Environmental load assessment for an integrated design of microalgae system of palm oil mill in Indonesia

Highlights: • An environmental load assessment for a proposed microalgae culture was conducted. • Palm oil mill effluent and flue gases were used as alternative nutrient sources. • The proposed system increased the energy-profit ratio and lessen GHG emission. • Co-products of animal feed and bio-fertilizer was ensured from defatted biomass. The environmental load of continuous bioenergy production from palm oil (Elaeis guineensis) included with a proposed 10 ha of microalgae production system were assessed to be implemented in Indonesia. Material and energy balances, greenhouse gas (GHG) emission, nutrient requirement and also water scarcity during bioenergy production cycle were evaluated. The integrated system was developed for 60 tons h⁻¹ of fresh fruit bunch (FFB) processing capacity of a conventional mill. Aggregate of energy-profit ratio from the proposed system was 5.20, which indicates a positive balance. The total water footprint for each palm oil and microalgae cultivation was 3.18 and 2.85 m³ kg⁻¹ of biodiesel production, respectively. Microalgae mix-culture has the potential to treat organic compounds from palm oil mill effluent (POME) and combined with flue gases from biomass and biogas power plant as the alternative nutrient sources contributed to net-reduction of GHG emission for 158.8 tons ha⁻¹ of microalgae culture, annually. The integrated system produced 26,471 tons of biodiesel that included 223 tons from microalgae and contribute to 39.90% of total GHG emission reduction from diesel fuel substitute. Additional co-product of 520.33 tons year⁻¹ of animal feed from defatted biomass also possible to be produced and have potential for environmental benefits.