43 



Does the general "fuels from biomass" concept, then, have any validity and, if so, 

 what kinds of biomass could conceivably be grown for that purpose? It would 

 appear, not only that species not presently cultivated must be grown for this new 

 purpose, but also that they must be grown in areas not suitable for the cultivation 

 of food and fiber crops. They must also be highly productive and they must be easy 

 and inexpensive to grow, harvest and process to a form suitable for their digestion 

 to methane. 



The seaweeds would appear to fit most of these requirements. Certainly the 

 oceans are the largest uncultivated and under-utilized pastures on earth. Some 

 species of seaweeds do have commercial value as food, in eastern countries, and for 

 their contained chemicals, but most have no commercial value and some (e.g., sea 

 lettuce) are considered esthetic nuisances when they grow or accumulate to high 

 densities in heavily-populated bays and estuaries. In general, cultivation of seaweeds 

 for energy would not compete for production of food or fiber crops in terms of space, 

 effort or economics. 



A few of the seaweeds used as food have been cultivated for a number of years in 

 Southeast Asia and the Orient, and, more recently, some of those used for their 

 chemicals have been grown, though that industry still relies primarily on the 

 harvest of natural populations. Cultivation of the food species has, for the most part, 

 employed intensive labor practices and a rather primitive technology. Yields from 

 such practices range widely, from less than one dry ton per acre per year for the 

 highly prized Porphyra or "nori" in Japan (whose price of more than $20 per pound 

 justifies this high labor-low yield activity) to the more impressive 20 tons/acre/year 

 for kelp grown in Northern China. The latter rivals the more productive terrestrial 

 crops such as napier grass and sugar cane, experimental yields of which in Puerto 

 Rico have recently been reported at 26 and 22 dry tons/acre/year respectively 

 (mean annual sugar cane production in mainland U.S. and Hawaii, including total 

 dry matter, are 10 and 16 tons/acre respectively). Seaweeds grown for their chemi- 

 cals in Japan, Taiwan and the Philippines have intermediate yields averaging about 

 five dry tons per acre per year, the same as the mean production of corn, including 

 residues, in the United States. 



The present author first grew seaweeds at the Woods Hole Oceanographic Institu- 

 tion as part of a waste recycling-aquaculture project in which the plants were used 

 as a polishing stage to remove the nutrients generated by a shellfish culture system 

 prior to discharge of the aquaculture effluent to the environment. When ERDA, 

 precursor of the U.S. Department of Energy, developed its "Fuels from Biomass" 

 program in the mid-1970's, the search began for highly-productive plant species that 

 could be grown over vast areas as "energy farms" capable of providing the organic 

 biomass needed to make a significant contribution to the country's energy needs — 

 then pegged at some 75 "quads" (quadrillion or 10 ^^ BTU) per year and estimated 

 to exceed 100 quads by the turn of the century. Because of the promising prelimi- 

 nary results with seaweed culture in the Woods Hole aquaculture project, support 

 was obtained to investigate the potential of seaweeds as a "biomass for energy" 

 source. At that point, the research was transferred to the Harbor Branch Founda- 

 tion laboratories in Fort Pierce, Florida because the milder climate and more 

 abundant sunshine of that location would permit year-round growth of the plants 

 and thereby better reflect the maximum potential of seaweeds for organic produc- 

 tion. 



Over 50 species of seaweeds native to Florida coastal waters, including representa- 

 tives of all of the major taxonomic groups — green, red and brown algae — were 

 screened in small outdoor culture units to select the most promising species with 

 respect to growrth rate throughout the year and the relative freedom from difficulty 

 of its cultivation. The best of the lot, by these criteria, was the red seaweed, 

 Gracilaria tikvahiae. 



Gracilaria was then grown throughout an entire year under what appeared to be 

 ideal culture conditions — vigorous aeration, rapid exchange of enriched seawater, 

 frequent harvest, with an annual production that averaged 35 grams dry weight/ 

 m May — equivalent to 51 dry tons/acre/year. 



It is, of course, misleading to extrapolate small-scale experimental results to large 

 areas where scaling factors and other complications may lead to significantly lower 

 yields. However, the productive potential of many terrestrial crops have been evalu- 

 ated in similar, small-scale experimental plots. None has surpassed that of Graci- 

 laria in the above experiment. It must be remembered, however, that Gracilaria, 

 like other seaweeds, contains a large fraction of its dry weight as mineral salts. 

 Ironically, the more ideal the culture conditions, particularly with respect to the 

 supply of essential nutrients, the greater the mineral or "ash" content of the plants, 

 those grown in the experiment described above having an ash content of approxi- 

 mately 50 percent of its total dry weight. But the purely organic yield of 25.5 tons/ 



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