Effect of lignocellulosic and phenolic compounds on ammonia, nitric oxide and greenhouse gas emissions during composting

Composting is recognised a promising technology for recycling and adding value to agro-food wastes. There are, however, potential environmental risks associated with composting, such as the emission of greenhouse gases (GHGs). The aim of this study was to quantify the emissions of carbon dioxide, methane, nitrous oxide, nitric oxide and ammonia during composting of five agro-food wastes originated from the broccoli, chestnut, olive and grape industries, and to study the relationship between the emissions and the lignin, cellulose, hemicellulose and phenolic contents of the wastes. According to physicochemical indicators monitored during the process, all agro-food residues tested were suitable for composting, with chestnut in the top and broccoli in the bottom of the range. Composting of chestnut and olive led to higher carbon dioxide, methane and nitrous oxide emissions, whereas lower emissions were observed with white grape. A positive correlation was found between phenolics and nitric oxide (r = 0.63; p < 0.01), but not with the other gases. Lignocellulose showed a positive correlation with nitrous oxide (r = 0.51; p < 0.05), but not with carbon dioxide and methane. The accumulation of lignin was highest in the chestnut compost, which was associated with lower nitric oxide and ammonia emissions relative to the other waste materials. The results show that wastes with high lignocellulose can be managed using composting with additional benefits on the environment in relation to mitigating nitrogen losses.