Effect of light and oxygen on the removal of inorganic nitrogen by Marichromatium gracile YL28

Abstract:

[Background] Light and oxygen are important limited factors for cell growth and the inorganic nitrogen removal of anoxygenic phototrophic bacteria (APB). Marichromatium gracile YL28, a member of purple sulfur bacteria in APB, can grow with nitrite as the sole nitrogen source and efficiently remove inorganic nitrogen. [Objective] This work aims to explore the relationship between light and/or oxygen and the removal efficiency of inorganic nitrogen by YL28, and acquire the optimal condition of light and oxygen for biological nitrogen removal processes. [Methods] A simulated seawater system with high concentration of co-exist inorganic nitrogen was used to investigate the effect of sample loading quantity (SLQ, it represents dissolved oxygen level) on the inorganic nitrogen removal efficiency by YL28 under the light or dark conditions. The three major factors of SLQ, light intensity and photoperiod were optimized by the response surface analysis. [Results] Under the light condition, the highest removal efficiency of inorganic nitrogen and cell growth were achieved at 80% of SLQ. When SLQ was in the range of 10% to 100%, the range of biomass value (OD660) was from 0.938 to 2.719 and the removal rate of ammonia, nitrite and nitrate reached 71.44%?89.09%, 99.22%?99.83% and 91.60%?97.33% when exposed to 7.16, 5.67, 4.83 mmol/L of ammonia, nitrite, nitrate, respectively. Under the dark condition, when SLQ was in the range of 20% to 100%, the removal rate of ammonia, nitrite and nitrate reached 48.07%?64.27%, 73.51%?86.42% and 42.57%?46.34%, respectively, however, the biomass (OD660, 0.615?0.903) decreased significantly. The response surface analysis showed that the cell growth and ammonia removal efficiency were increased by 21.28% and 14.11% under the 80.0% of SLQ (dissolved oxygen (DO) is approximately 0.32 mg/L), 2 800 lx of light intensity and 24L:0D of photoperiod condition. In practical application, more than 95% of cell activity was achieved under 72% to 89% of SLQ (DO is in the range of 0.26 to 0.63 mg/L), 2 240?3 460 lx of light intensity and 21L:3D?24L:0D of photoperiod conditions. [Conclusion] The 80% of SLQ is of benefit to YL28’s phototrophic growth and the inorganic nitrogen removal efficiency; YL28 remains the good nitrogen removal activity under anaerobically and/or aerobically in the dark. This study provides useful information for the removal of inorganic nitride by APB in bioreactor.