Stress Responses and Ammonia Nitrogen Removal Efficiency of Oocystis lacustris in Saline Ammonium-Contaminated Wastewater Treatment

Authors

Yuqi Zhu
Yili Zhang
Hui Chen
Lisha Zhang
Chensi Shen

Publication Date

5-10-2024

Journal

Toxics

Abstract

The increasing concern over climate change has spurred significant interest in exploring the potential of microalgae for wastewater treatment. Among the various types of industrial wastewaters, high-salinity NH₄⁺-N wastewater stands out as a common challenge. Investigating microalgae’s resilience to NH₄⁺-N under high-salinity conditions and their efficacy in NH₄⁺-N utilization is crucial for advancing industrial wastewater microalgae treatment technologies. This study evaluated the effectiveness of employing nitrogen-efficient microalgae, specifically Oocystis lacustris, for NH₄⁺-N removal from saline wastewater. The results revealed Oocystis lacustris’s tolerance to a Na₂SO₄ concentration of 5 g/L. When the Na₂SO₄ concentration reached 10 g/L, the growth inhibition experienced by Oocystis lacustris began to decrease on the 6th day of cultivation, with significant alleviation observed by the 7th day. Additionally, the toxic mechanism of saline NH₄⁺-N wastewater on Oocystis lacustris was analyzed through various parameters, including chlorophyll-a, soluble protein, oxidative stress indicators, key nitrogen metabolism enzymes, and microscopic observations of algal cells. The results demonstrated that when the Oocystis lacustris was in the stationary growth phase with an initial density of 2 × 10⁷ cells/L, NH₄⁺-N concentrations of 1, 5, and 10 mg/L achieved almost 100% removal of the microalgae on the 1st, 2nd, and 4th days of treatment, respectively. On the other hand, saline NH₄⁺-N wastewater minimally impacted photosynthesis, protein synthesis, and antioxidant systems within algal cells. Additionally, NH₄⁺-N within the cells was assimilated into glutamic acid through glutamate dehydrogenase-mediated pathways besides the conventional pathway involving NH₄⁺-N conversion into glutamine and assimilation amino acids.

Keywords

NH4+-N wastewater, microalgae treatment technology, Oocystis lacustris, NH4+-N utilization, stress responses