Deodorization of the off-gas from livestock manure aerobic composting tank using biotrickling filters and its mechanism

In this study, two biotrickling filters (BTFs) were fabricated to treat the off-gas produced during the aerobic composting of animal manure, namely: BTF-A (packed with volcanic rock) and BTF-B (packed with ceramsite). The results showed that the major contributors to the odor level of the off-gas were ammonia (NH3) and total volatile organic compounds (TVOCs). The removal efficiencies of BTF-B for NH3, TVOCs, and odor level (88.78 ± 5.03%, 70.25 ± 6.95% and 88.10 ± 13.21%, respectively) were superior to those of BTF-A. Partial nitrification was achieved in the circulating water with a pH of 7.0–8.2, dissolved oxygen (DO) content of 1–3 mg/L, and an average free ammonia (FA) content of 16.65 mg/L (without denitrification occurring). Ca. Nitrosoglobus was observed as the dominant ammonia-oxidizing bacteria in the BTF deodorization process. In addition, a deodorization mechanism based on Ca. Nitrosoglobus and Ralstonia sp. in the biofilm on packings was proposed.