Volume 35, Issue 1 (January 2012)
Instrumented large scale subsurface liquid injection model for bioreactor landfills
Bioreactor landfills are complex unsaturated systems where liquids are injected at relatively high pressures in on/off dosing cycles. In order to simulate hydraulic scenarios to improve understanding of leachate recirculation systems for landfills, 86 cm long by 30 cm wide by 56 cm tall unsaturated flow physical model was designed and fabricated. A permeable blanket was installed in the model to inject water. The blanket was 50 cm long × 30 cm wide × 2 cm thick and was made up of pea gravel. Uniform fine and coarse sands, which were thoroughly characterized for their hydraulic properties, were used in separate experiments to simulate waste. Pressure transducers and water content sensors were embedded in the model to monitor the migration of injected water in the blanket and in the underlying soils. Water was injected at flow rates ranging from 20 to 150 cm3/s in continuous and on/off modes to achieve transient and steady-state conditions. The responses of the pressure transducers embedded in the blanket in the model mimicked the responses of the pressure sensors embedded in an instrumented field-scale (55 m long × 9 m wide × 0.15 m thick) permeable blanket made up of crushed recycled glass used for recirculation of leachate at a municipal solid waste landfill. The effect of entrapped air present in the voids was evident from greater pressures developed during wetting which dissipated as the entrapped air escaped the system. This finding highlights the need to use of dual phase models for simulating pressures in bioreactor landfills.