Investigating the Performance of Black Soldier Fly Larvae (Hermetia illucens) in Fecal Matter Co-digestion for Optimum Protein

Abstract

Poor hygiene and limited access to safe sanitation, and large-scale open defecation, contribute to poor health, undermine economic growth, and pollute the environment. Thus, fecal waste management is an immediate and serious environmental problem facing urban municipalities, peri-urban and rural areas in low and middle-income countries. Residents in rural and urban informal settlements such as slums and refugee camps rely on On-Site Sanitation (OSS) technologies. Poor disposal of the fecal sludge results in environmental pollution and outbreak of diseases thus endangering education, productivity and life quality of the residents. However, fecal waste is a valuable resource that contains nutrients and energy value that are beneficial to human beings and the environment if reintegrated into the value chain. The Black Soldier Fly Larvae (BSFL) can act as an ecological engineer by co-digesting the fecal matter, adding value to it, reducing the volume and ultimately contributing to safe disposal of the end products. This study characterized the feed substrates which included urine-diverting dry toilets (UDDT) fecal matter from Kunene Primary School and kitchen waste from Meru University of Science and Technology cafeteria (1:0, 1:1, 2:1, 4:1 and 0:1) for their nutritive content. The effect of the co-digested substrates on waste weight reduction, Hermetia illucens’ larval weight gain, and crude protein content during co-digestion was also evaluated. Samples of larvae were collected after every 2 days for larval determination and protein content analysis using the Kjeldahl method of nitrogen determination. The waste reduction index (WRI) was determined after 50% pupation. The larvae grew on all substrates yielding 33–39% dry matter (DM) protein content and larval weight ranging from 1.1 to 1.7 g per five larvae. Results indicate that a 1:1 co-digestion ratio resulted in the highest WRI, DM crude protein content (39%), and larval weight. It was also noted that waste reduction efficiency, growth performance, and protein content of BSFL were greatly influenced by the characteristics of the rearing substrate provided. This study used the circular economy-based approach which provides a win–win situation to sanitation provision and environmental management while realizing products with potential for livelihood improvement. The findings provide significant insights for process scale up.