Abstract:

To address the nitrogen loss caused by ammonia volatilization during the storage and land application of biogas slurry from swine farm, a bio-trickling filter reactor equipped with micro-foam packing was designed in this study. Sequential batch single-factor experiments were conducted to investigate the effects of key parameters, including circulating water flow, packing height, and influent ammonia nitrogen (${{\mathrm{NH}}_{4}}^{+}$-N) concentration, on the ammonia nitrogen nitrification efficiency of biogas slurry. The results indicated that under ambient temperature conditions, the reactor exhibited excellent nitrification performance when the circulating water flow was 2.0-3.0 L·min^-1, the packing height was 90 cm, and the influent ${{\mathrm{NH}}_{4}}^{+}$-N concentration ranged from 80 to 100 mg·L^-1. The maximum 24 h ${{\mathrm{NH}}_{4}}^{+}$-N conversion rate reached 86.6%, the total nitrogen (TN) loss rate was 6.5%-13.8%, and the ratio of nitrate nitrogen (${{\mathrm{NO}}_{3}}^{-}$-N) production to ${{\mathrm{NH}}_{4}}^{+}$-N conversion [Δ(${{\mathrm{NO}}_{3}}^{-}$-N)/Δ(${{\mathrm{NH}}_{4}}^{+}$-N)] in effluent was as high as 0.90 or above. Microbial community analysis of the reaction processes with different influent ${{\mathrm{NH}}_{4}}^{+}$-N concentrations revealed that the dominant bacterial phylum in the packing biofilm was Proteobacteria, with a relative abundance exceeding 85%. This phylum showed higher relative abundance when the influent ${{\mathrm{NH}}_{4}}^{+}$-N concentration was 125-150 mg·L^-1, indicating its major role in the nitrification process. However, excessively high influent ${{\mathrm{NH}}_{4}}^{+}$-N concentrations exerted inhibitory effect on the dominant bacterial communities in the biofilm.

Key words: bio-trickling filter, ammonia nitrogen nitrification, swine farm, biogas slurry, parameter optimization