Unusual effects of triacylglycerol on the reduction of ammonia gas emission during thermophilic composting

Ammonia gas emission was reduced drastically during the composting process when triacylglycerols such as fat and oil were contained in the raw material. Lard was the most effective triacylglycerol, as ammonia gas emission was completely suppressed when lard was mixed with the raw material at a mixing rate of 33% on a dry weight basis; otherwise, 7% of nitrogen contained in the raw composting material is expected to be released during composting. A similar effect was observed when olive oil was used, whereas the effect was not as large when composting with hexadecane added as a model of mineral oil as when composting with lard. Furthermore, other carbon-rich compounds such as glucose, cellulose powder, and sawdust were mixed with the raw material in order to ascertain their effects on the reduction of ammonia gas emission. This was done by adjusting the C/N ratio to be the same as that for composting with 33% lard, i.e., approximately 60, and it was found that the C/N ratio was not good a indicator of the reduction of ammonia emission, and that lard was the most effective among all of the carbon-rich compounds used in the present research.