Earthworm farming for enhanced protein upcycling from spent mushroom substrate

Earthworm farming offers a sustainable method to convert organic residual streams into high-quality edible protein, enhancing nutrient recycling and food systems circularity. This study evaluates the effectiveness of earthworm farming in upcycling protein from maize stover through two pathways: directly feeding earthworms on maize stover or feeding earthworms spent mushroom substrate (SMS) derived from oyster mushroom cultivation on maize stover. Two earthworm species, Eisenia fetida and Eudrilus eugeniae, were farmed in mesocosms for 37 days and assessed for their biomass gain, protein yield, and essential amino acid composition. Results show significantly enhanced biomass gains when earthworms were fed SMS compared to maize stover alone, attributed to the lower carbon-to-nitrogen (C/N) ratio of SMS. E. fetida demonstrated 19.7 % higher total amino acid content, while the amino acid profiles of both species were nutritionally relevant, especially for lysine and tryptophan-critical for regions like Sub-Saharan Africa experiencing protein deficiencies linked to maize-based diets. Using Ugandan maize stover yields, we estimated that consecutive oyster mushroom and earthworm farming could upcycle up to 29 kg of crude protein per hectare annually, enhancing protein upcycling by 115 % compared to mushroom cultivation alone and by 238 % compared to direct stover-to-earthworm conversion. This highlights that, despite practical and logistical challenges, this waste-to-protein pathway offers significant potential for small-scale producers in resource-limited settings to enhance food security and profitability. Further research to optimize feed-specific stocking rates, and develop cost-effective technologies for small-scale production in Sub-Saharan Africa is essential to maximize protein upcycling and scalability.