yield of 140 bu/acre for corn corresponds the yields of various options that may be possi- to a photosynthetic efficiency of about 1.2 per- ble. cent over its 120-day growing season. Perennial crops, however, probably will have somewhat To this end, corn – a highly successful exam- lower efficiencies during the cold weather at ple of crop development– is used as the basis the beginning and end of their growing sea- for these estimates. Corn has the highest pho- sons. Consequently, it is assumed that peren- tosynthetic efficiency of any plant cultivated nials can achieve an average photosynthetic over large areas of the United States. As dis- efficiency of 1.0 percent. With these assump- cussed in chapter 3, an optimistic estimate for tions, and the others stated below, the follow- average corn grain yields would be about 140 ing yields may be possible. bu/acre (3.9 tons of grain/acre) by 2000. Many farmers routinely exceed this yield, as do ex- ● Dry matter yield.— With an 8-month growing perimental plot yields. This number, however, season in the Midwest, biomass production is quite optimistic for average yields from cul- could yield 15 ton/acre-yr of dry plant mat- tivation on millions of acres of average U.S. ter. For the Gulf Coast (12-month growing Ch. 4—Unconventional Biomass Production ● 93

season), the yields could reach 21 ton/acre- cent of the seed weight.3 Assuming that yr. plants which are 50-percent seed contain ● Grain yields.– Based on corn yields, average seeds that are 50-percent oil, the oil content grain production from some plants could may reach 25 percent of the total plant yield 3.9 ton/acre-yr. weight. ● Sugar yields.– Good sugar crops are 40- to Assuming the biochemical reaction pro- 45-percent sugar on a dry weight basis (e.g., ducing the oil is 75 percent as efficient as sugarcane, sweet sorghum). In the Midwest, that which produces cellulose, then for 1- sugar crops will probably be annual crops percent photosynthetic efficiency the oil leading to possible yields of 4 tons of production would be 16 bbl/acre-yr for a sugar/acre-yr. Along the Gulf Coast, there is plant that is 25-percent oil. For an oil-pro- a longer season. Current average sugar ducing reaction that is 50 percent as effi- yields are 4 ton/acre-yr. As with corn, the cient as the reaction that results in cellulose, yields could conceivably be increased by 40 the yield would be 12 bbl/acre-yr. percent to 5.6 ton/acre-yr. Plant material stored as hydrocarbons has ● Aquatic plant yields.– Estimates for water- also been proposed as a source of liquid based plants are more difficult to derive, fuels. Eucalyptus trees and milkweed, for ex- since there is considerably less experience ample, contain up to 12-percent hydrocar- and applicable information. Water plants bons. Assuming that this content could be have a continuous supply of water and are doubled, the same yields as for oil crops never water stressed. For maximum produc- would apply. tivity, nutrients and carbon dioxide (CO,) ● Arid land crop yields.– Another important (for submerged plants) would be added to and sometimes limiting factor in biomass the water and could be available continu- production is water. Generally plants will ously at near-optimum levels. The water grow well without irrigation in areas of the would prevent rapid changes in tempera- United States where the rainfall is 20 to 30 ture. All of these factors favor plant growth, inches or more. For high biomass-producing and if other problems with cultivating crops in relatively humid climates (like the aquatic plants can be solved, yields may be Midwest), the minimum water necessary for quite high (see “Aquiculture” and “Maricul- plant growth in open fields is about 200 ture”). Nevertheless the uncertainty is too weights of water for 1 weight of plant great to make a meaningful comparison growth. There has been interest, however, in with the land-based plants. As with other plants that can grow under more arid condi- plants, experimental yields will probably not tions. In desert regions with very low humidi- be representative of commercially achiev- ties, requirements are more typically 1,000 able yields. weights or more of water per 1 weight of ● Yields in greenhouses.– Yields in green- plant growth. (Some plants survive for long houses are also very uncertain, due to a lack periods of time without water, but they do of sufficient data and potential problems not grow. ) Assuming the 1,000:1 figure, the such as fungal attacks on plants, root rot, maximum plant growth that could be ex- and other problems with extremely humid pected in a region with 5 inches of rain and environments. If these and other problems no irrigation is 0.6 ton/acre-yr. Oil yields are solved, then crop yields approaching would be correspondingly low or less than 1 those estimated for the milder climates may bbl/acre-yr. be achieved. ● Natural systems. — In addition to agriculture, ● Vegetable oil or hydrocarbon yields. – In addi- there has also been interest in using biomass tion to solid material, plant biomass in- produced by plants in their natural state. In cludes oils. New seed oil crops typically con- ✎ ‘D. Gilpin, S Schwarzkopf, j. Norlyn, and R. M. Sachs, “Ener- tain 10-to 15-percent vegetable oil, and in gy From Agriculture– Unconventional Crops,” University of Cal- sunflowers the oil comprises up to 50 per- ifornia at Davis, contractor report to OTA, March 1979. 94 ● Vol. ii—Energy From Biological Processes

the natural state, most of the nutrients are Each plant is, to a certain extent, a special returned to the soil as the leaves drop off case. The experience with large-scale cultiva- or the plant dies and decays. Harvesting of tion of crops is limited to a few food, animal some of the biomass removes some of the feed, fiber, and chemical crops. Many plant nutrients, although animal excretions and scientists argue that maximum food produc- the natural breakdown of minerals in the soil tion implies maximum biomass production. provide new nutrients. The rate of replenish- However, few genetic and development pro- ment varies considerably from area to area, grams have been specifically aimed at max- however, and this determines the rate that imizing biomss output for crops suitable to biomass could be removed from natural sys- large areas of the United States. tems without depleting the soil. These contradictory factors mean that the The potential growth of biomass in contin- potential for biomass production is uncertain. uously harvested natural systems has appar- And the uncertainty of the estimated yields is ently not been studied. (Forestlands are an judged to be at least 50 percent. Consequently, exception, although the emphasis there has the yields could easily vary anywhere from 0.5 been on the production of commercial tim- to 1.5 times the numbers reported. ber rather than on total biomass.) It has been estimated, however, that some natural wet- It is highly unlikely, however, that average lands produce more than 5 ton/acre-yr of U.S. yields for corn will exceed 140 bu/acre growth, and that 11.4 million acres of range- before 2000, and perhaps not after then. And Iand produce more than 2.5 ton/acre-yr. 4 corn is one of the best biomass producers for While no estimates for the production of the U.S. climate known to man. Consequently, natural systems can be given, they will cer- the numbers reported represent reasonable tainly permit less harvestable growth than limits in terms of what is known today. Any intensively managed systems on comparable large-scale production of biomass that signifi- soil. cantly exceeds these yields would represent a In evaluating the possible yields for biomass major breakthrough. Estimates that are based production, all of the yield estimates here on projected yields significantly exceeding should be treated with extreme caution. None those in table 36 either: 1) are limited to the of these yields has been achieved under large- relatively small acreage of the best U.S. soils, scale cultivation (i. e., mill ions of acres) and the Table 36.–Optimistic Future Average Crop Yields for Plants estimates for oil-producing plants are particu- Under Large-Scale Productiona larly uncertain. Experimental plot yields, on Plausible average yieldb the other hand, exceed these yields for many Region Product (ton/acre-yr) plants. Midwest Dry plant matter 15 Moreover, several factors operate to prevent Gulf Coast Dry plant matter 21 Midwest Sugar 4 average yields from reaching these estimates Gulf Coast Sugar 5.6 for large-scale production of biomass. The Midwest Grain 3.9 most important are the less than ideal soils of Midwest Vegetable oil or 1.7- 2.2 hydrocarbons (12 -16 bbl) most potential cropland and the fundamental Area with 5 inches rainfall limitations of plant genetics with current per year and no knowledge. On the other hand, management irrigation...... Dry plant matter 0.6 Area with 5 inches rainfall practices improve with time and increased per year and no costs for farm products may eventually justify irrigation...... Vegetable oil or 0.1 more extensive management practices, such as hydrocarbons (0.7 bbl) additional fertilizers, extensive soil treatment, aln thl~ ~Ont~xt, lar~~.~~al~ @UC(iOfl means cultivation On mllllotls 01 acres of average U S cropland and expanded irrigation. * bEstlmaled Uricerfamly 250 percent *“An Assessment of the Forest and Range Land Situation in the SOURCE Otflceot Technology Assessm@ United States, ” Forest Service, U S Department of Agriculture, review draft, 1979 energy production or whether the necessary water WIII be avail- ● It is unclear whether Irrigation WIII be socially acceptable for able Ch. 4—Unconventional Biomass Production ● 95

2) rely on technologies that do not now exist that are not likely to be cost effective unless and are not anticipated in the near future, or there are dramatic increases in the prices for 3) require extensive management practices farm commodities,

Unconventional Land= Based Crops

A large number of plants not now grown Table 37.–incomplete List of Candidate a commercially in the United States are poten- Unconventional Bioenergy Crops tially energy crop candidates. Some are rela- Lignocellulose crops tively high biomass producers and others American sycamore Red alder could provide a source of a variety of chemi- Bermuda grass Russian thistle Big bluestem Salt cedar cals that could be used as fuel or as chemical Gum tree (eucalyptus) Sudan grass feedstocks. Unlike conventional crops, these Kenaf Switchgrass crops could be considered primarily for their Napier grass Tamarix Poplar Tall fescue value as fuel. (However, see also ch. 10.) Reed canarygrass Assessing and comparing potential yields for Vegetable oil and hydrocarbon crops Crambe Milkweed the unconventional crops from literature re- Guayule Mole plant (euphorbia) ports are extremely difficult, since these re- Gum tree (eucalyptus) Safflower ports often do not give dry yields, the plants Jojoba Turnip rape often are grown on unspecified soils and in dif- Starch and sugar crops ferent climates, and the water and nutrient in- Buffalo gourd Kudzu vine Chicory Sweet potatoes puts often are not given. Furthermore, it is a Fodderbeets Sweet sorghum well-known fact that experimental plot yields Jerusalem artichoke are larger than those achieved with large-scale asome of these crops are produced commercially today on a hmlted scale, but fIOt for their ener9Y commercial cultivation. For these reasons, the value SOURCE D Gdpm, S Schwarzkopf, J Norlyn, and R M Sachs, “Energy From Agrlculture– yields reported below should be treated with Unconventional Crops, ” Unwersity of Cahforrua at Davis, contractor report to OTA. extreme skepticism. Comparative cultivation March 1979, S Barber, et al , “The Potential of Producing Energy From Agriculture, ” Purdue Unwerslty, contractor report to OTA, and J S Bethel, et al , “Energy From experiments and crop development will be Wood, ” UnwersNy of Washington, contractor report to OTA needed in the various regions and soil types in since the perennials develop their leaf cover order to establish which crops are, in fact, sooner in the spring and do not need to gener- suitable or superior for bioenergy production. ate a complete root system each year. One In broad terms, the categories include: 1 ) ligno- would also expect grasses to be superior bio- cellulose, 2) vegetable oil and hydrocarbon, mass producers to trees because of their larger and 3) starch and sugar crops. Each group is leaf area per acre of ground, * but considerable considered briefly below, and an incomplete attention has been focused on trees, since the list of candidate bioenergy crops is shown in technologies for using wood are more ad- table 37. vanced. Experimental plot yields for short-rota- 5 Lignocellulose Crops tion trees are 5 to 20 ton/acre-yr. Yields of as much as 10 to 15 ton/acre-yr may be achieved Various species of hardwood trees (e.g., red for large-scale cultivation of some of these alder, hybrid poplar) and grasses (e. g., kenaf, crops in good soil (see “Crop Yields” section) Bermuda grass, Sudan grass, big bluestem) are but are likely to be 6 to 10 ton/acre-yr in poorer candidates for crops grown primarily for their soils. Since farming costs could be similar to high dry matter yields (Iignocellulose crops). corn, this could result in biomass for about $20 to $50/ton. Theoretically, one would expect perennial “Thereby reducing Ilght saturation, which lowers photosyn- crops (like trees and some grasses) to be su- thetic efficiency perior biomass producers to annual crops, 5Cllpin, et al , op clt 96 ● Vol. I/—Energy From Biological Processes

The trees would typically be grown for 6 to The theory of hydrocarbon and vegetable oil 10 years before harvest, while the grasses production in plants is not adequate to predict would be harvested several times a year. With possible yields. However, from other consid- fewer harvests for the trees, each harvest could erations (“Crop Yields” section) there may be a be considerably more expensive and consume significant potential for improvement. Further- more energy than grass harvests without unfa- more, some of these crops (e. g., guayule) may vorably affecting the economics or net energy do well on land where there is slightly less wa- balance. However, tree crops would require ter available than would be needed for con- that the land be dedicated to the crop for sev- ventional crops. a Others, such as milkweed, eral years and converting the land to other can be grown with brackish water which would uses would be more expensive, due to the de- be unusable for conventional food crops. ’ veloped root system. Also, if a disease were to Comparative tests under comparable condi- kill the crop, reestablishing a tree crop would tions will be necessary to determine which be more expensive. Both trees and some plants show the most promise for energy pro- grasses are perennial crops and, consequently, duction. would require fewer herbicides and would re- Because of the higher prices that can be duce erosion on erosion-prone land as com- paid for chemicals and natural rubber, the fact pared to annual crops. Grasses, having a more that these products are economic in some complete soil cover, would be more effective cases does not in any way imply that energy in preventing soil erosion. production from vegetable oil and hydrocarbon plants will be economic. Some proponents Vegetable Oil and Hydrocarbon Crops of hydrocarbon plant development have failed to distinguish between these end uses, a fact Vegetable oils and hydrocarbons are chemi- that has led to considerable confusion and cally quite different from petroleum oil. Nev- misunderstanding. ertheless, most vegetable oils and hydrocarbons can be burned and might prove to be a Critics of the development of vegetable oil substitute for fuel oils or, with refining, for and hydrocarbon plants for energy argue that other liquid fuels. However, appropriate meth- the production of these products by plants is ods for extracting the oil from the plant and considerably less efficient than normal chemi- for refining the oil are not well defined at pres- cal synthesis (e.g., to produce methanol or eth- ent. anol from dry plant matter). They also point out that the plant often must be subjected to A number of edible and inedible vegetable stress (drought or cold) to produce hydrocar- 6 oils are currently produced commercially. In bons, and this lowers the photosynthetic effi- addition, unconventional crops such as gum ciency. Consequently, they contend that the tree (eucalyptus), mole pIant (euphorbias), high yields being predicted (e.g., 26 bbl/acre10), guayule, milkweed, and others could be used will not be achieved in the foreseeable future. as vegetable oil and hydrocarbon crops (or for natural rubber). The maximum current yields At present, however, the theory of and ex- of commercial oil plants are in the range of perience with these types of plants is inade- 100 to 200 gal/acre (2.5 to 5 bbl) of vegetable quate to make a meaningful judgment. oil and/or hydrocarbon. Reports of 10 bbl/acre (420 gal) for euphorbia were apparently based on measurements of plants on the edge of a ‘K. E. Foster, et al., “A Sociotechnical Survey of Guayule Rub- field, which were 1.5 times larger than interior ber Commercialization, ” Office of Arid Land Studies, University plants. Also, in some cases, 16 months of of Arizona, Tucson, Ariz., prepared for the National Science growth were used to obtain “annual” yields, ’ Foundation under grant PRA 78-11632, April 1979. ‘W. H, Bollinger, Plant Resources Institute, Salt Lake City, 6Agricu/tura/ Statistics (Washington, D. C.: U.S. Department of Utah, private communication, 198o. Agriculture, 1978). ‘“J D. Johnson and C. W Hinman, “Oils and Rubber From Arid ‘Gilpin, et al., op. cit. Land Plants,” Science, VOI 280, p. 460,1980. Ch. 4—Unconventional Biomass Production ● 97

Starch and Sugar Crops Other plants such as fodderbeets, sweet potatoes, and Kudzu vine are also potential etha- Starch and sugar crops are of interest since nol crops. Comparative studies are necessary they can be used to produce ethanol with com- to determine which crops are best in each soil mercial technology. Current corn grain yields type and region of the United States. As was can be processed into about 260 gal of ethanol emphasized in chapter 3, this comparison per acre cultivated and sugar beets (usually ir- should include the displacement of other rigated) can produce about 350 gal/acre, on crops that can be achieved by the byproducts the average. Irrigated corn, however, would of ethanol production. This factor tends to match the sugar beet yield. Furthermore, ex- favor grains, but other possibilities do exist. ’2 perimental plot yields for corn produce about 430 gal/acre-yr and record yields exceed 850 gal/acre. In addition to the conventional starch General Aspects and sugar crops, several other plants have Intensive cultivation of unconventional been proposed as ethanol feedstocks including crops may cost about the same as corn, or $200 sweet sorghum and Jerusalem artichokes. to $400/acre-yr in the Midwest. These costs, Experimental plot yields for sweet sorghum together with the yield estimates given above, could be processed into about 400 gal of etha- allow an approximate comparison of the costs nol per acre year. Furthermore, this crop pro- for various unconventional land crops, which duces large quantities of residues that are suit- is shown in table 38. Since the exact cultiva- able for use as a distillery boiler fuel. The tion needs have not been established, a more yields for large-scale cultivation, however, are detailed comparison is not warranted at this still unknown, and concern has been expressed time. These costs estimates, however, show that droughts during parts of the growing sea- that unconventional crops may be economic son could reduce sugar yields significantly. energy sources. The ultimate costs will depend to a large extent on the yields that can actually Experimental plot yields for Jerusalem arti- be attained with intensive management and chokes have produced about twice the sugar the success of developing crops that can be yields of sugar beets under the same growing cultivated on land that is poorly suited to food conditions in Canada. Whether this result can production. be applied to other regions is not known. Jeru- salem artichoke, like the sugar beet, is a root The crops that are now grown in U.S. agricul- crop. Harvesting it, therefore, causes extensive ture were selected for properties that are unre- soil disturbance which increases the chances I IR Carl son, B commoner, D Freedman, and R Scott, “Inter- of soiI erosion. Im Report on Possible Energy Production Alternatives In Crop- Livestock Agriculture, ” Center for the Biology of Natural SVs- “Gllpln, et al , op clt tems, Washington University, St Louis, Mo , Jan. 4, 1979

Table 38.-Optimistic Cost Estimates for Unconventional Cropsa

Product Ultimate fuel Yield of ultimate fuel per acre cultivated Contribution of feedstock to fuel costb 6 Dry plant matter Combustible dry matter 15 ton (195 106 Btu) $20/ton ($1 .53/ 10 Btu) 6 Dry plant matter Methanol 1,500 gale (95 106 Btu) $0.20/gal ($3.15/10 Btu) Dry plant matter Ethanol 1,300 gald (107 106 Btu) $0.23/gal ($2.80/10’ Btu) Grain Ethanol 364 gal (31 106 Btu) $0.82/gale ($9.89/10’ Btu) Sugar (Midwest) Ethanol 540 gal (46 106 Btu) $0.56/gal ($6.50/10’ Btu) Vegetable oil or hydrocarbon crop Vegetable oil or hydrocarbon 504-670 gal (63-84 106 Btu) $0.45-$0.60/gal ($3.60-$4.70/10’ Btu) aBased on yields m table 36 bAssumlng $3i)o/acre cuttwatlon and harvest costs, does nOt include COnver510n costs cAssumlng yw,lds of 100 gal/ton of btornass dAssumes yields of 85 galiton of biomass e~s not ,n~lude by Droduct credit for distillers’ grain H byproduct Credits Included, the Sltuatlon becomes more complex as described m ch 3, in the section on “Energy Potential From Conventlonai Crops ‘‘ The bypro&ct credit would reduce the costs by roughly one-thtrd SOURCE Otflce of Technology Assessment 98 ● Vol. Ii—Energy From Biological Processes

Iated to energy. It ‘is likely, therefore, that Root plants (e.g., Jerusalem artichokes, other plants will prove to be superior to con- sugar beets, potatoes, sweet potatoes) will ventional crops for energy production. Beyond cause the most soil erosion. Annual crops will the yields of these crops, properties like insen- be next, and perennial grasses can virtually sitivity to poor soils, multiple products (e.g., eliminate soil erosion. vegetable oil, sugar, and/or starch plus dry Soil structure and climate are dominant plant herbage) displacement of other crops features controlling plant growth and these with crop byproducts (e. g., corn distillery by- can be controlled by man only to a very lim- product), the energy requirements to cultivate ited extent. Plants vary as to their sensitivity to the crop, the energy needed to convert it into a these factors and to the presence of nutrient form that can be stored (especially for sugar solubilizing mycorrhizae in the soil, ’3 but and starch crops), tolerance to adverse weath- yields will decrease on going to poor soils and er conditions, ease of harvesting and conver- climates. Crops grown in arid climates without sion to fuels, and the environmental impacts irrigation or an underground supply of water of growing the crop are all factors that should will give low yields; and social resistance to be considered when choosing energy crops. In using water for energy production in the West short, analyses of the net premium fuels could preclude irrigated energy crops, al- displacement per new acre cultivated (as was though some people maintain that this resist- done for various conventional crops in ch. 3), ance will not extend to crops. the cost, and the environmental impacts are needed to compare the options. Due to the di- Finally, any crop that grows very well in an versity of U.S. soils and climates, different area without inputs from man is likely to crops will no doubt prove to be superior in dif- spread and become a weed problem. ferent regions. Many of the possible unconventional crops appear promising, but the ultimate decisions will have to come from experi- ment and experience. (Typically it requires 10 to 20 years to develop a new crop.) Neverthe- “J. M. Trappe and R. D. Fogel, “Ecosystematic Functions of Mycorrhizae,” reproduced from Range Sci. Dep Sci., series No, less, some general aspects of plants can be ex- 26, Colorado State University, Fort Collins, by U S. Department pected to hold for the unconventional crops. of Agriculture.

Aquiculture

Aquatic plants comprise a diversity of types, systems for energy production. ’4 The general from the single-celled microalgae to the large conclusions were that the production of aqua- marsh plants such as cattails and even some tic biomass has near-term potential in conjunc- trees such as mangroves. Considerable interest tion with wastewater treatment and high-value exists in the cultivation of many different chemicals production. However, the develop- aquatic plants as energy sources. Examples are ment of large-scale “energy farms” based on the production of cattails in the extensive aquatic plants is less promising at present, marshes of Minnesota, the cultivation of water from both an economic or a resource potential hyacinths on wastewaters in Mississippi or viewpoint. Nevertheless, aquatic plants have Florida, and the establishment in the South- certain unique attributes, the key one being west of large-scale brackish water ponds for high achievable biomass production rates microalgal production of chemical feedstocks. - “J. Benemann, “Energy From Aquiculture Biomass Systems: OTA has prepared a detailed review of the po- Fresh and Brackish Water Aquatic Plants, ” Ecoenergetics, Inc , tential of fresh and brackish water aquiculture Vacaville, Cal if , contractor report to OTA, April 1979 Ch. 4—Unconventional Biomass Production ● 99

which justify continued research on a variety United States and the large fraction of biomass of approaches to the development of aquacul- present in the root system which may be diffi- ture energy systems. cult to recover. The submerged aquatic plants such as the notorious weed Hydrilla, are also Higher aquatic plants growing in or on not remarkable for their biomass productivity. water are not, as a rule, water limited — a com- Adaptation to the light-poor environment fre- mon and natural state of land plants. Thus, quently encountered below the water surface they are capable of higher rates of photosyn- has made these plants poor performers at the thesis by keeping their stomata (plant pores) high light intensities that would be the norm in open longer than land plants* thereby, increas- a biomass production system.

ing C02 absorption. Thus, plants such as the water hyacinth and cattails exhibit very high Finally, the case of the microalgae must be rates of biomass production, often exceeding considered. Being completely submerged they 20 ton/acre-yr. This high productivity is also are subject to significant light losses by achieved, however, by evaporation of large reflection from the water surface (at low solar amounts of water, exceeding by a factor of angles) and scattering of light. More important- two to four that transpired by land plants. ly, in a mixed algal pond, the cells near the sur- Thus, cultivation of water plants can only be face tend to absorb more light than they can considered where ample supplies of water ex- use in photosynthesis, resulting in a significant ist or where the systems are covered, such as in waste of solar energy. However, if a microalgal greenhouse structures. production system is designed to enhance mix- ing, then rapid adjustment by the algae occurs, Some aquatic plants, however, do not exhib- thus overcoming, to some extent, the handicap it very high biomass production rates. For ex- inherent in inefficient sunlight absorption by ample, the common duckweed (Lemna sp.) microalgal cultures. Therefore, microalgal cul- covers a water surface very rapidly; however, tures could be considered in a biomass produc- once this is achieved, further growth in the ver- tion system. A review of the rather sparse pro- tical direction is minimal. Thus, the productivi- ductivity data available, together with consid- ty of such plants is relatively low when com- eration of the basic photosynthetic processes pared to plants such as water hyacinths and involved, suggest that green algae and diatoms marsh plants which extend their shoots up to are promising candidates for mass cultivation, several feet into the air. Indeed, the high leaf probably with achievable production rates of area index (the ratio of the total leaf area to at least 20 ton/acre-yr, with blue-green algae, the ground area), sometimes exceeding 10, of particularly the nitrogen-fixing species, con- these plants, accounts, along with high trans- siderably less productive. piration rates, for their high productivity. It must be noted that the available data on Another type of aquatic plant that exhibits aquatic plant productivity are too limited to relatively low productivity is the salt marsh allow confident extrapolations to large-scale plant Spartina, which does not produce as systems. Most available data are based on much biomass as its freshwater analogues such natural systems where nutrient limitations may as Typha (cattails) or Phragmites (bullrush). The have depressed productivity or small-scale, high salt concentration tolerated by Spartina short-term experimental systems where edge also results in a decrease of transpiration and effects and other errors may have increased productivity. Even among the freshwater productivity. Actual yearly biomass produc- marsh plants, biomass productivities are lim- tion rates in sufficiently large-scale managed ited by both the seasonal growth patterns of systems must be considered uncertain for any the plants in the temperate climate of the aquatic plant, particularly if factors such as stand establishment, pest control, optimal fer- ‘Somata are closed to conserve water, but this also prevents carbon dioxide from entering the leaf tilizer supply, and harvesting strategy are con- ‘ ‘Ibid cerned. Thus, to a considerable extent, assess- 100 ● Vol. n-Energy From Biological Processes

ing the potential of aquatic plants in energy ponds have been used for several decades in farming, like that of other unconventional many wastewater treatment systems through- crops, involves more uncertainty than specific out the United States. More stringent water detailed knowledge. quality standards are resulting in a need for better microalgal harvesting technology and Among the uncertainties are the economics presenting an opportunity for fuel recovery of the production system, including the har- from the harvested microalgae. Several proj- vesting of the plants. Detailed economic anal- ects throughout the United States have demon- yses are not available; those that have been strated the beneficial effects of marsh plants carried out are based on too many optimistic in wastewater. treatment. In all cases, waste- assumptions to be credible or useful. Of water aquiculture appears more economical course each type of plant will require a dif- and less energy intensive than conventional ferent cultivation and harvesting system. How- technologies. 16 However, the total potential ever, in all cases, these appear to be signifi- impact of wastewater aquiculture on U.S. en- cantly more expensive per acre in both capital ergy supplies, even when making favorable and operations than the costs of terrestrial market penetration assumptions, is minimal — plants. This increased cost per acre can only be about 0.05 to 0.10 Quad/yr.17 justified by an increased biomass production rate or a specific, higher valued product. Be- For aquatic plants to make a more signifi- cause the productivity and economics of aqua- cant contribution to U.S. energy resources, tic plants are, to a large degree, unknown, the other types of aquatic biomass energy systems potential for aquatic plant biomass energy must be developed. One alternative is the con- farming is in doubt. version to fuel of aquatic plants already harvested from natural, unmanaged stands. Exam- One approach to improve the economics of ples are water hyacinth weeds removed by me- such systems is to combine the biomass energy chanical harvesters from channels in Florida system with a wastewater treatment function. and other southern States and cattails or bull- As aquatic plants are in intimate contact with rushes cut periodically in natural marshes in water, they can perform a number of very im- Minnesota or South Carolina to improve portant waste treatment functions—oxygen wildfowl habitats. However, the infrequent production (by microalgae) which allows bac- occurrence of such harvests, the small bio- terial breakdown of wastes, settling and filtra- mass quantities involved, and transportation tion of suspended solids, uptake of organics difficulties make energy recovery from such and heavy metals, and, perhaps most impor- sources essentially impractical. The conver- tantly, uptake of the key nutrients that cause sion, if practiced, of natural marsh systems to pollution. The relatively high concentrations large-scale managed (planted, fertilized, har- of nitrogen and phosphorus in aquatic plants vested) plantations will present significant eco- (e.g., about 10 percent nitrogen and 1 percent logical problems and, even if these are ameli- phosphorus in microalgae and 3 percent nitro- orated or overcome, opposition by environ- gen and 0.3 percent phosphorus in water hya- mental groups. Nonetheless, large areas of cinths), makes these plants particularly useful marshes do exist in the United States and they, in nutrient removal from wastewaters. Re- in the long term, may become resources that search in wastewater aquiculture is well ad- could be exploited on a multipurpose and sus- vanced, although some critical problems re- tained yield basis like the national forests. In main to be elucidated, and several large dem- the near term, however, the technology for onstration projects are being initiated through- aquatic plant biomass energy systems must be out the United States. For example, water hya- developed with presently unused or “margin- cinths are being used in wastewater treatment plants in Coral Gables and Walt Disney World, “’Ibid Fla., in projects which involve fuel recovery by “Ibid anaerobic digestion of the biomass. Microalgal “Ibid. Ch. 4—Unconventional Biomass Production ● 101

al” land and water resources. In addition, Microalgae are known to produce a variety relatively high-value biomass energy products, of useful chemicals. However, the develop- specifically chemicals and liquid fuels, should ment of such production technology is only be produced by such systems. Examples of just now beginning, and the potential resource such systems include the production of alco- base (land, water, nutrients) available for such hol fuels from cattails (either by hydrolysis of systems is not yet quantified. Thus, the future the areal parts or directly from the starches contribution to U.S. fuel supplies of aquatic stored in the roots) or the production of hydro- plant biomass energy systems cannot be pre- carbon fuels and specialty chemicals from mi- dicted. However, sufficient possibilities and croalgae. promise exist to warrant further R&D efforts.

Mariculture

This section describes problems and oppor- tivation techniques. A small test farm has been tunities associated with developing future installed along the California coast. 20 ocean farms which might use the giant kelp Large ocean kelp farms could theoretically (macrocysts) as a future biomass energy supply significant quantities of natural gas source. Other macroalgae have also been pro- (methane). Linked to a methane production posed as potential marine biomass crops. By system, for example, and assuming serious examining the possibilities of kelp and also technical problems are solved, a l-million-acre noting other proposals, OTA hopes to illustrate kelp farm could produce enough gas to supply the status of this technology in general, its 1 percent of current U.S. gas needs. future potential, the problems involved, and the Federal role in this segment of alternative It would be no easy matter to farm such vast energy research. tracts of ocean. Much still needs to be learned about macroalgae cultivation. But serious re Macroalgae are harvested around the world. search is reducing the areas of ignorance and About 2 million wet metric tonnes are now cut seaweed may some day become a biomass pro- annually, and estimates are that the total po- ducer. tential worldwide crop is 10 times this much— about 20 miIlion wet tonnes. 9 Algae are among the simplest and most primitive of plants. The larger macroscopic In recent decades seaweed cultivation has algae are commonly referred to as seaweeds or rapidly become more successful and has sub- macroalgae. Large seaweeds are the dominant stantially added to annual harvest figures. For plant in most shallow coastal waters including example, as of 1970 there were 130,000 acres those off California and Mexico, where they at- of sea surface under cultivation in Japan, tach themselves to rocks or some other hard about 25,000 acres in The Peoples Republic of substrate under water. China, and additional acreage in Taiwan, Korea, the Philippines, and elsewhere. None of To date, the seaweeds apparently most the current annual world harvest is being used adaptable to human cultivation are the red for energy production. and the brown algae. People have eaten red algae varieties for thousands of years, espe- In the United States, where wild seaweed cially in countries such as Japan and China. beds have been harvested for many years, the possibility is beginning to be studied of increasing production through ocean farm cul- 2“A. Flowers, statement before the House of Representatives Committee on Merchant Marines and Fisheries, Subcommittee ‘9G Michanek, Seaweed Resources of the Ocean, U.N, Food on Oceanography, p. 18, committee report serial No, 95-4, June and Agriculture Organization, Rome, 1975, 7,1978. 102 ● Vol. /l—Energy From Biological Processes

The brown algae group includes the giant Kelp may grow in length as much as 2 ft/day kelp Macrocystis (figure 13), already harvested or increase its weight by 5 percent per day under optimum conditions. The plants form natu- Figure 13.—Macrocystis Pyrifera ral beds up to 3 miles wide and several miles long in southern California. This kelp is now harvested and put to a variety of uses, prin- cipally in the food-processing industry. Fuels have never been produced from kelp except in minute quantities as part of research testing.22

Unfortunately, there is no consensus among the experts who have made projections as to the potential of ocean energy farms. Their estimated costs vary widely and are based on such very sparse data that they cannot be used to either support or reject ocean farm proposals. Estimates of production rates vary by factors of as much as 100. Better experimental data and more complete biological engineering tests will allow for better estimates in the future. The estimates used here lie approx- imately in the middle of responsible optimistic and pessimistic projections for a 400,000-hec- tare (1 million acre) ocean kelp farm:

● average productivity = 20 dry ash free (DAF) tons per acre per year, and ● average annual energy produced = 0.2 Quad (1 percent of U.S. gas consumption of 20 Quads/y r).

Such a system, if built, would provide the equivalent in energy supply of one large LNG- importing plant such as the one located at Cove Point, Md. It would, of course, be a do- mestic rather than an imported fuel, however.

(A: 1/64 natural size; B: 1/4 natural size.) The Giant Kelp is Experiments are underway into the best shown in the left part of the plate in a natural pose with the laboratory-reared seaweed farms. Eventually, long leafy stipes rising to the sea surface from the massive some researchers hope to produce a “pedi- holdfast. On the right is one of the leaf-like fronds showing greed” kelp bred specifically for high methane the gas-filled float bladder at its base and the distinctive teeth along the margin (Anon. 1954). production, fast growth, and hardiness. A key problem faced by potential ocean SOURCE: Velco, Inc. kelp farmers is to deliver enough nutrients to the plants to fertilize them. This is because, in the United States from wild and semiculti- while the deep waters of the ocean contain vated beds and considered at present as the many necessary nutrients, surface water is best candidate for intensive cultivation off often as devoid of nourishment as a desert is California and as a possible fuel producer. z’ ZZM. Neushal, “The C)cmnesticatlorl of the C iant Kelp, ~acro z ‘Neushal, et al., “Biomass Production Through the Cultiva- cystis as a Marine Plant Biomass Producer, ” presented at the Ma- tion of Macroalgae in the Sea, ” p 100, Neushul Mariculture, rine Biomass of the Pacific Northwest Coast Symposium, Oregon Inc , for OTA, Oct 6, 1978 State University, Mar. 3,1977 Ch. 4—Unconventional Biomass Production ● 103

devoid of water. One fertilizing technique be- age corn harvest is 6 DAF ton/acre-yr and Ha- ing tried is artificial upwelling of seawater, waiian sugarcane averages 14 DAF ton/acre-yr. which involves pumping nutrient-rich, deep OTA estimates that if about 1 million acres ocean water to the surface to benefit the kelp were ever farmed, the gross energy production plants. 23 could amount to 0.2 Quad. This is equal to ap- Current research on marine plants can be di- proximately 1 percent of current U.S. natural vided into two categories. gas consumption. These production estimates should be treated with caution since there are The first category, funded by several Federal no ocean kelp energy farms and nobody has agencies to a total of about $1 million in 1979, ever planted and harvested a macroalgae generally includes research projects aimed at a energy crop. better understanding of marine plants, their cultivation, and potential new uses of the Actual gross energy production from such a plants. huge hypothetical ocean kelp plantation has been projected by other researchers to range The other “category” is actually just one from 10 times OTA’s estimate to only one- project: the Marine Biomass Research Program tenth that figure. The entire project might jointly funded by the Gas Research Institute simply prove impossible, others caution. Years (GRI) and the Department of Energy (DOE), of experiments will be necessary before any which has funded over $9 million of directed projections can be confirmed. research as of 1979. There is even less data to draw on in esti- This ongoing marine biomass project in- mating net energy possibilities. In a report cludes a test farm off California. The farm prepared for DOE by the Dynatech R&D Corp., began artificial upwelling experiments late in net energy outputs were estimated to range 1978, but was forced to suspend operations in anywhere from a negative number to about 70 early 1979 due to storm damage. This proto- percent of crop energy .24 type is meant to provide biological information and research clues needed to operate Much of the technology to construct pres- much larger culture farms. It also aims at ex- ent concepts of open ocean farms is already perimental work into cultivation of giant kelp well known. Similar platforms, structures, and on moored structures in the open ocean. The moorings have been built for the offshore oil test farm, may lead to the actual operation of industry and the existing seaweed industry uses a full-scale ocean farm. mechanical harvesting techniques.

There is considerable difficulty at this time Less certain areas of ocean farm engineering in evaluating the appropriateness of the at present include nutrient distribution, disper- Marine Biomass Research Program because lit- sion characteristics of upwelled water, and tle has been produced. It is important that specific configuration of the structure to research results on the cultivation of kelp on which kelp plants will be attached. A major ocean farms be reported in a comprehensive problem for cultivated kelp beds may be to way and subjected to critical review if a future supply an ocean farm with proper nutrients in large program is to be justified. correct quantities. The extreme difficulties of noting the delicate balance of nutrients found Kelp and other seaweeds are potentially a in a natural environment and reproducing this highly productive source of biomass for fuels. in a cultivated one are well known to research- Estimates can vary drastically as to what may ers. be possible for future large ocean farms, but OTA’s evaluation of a hypothetical ocean kelp farm indicates productiveness could range 24 from a low value of 6 DAF ton/acre-yr to a high Dynatech R&D Co , “Cost Analysis of Aquatic Biomass Sys- terns, ” prepared for the Department of Energy, contract No value of 30. I n comparison, this country’s aver- HCP/ET-400-78/I 104 . Vol. II —Energy From Biological Processes

Test farms will upwell deep ocean water to is also needed on plant diseases, preda- supply kelp with proper nutrients. Reservations tors, and water movement and quality); about this procedure are twofold among skep- ● the possibility of developing shallow wa- tics. They worry that deep water could become ter kelp farms either in areas of natural stagnant under the farms, or that, once up- upwelling or in conjunction with other fer- welled, the water would dilute too rapidly and tilizing techniques (see ch. 10); sink again. ● hard data on net energy expectations is lacking; and As previously mentioned, this country’s ma- ● no plans are being readied at present as jor ocean biomass project is jointly supported alternatives to fertilization by upwelling. by CR I and DOE. The project may become the most heavily funded biomass program of the Since plans for future ocean biomass farms 1980’S, with grants projected to grow to over call for the use of millions of acres of ocean $50 million yearly by 1983. Plans for this proj- surface, there will be conflicts with other tradi- ect have been developed mainly by GRI, al- tional users. The dedication of large areas of though regular DOE approval for phases of the open ocean surface for a single commercial project is mandatory.25 purpose such as this is unprecedented. It would require complex, special regulation GRI estimates imply that ocean kelp farming after review of current local, national, and in- could be a commercially viable project for this ternational laws. country. The Institute’s fuel production cost estimates for methane generation from kelp Even though the ocean space within the 200- range from $3 to $6/million Btu. mile zone surrounding the United States is 1½ billion acres, conflicts can be expected with The previously mentioned Dynatech report such traditional ocean users as commercial on fuels from marine biomass comes to a dif- shipping, the navy, commercial and sport fish- ferent conclusion. Its estimates range from ing, offshore oil and gas operation, and recrea- $7/million Btu up to several hundreds of dol- tional boating. To date, no detailed investiga- lars per million Btu, should productivity prove tion of legal or institutional approaches to re- low and design costs high. solving conflicts has been accomplished. This Some critics of the GRI marine biomass pro- issue will need analysis prior to any large-scale gram contend that there is not enough data initiative in ocean farming, and will have a ma- available to justify the level of expenditures jor impact on feasibility, productivity, and cost for the biological test farm. of marine biomass in the future. Analyses of specific sites and siting problems will be cru- Critics have stated that the open ocean test cial to the ocean question. farm is an inappropriate and perhaps prema- ture step in a long, logical process of devel- OTA has found that Federal research pro- oping future deep sea operations. Considera- grams directed toward energy problems have tions which may be overlooked by this test not been adequately coordinated with similar farm approach include: research directed toward production of food, chemicals, or other products. the need for better information on kelp growth and productivity and limiting fac- Much research is needed to develop any tors in natural beds; suitable marine pIant culture regardless of the need for additional basic research into whether the end product is food or fuel. Such nutrients and productivity (much research basic research could be better supported and coordinated by all interested agencies. Pro- grams supported by Sea Grant and the Nation- al Science Foundation have tended to focus on ‘sGeneral Electric Co., briefing, “Energy From Marine Biomass Project, Program Review, ” for the Gas Research Institute, New- basic biological efforts or food production port Beach, Cal if., March 1978. goals while DOE programs are focused on pri- Ch. 4—Unconventional Biomass Production ● 105

mary fuel production. Since DOE now has the in deepwater, open ocean farms. This possibili- major funds available for seaweed research, ty would mean coordination of several existing the tendency has been to create programs fo- research efforts; expanding some, developing cused on fuel production. The encouragement some new ones, and generally integrating of further diversity in existing seaweed re- many efforts focused on basic biological ques- search efforts is essential to a long-term im- tions and food production as well as energy provement in the knowledge and capability of production. developing future marine plant culture programs.

One approach to conducting a systematic program for developing ocean farms would be to expand research in natural seaweed beds and shallow water farms prior to experiments

Other Unconventional Approaches

There are several other unconventional ap- captured by the plants as effectively as it proaches to biomass production. Because of could. Consequently, this approach would also the complexity of plant growth, it is likely that be expected to reduce the total biomass yields. many approaches will be tried and fail. How- ever, this complexity also gives rise to significant possibilities. While all unconventional ap- Chemical Inoculation proaches cannot be covered here, a few are By subjecting some plants to herbicides like discussed below. paraquat or 2,4-D, hydrocarbon or vegetable oil production can sometimes be increased. Multiple Cropping These chemicals block certain biochemical pathways, thus promoting greater production MultipIe cropping consists of growing two or of other products. Preliminary results with more crops on the same acreage in a year. guayule, for example, indicate that 2,4-D may Growing winter wheat on land that produced a cause a doubling of the natural rubber content summer crop is one example. The winter wheat of this plant.26 While it is too soon to assess can delay spring planting, so its use is ap- this approach, it may prove to be an effective plicable only for land where certain summer way of improving yields of these products. crops are to be grown. However, this is basical- ly a conventional approach. Energy Farms The unconventional multiple cropping con- 27 sists of growing more than one summer crop Energy farms have been proposed as a on an acreage by harvesting the first crop means of providing a reliable supply of large before it matures or developing species that quantities of biomass for large conversion mature rapidly. Since starches, sugars, vegeta- facilities located on or near the farm. The ble oils, and hydrocarbons are generally pro- basic idea is to have a large tract of land (tens duced in the greatest quantities in mature ‘6Gilpin, et al,, op. cit. plants, this approach would probably reduce “See, e.g., G, Szego, “Design, Operation, and Economics of the overall yields of these products. Also, the the Energy Plantation, ” Proceedings Conference on Capturing the time between the harvest of the first crop and Sun Through 6ioconversion (Washington Center for Metropoli- tan Studies, 1976); G C. Szego and C C Kemp, “Energy Forests the development of a full leaf cover in the sec- and Fuel Plantations,” Chemtech, p. 275, May 1973; and Si/vicu/- ond crop will be a time when sunlight is not ture Biomass farms (McLean, Va.: MITRE Corp., 1977).

67-968 0 - 80 - 8 106 ● Vol. Il—Energy From Biological Processes

of thousands of acres) dedicated to growing eral years. A pest infestation, however, the biomass feedstock for a nearby conversion could destroy the entire crop in which an facility. Although this is technically possible, a average of 3 to 5 years’ cultivation had number of practical and economic considera- been invested, and this could be financial- tions probably will limit investment in energy ly disastrous. If grass is the energy crop, farms. Moreover, this approach ignores the ef- or the time between tree harvests is re- fect that bioenergy production has on related duced, the loss from a pest infestation sectors. Some of the more important of these would be considerably less, but the yields points are: would fluctuate more from year to year, making it necessary to rely on outside ● Land. – The land available for energy sources of biomass in years with low har- farms has often been estimated to be sev- 2829 vests or to sell surpluses in years with eral hundred million acres. OTA’s bumper harvests. analysis, however, indicates that consider- ● Competition with other uses for the land. ably less land is available for biomass pro- – Because of the uncertainty about fu- duction (see ch. 3). Furthermore, there ture cropland needs for food production, would be practical difficulties with buy- it would be unwise to assume that tens of ing large contiguous tracts of the size millions of acres could be devoted to a needed for large conversion facilities (tens conversion facility for 30 years without af- to hundreds of thousands of acres). fecting the price of farmland and thus If cultivation on very poor or arid land food. proves to be feasible or if irrigation for ● Preclusion of nonenergy benefits. -OTA’s energy production is socially acceptable analysis indicates that bioenergy harvests, and the water is available, then these lim- if properly integrated into nonenergy sec- itations could be somewhat less severe tors, can provide benefits beyond the en- than they appear to be at present. ergy, such as increased growth of timber ● Estimates of future yields Crop yields.– suitable for paper and lumber. Attempting from short-rotation tree farms have been to isolate bioenergy production from as high as 30 ton/acre-yr,30 which OTA these other sectors would preclude some considers to be highly unrealistic. Yields of the potential benefits. of 6 to 10 ton/acre-yr are more realistic for the poorer soil that could be available for Although none of these factors is insur- energy farms. mountable, taken together they make energy ● Initial investment.– If short-rotation trees farms appear considerably less attractive than are used as the energy crop, there would numerous other bioenergy options. Particular- be a 6- to 10-year Ieadtime before the first ly because of the risk and the initial invest- harvest could be made. This would be ment, it is more likely that bioenergy crops will prohibitively long for many investors. be grown as one of the many crop choices Grasses, however, would reduce the lead- available to farmers, rather than on large time to a fraction of a year. In either case, tracts dedicated solely to energy production. the cost of acquiring the land would in- There is, however, no technical reason why en- crease the initial investment substantially. ergy farms cannot be constructed. ● Risk.— Using short-rotation trees as the energy crop would give yields that are less Biophotolysis sensitive to weather than grass because the growth would be averaged over sev- Biophotolysis is generally defined as the process by which certain microscopic algae ‘%zego, op. cit. can produce hydrogen (and oxygen) from wa- 29s;/v;cu/ture /3;c3fnass Farms, op. cit. ter and sunlight. Two distinct mechanisms are ‘OJ. A Allich, Jr., and R E Inman, “Effective Utilization of Solar Energy to Produce Clear Fuel, ” Stanford Research insti- known by which microalgae can carry out bio- tute, final report No NSF/RANN/SE/Cl 38723/FR/2 , 1974 photolysis: 1) through a “hydrogenase” en- Ch. 4—Unconventional Biomass Production . 107

zyme (biological catalyst) which is activated or due to the high energy consumption of the ni- induced by keeping the microalgae in the dark trogenase reaction. Also, the mixture of hydro- without oxygen for a period of time; or 2) gen and oxygen generated by such a system through the “nitrogenase” (nitrogen-fixing) en- may be expensive to separate. zyme which normally allows some types of mi- Whichever biophotolysis mechanisms or croalgae (the “blue-green” algae) to fix atmos- processes are eventually demonstrated to be pheric nitrogen to ammonia but which also capable of efficient and sustained solar energy can be used to produce hydrogen by keeping conversion to hydrogen fuel from water, they the algae under an inert atmosphere such as must take place in a very low-cost conversion argon gas. system. The development of an engineered In the case of biophotolysis with hydroge- biophotolysis conversion unit must meet strin- nase the key problem is that when simultane- gent capital and operational cost goals. As bio- ous oxygen production occurs, the hydroge- photolysis will be limited by the basic proc- nase enzyme reaction is strongly inhibited and esses of photosynthesis— probably no more the enzyme itself inactivated. Although it was than 3 to 4 percent of total solar energy con- recently demonstrated that simultaneous pro- version to hydrogen fuel —this sets an upper duction of oxygen and hydrogen does occur in limit to the allowable costs of the conversion such algae,31 it is uncertain whether it will be unit. In principle, the algal culture—the cata- possible to sustain such a reaction in a prac- lyst which converts sunlight and water to hy- tical system. This difficulty has led to propos- drogen and oxygen–can be produced very als for separation of the reactions either by de- cheaply; however, the required “hardware” to veloping an algal system which alternates oxy- contain the algal culture and trap the hydrogen and hydrogen production, (possibly on a gen produced may be relatively expensive. day-night cycle) or by developing a two-stage Biophotolysis is still in the early stages of process. Such systems are still at the concep- development. No particular mechanism, con- tual stage, although considerable knowledge verter design, or algal strain appears to be in- exists about the basic mechanisms involved. herently superior at this stage. Claims that Somewhat better developed is a biophotoly- near-term practical applications are possible, sis process based on nitrogen-fixing blue-green that genetic engineering or strain selection can algae. I n these algae the oxygen-evolving reac- result in a “super” algae, or that biophotolysis tions of photosynthesis are separated from the is inherently more promising than other bio- oxygen-sensitive nitrogenase reaction by their mass energy options are presently not war- segregation into two cell types — the photosyn- ranted. A relatively long-term (10 to 20 years) thetic vegetative cells and the nitrogen-fixing basic and applied research effort will be re- heterocysts. Heterocysts receive the chemicals quired before the practical possibilities of bio- necessary to produce hydrogen from vegeta- photolysis are established. tive cells but are protected from oxygen by their heavy cell wall and active respiration. Using cultures of such algae from which nitro- Inducing Nitrogen Fixation in Plants gen gas was removed, a sustained biophotoly- The biological process of nitrogen fixation, sis reaction was demonstrated: about 0.2 to 0.5 the conversion of nitrogen gas (not a fertilizer) percent of incident solar energy was converted to ammonia (a fertilizer) has only been found to hydrogen gas over a l-month period. How- to occur in bacteria and the related blue-green ever, significant problems stil exist in the de- algae. These primitive organisms maintain the velopment of a practical system —1 O times ecological nitrogen cycle by replacing nitrogen higher conversion efficiencies must be lost through various natural processes. The achieved, a goal which may not be reached capability for nitrogen fixation expressed by many pIants (soybeans, alfalfa, peas) is due “ E Greenbaum, Bioengineering Biotechnology Symposium, VOI 9, In press solely to their ability to Iive in a symbiotic 108 ● Vol. Ii—Energy From Biological Processes

association with certain bacteria (of the genus rich environment of a plant leaf. In principle, Rhizobia), which form the characteristic “root there would only be a relatively minor advan- nodules.” A certain fraction of the photosyn- tage for a plant to directly fix nitrogen rather thetic products of these plants are transferred than do so symbiotically. Much more basic to the roots where they are used (as “fuel”) by knowledge in many areas of plant physiology, the bacteria to fix nitrogen to ammonia which genetics, biochemistry, etc., as well as devel- is then sent (in bound form) to the protein syn- opments in genetic engineering and plant tis- thesizing parts of the plant. sue culture will be required before the potential for practical applications of such concepts This process is, in principle, energy inten- can be evaluated. sive, with each nitrogen atom (fixed) reducing the biomass production by several carbon atoms (about 2 to 3).32 In practice, significant Greenhouses inefficiencies in the process are often noted, most particularly the recent discovery that It is well known that increasing the C02 con- some Rhizobia bacteria in root nodules waste centration in the air results in significantly im- a large fraction of the “fuel” supplied by the proved plant growth for some plants. Depend- plant in the form of hydrogen gas.33 By using ing on the specific plant and the specific con- Rhizobia strains that can effectively recycle ditions of the experiments, a 50-to 200-percent the hydrogen gas, this loss may be overcome. increase in biomass production has been noted. Greenhouses have the additional ad- Although biological nitrogen fixation can vantages of providing a “controlled environ- substitute, to a large extent, for the fossil-fuel- ment” where pest control, water supply, and derived nitrogen fertilizers currently used in fertilization can be better managed, resulting agriculture, the tradeoff may be an overall in potentially high yields. The higher tempera- reduction in biomass yields. In an era of de- ture in greenhouses allows extended growing creasing fossil fuel availability, such a tradeoff seasons in temperate climates. Greenhouse may be desirable, particularly as the price of agriculture is rapidly expanding thoughout the commercial fertilizers is a limiting economic world to meet the demands of affluent coun- factor in many biomass production proposals. tries for out-of-season vegetables and horticul- However, nutrient recycling could be prefer- tural products. However, the high cost of able to de novo production, as it probably greenhouse agriculture and its high energy would be less costly and energy intensive. consumption make production of staple crops Alternatively to biological nitrogen fixation, unfeasible and proposals for biomass energy thermochemical conversions of biomass to production unrealistic at present. Although synthesis gas and their catalytic conversion to significantly lower cost greenhouse technology ammonia are feasible. Whether this is more fa- is feasible in principle, biomass production vorable both in terms of economics and energy costs in Arizona, for example, would still be 10 efficiency is uncertain. times as expensive as open-field biomass crops 34 A number of scientists have proposed that, grown in the Midwest. A significant inflation through genetic engineering, they could trans- in farm commodity, farmland, and water fer the nitrogen-fixing genes directly to the prices could make greenhouse systems more plant. However, such proposals face technical attractive. At present and in the foreseeable barriers. For example, the nitrogen-fixing reac- future, however, greenhouses do not appear tion is extremely oxygen sensitive and is unlike- economically feasible for bioenergy produc- ly to be able to take place in the highly oxygen- tion.

‘2K. T Shanmugan, F. O’Gara, K. Andersen, and P C. Valen- “L. H. de Bivort, T. B. Taylor, and M, Fontes, “An Assessment tine, “Biological Nitrogen Fixation,” Ann. Rev. Plant Physio/. 29, of Controlled Environment Agriculture Technology, ” report by p. 263,1978. the International Research and Technology Corp. to the National “Ibid. Science Foundation, February 1978.