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This paper focused on comparing the impact of two different chemical pretreatments on various characteristics of OPEFBs (i.e., physical, structural, and morphological properties), methane production, digestate characteristics, and kinetic modelling. The biochemical methane potential (BMP) test showed that alkaline-treated OPEFBs produced higher methane yields than acid-treated OPEFBs. Accordingly, the methane yields became far higher after NaOH pretreatment, showing 0.186–0.224 m3CH 4 /kg VS added compared with 0.102 m3CH 4 /kg VS added and 0.093–0.115 m3CH 4 /kg VS added from untreated and acid-treated OPEFBs. The best treatment was alkaline pretreatment of P2N3, which gave the highest methane yield increase (by 1.2-fold). The Scanning Electron Microscopy and Energy Dispersive X-ray (SEM-EDX) results of acid-treated OPEFBs indicated disruption of cell wall and loss of some minerals. However, alkaline-treated OPEFBs have more pores due to silica and other chemicals releases (i.e., lignin, hemicellulose, etc.). The kinetic study showed that all models (i.e., modified Gompertz, logistic, and transference) were in good agreement with the experimental data. Both experimental data and models confirmed P2N3 (i.e., NaOH concentrations of 3.8%) as the best results, indicated by the highest lignin reduction and methane production. This study showed an excellent opportunity to digest alkaline-treated OPEFBS, yet more in-depth investigations with sustainability and circular economy perspectives are needed. [ABSTRACT FROM AUTHOR]

Indonesia has an intensive agro-industrial sector which evolves large volumes of residues each year. Currently, these residues are under-utilized and have a deleterious impact on the environment, Oil Palm Empty Fruit Bunches (OPEFBs) in particular are highly abundant and offer good potential for conversion to bioenergy and bio-based products, in particular bioethanol and xylitol (widely used as an artificial sweetener and can substitute sugar in food and pharmaceutical industries). This paper provides a comprehensive review of the techno-economic opportunities and challenges for the wider utilization of OPEFBs for the generation of bioethanol and xylitol in Indonesia. This review highlights the significant potential for the valorization of OPEFB based on resource availability in the country (828 MWe/year or 45.86 Mt/year) and growing demand for both bioethanol (from 0.22 billion L in 2019 to 10.38 billion L in 2025) and xylitol (up to 2.20 kt in 2020). Various process configurations were explored to assess the potential for simultaneous co-production of bioethanol and xylitol. A mass balance and techno-economic assessment showed that the preferred scenario was Scenario 3 (co-production of bioethanol with xylitol and lignin) and that this has the potential to generate 46,145 kL bioethanol, 7.716 kt xylitol, and 25.704 kt lignin per year. This is significant given the limited production for both bioethanol and xylitol in the country currently. Further work is required to address challenges around technical, policy and supply chains. This work provides an original and novel strategy to support the wider adoption of commercially viable bioethanol production in Indonesia. • An abundance of oil palm empty fruit bunches (OPEFB) creates prospect for biorefining. • Manufacture and supply of bioethanol and xylitol in Indonesia is feasible. • Multiple scenarios are proposed for mono- and co-production of bioethanol and xylitol. • Co-production of bioethanol and xylitol promotes sustainable bioeconomy. • Challenges remain on scalability, financial incentives and supply chain integration. [ABSTRACT FROM AUTHOR]

Globally, bioenergy development depends on the efficacy and affordability of conversion technologies and the availability of renewable biomass sources. As a tropical country, Indonesia has a wide range of biomass sources, either from land or marine biomass (i.e. macroalgae). The current estimation of macroalgae potential in Indonesia is estimated at approximately 9.96 million tonnes or about 26.86% share of world production in 2021. Specifically, marine macroalgae (wild or cultivated) have received attention for their potential as renewable resources for the sustainable bioenergy production, supporting a move towards a circular economy. However, as a developing country, Indonesia still needs to evolve and further advances its technology and skill capacity to address research, development, and innovation challenges in this area. Thus, this paper examines the potential biorefinery approach for application and commercialisation in Indonesia. It discusses cultivation practices and the future direction of the most sustainable and feasible routes for bioenergy production from macroalgae, exploring recent developments, opportunities, and challenges towards circular processes. The study proposed that the biorefining of macroalgae into bioethanol, biogas, compost, and solid fuels, either as mono – or co-production, are potential. Therefore, this paper may offer to narrowing the literature's gap and adding a new perspective on the adoption of macroalgae-based bioenergy with integrated biorefinery and closed-loop systems approaches. [ABSTRACT FROM AUTHOR]

Indonesia has abundant oil palm empty fruit bunches (OPEFBs). However, high lignin content in OPEFBs may hinder their valorisation to bioenergy resources, as its degradation by microorganisms is rate-limiting. This paper aims to review OPEFB as feedstock in anaerobic digestion (AD) systems and sustainable strategies to enhance methane yield. This paper provides a comprehensive review of the availability of OPEFB, the prospective of AD technology, and compares various biological pre-treatment and co-digestion strategies for superior AD process. Improving the value-added benefits from OPEFBs and simultaneously making pre-treatment processes more sustainable is critical to wider application. Several scenarios were proposed by combining multi-stage pre-treatment of physical and mushroom cultivation pre-treatment prior to AD. This paper presents an original approach to establishing a commercially viable and sustainable AD of OPEFBs in Indonesia by integrating multi-product biorefinery and a circular economy. Further investigation is required to ensure cost-effective and eco-friendly configurations. Abbreviations: ABR: Anaerobic Baffled Reactor; AD: Anaerobic Digestion; AF: Anaerobic Filter; AFEX: Ammonia Fibre Expansion; AI: Artificial Intelligence; AnMBR: Anaerobic Membrane Bioreactor; ANN: Artificial Neural Network; ASP: Activated Sludge Process; CMM: Cattle Manure and Maize Silage; COD: Chemical Oxygen Demand; CPO: Crude Palm Oil; CPW: Cocoa Pods Waste; CSTR: Continuous Stirred-Tank Reactor; DH: Dry Husk; DM: Dry Matter; DMF: 2,5-dimethylfuran; EM: Effective Microorganisms; EGSB: Expanded Granular Sludge Bed; FBR: Fluidised Bed Reactors; FFB: Fresh Fruit Bunch; FTIR: Fourier-Transform Infrared Spectroscopy; GHG: Greenhouse Gasses; HRT: Hydraulic Retention Time; IC: Internal Circulation Reactor; IoT: Internet of Things; Lac: Laccase Enzyme; L-AD: Liquid-AD; LiP: Lignin Peroxidase; LRAD: Low-Rate AD; MARS: Multivariate Adaptive Regression Splines; MCC: Microcrystalline Cellulose; MDF: Medium-Density Fibreboard; MEMR: Ministry of Energy and Mineral Resources, Republic of Indonesia; ML: Machine Learning; MnP: Manganese Peroxidase; MPA: Marine Predators Algorithm; MSW: Municipal Solid Waste; OFMSW: Organic Fraction of Municipal Solid Waste; OLR: Organic Loading Rates; OPEFBs: Oil Palm Empty Fruit Bunches; OPF: Oil Palm Fibre; OPKS: Oil Palm Kernel Shell; OPMF: Oil Palm Mesocarp Fibre; OPT: Oil Palm Trunk; P(3HB): Poly(3-Hydroxybutyrate); PHA: Polyhydroxyalkanoate; PLTBg: Biogas Power Plants; POM: Palm Oil Mill; POME: Palm Oil Mill Effluent; SCG: Spent Coffee Grounds; SRF: Solid Refused Fuel; SRT: Solids Retention Time; SS-AD: Solid-State AD; TS: Total Solid; TSI: Torrefaction Severity Index; UASB: Up-flow Anaerobic Sludge Blanket; VFA: Volatile Fatty Acids; VP: Versatile Peroxide; VS: Volatile Solid; W2E: Waste-to-Energy. [ABSTRACT FROM AUTHOR]