Process efficiency and ventilation requirement in black soldier fly larvae composting of substrates with high water content

Cecilia Lalander,Evgheni Ermolaev,Viktoria Wiklicky,Björn Vinnerås

doi:10.1016/j.scitotenv.2020.138968

Cecilia Lalander, Evgheni Ermolaev + Show 2 more

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https://doi.org/10.1016/j.scitotenv.2020.138968

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Abstract

In order to transition from a linear to a circular economy in the organic waste management sector, more of the elements in waste need to be recycled. Use of black soldier fly (Hermetia illucens L.; Diptera: Stratiomyidae) larvae (BSFL) for organic waste treatment has potential to harvest more complex molecules than conventional methods. Many organic waste substrates have high water content (>80%), but the impact on BSFL treatment efficiency of substrate water contents >80% is not known. This study evaluated the impact of high water content food waste on BSFL composting efficiency in terms of waste-to-biomass conversion ratio, material reduction, larval survival and the ventilation required for enabling dry separation of larvae from residue. In total, six water contents ranging from 76% to 97.5% were evaluated in two experimental trials. It was found that increasing water content reduced biomass conversion ratio and survival rate of the larvae, from 33.4% of volatile solids (VS) and 97.2% survival in 76% water to 17.5% of VS and 19.3% survival in 97.5% water. Furthermore, we found that the ventilation requirement for achieving dry separation of larvae from residue could be modelled by estimating the amount of water that would need to be removed, taking into account the water bound in the larvae, and knowing the specifics of the ventilation set-up of the modelled system. The findings could have implications on the waste management sector interested in implementing BSFL treatment, as the findings demonstrate that it is possible to treat wet substrates (such as fruit and vegetable wastes) without any pre-treatment other than grinding and attain an adequately dry residue for enabling dry separation of the larvae from the residue.

Highlights

In 2015, the European Commission (EC) launched an action plan on waste handling and a circular economy in the European Union (EU), in which reusing the resources contained in waste is mentioned as one way to reduce dependence on new resources, and as an important step in transition from a linear to a circular economy model (European Commission, 2015)
This study evaluated the impact of high water content food waste on BSFL composting efficiency in terms of waste-to-biomass conversion ratio, material reduction, larval survival and the ventilation required for enabling dry separation of larvae from residue
The substrate water content used for fly larvae composting in previous studies has been within the range 65–85% (Banks et al, 2014; Cheng et al, 2017; Li et al, 2011; Meneguz et al, 2018)

Summary

Introduction

In 2015, the European Commission (EC) launched an action plan on waste handling and a circular economy in the European Union (EU), in which reusing the resources contained in waste is mentioned as one way to reduce dependence on new resources, and as an important step in transition from a linear to a circular economy model (European Commission, 2015). A new waste management technique that has attracted considerable interest among researchers, the media, the public and waste handling entrepreneurs in recent years is fly larvae composting (Čičková et al, 2015). This is a robust and efficient biodegradable waste treatment that increases the value of the waste by utilising more complex molecules in the waste, such as amino acids and lipids, whereas current systems focus on simpler elements such as ammonia and methane (Lohri et al, 2017). The treatment residues can be used as organic fertiliser (Setti et al, 2019) or as feedstock in the anaerobic digestion process (Lalander et al, 2018)

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