Microbial nitrogen transformation during waste degradation

Landfills and old waste deposits pose a large risk potential for humans and the environment. Numerous studies have demonstrated that the environmental hazards emanating from conventional municipal solid waste (MSW) landfills may last for centuries. Leachate emissions are the main reason for this since their pollution burden will remain at an environmentally incompatible level for hundreds of years. In particular, the persistence of Ammonium-Nitrogen in the leachate constitutes one of the most significant long-term pollution problems. In order to reduce the environmental hazards emanating from MSW landfills to an acceptable level, different in-situ treatment methods have been proposed to accelerate the decomposition of the waste. The most prominent methods are the flushing and the aeration of landfills, whereby the latter has been recognized as a promising and efficient in situ stabilization method for MSW landfills. Existing results from various experiments demonstrate that the landfill aeration is accompanied by a significant reduction of the Nitrogen load in the landfill leachate. However, to which extent this reduction is limited to the time of aeration only, and whether a significant increase in the Nitrogen load has to be expected after the landfill returns to its previous anaerobic state, is until now widely unknown. The proposed project aims to investigate the long-term effect of aeration on the metabolism of Nitrogen in landfills. To do so lab scale landfill simulation reactors will be operated under aerobic and anaerobic conditions, respectively, and all Nitrogen flows (gaseous and liquid N emissions) and stocks (quantitative and qualitative characterization of N pool remaining within the reactors) will be measured. Based on these data, detailed Nitrogen balances will be established. In order to also quantify the significance of single Nitrogen transformation pathways tracer tests using stable isotopes (15N) will be conducted. In addition to the Nitrogen balances, the population of decomposing microorganisms and their activity under aerobic and anaerobic conditions will be quantified. The present project will provide for the first time a detailed balance on the N flows and stocks in aerated landfills. In addition main parameters influencing the fate of N in aerated waste deposits will be highlighted and the involved microorganisms and their respective activities will be quantified. Thus, the project not only contributes to a better insight into the metabolism of landfills, but also allows an optimization of current in-situ remediation methods. The expected outcomes of the project include: 1. Quantification of the Nitrogen flows and stocks in aerated landfills. 2. Characterization & quantification of microorganisms relevant for the N metabolism 3. Quantificationof transformation pathways for Nitrogen (including N-uptake by microorganisms) during aeration of landfills 4. Information about the success of landfill aeration with respect to the sustainable reduction of Nitrogen emissions

Landfilling of untreated municipal solid waste has been banned in Europe for at least a decade, but the emissions from such landfills continue to pose problems for coming centuries. In-situ aeration offers a reduction of methane and ammonium emissions released by such landfills and its applications are widespread over Europe. However, the operation has to be terminated someday. Nine landfill simulation reactors (LSR) were operated for more than two years in three different aeration regimes: completely aerobic, completely anaerobic and aerobic-anaerobic. For the last group, aeration was terminated after approximately one year thus simulating the end of remediation. With 10 months lag, recurring (minor) methane and ammonium emissions were detected. Balancing nitrogen revealed that hardly any nitrogen was removed by aeration. More than 83% of initial nitrogen remained in solids and was subject to internal recycling. This observation is in line with the natural nitrogen cycle. The application of chloroform fumigation-extraction led to conclusion that the reduction of emissions in leachate is not caused by incorporation in biomass (as assumed beforehand) than rather by persisting changes in sorption capacity. Hence, the release of pollutants (especially ammonium) might be weakened, but also prolonged.