PhDThesis Manzo
Ciro ManzoAssessment of biogas emission from landfills is a relevant issue, both for environmental and economic reasons. In fact methane, a greenhouse gas, is one of the main components of biogas released in the atmosphere from landfills; moreover unexploited methane represents a loss of income for landfill power plants. Only part of the Biogas produced is exploitable and so it’s interesting to develop different and independent biogas measurement procedures to define the actual emissions. In fact the theoretical models for biogas production provide rough estimation. So it is important to be able to measure directly and accurately fugitive emissions, in order to improve landfills management and landfills performances monitoring. In Italy no national/local specific technical rules are in force for landfill gas emission assessment so the procedure recommended by the English Environmental Agency (EA) is commonly applied. This procedure is based on the integration of punctual flux emission measurements from the surface of the landfill, but it was developed only for closed site. In this work we propose an alternative method of landfill biogas emission measurement, based on the hypothesis that emitted biogas in stable atmospheric condition (constant wind with velocity lower than a fixed threshold) pertains to an emissive gas plume. The plume may be intercepted by a regular mesh of points located downwind of the landfill, where methane concentration is measured. Afterwards, atmospheric dispersion modelling allows us to estimate the methane emission from the landfill. In order to fulfil the above objective, we handled the following main steps: a) Identification and set up of methods for measuring biogas concentration; b) Calculation of total emission by modelling acquired data; c) Comparison among results obtained applying different measurement methods. We repeatedly (summer and winter seasons) applied the proposed methods to a set of municipal solid waste (MSW) landfills, either in activity or closed. We estimated methane concentration by means of the Tuneable Diode Laser technique which is adopted in the USA by the Environmental Protection Agency (EPA). The device utilised is Gasfinder 2.0 from Borel Laser, consisting of an integrated transmitter/receiver unit and a remote, passive retroreflector array which allowed us to obtain time-series of path-integrated concentration measurements along horizontal and vertical planes located above the landfill surface. The sensitivity of the device is up to 0.01 ppm for 100m path length. We also performed direct sampling of the emissive plume by using a set of bags and remotely controlled air sampler devices, arranged to identify a vertical surface downwind of the landfill. We then measured methane concentration within the bags with a FTIR multigas analyzer. In order to assess total methane emission, we processed the data obtained by the two above measurement methods by using a numerical code implementing an atmospheric dispersion model. We finally compared these outputs with total emission estimated by applying the EA recommendations as well as with emission estimated by using the BIO5 stoichiometric numerical model.
