Bioreactor Monitoring: Assessment of Performances

A field research program is being performed by CReeD, the research department of Veolia Environnement group in order to assess the performance of a bioreactor landfill and determine an optimal bioreactor working face. The project compares two independent full scale landfill cells on the same site with the same quality of waste: the first one is managed as a bioreactor cell with leachate recirculation and the second one as a control cell without recirculation. The bioreactor cell is characterized by a watertight and gastight top cover (HDPE geomembrane) to minimize odors/gas emissions, to provide better biogas quality (no air intrusion), and to permit improved control of the hydraulic mass balance (no rainwater entrance). The injection system is composed of 18 vertical wells including 8 telescopic wells. These were designed and located in order to have the best moisture distribution in the waste mass. Geophysical instrumentation was installed in this cell to evaluate injection performance (range of injection wells, moisture distribution fields). For each cell, the biogas is collected using vertical wells. However, the number of wells was increased and an horizontal subsurface network was added in the bioreactor cell in order to collect the overproduction of biogas due to the acceleration of the waste biodegradation. Gas and leachate in the two cells are collected separately. An analysis and a control of the following physical, chemical and mechanical parameters for each cell is therefore possible during the period of waste stabilisation: (1) the quality and the quantity of leachate produced; plus the quantity and the quality of the injected leachate in the bioreactor cell; (2) the quality and the quantity of biogas produced; (3) the estimation of Biological Methane Potential (BMP tests) and moisture of waste samples versus time; and (4) the waste settlement. Injection into the bioreactor cell started in September, 2003. No clear trend relative to the leachate recirculation can be identified because we have only six months of data. However, first results highlight the influence of the watertight and gastight topcover: in the biogas coming from the bioreactor, there is no or few oxygen. We also identified the necessity to modify the way of working on the bioreactor cell in order to emphasise the leachate recirculation effects on the waste degradation. Improvements are presented.