KWRRI Research Reports


The decomposition and associated nutrient regeneration of three unialgal cultures and one mixed culture containing an indigenous population of bacteria and microscopic animals were studied under dark, constant temperature laboratory conditions. After periods of nutrient-deficient growth ranging from O to 30 days, these cultures were inoculated with decomposer populations and subjected to anaerobic and aerobic environments for the decomposition studies. The extend of decomposition was determined from the percentage volatile suspended solids and percentage particulate COD remaining after 200 days of decomposition. The average extent of decomposition was greater for aerobic than for anaerobic conditions. However, significant portions of the algae remained undecomposed in both cases. A fraction of the initial nitrogen and phosphorus was held within this refractory organic fraction, and the average extent of regeneration of both nitrogen and phosphorus was also greater for aerobic than anaerobic conditions. A correlation between the initial composition of algal matter and the extent to which it decomposed was made. The extent of both anaerobic and aerobic decomposition apparently increased with increasing protein and lipid content and decreased with increasing carbohydrate content. The mathematical model for predicting the extent of nitrogen and phosphorus regeneration proposed by previous researchers was further evaluated. Simplifications and various parameter assumptions were suggested. The critical nitrogen and phosphorus levels in the algae above which excess regeneration occurred were 7% and 0. 7% by weight, respectively.

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The work upon which this report is based was supported by funds provided by the United States Department of the Interior, Office of Water Resources Research, as authorized under the Water Resources Research Act of 1964.