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-Nitrogenin 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.

This 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 Nitrogenflows and stocks in aerated landfills.

2. Characterization & quantification of microorganisms relevantfor the N metabolism

3. Quantification of 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

Duration: 01.09.2016-31.08.2020

Funding agency: Austrian Science Fund (FWF): P 29168

Project leader: Prof. Johann Fellner, Technical University of Vienna, Austria

Participants: Christa Schleper