Effect of ammoniacal Nitrogen on methanogenic metabolic pathways during MSW anaerobic digestion

Municipal solid waste (MSW) represents an important renewable energy sources and the sustainable management of organic wastes is a major environmental and economic issue. The anaerobic digestion of MSW, which occurs inlandfills and methanization treatment plants, is a very complex process. The final step of the waste degradation, i.e.methanogenesis, which produces methane, leads to the production of a biogas that could be transformed into heat,electric power and fuel gas (renewable energy). In order to produce more efficiently this renewable energy and toenhance the degradation of the organic fraction of waste, bioreactors landfill and methanization treatment plants are twopromising management strategies.

Further Authors:
J. Epissard - Irstea
M. Lemunier - Suez Environnement

However, these new strategies induce new processes failure. One of those is theaccumulation of ammonia produced from nitrogeneous compounds. The reason is that there is no efficient ammoniaelimination process under anaerobic conditions.An acetate-adapted landfill leachate microbial community was incubated anaerobically under mesophilic conditions(35°C) with acetate (3.3 g.L-1) at four different ammonia concentrations (0.180 g.L-1 to 5.4 g.L-1). Standardphysicochemical parameters were monitored together with CH4 and CO2 stable carbon isotopic signatures. Asmethanogenesis from H2/CO2 results in a larger fractionation against 13C than acetoclastic methanogenesis, the use ofstable isotopic signature of CH4 (δ13CH4) and CO2 (δ13CO2) can then allow to determine by which methanogenicpathways methane is produced. The objective of this study is to monitor methanogenic metabolic changes duringmethanization of acetate at various ammonia concentrations using the natural stable carbon isotopic signature ofmethane and carbon dioxide.Using this new tool, combined with standard physico-chemical monitoring, the results obtained in this work show that asudden increase of ammoniacal nitrogen concentration significantly influenced the methanogenic process of an acetateadapted-landfill inoculum. Indeed, ammonia concentration increase leads to various effects. CH4 stable carbon isotopecomposition evolution indicates a shift from the acetoclastic to hydrogenotrophic methanogenic pathway in function ofthe ammonia concentration. These results demonstrate that at high ammonia concentration acetate is consumed first byacetate oxidation followed by hydrogenotrophic methanogenesis (this reaction is then called syntrophic acetateoxidation). Ammonia concentration could then induce inhibition of acetoclastic methanogenesis. Even if the quantity ofmethane produced was the same at the end of all incubations, reaction rates of methane production were lower whenacetate was oxidized first.This work underlines the potential of the approach using carbon stable isotope measurement to study methanogenicprocesses. Indeed, isotopic approach could be a very useful tool to study AD process at different studies scales (i.e.laboratory and operational) as it allows a rapid and accurate monitoring of metabolic pathways involved duringmethanogenesis. A combination with microbial community structure analysis (using molecular microbiology techniques) could be very powerful to obtain a better understanding of methanogenic reactions.

Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2012 (Juni 2012)
Seiten: 8
Preis inkl. MwSt.: € 8,00
Autor: Théodore Bouchez
Dr Laurent Mazéas
J. Grossin-Debattista
H. Budzinski

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