Nitrogen transformation and loss during the composting of food wastes with different nitrogen contents

This study investigated nitrogen transformation and loss during the composting of food wastes with added sawdust. Three kinds of food wastes (defined as N0, N1 and N2) were used, containing 32.4 g·kg-1, 45.3 g·kg-1 and 58.2 g·kg-1of nitrogen. An aerated static pile compost system was employed to compost the food wastes. The results showed that total nitrogen in the compost first increased and then decreased. Part of the organic nitrogen was transformed into ammonium and which resulted in increased pH of the composting pile. Under the combined effect of high temperature and ventilation, ammonia volatilization from the pile led to nitrogen loss. As the nitrogen content in the food wastes increased, the rate of ammonia emissions and amount of nitrogen loss from the pile was also enhanced. At the end of composting, the accumulated ammonia emissions from all three food wastes, N0,N1 and N2, were 7.0g·kg-1, 9.8 g·kg-1 and 29.4 g·kg-1, respectively. The content of total nitrogen decreased by 16.4%, 26.3% and 21.7%, respectively. The lost amount of nitrogen was 35.0%, 49.9%and 53.0% of the initial total nitrogen amount.Most ammonia volatilization took place in the intermediate and later composting phases at high temperature. Nitrogen losses were attributed mostly to ammonia volatilization.