The Districts' solid waste management activities have traditionally centered around sanitary landfills as the primary means for solid waste disposal. Solid waste begins to decompose biologically shortly after being buried in landfills and, through the anaerobic decomposition process, generates landfill gas (LFG). Landfill gas, comprised primarily of methane (CH4) and carbon dioxide (CO2), would contribute to the formation of smog or global warming, cause odors, and even pose safety and health hazards if not properly controlled. The Districts were among the leaders in the landfill industry to install extensive networks of LFG collection systems on all of its sanitary landfills for controlling gas migration and eliminating LFG pollution or hazards. The collected landfill gas is either utilized as a valuable renewable energy source or safely disposed through thermal incineration in landfill gas flares. The majority of the collected landfill gas is utilized for electrical power generation in three steam power plants and one gas turbine facility.
Landfill gas is combustible and can be used as an energy source. To convert landfill gas to energy, the Districts constructed, in the mid 1980's and continues to operate:
- Three gas-to-energy facilities
- A compressed natural gas (CNG) facility that dispenses fuel for vehicles.
These energy programs offer four significant benefits:
1. Beneficial use of methane gas collected at landfills.
2. Revenue from the sale of energy and landfill gas
3. Substantial reductions in emissions by not burning gas by using flares
4. Substantial reductions in emissions that would otherwise be generated by traditional power plants.
The gas-to-energy facilities are conventional Rankine Cycle Steam Power Plants using landfill gas as fuel to generate electricity. Landfill gas is fired in the plant's boilers producing superheated steam. The superheated steam is used to drive the steam turbine/generator to generate electric power. Currently, the three gas-to-energy facilities produce approximately 64 megawatts (MW) net of electric power. The power is sold to the local utility company, Southern California Edison (SCE).
Power sales contracts were negotiated with the utility company during the mid 1980s. At that time, power was in demand, and thus favorable power rates and terms were offered in the contracts. Since the plants' commercial operation, the sales of electricity to the utility company have generated substantial revenues for the Districts. Capital debts for the three facilities have been paid off and the only cost for power production are the operation and maintenance costs. The O&M costs which range from $0.023/kwhr for the Puente Hills Facility to over $0.078/kwhr for the other two smaller facilities.
By using boilers to combust the gas and a landfill gas pretreatment system customized for each facility, the Districts maintain emission rates well below those required by the South Coast Air Quality Management District (SCAQMD) and those of natural, gas-fueled utility power plants. Overall, the three facilities have successfully demonstrated that a landfill gas-to-energy plant can combust low-Btu landfill gas as boiler fuel, reduce air emissions, and provide significant economic benefits for landfill owners.
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