Techno-economic and environmental impact assessment of biogas production and fertiliser recovery from pelagic Sargassum: A biorefinery concept for Barbados

Abstract

Pelagic Sargassum inundation of coastlines across the North Atlantic is an ongoing challenge but presents new opportunities for value-added resource recovery. This study assessed the techno-economic feasibility and environmental impact of utilising these invasive brown seaweed, and food waste as feedstock for energy production and fertiliser recovery in Barbados. The biorefinery concept evaluated was designed with hydrothermal pretreatment (HTP) and anaerobic digestion (AD) technologies. Financial analyses of four varied feedstock and process scenarios (S1-S4) established a linear relationship between profitability and the sale of products (electricity and fertiliser). In all cases, simple sale of power generated to the national grid resulted in a negative cash flow and required the introduction of fertiliser sales to achieve positive cash flows. Moreover, the net loss in the electricity only scenarios exceeded that of the landfill disposal, the present operation employed on the island for Sargassum management. The addition of the solid digestate to the revenue stream increased the profit margin and financial attractiveness of the process. Maximum income generation could be attained through 100% supply of the digestate to international markets. However, this approach provides zero support to local food security. The preferred option involves the 50/50 split utilisation of the solid digestate in local and international agricultural practice. While HTP is energy-intensive technology, the recirculation of waste heat generated by a combined heat and power unit for HTP reduced the input energy demand. It also lowered the potential environmental impact by more than 10-fold, relative to landfill disposal. Recycling of the liquid digestate also reduced the fresh water demand and its associated costs. Despite the promising results, process scale-up and commercialisation remain a main challenge, primarily due to the seasonality and variability of Sargassum seaweed for continuous bioprocessing.