Minimizing ammonia emissions from dairy manure composting by biofiltration using a pre-composted material as the packing media.

Compost-based biofiltration is a method widely used to mitigate ammonia emissions during composting. To improve the efficiency of a composting-biofiltration system, it is necessary to determine the most effective degree of composting at which to process the packing media used in the biofiltration system. In this study, materials pre-composted for 20 and 30 d (C20 and C30, respectively), and mature compost (CM) that had been treated for 60 d, were applied as biofilter media to remove ammonia from dairy manure composting exhaust gases. A comparison of the results revealed that the C30 biofilter not only completely removed ammonia, but also produced the least nitrogen loss (1.84%). The C20 biofilter exhibited an inferior performance, indicating that enough pre-composted time is necessary for material used as the packing media. Though the CM biofilter displayed good performance with regard to ammonia removal (97.8%), it had a high nitrogen loss (6.46%). A spearman rank correlation matrix revealed that the abundance of nitrogen cycle genes including amoA, nosZ, nirK, and nirS, had a strong correlation with the physicochemical properties such as nitrate content, carbon source, moisture content, and pH of the biofilter media. C30 provided advantageous conditions and contained a relatively high abundance of nitrifiers and the lowest abundance of denitrifiers. As a result, C30 rather than CM was a more appropriate biofilter media for ammonia removal. Moreover, the occurrence of biological nitrification during the dairy manure composting process indicates the effectiveness of a material for use as biofilter media.