Studies on Carbon Fixation and Carbon Storage in seabed for Hydroxyl Radical-inactivated Red Tide Algae Rapidly

Ocean microalgae is the unicellular algae with 5-50 µm, absorbing CO₂ efficiency is 10-50 times that of land plant, and fixing CO₂ is more than 40% of globe. Dried microalgae contain 50% C, and 1 kg microalgae could fix about 1.83 kg CO₂. Red tide explosion has the negative effect on ocean carbon storage. Red tide cause CO₂ release to atmosphere, Ocean become the “carbon source” not the carbon sink of atmosphere CO₂; Furthermore, red tide as well as eutrophication damage the coastal eco-environment, reducing the efficiency of carbon fixation and weaking the function of carbon sink greatly. Therefore, an emergency response technology system employing hydroxyl radicals (•OH) has been developed for the red tides treatment in ship. In the system, microalgae with density ranging from 10⁵~10⁶ cells/L is pumped from the ocean surface into a primary pipeline in ship, and concentrated to densities of 10⁷~10⁸ cells/L by algal concentrator. In the main pipeline, the •OH at low concentration of 1mg/L could inactivate microalgae with the efficiency of ~100% and short time of 6~10s. The microscopic examination results showed that the algal cell integrity was maintained with •OH inactivation without the release of internal organic matters. Finally, flocculants are applied to the main pipeline to facilitate the flocculation of the dead algae. Inactivated microalgae combined with flocculant were pumped to 5 m below the surface, and subsequently sedimented to seabed. Under the conditions of low-temperature, high-salinity and high-density, the dead microalgae were forced in the deep ocean, and then enter the millennial scale carbon cycle, realizing carbon fixation and carbon storage.