In this study, the biomethane potential of five agricultural crop residues (ACR's) (rice straw, vegetable waste, maize straw, coffee husk and oil palm empty fruit bunches (OPEFB)) and five Fruit-Based Agro-Industrial Wastes (FBAIW's) (jackfruit straw, banana, orange, apple and pineapple peel waste) were evaluated. The carbon and energy balance for each waste was also theoretically modelled for two biogas conversion scenarios (AD with CHP or biogas upgrading). A standard biomethane potential test (BMP) was operated over 30 days at 37 o C. Specific methane potential (SMP) of FBAIW's was generally higher than that of the ACR's, except for vegetable waste. Vegetable waste was identified as having the highest SMP (0.420 m 3 /kgVS added ). With respect to ACRs, OPEFB and coffee husk had the lowest SMP values of 0.185 and 0.181 m 3 /kgVS added , respectively. This was attributed to the higher lignin content of these wastes which can impact on biodegradation and subsequent biogas production. Theoretical estimations showed a positive energy balance for all wastes tested. In terms of exportable energy, apple peel waste was shown to have the highest exportable energy potential. The FBAIW's also exhibited greater emissions savings than ACR's (with the exception of vegetable waste). This study concluded that there is good potential to valorise these wastes using AD and that this could address the challenges of waste management and clean energy provision in Indonesia.

High consumption of fossil fuels in Indonesia needs to be reduced by using renewable energy, such as from biomass. In Indonesia, as one of the largest maritime countries, macroalgae (i.e. seaweed) are also considered as potential renewable biomass feedstocks for substituting any land biomass. This study aimed to investigate biodegradability and biogas potential of macroalgae (Gracilaria sp.) as single-or co-digestion feedstock using anaerobic digestion technology. The biochemical methane potential (BMP) test was carried out for 28 days at temperature of 37 °C to investigate the specific methane potential. All samples were in triplicate. Combinations of Gracilaria sp. with various biomass feedstocks (i.e. food waste, tofu dregs) were also tested. The findings indicated a potential valorisation of macroalgae for biogas production either as single or co-digestion feedstock, as well as a potential for electricity generation. However, further optimisation process is required for better and higher degradation process.

The anaerobic digestion, AD, process presents a solution for sustainable waste management, greenhouse gas mitigation and energy production for growing population needs and requirements. Adopting a biorefinery approach that utilises different feedstock may enhance energy production and support optimisation of the anaerobic digestion process. Algae is a promising feedstock that could be used for energy production via the anaerobic digestion process. Microalgal biomass is rich in carbohydrates and lipids; however, many species of algae exhibit tough cell walls that could also be difficult to digest and may influence or inhibit the efficiency of the AD process. This study concentrated on the comparison of AD remediation of two marine algal biomass species, Tetraselmis suecica and Nannochloropsis oceanica. The two species were pre-treated with an ultrasound technique and compared for their methane production using biochemical methane potential tests. For Tetraselmis, a specific methane production of 0.165 LCH4/KgVS was observed; however, for Nannochloropsis, a value of 0.101 LCH4/KgVS was observed for the samples treated with ultrasound. The BMP results from this study show that among the two micro-algae species tested, Tetraselmis suecica is found to be a better substrate for methane production potential. Contrary to increasing the specific methane production, ultrasound cavitation caused a slight decrease in the specific methane production values for both Nannochloropsis oceanica and Tetraselmis suecica biomass residues. The pre-treatment of the biomass using ultrasound techniques provided comparable results and can be recommended for effective bioenergy production. However, further research is required for the optimisation of the pre-treatment of microalgae and for the integration of microalgal biorefineries for circular economy.

Like many countries, Indonesia generates large quantities of food waste. Food waste is poorly managed due to inadequate treatment practices, which has a harmful impact on the environment. This paper demonstrates the high potential for food waste valorization in Indonesia and outlines the optimal valorization pathways to inform future decision-making surrounding the management of this waste. This paper also compares various conversion technologies for transforming food waste into liquid, solid, and gaseous biofuels. The challenges and opportunities for wider implementation are also considered, including the integration of supply chains and the logistics of food waste management, the technological feasibility, and the persistent behaviors surrounding food waste and energy in Indonesia. The economic and environmental benefits, the perspectives of improved food waste management practices and sustainable fuels, as well as the policy landscape surrounding waste and sustainable energy are also explored. The challenges of scalability and commercialization are also highlighted in this paper. This review demonstrates the best pathways from food waste valorization to bioenergy, including biogas or biodiesel integrated with a black soldier fly larvae (BSFL) composting system. Despite the scale of resources in Indonesia, the pathways and technologies for processing food waste are lacking. Further in-depth studies are required to demonstrate the sustainability and feasibility of food waste transformation into bioenergy to realize its high value.

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