COMPOSTING OF SALMON-FARM MORTALITIES

This study investigated the effectiveness of composting fish-farm mortalities using a layering method. This is a modified static-pile method that avoids the need to mix the initial raw materials by piling alternate layers of morts and bulking agent. The use of different ratios of morts to sawdust was investigated. Temperature profiles and volumetric shrinkage were monitored to assess the progress of the composting process. The quality of the composts after 60 days was assessed on the basis of the carbon/nitrogen ratio and moisture, ammonia, nitrate and organic acid contents. The results indicate that within the range of fish morts to sawdust ratios tested, whole fish were completely composted and thermophilic conditions attained, thus satisfying the EPA PFRP temperature requirements. The temperature profiles indicate that the distribution of morts and bulking agent within layers was important: thinner layers of morts improved the temperature profiles. The 3:1 mix was judged to be the most advantageous, since it allows more morts to be composted per unit area.