Valorization of Rice Straw and Tofu Residue using Hermetia illucens to Produce Protein Rich Biomass and Organic Fertilizer

The aim of this study was to investigate the potential bioconversion of rice straw and tofu residue using larvae of Hermetia illucens assisted by microbes to produce protein-rich biomass and organic fertilizer. Larvae of Hermetia illucens were cultivated in rearing containers (25×20 cm) with three different types of substrate containing rice straw, tofu residue and solution containing consortium of microbes. The rice straw used in this study contains 22.1% hemicellulose, 30.3% cellulose, 8.0% lignin and 6.8% protein (weight basis) while the tofu residue contains 20.9% protein (weight basis). The substrate rate was set at 150 mg/larva/day and the ratio of rice straw: tofu residue was varied from 1:0 to 1:3. The highest prepupal biomass productivity of 179.8 g/m²/day on a dry weight basis with an assimilation efficiency of 21.5% and efficiency of conversion of digested substrate of 34.9% was obtained when the larvae were fed with rice straw and tofu residue (1:3) that had been pre-treated with a solution containing 10⁷ cell/mL microbes. At this condition, the prepupal biomass has protein and fat content of 31.8 and 15.5% (weight basis), respectively. The cultivation residue contains a relative high amount of organic carbon (43-46%) with pH 7.16-7.82 and carbon to nitrogen ratio of 22-47 and a total macronutrient of 2.33-3.21% and functional microbes of 2.0-4.5×10⁸ CFU/mL. The results highlight the potential of black soldier fly larvae as a bioconversion agent to convert agricultural waste into protein-rich biomass and organic fertilizer.