Performance of autotrophic denitrification enhanced by microalgae aeration and anaerobic ammox

Key words:  chlorella  algal and bacterial coupling system  short-cut nitrification and anammox  biological membrane  autotrophic nitrogen removal

Abstract:

A sequencing batch biofilm (SBR) reactor was used to cultivate an algae-coupled biofilm system based on short-range nitrification/anaerobic ammonia oxidation biofilm with Chlorella vulgaris at a temperature of 30 ℃. The system was operated for 85 d by changing the combination of light duration and aeration. The nitrogen removal performance, algae-coupled system characteristics and nitrogen conversion pathways were analyzed to obtain the optimal nitrogen removal conditions and algal-bacterial coupling nitrogen removal mechanism. The results show that when the influent ammonia nitrogen concentration is 400±50 mg/L, the light/dark ratio is 6 h/4 h, and the aeration intensity is 200 mL/min, the best denitrification effect was achieved, in which the average removal rates of NH₄⁺-N and total nitrogen were up to 92.31% and 87.56%, respectively. The ratio of cMLVSS(wastewater mass concentration) to calgae(dry weight of chlorella vulgaris) is always around 5.5 during the operation of the algae coupled system, which indicates that the ratio of algae and bacteria in the biofilm reaches a relatively stable state and forms a good mutually beneficial symbiotic relationship. The oxygen produced by the photosynthesis of Chlorella vulgaris concentrated outside the biofilm is consumed by nitrifying bacteria, and nitrifying bacteria provided anaerobic environment and nitrite substrate to maintain the activity of anaerobic ammonia oxidizing bacteria. In the nitrogen removal mechanism, the biological uptake accounts for about 45.71%, and the amount of N₂ production and nitrogen loss in the PN/A(partial nitrification-anaerobic ammonium oxidation) process accounts for about 54.29%.