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The Cardinal Edge

Abstract

This study provides a mixed-methods approach in analyzing a potential closed-loop system between renewable biogas production from anaerobic digestion, vermiculture production, aquaculture production, and organic wastes with a particular focus on stillage wastes. Such system may hold significant promise for significantly reducing organic carbon and methane emissions from its components, and should be assessed for such. The 2021 IPCC report essentially identified methane reduction as the single fastest way to slow global warming (IPCC, 2021), making the study and implementation of methane-reducing systems and supportive policy for them critical. Knowledge gaps to implementing this system were qualitatively identified as disconnect between digestate management of biodigestion and aquaculture production. This gap was addressed by conducting a vermiculture rearing trial utilizing a digestate-infused substrate (along with an organic sorbent and stillage wastes) for Black Soldier Fly Larvae (BSFL, Hermetia illucens). Those larvae were then analyzed for nutritional content, to consider in comparison to other Hermetia illucens used in commercial BSFL products for aquaculture feed production. In a separate aquaculture production trial, said BSFL ingredients were formulated into two different aquaculture feeds to assess a comparison with commercial aquaculture feed for Nile Tilapia (Oreochromus niloticus) which is one of the most widely cultured species. Results provide that BSFL feed is readily accepted by Tilapia, and that BSFL reared on the digestate infused substrate are of comparable proximate nutritional content. This study verifies the efficacy of a directional link between anaerobic biodigestion, vermiculture, and aquaculture and, therefore, holds great potential to implement a more closed-loop sustainable system with the primary outputs of food products and renewable biogas energy from anaerobic biodigestion in such a manner that may reduce methane emissions from component practices of the more closed loop model. The conclusion of this pilot scale work urges large-scale implementation, which necessitates collaboration between scientific and industrial communities along with support from policymakers and legislative bodies to incentivize synergetic behavior across multiple sectors and components of the system.

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