CO 2 -Inorganic Carbon Auto-Buffering System for Efficient Ammonium Reclamation Coupled with Valuable Biomass Production in a Euryhaline Microalga Tetraselmis subcordiformis.

The performance of microalgae-based wastewater treatment processes for ammonium-N (NH₄⁺-N) removal depends on the maintenance of a favorable pH that is critical for minimizing nitrogen escape in the form of free ammonia (NH₃) and preventing high-NH₃ or extreme-pH stress. This study developed a CO₂-inorganic carbon (CO₂-IC) buffering system that automatically stabilized pH with the supply of a carbon source for efficient photosynthetic reclamation of NH₄⁺-N by a euryhaline microalga Tetraselmis subcordiformis. The soluble (NaHCO₃) and insoluble (CaCO₃ and MgCO₃) ICs were compared for this purpose. The pH was well controlled in the range of 6.5~8.5 in the CO₂-IC system, which was suitable for the photosynthetic growth of T. subcordiformis. The NH₄⁺-N (100 mg/L) was almost completely removed in three days, with the maximum removal rate of 60.13 mg N/L/day and minimal N escape of 19.65% obtained in the CO₂-NaHCO₃ system. The CO₂-IC system also restricted the release of extracellular organic matter by preventing stress conditions. The CO₂-NaHCO₃ system enabled the highest "normal" starch production suitable for fermentation, while the CO₂-CaCO₃/MgCO₃ system facilitated high-amylose starch accumulation that was conducive to producing bio-based materials and health-promoting ingredients. The proteins accumulated in T. subcordiformis were of good quality for animal feeds. [ABSTRACT FROM AUTHOR]