Recycling 2023, 8, 1. https://doi.org/10.3390/recycling8010001 www.mdpi.com/journal/recycling Article The Potential of Valorized Sisal Decorticated Waste in Rearing of Black Soldier Fly Aziza Athumani Konyo 1,2, *, Revocatus Machunda 2 , Liliane Pasape 2 and Anthony Mshandete 2 1 Department of Biology, College of Natural and Mathematical Sciences, The University of Dodoma, Dodoma P.O. Box 338, Tanzania 2 The Nelson Mandela African Institution of Science and Technology, Tengeru Arusha P.O. Box 447, Tanzania * Correspondence: azizaakonyo@gmail.com Abstract: The use of sisal decorticated waste (SDW) for various applications is limited due to its high acidic content. This is the first study of its kind regarding the use of SDW as a substrate for the growth of the black soldier fly (BSF). Pre-treatment was a necessary and challenging step performed on the waste to meet the minimum requirements for the rearing of BSF. The SDW was sun dried, sieved, and decomposited and neutralized to form the final products that were used for the rearing of BSF. The resultant waste had fourteen (14) elements; the essential elemental form results were Ca, P, K, Mn, Fe, Cu, and Zn at varying levels, which are all essential for animal growth. The SDW contained 10 ± 0.01 percent of crude protein, 11 ± 0.02 moisture and energy (1615 kcal/g of sisal decorticated waste). The sun dried BSF larvae were reared on SDW that contained 53 ± 0.005 percent of crude protein, 4 ± 0.01 percent of crude fat, a moisture content of (10 ± 0.1)%, carbohydrate percent of (43 ± 0.01)%, and ash percent of (37 ± 0.08). When rearing was finished, 3000 g of dried pre-treated waste yielded more wet BSF larvae, (336 ± 41.3) g, compared to 3000 g of fruit waste, which yielded (244 ± 4.16) g of wet BSF larvae. Therefore, based on this study, SDW is a promising potential feed for rearing BSF because it had a better reduction of the waste by 52%. Furthermore, the harvested BSF larvae contained sufficient nutritional value to feed poultry and fish. Keywords: black soldier fly; environmental management; industrial wastes; sisal decorticated waste; waste treatment 1. Introduction Managing sisal decorticated waste (SDW) as an industrial waste in most Tanzanian sisal factories is still challenging [1–3]. Applying sisal decorticated waste in the rearing of the black soldier fly (BSF) and obtaining the viable agricultural products (animal feed and organic fertilizer) has not been performed so far. This is due to existing challenges, includ- ing the presence of sisal fibers and low pH in the SDW, which affects the feeding rate and growth of BSF [3]. Therefore, it needs to be pretreated for better results. This study antic- ipated the use of SDW as a substrate for BSF growth, as it is easily available and bears low cost. The sisal fiber, which is produced during the decorticating process, accounts for only 3 to 6% of the total weight, with the remainder being waste [4,5]. This huge amount of generated sisal waste (about 94 to 97%) should be effectively managed as resource recov- ery in attempt to avoid the negative effects that it has on the environment, including soil and underground water pollution [6,7]. Various studies show that sisal decorticated waste is used in biogas production [8–10], mushroom cultivation [5,11] as animal feed [12,13], and it goes further in the fattening of goats and sheep [14,15]. However, in all reported studies, SDW needs to be pre-treated for better results [16,17]. Citation: Konyo, A.; Machunda, R.; Pasape, L.; Mshandete, A. The Potential of Valorized Sisal Decorticated Wastes in Rearing of Black Soldier Fly. Recycling 2023, 8, 1. https://doi.org/10.3390/ recycling8010001 Academic Editor: Leonel Jorge Ribeiro Nunes Received: 23 September 2022 Revised: 17 December 2022 Accepted: 20 December 2022 Published: 23 December 2022 Copyright: © 2022 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distrib- uted under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecom- mons.org/licenses/by/4.0/).