Toward A Twenty-first Century Landfill in Yolo County

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Accelerated Anaerobic and Aerobic (Controlled Landfill Bioreactor)
Composting Project Publications:

(All questions regarding these projects should be directed to the Project Manager, Dr. Ramin Yazdani)

For more information regarding Yolo County's Project XL see the EPA site

Placement of the geonet on the base liner
(Placement of the geonet on the base liner.)

The Yolo County Central Landfill is demonstrating an innovative landfill management strategy called "enhanced or controlled" landfilling to manage solid waste. Controlled landfilling has the potential to provide reliable energy generation from solid waste, as well as significant environmental and solid waste management benefits.

Landfill Processes
    • Summary

Benefit of Landfill Bioreactors
    • Energy Generation
    • Reduced Pollution Threat 
    • Reduction of Greenhouse Gas Emissions 
    • Landfill Life Extension 
    • Reduced Post-Closure Maintenance

Bioreactor's Basic Facts
    • Construction 
    • Instrumentation 
    • Gas Production 
    • Liquid Recirculation


Summary
There is something new going on at the Yolo County Central Landfill that could change the direction of solid waste management. The concept is to accelerate the decomposition process of the waste through controlled additions of liquid and leachate recirculation, which enhances the growth of the microbes responsible for solid waste decomposition. Conventional landfilling practices are designed to keep the waste as dry as possible, which prolongs the decomposition process for long periods of time, often many decades. The goal of the project is to show that landfilled waste can be decomposed or "stabilized" in 5 to 10 years. The project consists of two demonstration landfill cells; each is filled with about 9,000 tons of curbside garbage. One cell receives controlled liquid additions and recirculated leachate, while the other cell serves as a control to represent a conventional landfill. The cell that receives liquid additions is called the "enhanced" cell. Several benefits of this landfilling approach are outlined below.

Energy Generation
Controlled landfilling will shorten the time frame for landfill gas generation. This renders projections of landfill gas generation rates and yields that are much more reliable. This serves to improve the economics of landfill gas to energy projects.

Reduced Pollution Threat
Through anaerobic composting, a landfill bioreactor actively manages the solid waste in the near term. Complete landfill gas and leachate generation occurs while the protective containment system is relatively new and least likely to fail. Environmental liabilities associated with prolonged waste decomposition are therefore significantly reduced for future generations. 

Reduction of Greenhouse Gas Emissions
The release of greenhouse gas emissions is reduced both by higher recovery rates of landfill gas and from offsetting fossil fuel use with landfill gas energy. Methane, which comprises about 50-60% of landfill gas volume, is about 24.5 times more potent (mass per mass) as a greenhouse gas than carbon dioxide. Controlled landfilling also eliminates fugitive emission beyond the 30-year post closure period.

Landfill Life Extension
Waste decomposition results in the conversion of biodegradable solid waste into gas, thereby creating additional landfill space. In conventional landfills, this settlement usually occurs after landfill closure when it is too late to use the space. By accelerating the decomposition process, new landfill space is created sooner, which may be reused for additional waste placement. Recycling valuable landfill space could potentially extend the landfill life by 20%. From May 1996 to January 1998, the enhanced cell has settled and average of 41.6 inches and the control cell has settled and average of 12.0 inches. 

Reduced Post-Closure Maintenance
Landfills are mandated to be monitored and maintained for at least 30 years following closure. Accelerated waste decomposition can significantly reduce costs for operation and maintenance of landfill gas control systems, leachate treatment, and final cap systems. Beneficial end uses of the landfill site could also be implemented sooner. 

Acknowledgments
Yolo County wishes to acknowledge the contributions and efforts of the following organizations that have made the Yolo County Landfill Bioreactor a success:

California Energy Commission

Sacramento County

California Integrated Waste Management Board

US Department of Energy through the Urban Consortium Energy Task Force

Western Regional Biomass Energy Program

Don Augenstein of the Institute for Environmental Management of Palo Alto, CA

John Pacey of EMCON Associates

 


Publications

D. Augenstein, R. Yazdani, R. More and K. Dahl (1997). "Yolo County Controlled Landfill Demonstration Project", Proceedings of the 20th Annual Solid Waste Association of North America (SWANA), Landfill Gas Symposium, August, Sacramento, CA. P43-87.

Dahl, K. (1998). "Reuse of Shredded Waste Tires for Landfill Gas Collection and Leachate Injection Systems in the Yolo County's Landfill Bioreactor Demonstration Project" Proceeding of the SWANA's 21st Annual Landfill Gas Symposium, Austin, Texas. P103-117.

R. Moore, K. Dahl and R. Yazdani, (1997). "Hydraulic Characteristics of Municipal Solid Waste: Findings of the Yolo County Bioreactor Landfill Project" Proceedings from the 13th International Conference on Solid Waste Technology and Management, Philadelphia, PA. p8A.

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  BASIC FACTS OFTHE YOLO BIOREACTOR  

 (September to October 1998) 

Construction:


Control Cell

Enhanced Cell

Footprint 0.27 Acres 0.27 Acres
Average Depth 40 Feet 40 Feet
Construction of Base Liner 1993 1993
Waste Filling of Cells April to October, 1995 April to October, 1995
Total # of Waste Lifts (5 Foot Lifts) 9 9
Total Solid Waste (Residential and commercial, no bulky waste) 8,726 Tons 8,557 Tons
Amount of Alternative Daily Cover 1,443 Tons 1,326 Tons
Green Waste, Placed Between Lifts (Green Waste is typically 18.5% of residential municipal solid waste (Tchobanoglous, 1993)). 17% of Total 16% of Total
Average Waste Compaction 1,014 Lbs./Cubic Yard 1,027 Lbs./Cubic Yard
Total Amount of Shredded Tires Used for Gas Collection Systems 200 Tons (~20,000 Tires) 295 Tons (~29,500 Tires)
Instrumentation:


Control Cell

Enhanced Cell

Temperature Sensors 11 Thermistors 13 Thermistors
Moisture Sensors 15 Gypsum & 4 PVC 25 Gypsum & 12 PVC
Cell temperatures at…                                        

Bottom of Cell (Level 1)

78°F (26°C) 93°F (34°C)

15' from Bottom (Level 2)

94°F (34°C) 110°F (43°C)

 35' from Bottom (Level 3)

 95°F (35°C) 109°F (43°C)

Landfill Gas:


Control Cell

Enhanced Cell

Gas collection Systems Vertical shredded tire gas well Vertical gravel gas
Total Landfill Gas Volume (Measured 10/21/98)  15.24 x 106 SCF  28.7 x 106 SCF
 Average Landfill Gas Flowrate 0 SCFM 11.88 SCFM
Average Methane Content 31% 57%
Average Total Settlement of Cells (5/96 to 6/98) 11 Inches 46 Inches


Liquid Additions to Enhanced Cell: 

(Liquid Additions to the Enhanced Cell began 10/23/96)

Total Amount of Liquid Added (Groundwater and Leachate 10/21/98)                         1,139,965 Gallons
Total Amount of Groundwater Added (87% of the groundwater was added from 10/96 to 12/96)                                                        377,690 Gallons
Total Amount of Recirculated leachate (June 22, 1998)     762,275 Gallons (669 Gal/Day)

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