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 re- sistance). 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 iso- late 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 di- rectly. 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 proc- esses 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.