Tryptophan concentration of animal wastes and organic fertilizers

The concentration of tryptophan in organic wastes and in several fertilizers produced from them via aerobic or anaerobic transformation and drying was determined using a high-performance liquid chromatography method. The concentration of both free and fixed tryptophan present in proteins and peptides was measured. Litter dung contained the highest level of tryptophan among the organic wastes examined, followed by activated sludge, liquid dung, and wastewater sediment. Among the fertilizers, Bamil, produced from a mixture of activated sludge and pig-farm wastewater sediment, contained the highest level of tryptophan (388.5 mu g g(-1)). The detected levels of tryptophan suggest that the application of organic fertilizers can increase the concentration of tryptophan in soil to physiologically relevant values. (c) 2006 Elsevier B.V. All rights reserved.