Improvement of the composition and humification of different animal manures by black soldier fly bioconversion

Abstract

Black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae) biotreatment has been accepted as an eco-friendly alternative means for organic waste disposal; it can efficiently convert animal manure into biodiesel and biofertilizer. However, information about black soldier flies related to the organic matter transformation of different manures is limited. In this study, chicken manure (CM), pig manure (PM) and cow manure (COM) were treated by black soldier fly larvae for nine days, and the manures without black soldier fly larvae were noted as control. The dissolved organic matter (DOM) obtained from the initial and digested manures were studied by UV–vis, fluorescence, and Fourier transform infrared (FTIR) spectroscopy. The results showed that black soldier fly larvae decomposed the carboxylic, alcohol and aliphatic components in PM and CM, while they increased the carboxylic substances in COM. After black soldier fly digestion, the proteinaceous materials in all manures decreased, while the aromatic polycondensation, molecular weight and polar functional groups of DOM increased. Furthermore, according to analysis of the fluorescence spectra, the simple structural organic matter (5.99–29.50%) obviously decomposed and converted into the humic-like substances after black soldier fly digestion. Meanwhile, the humification degree of digested CM and COM (57.07–63.74%) are higher than that found in PM (42.45%).