A state-of-the-art review on dual purpose seaweeds utilization for wastewater treatment and crude bio-oil production

Due to the negative environmental impacts of fossil fuels and the increasing global energy demands, biofuels are receiving increasing attention as the best short-term substitute for petroleum. Recently, thermochemical con- version of seaweeds is in industrial focus to obtain high-value products with more potential applications than the conventional raw material. Beside biofuel production and due to their autotrophic growth, seaweeds are receiving a great attention in the field of bioremediation. Thus, pyrolysis of seaweeds is a promising approach for renewable bio-oil production with positive environmental impacts. However, a pretreatment drying step is required to improve the conversion process of the biomass. Application of electro-osmotic dewatering as well as on-site mechanical dewatering methods prior to the drying process were reported as useful techniques to reduce the energy requirements. On the other hand, the bio-oil produced from pyrolysis of seaweeds usually has high contents of oxygen-, nitrogen- and sulphur-containing compounds, which should be as minimum as possible to enhance the bio-oil stability and reduce NOx and SOx emissions. The present review introduces a suggested route combining a number of technologies that create an economically-feasible process for conversion of seaweeds to high-grade crude bio-oil through pyrolysis. In addition, the paper sheds light on the environmental impacts and economic feasibility of the crude bio-oil production from seaweeds. The current status and challenges related to pyrolysis, as well as future perspectives for enhanced conversion and upgraded bio-oil production, are discussed.