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The Commerce Refuse-to-Energy Facility burns trash to provide heat for a steam turbine.

Sanitation District a bright spot in the energy picture

Among the utilities that deliver electricity in California, the Sanitation Districts of Los Angeles County would rank in the top 20 — not bad for an agency where power generation is a mere side issue.

“We’re a waste disposal agency,” said Don Avila, Assistant Information Officer for the Sanitation District.

The Sanitation District collects, processes and disposes of trash and sewage for more than 5 million people in Los Angeles County. This requires treating about 525 million gallons of wastewater and recycling or disposing of 20,000 tons of solid waste — every day.

And as a byproduct, the Sanitation District generates about 117 megawatts of electricity — 87 megawatts more than the Sanitation District needs to operate its countywide facilities.

“We only use 26 percent of what we generate,” Avila said. “We still have enough power to sell to Edison to supply almost 200,000 Southern California homes.”

The Sanitation Districts has a long-term contract to sell that excess energy to Edison. Though the price does fluctuate with the market, the Sanitation District hasn’t altered its pricing structure during the current power crisis.

“We’re locked into a formula we settled on with Edison,” said Joe Haworth, Information Officer for the Sanitation District.

The district uses refuse in two ways to create fuel to make energy. It burns trash directly in two refuse-to-energy plants and it collects the biogas generated by waste decomposition.

The Commerce Refuse-to-Energy Facility — owned jointly with the city of Commerce — and the Southeast Resource Recovery Facility — jointly owned with the city of Long Beach — burn some 1,600 tons of trash per day. The heat is used to create steam which turns a generator turbine. Together the two plants produce about 40 megawatts of electricity, which is provided to the Edison electical grid.

The biogas facilities do even better.

Primarily methane and carbon dioxide, biogas is the result of natural decomposition. It’s the waste product of the anaerobic microbes that eat our waste products.

When refuse is covered over in a landfill, anaerobic bacteria — ones that don’t need oxygen — begin eating the trash. As they grow, they give off methane and carbon dioxide, the same way people exhale carbon dioxide.
“It’s nature in a concrete box,” Haworth said. “We’re using natural processes. It’s not something a scientist made up in a laboratory. It’s something nature made up a billion years ago — which means we believe in tried technology.”

Older landfills burn the biogas in flares to dispose of it, but the Sanitation District burns it in generators. At Puente Hills, the district’s largest landfill, the gas is delivered to the Puente Hills Energy Recovery from Gas (PERG) Facility where it is burned in a boiler creating steam which turns a turbine to generate electriticy.

“It’s like boiling water on a stove to turn a windmill,” Haworth said. The landfill gas takes the place of natural gas to provide heat for that stove.

PERG creates about 50 megawatts per day. Together, the district’s three landfills create about 63 megawatts per day.

The Sanitation District’s Joint Water Pollution Control Plant (JWPCP), its largest wastewater treatment facility, also generates biogas as a byproduct of processing 350 million gallons of sewage per day.

“The two processes are very similar but one’s in a dirt container and one’s in a concrete container,” Haworth said.

As sewage comes in, organic solids are separated from the water. The sludge goes into a concrete tank called a digester where those anaerobic bacteria begin to chow down again.

The biogas is collected and used to power not one but two types of generators. First it goes into a gas turbine — somewhat like a jet engine, Haworth said. The burning gas powers the turbine and generates both electricity and heat. The excess heat is channeled into a heat exchanger which makes steam that powers a steam turbine to generate more electricity. The leftover heat from that process is used to keep the digesters warm so the bacteria can continue to burp out more biogas.

“The generators provide all the power and lighting needs for the facility and excess energy to sell to Edison,” Avila said.

JWPCP generates about 14 megawatts and uses about 13 itself.

In addition to creating electricity, the Sanitation District tries to save energy whenever it can.

As far back as 1938, the gas from wastewater sludge digesters was used to fuel internal combustion engines to generate power for the JWPCP treatment plant. In the 1980s, the district won awards for the improving the energy efficiency of San Jose Creek and the other nine water reclamation plants.

“We’re constantly looking at ways to cut our energy usage,” Avila said. “We switched our water treatment plant from coarse bubble diffusers to fine bubble diffusers. It cost $2 million to install the new system, but we save $1 million a year in electricity costs. It not only reduces costs, it reduces our energy demand.”

The bubble diffusers supply air to the aerobic bacteria that help clean up waste water after it’s separated from the sludge. Fine bubbles distribute oxygen more efficiently, using less air and less energy.

The Sanitation District is also conducting research into innovative power generation technologies such as microturbines (small gas turbine generators) and fuel cells which can convert biogas directly into electricity.
The Sanitation District is always looking for new ways to get something from nothing.

“Think about it. We’re taking everyone’s waste products, their sewage and their trash,” Haworth said. “After everyone else flushes it or puts in in the trash can, we’re able to do something with it.”
It’s an electrifying idea.

By Karen E. Weber
Staff Writer