Growth characteristics of acclimated strain of Chlorella vulgaris under high concentrations of ammonia nitrogen and phosphorus

Treatment and recycling of high concentrations of ammonia nitrogen (NH4+-N) and tatal phosphorus (TP) is a major challenge in today's wastewater industry, while microalgae not only captures CO2, but also provide a safe and cost-effective alternative to wastewater treatment according to its growth characteristics. However, we found that excessive NH4+-N is harmful to microalgae. Significantly higher accumulation rate of the biomass and chlorophyll, as well as removal rate of ammonia nitrogen and phosphorus were observed in an acclimated strain of Chlorella vulgaris (HPN-3#) compared to those of the original strain (CK). The results of photosynthetic performance indicated that although photosystem of both strains were inhibited by the stress of high concentration of NH4+-N. The photosynthetic efficiency of HPN-3# was also higher than that of CK. The results of chlorophyll fluorescence transients and parameters suggested that HPN-3# showed better performance of energy flux regulation and electron transportation that mitigates NH4+-N inhibition, whereas the mixotrophic cultivation strategy using additional carbon source also reduced the stress and helped to maintain the accumulation of microalgae. In addition, acidified environment has a negative effect on the luxury uptake of P, and subsequently reduced its removal efficiency.