Achieving deep autotrophic nitrogen removal from low strength ammonia nitrogen wastewater in aeration sponge iron biofilter: Simultaneous nitrification, Feammox, NDFO and Anammox

Partial nitrification and anammox process is considered to be a good choice for nitrogen removal. Nevertheless, it is difficult to achieve in low ammonia wastewater because of the need to control further oxidation of nitrite. Nitrification combined with Feammox (anaerobic ammonia oxidation coupled to Fe (III) reduction) and NDFO (nitrate/nitrite-dependent Fe (II) oxidation) can achieve autotrophic removal of low ammonia. And sponge iron can avoid the disadvantage of continuously adding iron sources in this process. Therefore, a sponge iron biofilter (SIBF) treating low ammonia wastewater under aeration was explored in this study. The optimal operating conditions for SIBF were hydraulic retention time (HRT) of 9 h and gas-water ratio (R) of 9:1, at which the total inorganic nitrogen removal efficiency was up to 77.2 %, and effluent ammonia and total inorganic nitrogen concentrations were less than 5 mg/L and 15 mg/L, respectively. This met the 1A discharge standard of municipal wastewater in China. Stable ratio isotope results indicated that Feammox, NDFO and Anammox resulted in high nitrogen loss in SIBF. And different nitrogen transformation contribution tests indicated NDFO had the dominant contribution, which accounted for 55.7 %. Besides, the production of N2O was minimum under HRT of 9 h and R of 9:1, in which the N2O emission factor was 0.7 %. Stable isotope tracing analysis showed that 92.8 % of N2O was derived from ammonia and the dominant production pathway was nitrifier denitrification. The results of microbial community showed that the nitrification bacteria-Nitrosomonas, Nitrotoga, Nitrospira, Feammox bacteria-Dechloromonas, NDFO bacteria-Thiobacillus and anammox bacteria-Brocadia played major roles in SIBF. Therefore, SIBF shows superior performance and application potential in autotrophic nitrogen removal from low-ammonia nitrogen wastewater under aeration.