Enhanced removal of NH3 during composting by a biotrickling filter inoculated with nitrifying bacteria

A biotrickling filter (BTF) was used to treat NH3 emitted from the exhaust gases of cattle manure compost. Results of the non-biofilm experiment suggested that NH3 could not be removed effectively only through biofilm adsorption. The absence of NH4+ bio-oxidation resulted in an increase in free ammonia, which had a negative effect on NH3 removal. After biofilm culture, NH3 removal efficiency fluctuated between 67.2% and 94.3% because the presence of a biofilm extended the liquid residence time in the packing. When the biofilm was inoculated with nitrifying bacteria comprised of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), which were screened from a cattle manure solution, the average removal efficiencies became 59.9% and 15.0% higher than those of the non-biofilm and biofilm culture experiments, respectively. AOB and NOB could still oxidize ammonia and nitrite, respectively, even when the free nitrous acid concentration was as high as 37.6 mg/L. With an empty bed retention time of 96.0 s and a removal efficiency of 99%, NH3 elimination capacities were attained at 57.1, 28.6, and 23.7 g-N/(m3 h) for the first segment, the first and second segment, and the whole BTF, respectively. These results demonstrate that the BTF under study is a viable alternative for the treatment of NH3 during composting.