Seaplant biomass can be converted into hydrochar with Hydrothermal Carbonization (HTC) technology to serve as a soil amendment and substitution for fertilizer with liquid urea which is produced during the HTC process and contains 46% nitrogen. Seaplant hydrochar would also lower the environmental cost of fossil-based nitrogen and supplement dwindling phosphate reserves. Furthermore, seaplants provide beneficial ecosystem services, do not require precious freshwater or land usage, and are a renewable resource not requiring fertilizer. Seaplants also absorb carbon dioxide for mitigating ocean acidification - the evil twin of climate change.
HTC, or wet pyrolysis, is a relatively new process that treats biomass with hot compressed water instead of drying which offers several advantages for processing wet feedstock such as seaplants. The product, called hydrochar, is a valuable resource for soil conditioning and carbon storage and can achieve up to 95% carbon efficiency in matter of hours using mild temperatures and pressure for recovery of nitrogen (N), phosphorus (P), and potassium (K) the key elements in fertilizer.
A recent paper published in March 2021 by Canadian scientists, Hydrothermal Carbonization (HTC) of Seaweed (Macroalgae) for producing hydrochar, shows encouraging data for seaplants helping to fill the looming fertilizer gap when used as a soil amendment. The research revealed that hydrochar, produced in 120 minutes at 220 C, showed carbon content at 48.5% and the energy density and carbon to nitrogen ratio in the hydrochar increased significantly as compared to raw seaweed. Moreover, HTC reduced the ash yield and volatile compounds of the seaweed while retaining the phosphorus along with the potassium with a higher carbon to nitrogen ratio.
Another paper by the Swiss Federal Institute of Technology in Zurich, The Fate of Nitrogen and Phosphorus in Hydrothermal Carbonization, concluded "Nutrient analysis revealed that most N was in the form of organic-N and was contained in the hydrochar, whereas most P was measured in the process water. One third of the output-N and more than half of the P contained in the hydrochar were readily plantavailable, indicating that the output materials from HTC have good short-term plant fertilising properties."
Catalina BioTech is developing a 3-liter HTC prototype which will be constructed in a shipping container and designed as modular for incremental scaling to meet the commercial demand for fertilizer substitutes to overcome African micronutrient soil deficiency. African soils have an inherently poor fertility because they are very old and lack volcanic rejuvenation. Inappropriate land use, poor management and lack of input have led to a decline in productivity, soil erosion, salinization, and loss of vegetation. Seaplant fertilizer produced by HTC has the potential to foster a ‘Green Revolution’ for fighting famine and malnutrition throughout the African continent.
