Compilation of Black Soldier Fly Frass Analyses

Daniel Gärttling,Hannes Schulz

doi:10.1007/s42729-021-00703-w

Abstract

In the context of black soldier fly (BSF) rearing, often the residues from production — mainly faeces but also undigested substrate — are addressed as frass in a broader sense. As BSF production is expanding, the valorization of BSF frass as organic fertilizer is gaining importance. However, in contrast to established organic fertilizers, little is known on the properties and variation of this by-product, which is essential for assessing possible application purposes. To elaborate a first overview on this relatively new waste stream, BSF frass analyses from the literature and anonymized frass analyses enquired from BSF producers were compiled. For a possible agricultural use as a fertilizer, their nutrient patterns were assessed. With a balanced nitrogen:phosphorous pentoxide:potassium oxide (N:P2O5:K2O) ratio of 1:0.9:1.1, BSF frass can be characterized as a slightly alkaline (pH 7.5), nutrient-rich compound fertilizer, with the nutrient and especially the micronutrient contents showing high variation. The comparably high carbon-to-nitrogen ratio and low shares of ammonium nitrogen indicate a limited immediate nutrient release and point to possible applications of frass as a long-term fertilizer. The use of frass as an organic fertilizer as one element in a fertilization strategy is promising. By improving nutrient cycling back to the field, BSF frass can represent an important element of sustainable circular agriculture. However, more information on BSF feed and production systems needs to be combined with the nutrient analyses to better understand the variation in frass nutrient contents.

Highlights

With the intensification of livestock production in the last decades, the size of livestock farming units increased considerably (Steinfeld et al 2006)
In the context of shaping a circular economy, insect and especially black soldier fly (BSF) (Hermetia illucens L.) production is expected to play an important role: BSF can be reared on manifold organic waste substrates, even manures (Diener et al 2011), and the processed larvae can be used as protein component in animal feeds such as for pets (Freel et al 2021), poultry and pigs (Barragan-Fonseca et al 2017) or in aquaculture (Belghit et al 2019; Barragan-Fonseca et al 2017; Cummins et al 2017)
BSF frass is considered to constitute a major output from these production systems (Schmitt and de Vries 2020), and with the upscaling of BSF production, the valuation of frass is getting more economic and ecological weight

Summary

Introduction

With the intensification of livestock production in the last decades, the size of livestock farming units increased considerably (Steinfeld et al 2006). Specialization of farms promoted a decoupling of livestock production and the areas for feed production and manure spreading, leading to adverse effects for the environment as a result of the unsustainable management of livestock manures (Zhang et al 2019). BSF frass is considered to constitute a major output from these production systems (Schmitt and de Vries 2020), and with the upscaling of BSF production, the valuation of frass is getting more economic and ecological weight. The use of frass as a fertilizer is expected to be promising (Schmitt and de Vries 2020) and would increase the circularity of the production system (Cadinu et al 2020).

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