Évolution biochimique des résidus de désencrage dans un contexte de valorisation comme barrière de recouvrement
Echevengua Teixeira, Claudia
Deinking residues (DR) are produced in the first steps of paper recycling. Most of the Quebec's production, approximately 500 000 humid tons per year, is still sent to dedicated landfills. However, new DR valorization approaches have been proposed, such as their use as geotechnical replacement material for fine-textured soil in the construction of cover systems for landfills or tailings that generate acid mine drainage (AMD). Due to the high organic content of DR, biochemical and chemical evolution (degradation) can take place and impact not only the environment that they aim to protect, but also the geotechnical properties of DR. In this context, the purpose of this study was to understand DR degradation mechanisms, evaluate their long-term state, and appraise the impact of degradation on the behaviour of DR in the laboratory and in the field. To attain this goal, this study was divided into three steps: (1st) DR characterization; (2nd) laboratory degradation tests; and (3rd) evaluation of DR degradation in the field. According to tests carried out, it is possible to state that DR degradation follows the degradation phases of domestic waste in sanitary landfills, from the point of view of biogas production evolution as well as the quality of leachate parameters. After 400 days of tests under controlled conditions, a total mass loss of approximately 16% was obtained for the tests at 38 [degrés Celcius] and 21 [degrés Celcius]. The loss for a test at 12 [degrés Celcius] was approximately 10%. In the case of the tests at 38 [degrés Celcius], the mass loss by gas production became greater than that by leaching. Microbiology studies identified bacilli and fluorescent sarcina as the predominant morphologies, although they were not as numerous compared to what can be found in domestic wastes. Based solely on observations with the naked eye or with a low-level magnification electronic microscope, it isn't possible to observe a noticeable change in DR appearance, structure and morphology. However, with stronger magnification, we observe areas with significant alteration, accompanied by high microorganism density. Geotechnical tests and monitoring of certain geomechanical and hydraulic parameters show that: degradation caused an increase in water content; degradation affects DR compressibility and causes a decrease in hydraulic conductivity. With loading, DR undergoes significant volume variations (creep), which are potentialized by degradation. Field results demonstrate that several follow-up parameters evolved very similarly in the case of barriers installed at the Eustis and Clinton mine tailings, notably biogas composition ([approximate] 40% CH[subscript 4] and [approximate] 50% CO[subscript 2]) and the quality of leachate collected (concentration in total solids around 25 g/l). However, mass loss by leaching is slow, due to low infiltration speeds (evaluated based on water collected in lysimeters). According to the results obtained and observations made during this study, the relevant properties of DR do not seem to be negatively affected by the degradation level attained in the laboratory.
- Génie – Thèses