Frass chemistry, Bioconversion Efficiency, and Fungal Diversity from Black Soldier Fly Larvae Reared on Pre-composted Palm Oil Wastes

Abstract

The increasing demand for sustainable fertilizers has driven exploration of organic alternatives from waste bioconversion. Black soldier fly (BSF; Hermetia illucens) larvae efficiently transform agro-industrial by-products into nutrient-rich frass. This study examined chemical properties and fungal biodiversity of BSF frass derived from pre-composted palm oil wastes: empty fruit bunches (EFB), solid decanters, palm kernel cake (PKC), and their mixtures. Results showed substrate quality significantly affected BSFL growth, waste reduction efficiency (WR), and frass characteristics. PKC yielded the highest WR (75.23%), significantly exceeding previously reported values, while EFB gave the lowest one. BSFL fed PKC exhibited higher protein and lipid contents than other treatments. Frass showed C/N ratio ≤25, high pH, and substantial nitrogen, phosphorus, K, Ca, and Mg contents, confirming its viability as organic fertilizer. Fungal biodiversity (Shannon and Simpson indices) ranged from moderate to high and varied by substrate; mixed substrates produced frass with greater microbial evenness, reflecting substrate-driven community stability via niche pre-emption. These findings underscore BSFL’s potential for oil palm waste valorization, sustainable fertilizer production, and microbial ecology insights, advancing circular bioeconomy.