Waste-to-energy from marine biomass and processing wastes: A review

Marine biomass and fish by-products represent an underutilized resource, often discarded as waste by the fishing and processing industries, but with great bioenergy potential. This review explores their use as feedstocks in thermochemical processes such as combustion, pyrolysis, and gasification. Recent advancements in these conversion methods are discussed alongside a detailed thermochemical characterization of fish waste, macroalgae, microalgae, and shellfish to better understand their energy potential. Tons of fish waste can be transformed into heat via combustion, reaching up to 84% carbon conversion efficiency. Additionally, pyrolysis yields biochar with a fixed carbon content of up to 78 wt% and higher heating values reaching 26 MJ kg⁻¹, making it suitable for energy and soil conditioning due to high nitrogen fractions. Pyrolytic bio-oil yields range from 17 wt% to 50 wt%. This bio-oil can be upgraded to biodiesel through transesterification, achieving conversion efficiencies of 98.2% and producing a fuel with a calorific value of 43 MJ kg⁻¹. Scales, bones, and shells are promising sources of heterogeneous catalysts, also favoring biodiesel production from other biomasses. This integrated approach promotes waste valorization and energy recovery and strengthens the concept of “energy from the oceans,” driving forward a more circular and sustainable bioeconomy.