A novel partial complete nitrification coupled microalgae assimilation system for resource utilization of high ammonia nitrogen wastewater

In order to evaluate the feasibility of the partial complete nitrification (PCN) in removing the ammonia inhibition during culturing microalgae with synthetic high ammonia nitrogen wastewater, biological aerated filters (BAFs) coupled microalgae culture system were constructed. Firstly, after the successful start-up of the biofilter, the controllable nitrate nitrogen conversion rate (NCR) (approximately 88%, 77%, and 48%) was realized through alkalinity/NH4+-N regulation (8:1, 5:1, and 3:1, respectively). Experiments revealed that under continuous operation mode, the proper control of the degree of PCN was more conducive to the microalgae (Chlorella pyrenoidosa) growth and biomass production (maximal accumulated harvested biomass of microalgae of 16.81 g was recorded when NCR was 77%). Furthermore, based on the comparison between the experimental data of day 5 and day 11, it was shown that the crude protein content in biomass on day 11 slightly increased while the carbohydrates content slightly decreased. More importantly, it was observed that the lipid content significantly increased (a maximum of 41.43% was recorded in 48% NCR coupled microalgae culture system), and the degree of increase was negatively correlated with the alkalinity of upstream BAFs influent.