TURNING WASTE INTO ENERGY:
YOLO COUNTY'S CUTTING-EDGE LANDFILL
By Dave Rosenberg
Yolo County Supervisor, District Four
No one is offended by being called a "consumer." It's a true statement
of fact. Each and every one of us are consumers - some more than others
- of food, clothing, goods and products of all kinds. But if someone were
to call us a "waster," we would take offense, perhaps serious offense, at the
description.
Yet, it's an absolutely true statement of fact. Each and every one of
us are "wasters" - some more than others. We, as individuals and as
a society, produce remarkable amounts of waste. And although most of us don't
talk about it (try not to even think about it most of the time), the movement
and disposal of waste is an important task. It's one that I, as a County Supervisor,
think about a lot.
It may surprise you to know that Yolo County's landfill is on the
cutting-edge of solid-waste technology. A little "landfill primer" might
be in order.
The United States produces over 150 million tons of solid waste every
year. The main way we dispose of this waste is to send it to sanitary landfills.
Typically, these wastes are delivered to the landfill, spread out, compacted
and covered at the end of the day with a thin layer of soil (or other cover material)
until a planned depth is reached. The wastes are then covered with a final layer,
typically clay. Present rules require or encourage landfills to remain relatively
dry. These so-called "conventional landfills" allow decomposition to
occur over many decades. The United States is full of such conventional landfills.
Yolo County, and a few other landfills, however, are doing it
differently. They are in the forefront of developing "bioreactor landfills." It's
an amazing technological step forward.
Here's how it works.
In the bioreactor landfill, more environmentally sound management
practices are used and more liquid is added to the waste. The result has a double
benefit: (1) Decomposition can occur in only 5 to 10 years, and (2) the bioreactor
landfill produces landfill gas which, if properly "mined," can be an
important source of energy.
In Yolo County's bioreactor landfill project, a substantial amount of
water is added to the solid waste to dramatically accelerate decomposition.
Additionally, instead of using soil to cover the layers of waste at the end
of the day, Yolo County uses a daily cover of "greenwaste" (grass clippings and prunings
shredded to a compost-like state). Yolo County's soil is heavy in clay and would
otherwise impede the flow of water. Greenwaste allows the water to flow freely
through the waste, stimulating rapid decomposition.
The problem with conventional landfills and dry decomposition is that
it takes several decades for the waste to fully decompose. Landfills have
low permeability bottom liners to protect the liquid that drains from garbage
(called "leachate")
from entering the groundwater. However, no one really knows how well these liners
will work to protect our groundwater after 30, 40, 50 or more years! Dry landfilling
practices have, accordingly, been called "ticking time bombs" because
of the fear that landfill liners will fail sometime in the future and groundwater
will be seriously contaminated.
A bioreactor landfill avoids the problem of future liner failure
because the waste decomposes in only 5 to 10 years.
But there's more. Landfill wastes produce gases, principally methane,
as they decompose. Better methods of "methane mining" in landfills
have a couple of major benefits. First, the use of landfill gas as an energy
source (primarily electricity) has great potential. The United States EPA estimates
that use of landfill gas for electricity has only reached 10% of its potential.
It has been estimated that if 50% of the waste in the United States were directed
into the new technology, and if it were methane-mined, the amount of renewable
methane energy would equal 100,000 barrels of oil per day. Second, capturing
and using methane gas for power would prevent it from escaping into the atmosphere,
decreasing greenhouse gas emissions by an estimated 40 million metric tons per
year.
As long as we're producing waste - and we will - let's be kind to our
environment and let's tap into a renewable energy source. That's precisely
what the Yolo County Landfill is doing today. Yolo County, today, is using
the landfill technology of the future.