Sanitation District a bright spot in the energy picture
Were 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 hasnt altered its pricing structure
during the current power crisis.
Were locked into a formula we settled on with
Edison, said Joe Haworth, Information Officer for the Sanitation
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
The biogas facilities do even better.
Primarily methane and carbon dioxide, biogas is the result
of natural decomposition. Its the waste product of the anaerobic
microbes that eat our waste products.
When refuse is covered over in a landfill, anaerobic bacteria
ones that dont need oxygen begin eating the trash.
As they grow, they give off methane and carbon dioxide, the same way
people exhale carbon dioxide.
Older landfills burn the biogas in flares to dispose of
it, but the Sanitation District burns it in generators. At Puente Hills,
the districts 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.
Its 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
districts three landfills create about 63 megawatts per day.
The Sanitation Districts 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
The two processes are very similar but ones
in a dirt container and ones in a concrete container, Haworth
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
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.
Were 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
The bubble diffusers supply air to the aerobic bacteria
that help clean up waste water after its separated from the sludge.
Fine bubbles distribute oxygen more efficiently, using less air and
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
Think about it. Were taking everyones
waste products, their sewage and their trash, Haworth said. After
everyone else flushes it or puts in in the trash can, were able
to do something with it.
By Karen E. Weber