Milind V. Khire

Start-up performance of a full-scale bioreactor landfill cell under cold-climate conditions

A 0.49-ha bioreactor landfill cell containing approximately 32,400 metric tons of municipal solid waste was constructed and operated at the Northern Oaks Recycling and Disposal Facility in Harrison, Michigan, USA. Design of this full-scale research cell included a network of 48 temperature and moisture sensors, leachate collection basins, and gas sampling ports, which provided for continuous temperature and moisture data and periodic measurements of both the quantity and composition of the leachate and gas produced. The data indicated that methane generation started approximately 3 months after filling in lifts that were placed during summer, but not until 8 months for those filled during the winter. Temperature data indicated that near-0 degrees C temperatures persisted within the lifts filled during winter for more than 6 months, and that gas production was minimal during this period. These results suggest that in addition to maintaining optimal moisture levels within the waste mass, temperature control must be a key design consideration in cold climates.

Two-Phase Modeling of Leachate Recirculation Using Vertical Wells in Bioreactor Landfills

AbstractLeachate recirculation or liquid injection is an established practice for operating landfills as bioreactors to enhance the biodegradation of municipal solid waste (MSW). Among other subsurface liquid injection methods, vertical wells (VWs) represent one of the most common methods used for active or closed landfills. The current design and operation of VW systems does not consider the effect of additional liquid injection on the increase in gas pressures. In this study, a two-phase model that assumes landfill leachate and gas as immiscible phases was used to predict the moisture distribution and pore water and pore-gas pressures in a typical bioreactor landfill that uses VWs as its leachate injection or recirculation system. The unsaturated liquid and gas properties of MSW were simulated based on the van Genuchten model. The study evaluates the effect of the unsaturated hydraulic conductivity of MSW, the heterogeneous and anisotropic nature of the MSW, and the geometric configuration of VWs on moi...

Field Data and Numerical Modeling of Water Balance of Lysimeter versus Actual Earthen Cap

AbstractTo evaluate the differences in the hydrological performance of actual earthen cap overlying municipal solid waste (MSW) versus a lysimeter, which is commonly used to measure the hydrologic water balance, a field-scale test section (30×20×2  m) of an earthen cap made up of compacted native glacial clay was constructed and instrumented at a landfill near Detroit. A lysimeter pan was installed within the middle of the test section, and the instrumented area of the test section was expanded upslope and downslope of the lysimeter to monitor water balance parameters within and beyond the lysimeter footprint, in order to evaluate the effect of artificial drainage boundary introduced by the lysimeter. About 50 sensors were installed to monitor meteorological parameters, water content, water potentials, soil temperatures, water levels, gas pressures, percolation, and subsurface lateral flow. The water balance model called Unsaturated Soil Water and Heat Flow Model (UNSAT-H) was used to simulate the water b...

Field-Scale Evaluation of Lysimeters Versus Actual Earthen Covers

This paper presents the design, construction, and monitoring of two uncompacted and one compacted clay field-scale test sections that were built and instrumented at a landfill near Detroit (Michigan). This was accomplished to capture the differences in the hydraulic and hydrologic responses of actual caps overlying the municipal solid waste (MSW) versus the corresponding lysimeters. While the lysimeter pans were installed in the middle of each of the three test sections to measure percolation, the instrumented area of the test section was expanded upslope and downslope of the lysimeter to monitor the soil water storages within and beyond the lysimeter footprint. About 35 sensors were installed in each of the three test sections to monitor water contents, water potentials, soil temperatures, water levels, and gas pressures. The soil water storages for the uncompacted test sections that were underlain by the waste were typically greater than those for the corresponding lysimeters. However, for the compacted test section, there was no significant difference between the soil water storage for the actual cap and the lysimeter. The percolation rate for the compacted clay test section was on the order of a few millimeters per year, while that for the uncompacted test sections were in the order of tens of centimeters per year. This difference is attributed to the two order of magnitude lower hydraulic conductivity of the compacted clay. The field data collected in this project validates previously published numerical results regarding hydraulic differences between lysimeters and actual caps.

Geotechnical sensor system to monitor injected liquids in landfills

A field-scale horizontal permeable blanket made up of crushed recycled glass was built in an active municipal solid waste (MSW) landfill to recirculate leachate. The permeable blanket is a new method for subsurface leachate recirculation or liquid injection. Leachate injection rates in the blanket ranged from 1.1–3.6 m3/h/m. An automated sensing system consisting of moisture content sensors, pressure transducers, and temperature sensors was designed to monitor the migration of injected leachate inside the blanket. The sensors were embedded in the blanket and connected to a data logging system. All sensors were able to detect the leachate migration within the blanket. The TDR and impedance moisture content sensors could not detect the migration of injected leachate once the surrounding medium got saturated. The pressure transducers and temperature sensors were able to detect leachate migration irrespective of the degree of saturation of the blanket. Unlike thermistor sensors, temperature readings measured by thermocouple sensors were influenced by air temperature.

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.

Lysimeters versus actual earthen caps: numerical assessment of soil water storage.

Lysimeters are commonly used for field-scale assessment of water balance of earthen caps, commonly referred to as evapotranspirative (ET) caps. While lysimeters are the only direct tool to measure percolation through a cap, the lower hydraulic boundary of a lysimeter is significantly different compared to an actual ET cap. In this study, numerical simulations of water balance of lysimeters and ET caps were carried out using Vadose/W for a range of hydraulic properties of the soils and waste. The numerical results suggest that due to the presence of waste below the cap, the soil water storage of an ET cap is greater than an equivalent lysimeter. This greater water storage capacity in an actual ET cap results in lower percolation than for an equivalent lysimeter.

Influence of the Waste Layer on Percolation Estimates for Earthen Caps Located in a Sub-humid Climate

In this numerical study, an alternative cap consisting of a vegetative layer and a moisture storage layer was simulated with a bottom boundary consisting of either a lysimeter or an underlying waste layer for a sub-humid northern climate (Detroit, Michigan) using the water balance model Vadose/W. Various combinations of saturated and unsaturated hydraulic properties of the cap layers and the waste layer were simulated using the numerical model. In this study, simulated percolation rates were more for lysimeters compared to caps underlain by the waste.

Field-Scale Unsaturated Hydraulic Properties of Compacted and Uncompacted Earthen Covers

Unsaturated hydraulic properties influence the field hydrology of engineered earthen covers. Field measured hydraulic properties of soils are recommended because they closely represent the field structure of the soil. This paper presents unsaturated hydraulic properties of two field scale test sections, composed of compacted vs. uncompacted clay. The unsaturated hydraulic properties were estimated using continuous measurements of water contents and matric suctions. The water contents and matric suctions were measured by sensors installed in the field test sections. The unsaturated hydraulic conductivities were estimated using the instantaneous profile method. The water content versus suction relationships for the two test sections showed significant differences at low suctions and the relationships were similar at higher suctions. The only difference between the test sections was the compaction state. The compacted clay test section had higher dry unit weight than the uncompacted clay test section. The uncompacted clay had greater volume of interclod voids (macropores). The differences in water content versus suction relationships at low suction could be because of macropores which empty out first and fill up last under unsaturated condition. At higher suctions, the relationships were similar because the flow is controlled by the micropores which existed in both test sections.

Liquid Head on Landfill Liners Due to Leachate Recirculation

Due to the financial and environmental incentives offered by leachate recirculation, leachate recirculation is a widely used leachate management option for municipal solid waste (MSW) landfills. However, more commonly, leachate collection systems (LCSs) of landfills are designed primarily for leachate impingement from infiltration of precipitation. Hence, when leachate is recirculated in landfills, many LCSs do not have the hydraulic capacity to drain the recirculated leachate and maintain the leachate head on the liner below the federal regulatory requirement equal to 0.3 m. Leachate head build up data for injected liquids in MSW landfills is virtually non-existent. In this study, we have numerically simulated leachate injection using two most commonly used methods: (1) horizontal trenches; and (2) vertical wells. We used the saturated/unsaturated flow model HYDRUS-2D. The simulations were conducted for a range of hydraulic conductivities of waste and the LCS drainage material and liquid injection rates. We have presented the results in such a way that designers can select appropriate design parameters to minimize excess liquid heads on liners. The simulated results indicate that pea gravel or materials having hydraulic conductivity greater than 1 cm/s offer a better choice for LCS drainage material. Use of material having hydraulic conductivity less than 0.01 cm/s (e.g., sand) resulted in liquid head greater than 0.3 m for typical leachate injection rates used in landfills.