EVALUATION OF THE MATURITY OF COMPOST MADE FROM SALMON FARM MORTALITIES

The concentrations of phytotoxic organic acids and phenols in a compos t produced from salmon farm mortalities (morts) were investigated as i ndices of compost maturity. A recently developed headspace-gas chromat ograph (HS-GC) technique was used to determine the concentrations. A m odified static pile method was employed in this composting study. Thre e different weight ratios of morts to sawdust were used in two separat e runs, as were different configurations of layers of the composting m aterials. 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 sh owed very high concentrations of organic acids and a significant amoun t of phenol. The trend was for the phytotoxic organic acids and phenol to decrease as storage time increased. Organic acids and phenol disap peared much more slowly for the non-aerated products than for the aera ted ones. The concentrations of organic acids and phenol served as a m ore reliable indicator of the degree of maturity of the composts than did moisture content, pH or the carbon to nitrogen ratio. The headspac e analysis technique provided a relatively simple and effective method for the detection of these phytotoxic components of fish composts. Re sults also showed that the distribution of morts and sawdust within co mposting piles was important.