Ammonia and nitrogen fluxes in landfill sites: applicability to sustainable landfilling

European legislation imposes tough restrictions on the quality of landfill leachate discharges, of which a major component is ammonia. Thus, there is a pressing need, particularly for operators who will have to meet these discharge standards, for a greater understanding of the origin and transformations of ammonia and other nitrogenous compounds from landfills. Moreover, with the concept of 'sustainability' being applied to landfilling, the industry will need to meet the challenge of accelerating the rate of refuse decomposition. Ammonia is both a potentially toxic product of refuse degradation and an essential nutrient for the bacteria responsible for this. The quantities present in municipal solid waste (MSW) are known but prediction of the amounts released during decomposition is hampered by the lack of long term data on ammonia concentrations in leachate either from landfills or experimental systems with a measured initial nitrogen content. For the treatment of ammonia from landfill regimes designed to accelerate refuse degradation, it is vital to understand the nitrogen requirements of the degradation processes, in order to minimise potential ammonia toxicity while ensuring sufficient concentrations to support the rate of decomposition. The authors found little experimental evidence to support current views on the nitrogen transformations that occur in MSW, although new experimental data support the hypothesis that denitrification occurs in landfill sites. It is generally considered that the high ammonia concentrations in leachate provide evidence that ammonia is released from the decomposition of protein in refuse, even though the concentrations of the various nitrogenous components in refuse during decomposition are not known. Although the concentrations of nitrogenous components in leachate have been characterised, these do not necessarily reflect the degradation of MSW.