Optimizing ammonium supply strategies for mitigation of free ammonia inhibition in the mass cultivation of Limnospira fusiformis

Abstract

Ammonium is abundant in agro-industrial effluents, providing a cost-effective and sustainable nitrogen source for cultivating the cyanobacterium Limnospira fusiformis. However, under high pH conditions, ammonium converts into free ammonia (NH₃), causing inhibition. Therefore, an optimal ammonium supply strategy is required. This study assessed L. fusiformis growth under intermittent, continuous, and nighttime ammonium supply methods across four nitrogen loading rates: 3.9, 5.8, 11.6, and 17.4 mg NH₄⁺-N L⁻¹ d⁻¹ . At a loading rate of 11.6 mg NH₄⁺-N L⁻¹ d⁻¹ , intermittent and continuous supply yielded higher productivities (0.22 and 0.20 g L⁻¹ d⁻¹, respectively) than the nighttime method (0.15 g L⁻¹ d⁻¹) (p < 0.05). Increasing the loading rate to 17.4 mg NH₄⁺-N L⁻¹ d⁻¹ resulted in elevated NH₃ concentrations, leading to growth inhibition and productivity declines to 0.09, 0.10, and 0.06 g L⁻¹ d⁻¹ under intermittent, continuous, and nighttime supply, respectively (p < 0.05). This study is the first to demonstrate that continuous or intermittent ammonium supply strategies can be effectively applied in the mass cultivation of L. fusiformis.