Municipal Solid Waste (MSW) Landfill MACT
Summary
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8. What Are the Additional Requirements for Bioreactors?
 A bioreactor is
defined as a MSW landfill or portion of a MSW landfill where any
liquid other than leachate (leachate includes landfill gas condensate)
is added in a controlled fashion into the waste mass (often in
combination with recirculating leachate) to reach
a minimum average moisture content of at least 40 percent by weight
to accelerate or enhance the anaerobic (without oxygen) biodegradation
of the waste. The US EPA considers landfill gas condensate to
be a constituent of leachate. Addition of wastewater sludges to
the waste mass is considered addition of liquids other than leachate.
Bioreactors at active landfills that meet the design capacity
criteria are required to install and begin operating gas collection
and control systems in a timely manner. The timing for extending
the collection and control system into new cells or areas of the
bioreactor is also different from conventional landfills. Once
control of a bioreactor is required, the operator must install
collection and control systems in new areas or cells of the bioreactor
prior to initiating liquids addition to that area, cell, or group
of cells.
Controls may be removed from the bioreactor portion of the landfill
either:
(1) When the criteria for control removal specified in the
landfills EG/NSPS are met, or
(2) When the bioreactor is permanently closed, liquids addition
has ceased, and liquids have not been added to the bioreactor
for at least 1 year.
 At some landfills, a portion of the landfill is a bioreactor
and the remainder is designed and operated
as a conventional landfill. In these situations, the control requirements
and the timing of control installation for the conventional portion
of the landfill do not change.The operator must continue to use
the equations and factors in the EG/ NSPS to calculate the annual
estimated uncontrolled NMOC emissions for the landfill as a whole
(including the total waste placed in the bioreactor area and the
conventional area). When the source's calculated uncontrolled
NMOC emissions equal or exceed 50 Mg/yr, then they must install
a collection and control system for the conventional portions
of the landfill according to the schedule in the NSPS, or the
applicable State, Tribal, or Federal plan that implements the
EG. Only the bioreactor portion of the landfill must meet the
control schedule for bioreactors.
Note that as a general rule, it is currently difficult for an
owner/operator of a MSW landfill to operate a large bioreactor
as defined in the final rule. This is because of the Federal criteria
regulating MSW landfills, specifically 40 CFR part 258.28 which
prohibits the addition of liquids other than leachate and gas
condensate to a landfill and 40 CFR part 258.26 which limits the
entry of rainwater into MSW landfills through specified run-on
control systems. A few landfills have gained site specific variances
under Project XL to operate landfill bioreactors.
However, on June 10, 2002, EPA proposed a revision to 40 CFR
part 258 that would allow the Director of an approved State to
issue a research, development, and demonstration (RD&D) permit
for a MSW landfill (67 FR 39662). That proposed RD&D rule
would allow the States to grant variances to certain parts of
the MSW landfill criteria (40 CFR part 258) through the issuance
of RD&D permits. As a result, once the RD&D rule becomes
final and an approved State integrates the new Federal regulations,
the Director of an approved State may issue permits which could
potentially allow for the operation of a bioreactor landfill as
long as there is no increased risk to human health and the environment
(as compared to a MSW landfill permitted under the existing 40
CFR part 258 criteria). Therefore, once the proposed rule allowing
RD&D permits for MSW landfills becomes final, the US EPA expects
the number of bioreactor landfills to increase.
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