tion and flotation technique will be used to recover the bacteria. And the entire operation will run under sterile conditions. ICI isn't the only company that has been studying ways of producing single cell protein (SCP) for animal feed. A number of companies throughout the world, including British Petroleum, Liquichimica Biosintesi, Royal Dutch/Shell, and Standard Oil Co. (Ind.), are engaged in active research programs or already have built large plants for making SCP from a variety of organisms and a range of growth media (C&EN, May 5,1975, page 24). But it is probably fair to say that ICI is the farthest along in developing a commercial route for growing bacteria on methanol. There will be no shortage of feedstock, since ICI is a major producer both of ammonia and methanol from North Sea gas. The company's annual ammonia capacity in the U.K. currently approaches 1.5 million metric tons. That of methanol is about 600,000 metric tons. Peter King, I d ' s protein director, lists a number of reasons for concentrating on methanol as a substrate. It is comparatively cheap. The commercial product is pure. It is both volatile and water soluble, facilitating its complete removal from the protein. And it may be made from oil or coal as well as from natural gas. In contrast, Shell researchers in the U.K. and the Netherlands have been concentrating their SCP efforts on growing bacteria on methane. The decision to build the Pruteen plant marks the culmination of some eight years of basic research on fermentation methodology at ICI. All told, some $20 million has gone into the development to date. Initially, attempts were made to grow bacteria on methane but without very much success. "We were almost about to give up," King recalls, "when Dr. J. Rodney Quayle at Sheffield University's microbiology department, in a very elegant piece of research, showed that microorganisms that live on natural gas turn it first into methanol. ,, The conversion of methane to methanol may be a rate-limiting step in the growth of the organisms. For instance, methanol, being a watersoluble liquid, avoids the gas transfer problem associated with gaseous methane "As far as we were concerned," King says, Quayle's discovery "was one of those eureka situations. For if there is one thing we can do, it is make methanol from natural gas very efficiently." M. methylotrophus "does extraordinarily well" in a simple diet, King observes. It doubles itself every five hours. And it consists of more than 70% protein. In the continuous fermentation process, air and ammonia, methanol, and a mixture of salts and acid are sterilized before being fed separately into the base of the pressure cycle fermenter. ICI engineers designed the unit to provide the culture with sufficient oxygen rapidly enough to maintain the high reproduction rate. "It's 26
C&EN Oct. 11, 1976
Feeding trials by ICI have established high nutritional value of Pruteen so simple, we can't think why no one thought of it before," King muses. It works on the fairly obvious principle that oxygen from the air dissolves rapidly in the growth medium at the base of the fermenter because of the great pressure exerted by the height of the fluid. At the top, where the pressure is low, carbon dioxide that the organisms generate bubbles free. "The effect is that the culture is breathing in at the bottom and breathing out at the top," King explains. "What we have is a huge hydrodynamic lung. If you get the shape of the vessel right, the air supply and the contents go round and round." King points to a number of advantages of the pressure cycle fermenter. For one, it can be scaled up to very large sizes. For another, it doesn't need a stirrer so there is a saving of energy. More significant, however, is that the absence of a shaft and paddle makes it easier to keep the contents sterile. "That is very important to us," King says. "To maintain product quality we permit nothing but our chosen microorganisms to grow inside the fermenter." The rates of nutrient input and product removal are balanced carefully against the rate of growth of the bacteria. The creamy suspension of cells drawn off is flocculated by a process that avoids use of flocculating agents. After flash drying and processing to granules or to a fine powder the product is ready for shipment. Extensive trials in the U.K. and elsewhere using SCP from ICI's 1000 metric-ton-per-year pilot unit have established the high nutritional value of Pruteen and the absence of any harmful effects, King claims. Combined with whey powder, it can be used instead of skimmed milk in milk replacer diets for calf rearing. In poultry diets, Pruteen results in higher growth rates and increased feed conversion efficiency, he adds. The bulk of the new plant's output will go to markets in continental Europe. Pruteen won't be particularly cheap, however. ICI hesitates at this point to put
a projected firm price on the product. With its more than 70% by weight protein content, it will be offered as a competitive alternative to spybean meal and fish meal in animal and poultry feedstuff formulations, probably for at least $600 per metric ton. Soybean meal, practically all of it imported from the U.S., has a 40% by weight protein content. It currently sells in the U.K. for about $250 per metric ton, although this price is subject to wide fluctuations. And European fish meal supplies are tight. ICI market researchers see SCP demand in Western Europe reaching about 2 million metric tons per year in the 1980's creating a need for 10 to 15 commercialscale fermentation plants. Worldwide, the total could be 5 million metric tons. D
Booklets on chemical hazards being updated The National Fire Protection Association is revising its two publications on chemical hazards. It is seeking information on potentially hazardous chemicals and reactions to be included in the "Manual of Hazardous Chemical Reactions" or "Hazardous Chemical Data." The first of these publications lists more than 3500 hazardous chemical reactions, briefly summarizing their hazards and listing references. "Hazardous Chemical Data" gives more comprehensive information on several hundred chemicals, emphasizing the fire hazards associated with them. The technical committees preparing the new editions are seeking information on chemical reactions that are known to be hazardous or are potentially so from an energy standpoint, both for chemicals listed in the present edition of "Hazardous Chemical Data," and for hazardous chemicals that could be added in the next edition. Information should be sent to Robert P. Benedetti, National Fire Protection Association, 470 Atlantic Ave., Boston, Mass. 02210. D
