Identification and characterization of microorganisms from earthworm viscera for the conversion of fish wastes into liquid fertilizer

Five bacteria isolated from earthworm viscera and identified as Brevibacillus agri, Bacillus cereus, Bacillus licheniformis, and Brevibacillus parabrevis by 16S rRNA sequencing were employed in the conversion of fish wastes generated from a restaurant specializing in sliced raw fish into fertilizer. Within 120 h after inoculation of autoclaved fish waste with 5.15 × 105 CFU ml−1 mixed isolates, the amount of dry sludge decreased from 29.4 to 0.2 g, the pH changed from 7.05 to 5.70, and the cell number reached 6.45 × 105 CFU ml−1. Analyses of an 84-h culture of inoculated fish waste indicated low phytotoxicity in a seed germination test, an amino acid content of 5.71 g 100 g−1, a low concentration of heavy metals (Pb, As, Cd, Hg, Cr, Cu, Ni and Zn), and a N/P/K level of 2.33%. Therefore the converted fish waste has the potential for use as liquid fertilizer, although the low NPK level is a concern. This is the first demonstration of the reutilization of fish wastes as a liquid fertilizer.