Anaerobic Digester Liquor as a Source of Ammonium and Phosphate For Single-Cell Protein Production
It has been shown in the literature that some yeasts will grow in anaerobic digester liquor with an external source of carbohydrate for energy. In this research tests were performed to determine the optimum conditions for growth of the yeasts Candida utilis and Kluyveromyces fragilis. It was found that a pH of 4.0 and a temperature of 30°C yielded optimum growth. The optimum carbohydrate concentration differed with the organism and the sugars tested. The uptake of the inorganic nutrients, phosphate and ammonia, was measured. C. utilis removed 100% of the phosphate and ammonia from the medium within 24 hours while K. fragilis removed about 80% of the phosphate and ammonia within 24 hours. Batch cultures and continuous cultures of C. utilis produced essentially the same results. The conversion of sugar and ammonia into protein was measured with C. utilis and K. fragilis. The efficiencies of this conversion were about 21% and 24% respectively. A two-membered culture of C. utilis and Streptococcus sp. were tested for maximum growth with C. utilis and S. faecalis yielding the most growth. The raw lactose source, whey, was tested as a source of carbon and energy but it proved too dilute for K. fragilis to produce satisfactory growth.
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