Methane from waste should not be wasted: Exploring landfill ecosystems


Date:
April 15, 2022
Source:
Arizona State University
Summary:
Scientists explore microbial communities flourishing in leachate,
a liquid percolating through solid waste in a landfill. They find
that the composition and behavior of specific microbes found in
arid landfills, like those in Arizona, are distinct from similar
communities in more subtropical or temperate climates. Microbial
composition also differs depending on the age of the landfill
deposits.



FULL STORY ==========================================================================
Each year, humans across the globe produce billions of tons of solid
waste.

Roughly 70% of this refuse ends up deposited in landfills, where it slowly decays. Yet, what may seem an inert accumulation of useless debris, is
in reality, a complex ecosystem, teeming with microbial activity. Vast communities of microorganisms feed on the waste, converting it into
byproducts -- primarily carbon dioxide (CO2) and methane.


========================================================================== While most landfill methane is captured and flared away, researchers hope instead to make use of this resource, which can be converted into fuels, electricity or used for heating homes (see below).

In a new study published in the journal Applied and Environmental
Microbiology, lead author Mark Reynolds, along with his Arizona State University and Industrial colleagues, explore these microbial communities flourishing in leachate, a liquid percolating through solid waste in
a landfill. They find that the composition and behavior of specific
microbes found in arid landfills, like those in Arizona, are distinct from similar communities in more subtropical or temperate climates. Microbial composition also differs depending on the age of the landfill deposits.

The project was carried out at the Salt River Landfill located in
Scottsdale, near ASU's Tempe campus. The facility receives about 1,600
tons of municipal solid waste daily.

Solid waste: a breakdown The study explores ecosystem-level microbial composition in leachate. Diverse environmental conditions seemingly affect
the microbial niches that are compartmentalized across the landfill's
143 acres.



==========================================================================
"I think of a landfill as like a big carbon buffet to these
microorganisms," says Reynolds, a researcher in the Biodesign Swette
Center for Environmental Biotechnology. "Our trash is mostly paper-heavy
and it's really rich in cellulose and hemicellulose. These are readily degradable under anaerobic (oxygen-free) conditions." The capture and
use of gases produced in landfills can help reduce hazards associated
with landfill emissions, and prevent methane from escaping into the
atmosphere. Further, energy projects associated with the capture and
processing of landfill gas can generate revenue and create jobs in
the community.

By better understanding the behavior of these methane-producing
microorganisms, researchers hope to improve the capture of this vital
resource and possibly limit the escape of methane and CO2 -- two potent greenhouse gases and leading contributors to climate change -- into
the atmosphere.

"We're diving into ecological theory to try to get to the source of what
might be driving the organizational patterns of the methane-producing organisms," Reynolds says. The study's multifaceted analysis indicates
that temperature and dissolved solids are the two key parameters governing their abundance and diversification. This is good news, because this data
is routinely captured at landfill sites commonly on a monthly basis and
can provide accurate diagnostics -- telltale indicators of broad trends
in overall methane production.

From garbage to fuel Municipal solid waste landfills accounted for over
15% of methane emissions in 2019, representing the third largest source
of global methane emissions. As the study notes, emissions of methane from landfills amount to the equivalent of a billion tons of CO2,or roughly the greenhouse emissions produced by nearly 22 million cars driven for a year.



========================================================================== Typically, most of the methane released by microorganisms in a landfill
is captured as biogas and subsequently flared off, converting it to CO2.Although this method limits the climate-damaging effects of the
methane itself, it is a short-term and inadequate solution to the problem
of greenhouse gas emission from landfills.

In addition to its adverse effect on the climate, the lost methane
represents a missed opportunity to capture this valuable resource. The
study estimates that approximately one-fifth of the nation's landfills
would be suitable for such capture and processing, if economic and other hurdles can be overcome.

Currently, microorganisms degrading municipal solid waste generate
landfill gas consisting of roughly 50% methane and 50% CO2. By
understanding the subtle workings of these microorganisms -- particularly, methanogenic Archaea, which are the real workhorses in the methane
production cycle -- researchers hope to boost methane output.

The increased methane can be harvested and used to create electricity,
carbon neutral fuels or to heat homes. The latter option is
particularly attractive as no further processing of the methane would be required. Alternately, modifying microbial communities could potentially
be used to limit methane output, where mitigation is desired.

On the hunt for archaea Landfills provide an ideal setting for the
detailed study of Archaea, which are notoriously challenging to culture
in the laboratory. Roughly 80% of archaea diversity remains largely
unexplored. "Our labs are really interested in the methanogens because
the same metabolism they enact in the wetlands, which make them the
highest source of methane, or instead the human gastrointestinal tract,
they enact in the landfills," Reynolds says.

Because the methanogens are primitive, single-celled organisms, they can equally make use of plant, or food matter, or paper products. While the
study found similar methane concentrations at their arid landfill site
compared to other landfills, different communities of methanogens are
doing the heavy lifting. The study demonstrates that microbial behavior
is also dependent on the age of the solid waste deposited. Younger waste
is higher in temperature compared with older waste and degrades according
to different regimes. The aridity has also been shown to greatly affect
solid waste breakdown over time.

"There's a restructuring or reorganization of these arid climate microbes
in landfills," Reynolds says. Future investigations will be aimed at
clarifying the distinctions in these communities relative to their
temperate and humid counterparts.

Further research will explore landfill microbial communities in greater
detail as well as the use of biostimulants or other techniques that
could be used to modify methane production.


========================================================================== Story Source: Materials provided by Arizona_State_University. Original
written by Richard Harth. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Mark C. Reynolds, Damien Finn, Analissa F. Sarno, Richard Allen,
J. David
Deathrage, Rosa Krajmalnik-Brown, Hinsby Cadillo-Quiroz. Delineating
the Drivers and Functionality of Methanogenic Niches within an
Arid Landfill.

Applied and Environmental Microbiology, 2022; DOI:
10.1128/aem.02438-21 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220415124716.htm

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