sustainability Article Energy Potential of Oil Palm Empty Fruit Bunch (EFB) Fiber from Subsequent Cultivation of Volvariella volvacea (Bull.) Singer Noor Azrimi Umor 1,2 , Sumaiyah Abdullah 1, * , Azhar Mohamad 3 , Shahrul Bin Ismail 4,5 , Siti Izera Ismail 1 and Azizah Misran 1   Citation: Umor, N.A.; Abdullah, S.; Mohamad, A.; Ismail, S.B.; Ismail, S.I.; Misran, A. Energy Potential of Oil Palm Empty Fruit Bunch (EFB) Fiber from Subsequent Cultivation of Volvariella volvacea (Bull.) Singer. Sustainability 2021, 13, 13008. https:// doi.org/10.3390/su132313008 Academic Editors: Codruta Jaliu, Mircea Neagoe, Radu Săulescu and Alberto-Jesus Perea-Moreno Received: 28 September 2021 Accepted: 15 November 2021 Published: 24 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Faculty of Agriculture, Universiti Putra Malaysia, Serdang 43400, Malaysia; noorazrimi@gmail.com (N.A.U.); izera@upm.edu.my (S.I.I.); azizahm@upm.edu.my (A.M.) 2 Faculty of Applied Sciences, Universiti Teknologi MARA Cawangan Negeri Sembilan, Kampus Kuala Pilah, Kuala Pilah 72100, Malaysia 3 Malaysian Nuclear Agency, Bangi, Kajang 43000, Malaysia; azhar_m@nuclearmalaysia.gov.my 4 Faculty of Ocean Engineering Technology and Informatics, Universiti Malaysia Terengganu, Kuala Nerus 21030, Malaysia; shahrul.ismail@umt.edu.my 5 BioNexG Sdn. Bhd., ICE-Hub, Kuala Nerus 21300, Malaysia * Correspondence: sumaiyah@upm.edu.my Abstract: EFB and EFB-based mushroom compost (SMC) from Volvariella volvacea cultivation is a promising energy feedstock because it has adequate nutrient quality. The biochemical methane potential (BMP) and calorific value (CV) of this biomass are investigated. Other analyses such as proximate, compositional, and final analysis; thermogravimetric analysis (TGA); and Fourier transform infrared spectroscopy (FTIR) are also performed. The biomass samples consist of two types of EFB, namely fibers (F) and pellets (P) and SMC from the subsequent cultivation of Volvariella volvacea, with samples FS and PS from the first cultivation and FS2 and PS2 from the second cultivation. P produces the highest biological efficiency (BE) of 28% compared to 9.83% for F. Subsequent cultivation with FS and PS then produces only 2.9 and 6.83% of BE. A higher amount of methane is measured in samples P and PS2, while better biodegradability is observed in PS2 and FS2, suggesting that subsequent cultivation is a good pretreatment of the substrate for anaerobic digestion (AD). CV is highest in F (20.57 MJ/kg), followed by P (19.06 MJ/kg), which is comparable to commercial wood pellet. Samples F, FS, and FS2 have higher ash content, which is due to higher mineral content. The cellulose composition is reduced to almost 50% during cultivation due to fungal metabolism, which is also evidenced by FTIR analysis. TGA analysis revealed that EFB-based SMC exhibits higher weight loss during combustion compared to EFB, which reduces its thermal properties. SMC of EFB is a high potential biomethane feedstock, but not recommended as a fuel pellet. Keywords: empty fruit bunch; spent mushroom compost; bioenergy; biomass pellet; biomethane 1. Introduction Biomass is a promising renewable energy source as it is abundant and derived from various sources such as agricultural waste, wood and grass [1]. The global biomass resources contributed to more than 467 EJ of energy conversion potential per year [2]. Palm oil is the most widely grown edible oil in the world, with a market share of nearly 30% [3]. It is widely used for cooking, frying, and baking as it has a stable cooking point. The industry contributes to a high percentage of solid waste from the plantation and production process. The most significant percentage term is the empty fruit bunch (EFB) which is typically discarded after harvest. It is estimated that about 20 million tons of EFB are generated as waste from plantations in Malaysia every year [4]. EFB can be converted into cellulosic ethanol, a form of biofuel that does not compete with land use for food production [5]. Sustainability 2021, 13, 13008. https://doi.org/10.3390/su132313008 https://www.mdpi.com/journal/sustainability