Biogas production with Sargassum algae in Grenada : Optimization of process and market analysis

Abstract: This study has been carried out within the framework of the Minor Field Studies ScholarshipProgramme (MFS), which is funded by the Swedish International Development Cooperation Agency,Sida. The field study was conducted in Grenada in the spring of 2023. Grenada, along with severalcountries in the Caribbean, has under the last couple of years experienced an increasing influx ofSargassum seaweed. The seaweed accumulates on beaches and causes complications relating tohealth, recreation, economy and the ecosystems by the coast. Moreover, Grenada is dependent onimported fossil fuels which causes the country to have a relatively high ecological footprint as well asmaking the country sensitive to volatile oil prices. To produce biogas with Sargassum, and morespecifically for generating electricity, is one possible solution to the aforementioned issues. However,there is a need to investigate the prerequisites for such a solution. This was done by conducting anexperiment and a market analysis. The experiment aimed to investigate how the methane content inthe biogas is affected by mechanical pretreatment of the seaweed. The market analysis delved into thepossibilities of using biogas to generate electricity in Grenada. For the experiment, a small-scale biogas digester was used, which was located at the True Blue BayBoutique Resort. Feeding of the digester was divided into three batches with two differentcompositions of food waste and Sargassum; untreated and mechanically pretreated Sargassum. Thedigester was fed for 42 days in total while the measurements were conducted for 28 days. In terms ofthe market analysis, a literature study and 4 interviews with relevant actors were conducted. Theinterviewees were approached based on local suggestions. For the analysis, four different areas ofinterest were selected: Electricity system in Grenada, Policy and regulation, Infrastructure andAvailability of organic waste for co-digestion. The experiment revealed a weak yet positive trend in the methane yield over the measured period,indicating that mechanical pretreatment of the Sargassum could potentially increase methane yields.Specifically, the average methane concentration by volume was 57% for the untreated batch and 63%for the mechanically pretreated batch. However, it is important to note that the project's duration wasinsufficient to draw definitive conclusions. Furthermore, there might be other factors that contributedto the unusually high methane yield observed in this experiment. Firstly, the storage method of theseaweed in fresh saltwater may have played a role. Secondly, uncertainties related to gas fluxmeasurements and estimated thermal efficiency have a significant impact on the calculated final valueof the methane concentration. In terms of the market analysis, the results indicate that electricity generation through large-scalebiogas production will face challenges. The structure of the electricity system in Grenada allows forgeneration from biogas and Sargassum to exist. Moreover, such operations can play a significant rolein realizing the goals set forth by Grenada’s main policies in terms of sustainability and energy.However, the challenges that need to be dealt with include establishing regulations and policiesspecifically targeting biogas and Sargassum. Supporting infrastructure and a reliable source ofbiodegradable waste also needs to be established before electricity generation fromSargassum-derived biogas can be carried out. The aforementioned challenges relate to electricityproduction for distribution and may not be as significant for power generation for self-consumption.