1. Raco B.1, Battaglini R2, Dotsika E.3,1, Poutoukis D4 and Karalis P2
ISOTOPIC INVESTIGATION OF GAS (13CCO2-13CCH4 ) AS A TOOL TO CHARACTERIZED POLLUTION FROM WASTE MANAGEMENT.
Raco B.1, Battaglini R2, Dotsika E.3,1, Poutoukis D4 and Karalis P2
1 Institute of Geosciences and Earth Resources, Via G. Moruzzi 1, Pisa, Italy,
2 Massa spin-off Largo Guido Novello, Firenze Italy,
3 Stable Isotope Unit, Institute of Materials Science, NCSR Demokritos, Agia Paraskevi Attiki, Greece,
4 General Secretariat for Research and Technology, Mesogion Ave., Athens, Greece,
Introduction
3. Chemical results
Samples of biogas were taken from different landfills areas. Other samples have been collected by executing vertical profiles (25, 50 ,75 cm of depth). The gases were analyzed chemically (CO2, CH4, N2, O2, H2S, H2, CO and NH3) and isotopically (13CCO2, 13CCH4 ,2HCH4). Moreover direct measurement of biogas flow from landfill cover was measured by accumulation chamber device for methane and carbon dioxide determination. For the chemical and isotopic analysis of gas widely standardized methodologies (gas chromatography and IRMS) have been used;
The obtained isotopic results were used to characterize the gas emissions and the grade of gas maturation, to discriminate the origin of contamination and to study the different geochemical processes (reduction biogenic of CO2, oxidation of CH4, bacterium oxidation..). The obtained results show also the possibility to discriminate the pollution due to the presence of landfill sites.
Oxydation path
oxydation path
1. The locations
Different landfills are located in Italy: Tuscany (Legoli, Rosignano M.mo, Montespertoli, Firenze, Literno – Elba Island), Emilia Romagna (Ravenna), Veneto (Vicenza); and Greece: (Komotini, 2 landfills). All the studied sites are MSW landfills, except Ravenna that dedicated to hazardous wastes.
Sampled biogas show different oxidation rates with CH4/CO2 almost constant (~1.3) and increasing content of “air” fraction. Ravenna samples show a different pattern with the higher CH4/CO2 ratio (~10). This is probably related to the peculiarity of the landfill that hosts hazardous wastes.
Biogas vertical profiles increasing oxidation path with the diminution of sampling depth (e.g. L2 75, L2 50, L2 25). These observations are in agreement with the results of deep biogas. CH4/CO2 ratio is lower than landfill gas sampled from wellhead of biogas collecting systems (~1).
4. Isotopic results
2. Material and methods
Then the gas was aspired, by a syringe provided with a-three-ports valve, in a pyrex vial. Gas samples have been collected utilizing a small stainless steel probe plunged at cm of depth. For each gas that chemical and isotopic analyses are concerned, widely standardized methodologies have been used; in particular gas chromatography for CO2, CH4, O2+Ar, N2 concentrations and mass spectrometry for carbon and hydrogen isotopic composition have been utilized.
δ13C in CO2 and CH4 molecules, and δD in methane, have been analyzed.
δ13C of CO2 and CH4 confirm the chemical differences among Ravenna samples and all the other landfill gas specimens. All the other samples are in perfect agreement with typical chemical and isotopic biogas compositions. Firenze samples show the widest spread along the oxidation path, moreover one of these samples is located in the biogenic CO2 reduction area. The most oxidized sample is N29 of Literno landfill. Chemical composition (CH4=51%; CO2=36%)of this last sample seems to not confirm isotopic data (δ13C CO2=-26‰; δ13C CH4=-28‰).
Vertical profile samples show maximum oxidation rate for shallower specimens.
5. Environmental applications: Vicenza case study
The studied landfill is located in an area of the north eastern part of Po river valley characterized by the presence of natural gas manifestations with high CH4 percentages (up to 80% ca.). The landfill is isolated from the hosting sediments by a basal impermeable clay layer and external bentonite diaphragm built-up to avoid lateral escapes of landfill gas (LFG). A network of monitoring wells is distributed inside and outside of the diaphragm, as check-points for this kind of fugitive emissions. The matter was to understand if CH4 found in external gas spy wells was originated by LFG escape or by natural emission. The problem has been managed by chemical and isotopic (δ13C of CO2 and CH4 )characterization of LFG, known natural emission (indicated as Farm) and of gas sampled in external an internal monitoring wells and other bores.
Results, shown in figure, revealed a LFG derivation for most of the samples. Just two specimens seem to come from natural gas. One of the monitoring wells sample show a complete similarity with LFG.
To achieve a better characterization of methanogenesis processes (reduction biogenic of CO2, oxidation of CH4, bacterium oxidation..), δD of methane has been analyzed for Literno biogas, and for vertical profiles samples. Samples align along oxidation path, but with different impact of CO2 reduction.
6. Conclusions
Isotopic and chemical analysis of gas are a useful key to understand both characterization of waste fermentation processes and origin of gas emission in surrounding of landfill sites.