An integrated seawater energy and agriculture system (ISEAS) can produce bio-fuel for the aviation sector with fewer greenhouse gas emissions than its fossil counterpart, along with sustainable aquaculture food products without freshwater, according to a study by researchers from Qatar University (QU) and Masdar Institute of Science and Technology (Masdar Institute) and funded by Boeing Corporation.
In a new article appearing online in the International Journal of Life Cycle Assessment, co-authored by QU Centre for Sustainable Development research assistant Prof Dr J Jed Brown, a life cycle assessment (LCA) of a potential ISEAS was conducted. The team quantified the energy and material flows throughout the system and calculated the resulting net greenhouse gas emissions. The LCA results showed that the aviation biofuel produced from this ISEAS system emits up to 68% less greenhouse gases compared to fossil jet fuel and yields an overall positive net energy balance.
In the ISEAS, seawater is pumped into ponds where high value shrimp and fish are grown for human consumption. The nutrient-rich effluent exits the ponds and flows into fields of salt-tolerant plants. The team examined a Salicornia bigelovii halophyte - commonly known as glasswort or samphire - which produces oilseeds similar to soybeans.
The oil extracted from the seeds can be processed into a drop-in bio-fuel for airplanes, Dr Brown said, adding, “The portion of the seed that remains after oil extraction is high in protein and can be recycled into feed for fish and shrimps. The dried straw that remains after the oilseeds can be used to generate electricity. Water that leaves the halophyte fields flows into a mangrove wetland where most of the remaining nutrients will be absorbed into mangrove biomass. Branches and leaves from the mangroves can be periodically trimmed to generate electricity with the Salicornia straw.”
"In a conventional aquaculture system, nutrient-rich aquaculture effluent is frequently discharged untreated back into the sea, which can have negative impacts on water quality of the receiving water body. In the ISEAS system, the effluent serves as a fertiliser source for the halophytes and mangroves, which clean the water by removing nutrients. Mangroves are also used in many parts of the Gulf region to stabilise erosion-prone coastal regions, rebuild habitats for marine life, and provide permanent carbon sequestration in their biomass.”
Dr Brown pointed out that "as the human population continues to rise in the Gulf region, there is a greater need to provide food, water and low-carbon energy for the populace. Since there is a great scarcity of freshwater in this region, any agriculture or bio-energy projects that rely on freshwater will be unsustainable. However, the countries of the Arabian Gulf have access to seawater and high salinity groundwater. If this saline water can be used to produce food and bio-fuel sustainably, then limited freshwater resources can be conserved.”