[Pilot-scale bioremediation of rare earths wastewater by <i>Chlamydomonas</i> sp. YC].

The extraction of rare earth elements (REEs) through <i>in-situ</i> leaching with ammonium sulphate [(NH₄)₂SO₄] had resulted in the production of a large volume of ammonium-rich wastewater, causing severe environmental pollution. This study aimed to assess the ability of an indigenous microalga <i>Chlamydomonas</i> sp. YC, isolated from REEs wastewater, to directly treat real REEs wastewater under outdoor conditions in 50 L airlift photobioreactors (AL-PBRs) and 5.0 m³ open race-way photobioreactors (ORWPs). Additionally, the harvested <i>Chlamydomonas</i> sp. YC biomasses from these two pilot photobioreactors were comprehensively analyzed to evaluate the nutritional values. The results showed that <i>Chlamydomonas</i> sp. YC in AL-PBRs exhibited higher biomass production (1.1 g/L), greater removal efficiencies in NH₄⁺-N (24.9%) and total nitrogen (20.4%), as well as higher CO₂ fixation rate (125.0 mg/(L·d)), compared to those of ORWPs. Moreover, the <i>Chlamydomonas</i> sp. YC biomasses obtained from the two pilot photobioreactors contained 44.5% and 49.4% protein, 9.1% and 14.3% lipids. Moreover, <i>Chlamydomonas</i> sp. YC in the two pilot photobioreactors displayed essential amino acid indexes (EAAI) of 0.900, which was higher than that of soybean protein (0.657), indicating superior nutritional values. In conclusion, the implementation of the process involving <i>Chlamydomonas</i> sp. YC in AL-PBRs under outdoor conditions holds promise as a coupled microalgal biotechnology for the simultaneous removal of NH₄⁺-N from REEs wastewater, and the capture of CO₂ for the production of valuable biomass.