Mechanical preprocessing and black soldier fly (Hermetia illucens) larvae bioconversion of diaper waste: A scoping review with an illustrative prototype case study

Abstract:

Background: Disposal of single-use diapers is a growing solid waste issue because they are composed of a mix of composite materials, non-biodegradable, and have a high moisture and pathogen content. Although Black Soldier Fly (BSF, Hermetia illucens) larvae bioconversion is being increasingly proposed as sustainable biotechnology for valorisation of organic-fraction waste, diaper waste has a different composition compared to homogeneous feedstocks that most BSF studies have been performed on.

Objective: This scoping review aims to map the published evidence regarding the composition of diaper waste, environmental impacts, disposal practice, mechanical pre-treatment, and BSF bioconversion to characterize the extent and nature of evidence of combining mechanical shredding with larval bioconversion of diaper waste.

Methods: The literature search was carried out using a scoping review approach that involved identifying, charting, and thematically synthesising the literature on diaper waste management, shredding pre-treatment, and BSF larval bioconversion. The evidence is summarised and organised by themes and a prototype shredding-sterilising machine is provided as an operational example of the evidence gap identified.

Results: Based on the literature reviewed, diaper waste is found to be a very complex waste structurally, which is not suitable for direct biological treatment; mechanical shredding is well known as a pre-treatment technique in composting and anaerobic digestion, and BSF larvae is an efficient bioconverter for homogeneous organic wastes. No integrated experimental system was found that could integrate mechanical pre-treatment and BSF bioconversion for the diaper waste. An illustrative case study is presented, describing a combined shredding and steam-sterilising unit which would help to overcome this challenge by both decreasing particle size and controlling pathogens before larval feeding.

Conclusion: There is a definite gap in the research on the combination of mechanical pretreatment and biological conversion of diaper waste using BSF. These gaps can be filled by standardised and integrated experimental studies that quantify the effect of particle size reduction and pre-treatment on the larval performance, pathogen load and resource recovery.