Single Cell Protein

Project 1

Purple Sulfer bcteria Study (Thiopedia)

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Abstract :

Wastes from agricultural related activities (from both crop and animal production) are consistently identified as the most pervasive non-point pollution source in the United States. Agricultural waste is one of the leading causes of surface water quality problems and ground water contamination (Jensen, 1991; Sweeten and Melvin, 1985). The most common method of treating agricultural waste is with lagoons. Lagoons have been used for treating a variety of wastes, ranging from agricultural, municipal to industrial activities. They are very effective especially for treating animal waste. Red, pink, or purple pigmentation of lagoon water has been frequently observed. This pigmentation is attributed to the presence of purple sulfur bacteria that grow in anaerobic lagoons. The presence of these bacteria has been associated with reduced odor from lagoons (Lotringen and Gerrish, 1978). In addition to odor reduction, purple sulfur bacteria have been considered as a supplementary feed for animals, especially fishes and poultry (Kobayashi and Tchan, 1973). Purple sulfur bacteria are found in nearly all aquatic environments. They are present where light reaches anaerobic, sulfide-containing zones in lakes (Takahashi and Ichimura, 1968; Guerrero et al., 1985; Overmann et al., 1991), in lagoons treating a variety of wastes (Sletten and Singer, 1971; Hart and Turner, 1965; Holm and Vennes, 1970), and in sewage treatment plants (Siefert et al., 1978). They grow anaerobically in the presence of light and use H2S as an electron donor for photosynthesis. By utilizing H2S (the main cause of lagoon odor) purple sulfur bacteria reduce the odor level from anaerobic lagoons. In addition, cell protein of the purple sulfur bacteria is a useful by-product that can be included in the diet for poultry and fish. Effective treatment of animal waste and production of bacterial biomass requires knowledge of environmental conditions that favor growth of purple sulfur bacteria. Light intensity, anaerobic conditions, sulfide concentration, temperature, and pH have been reported to affect the growth of purple sulfur bacteria (Pfenning and Truper, 1989) with light intensity and sulfide concentrations the most important factors. However, light penetration and sulfide concentration are influenced by depth of the lagoon and the concentration of the waste. Studies in the past have focused on monitoring the presence of purple sulfur bacteria and the environmental conditions that existed where they were found. Most of these studies were done in lakes where the sulfide concentration and other nutrients are low and extent of light penetration is deeper than in waste treatment lagoons. The main emphasis of this research is to determine the effect of depth and surface area of a reactor on growth of purple sulfur bacteria using cattle waste as a substrate.