Principal component analysis of nutrient composition in black soldier fly larvae frass leachate from different organic waste substrate

The black soldier fly ( Hermetia illucens, BSFL) larvae can rapidly and efficiently decompose various types of organic waste, producing nutrient-rich solid frass and leachate as valuable by-products. However, the chemical composition of the leachate is highly dependent on the substrate type, which limits its consistency as a liquid biofertilizer. This study aimed to evaluate and compare the nutrient composition of leachate derived from different organic substrates degraded by BSFL and to identify the key factors influencing its variability. The research contributes new insight into how substrate type regulates the balance of macro–micro elements and the distribution of heavy metals within BSFL leachate, providing a theoretical basis for substrate-specific formulation of liquid biofertilizers. Leachate samples obtained from rotten fruit, rotten vegetables, and tofu pulp substrates were analyzed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) to determine the concentrations of macro elements (N, P, K, Ca, Mg, Na) and micro elements (Fe, Mn, Zn, Cu, Pb, Cd, Cr). The data were further examined using Principal Component Analysis (PCA) and Spearman correlation to identify elemental clustering patterns. The results revealed distinct separation among substrate groups. Tofu-pulp leachate contained the highest levels of P, Zn, and Cu; vegetable-based leachate was enriched with Ca, Mg, Fe, and Mn; while fruit-based leachate exhibited the highest K concentration. Heavy metals (Pb, Cr, Cd) were detected at trace levels well below international safety limits. These findings highlight that substrate composition plays a decisive role in determining leachate quality and support its potential use as a safe and sustainable liquid biofertilizer.