Design Guidance for Landfill Bioreactors

Bachus, R.C., "Design Guidance for Landfill Bioreactors," Second International Landfill Research Symposium, Asheville, North Carolina, 2003.

Waste Management, Inc. and GeoSyntec Consultants recently collaborated on a study that resulted in the development of design guidance related to bioreactor landfills. The collaborative study focused on understanding the design of liquids injection and gas extraction systems for bioreactor landfills, as well as the factors that affect the design, operation, and performance of bioreactor landfills. The study focused on the following three topical areas and the results will be presented at the symposium:

• Liquids Infiltration: A numerical model was developed to simulate liquids infiltration into waste and a parametric study was performed to assess the effects of several parameters on the vertical and lateral movement of the wetting front in the waste mass. Design guidance is provided with respect to the following parameters: (i) infiltration pipe dimensions; (ii) infiltration trench dimensions and properties; (iii) waste hydraulic conductivity; (iv) liquids injection pressure; and (v) liquids injection time.

• Waste Degradation: A numerical model was developed to study waste degradation and the accompanying gas generation mechanisms as a function of waste composition and the liquids injection history in the bioreactor environment. Design guidance is provided with respect to the influence of the amount and type of organic material in the waste stream on the gas generation potential.

• Gas Extraction: A numerical model was developed to simulate gas extraction from the degraded waste. This model was used to assess the vacuum requirements in the gas extraction pipe network and the extraction schedule for a given pipe network design. Design guidance is provided with respect to the sizing of the gas extraction and transmission pipes, as well as the phasing of the gas extraction system The results of the study demonstrate the importance of matching the liquids injection piping network design to the quantity of liquids available for injection into the bioreactor. The role of the distribution pipe diameter, distribution trench geometry and waste hydraulic conductivity was also studied and summarized. The study also provided valuable insight regarding the importance of liquids and waste composition on the gas generation rates. Finally, the study provided guidance regarding the design and operation of the extraction pipe and blower. This presentation will introduce proposed design procedures for bioreactor landfills. Importantly, this presentation will demonstrate the role of critical design components and the effects of improper design consideration. Finally, several specific recommendations are made with respect to performance monitoring that should be implemented at active bioreactors landfills.

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