AMINO-ACID-COMPOSITION OF COMPOSTING COTTON WASTE

Amino acids are an essential part of the active fraction of organic ma tter in compost which is associated with its capability to act as a fe rtilizer. Their composition might also be used as a means to assess co mposting processes. We studied the influence of composting conditions on the amino acid composition of two composts obtained from the same l ignocellulosic substrate (cotton waste from carding). Samples of compo sting substrate were taken at the end of the thermophilic, mesophilic and curing phases of two different composting processes involving diff erent C/N ratios, forced air ventilation (compost 1) and manual turnin g (compost 2). The total amino acid content increased with time in bot h processes, but was greater throughout the experiment in compost 1, r eaching 145.19 g/kg after 85 days. The total concentration of neutral amino acids increased sharply during the first few days of composting and remained fairly constant after 40 days in both composts. In compos t 2 the total concentration of acidic amino acids was more than twice the amount of total basic amino acids during the first stages of compo sting, and decreased afterwards. The relative molar distribution (RMD) of aspartic and glutamic acids decreased steadily with time in compos t 2. A sharp increase (+140%) of the RMD of lysine was found in this c ompost at the end of the curing period. On the contrary, in compost 1, the RMD of aspartic acid increased during composting, while that of l ysine dropped to approximately 50%. Changes in the amino acid composit ion were found to reflect the changes in the composition of the microb ial population.