Properties and Salinity of Sedimentation Solid Discharged from Aquaculture Tanks for Farmland Application

The fertilizer components and salinity of sediments (fish feces, leftovers, etc.) collected from aquaculture tanks, where saltwater fish are raised, were investigated for application to farmlands. The sedimentation solids were acidic at pH 4.9, and the C/N ratio was lower than those of cattle manure and swine manure. Total nitrogen and phosphate were higher than those of cattle manure and swine manure, but potassium was much lower than those of cattle manure and swine manure. The content of heavy metals in the sedimentation solids was well below the allowable amount for sludge fertilizer. The sedimentation solids contained high concentrations of chloride (Cl-) and sodium (Na+) ions. The origin of the Cl- and Na+ was thought to be due to seawater in the sedimentation solids. Since commercial compost made from cattle manure contained about 1.82% Cl- and 0.57% Na+ in dry matter, it was considered that the sedimentation solids would not be a problem in application to agricultural land if the Cl- and Na+ contents were similar or lower.