control infestations and disease are major sources of the pollutants released by food-producing agriculture, and these pollutants should be expected to be a significant feature of biomass production. One possible problem is escape of the biomass plant species from the confines of the energy farm. A plant that grows extremely rapidly under marginal conditions, with no extra water or nutrients, has little to prevent it from becoming widely dispersed and displacing native plant species.
Another question would be raised in the event that a very fast growing plant that prospers in marginal conditions can be developed. There would then be great incentive to adapt this plant to produce food for human consumption, or at least feed for livestock. We assume that efforts in this direction would be made, and that if successful they would put biomass production and food crops again in direct competition for even marginal land.
Another approach to biomass growth is to use the nutrients in liquid wastes from homes, industry, and agriculture to support the growth of algae in ponds. Such systems use bacteria to oxidize waste materials and produce nutrients to feed algae, which in turn collect solar energy to produce biomass. The advantage of this method is that it can be done with efficiencies of better than 5 percent and that it does not compete with agriculture for nutrients. In fact, it consumes waste nutrients that are responsible for eutrophying bodies of water. However, algae produced in such ponds might have a higher value as animal feed than as either a source of energy or a chemical feedstock.
In the long term, solar energy can be used with a number of chemical processes that supply fuels without the need for producing or gathering biomass. All must be considered speculative for one reason or another; some await a great deal of technical progress, while others are barred from near-term use by their high costs. The methods being investigated hold the promise of supplying fuels in virtually unlimited amounts, however, and much greater attention should be paid them in federal research and development programs. Commercialization is not likely in this century.
One attractive long-term alternative to the growth and conversion of biomass is direct solar fuel production by photochemical conversion. The processes now being most widely investigated involve photolysis, the decomposition of water to produce hydrogen by means of radiant energy.