EVALUATION OF THE MATURITY OF COMPOST MADE FROM SALMON FARM MORTALITIES

The concentrations of phytotoxic organic acids and phenols in a compost produced from salmon farm mortalities (morts) were investigated as indices of compost maturity. A recently developed headspace-gas chromatograph (HS-GC) technique was used to determine the concentrations. A modified static pile method was employed in this composting study. Three different weight ratios of morts to sawdust were used in two separate runs, as were different configurations of layers of the composting materials. After 60 d of active composting with aeration, the products from Run 1 were stored without aeration, while aeration was continued for 6 h daily to those from Run 2. HS-GC analysis of these products showed very high concentrations of organic acids and a significant amount of phenol. The trend was for the phytotoxic organic acids and phenol to decrease as storage time increased. Organic acids and phenol disappeared much more slowly for the non-aerated products than for the aerated ones. The concentrations of organic acids and phenol served as a more reliable indicator of the degree of maturity of the composts than did moisture content, pH or the carbon to nitrogen ratio. The headspace analysis technique provided a relatively simple and effective method for the detection of these phytotoxic components of fish composts. Results also showed that the distribution of morts and sawdust within composting piles was important.