The Ecology of a Biotic Community Consisting of Algae and Bacteria

Two important areas for the application of biological processes are the reclamation of water and organic nutrients from waste waters and the complete control of enclosed environments. The former may be accomplished through the agency of biotic communities consisting of algae and bacteria grown in especially designed lagoons known as "high-rate oxidation ponds." These ponds have been described by Oswald and his colleagues (1954, 1957, and 1958). The biological control of enclosed environments, such as in atomic submarines or in space vehicles, may also be brought about through the collective activity of algae and bacteria and has been described by Golueke and Oswald ( 1958). The successful application of a biological process to such widely divergent and, paradoxically? closely related functions as the control of the environment in a space vehicle and the treatment of wastes in a high-rate oxidation pond requires an extensive knowledge of the ecology of the organisms involved in the process. This is true because effective biological control requires an optimum relationship between the environment and the biotic community concerned, and this can be accomplished only by providing proper environmental conditions. To establish such a relationship, it is necessary to know the nature and extent of the influence of the principal environmental factors involved. Among the key factors to which an algal-bacterial community is subject, whether in an oxidation pond or in a space ship, are carbon dioxide concentration, light intensity and length of duration of light per day, length of growth period, and temperature. In a space ship these factors can be regulated mechanically, and in an oxidation pond, by engineering and geographical location. Although much has been written on the effect of the key environmental factors on individual algal species, there is a paucity of information in thle literature on the effect of these environmental factors, either individually or collectively, on such organisms when living as members of a biotic community. Inasmuch as the influence of these factors are modified by the collective action of different types of organisms living together in the same community, and by the nature of the action of one group upon the other, information gained from studies of an organism grown as a pure culture cannot be applied unequivocally to the same organisms when living as a member of a biotic community. This paper treats that part of an investigation on the biological control of enclosed environments which deals with the influence of certain environmental factors in determining the nature and over-all activity of climax associations of algae and bacteria resulting from the application of a given set of factors. In the description to follow, the term "culture" will he used synonymously with "biotic community," inasmuch as the microorganisms were grown in a prepared nutrient medium under controlled conditions. The author wishes to express his appreciation for counsel given him by Dr. WV. J. Oswald, Dept. of Civil Engineering and School of Public Health, University of California, Berkeley.