Landfills are packed full of value
Landfill mining and reclamation (LFMR) is a process whereby solid wastes
which have previously been landfilled are excavated and processed.
Processing typically involves a series of mechanical processing operations
designed to recover one or all of the following: recyclable materials, a
combustible fraction, soil, and landfill space. In addition, LFMR can be
used as a measure to remediate poorly designed or improperly operated
landfills and to upgrade landfills that do not meet environmental and public
health specifications (1). Typical equipment used in simple LFMR operations
are excavators, screens, and conveyors. Complex LFMR operations recover
additional materials and improve the purity of recovered materials, and
therefore have equipment in addition to that of simple operations.
Landfill mining was first described in 1953 in an article that documented
the processes used at a landfill operated by the City of Tel Aviv, Israel
(2). The primary objective was to excavate the waste for the recovery of a
soil amendment. The excavation equipment consisted of a front-end loader and
a clamshell, and the processing equipment included several conveyors and a
rotating trommel screen. The screen was about 7 metres long, 2 metres in
diameter and rotated at about 13 rpm. The screen had openings of
In the process, waste material was excavated and transported to a conveyor
belt. The conveyor belt transferred the waste to the trommel screen.
Material that passed through the screen openings was used as soil amendment,
and material that was retained in the screen was taken by conveyor belt to a
resource recovery area where manual separation was used to recover ferrous
metals and other recyclable materials.
In the Tel Aviv LFMR project, the soil amendment had a total nitrogen,
phosphorous, and potassium (NPK) concentration of 1.4%. The soil amendment
was used primarily in citrus groves; due to the relatively high
concentration of broken glass, the material was not used in other
agricultural applications. According to the literature, the operation in Tel
Aviv remained the only application of LFMR until the 1980s.
Two developments took place in the USA between 1950 and 1980 that impacted
on landfill mining. One was the emergence of a modular processing system
designed to process mixed waste as it arrived at landfills or at transfer
stations, primarily for the purpose of recovering steel containers. The
second development took place in the late 1960s/early 1970s, and dealt with
an assessment of the technical feasibility of composting landfilled
municipal solid waste (MSW) in situ. The project involved the construction
of especially designed cells in a landfill. Some of the cells were filled
with sorted MSW and other cells with mixed MSW, and covered with a soil
layer. A forced aeration system was set up to supply the oxygen for the
The project was not implemented at full-scale because of the lack of
technical feasibility. In addition, several fires in the cells were
attributed to spontaneous combustion. Although the project was not adopted,
it provided information on the acceleration of the degradation of organic
matter in a landfill as well as emphasised the importance of a cellular
structure in a sanitary landfill (3). The modular concept of processing
wastes at disposal facilities, in conjunction with in situ processing of
landfilled wastes, has become the basis of many current and planned LFMR
In 1982, a proposal was made to the Metro Manila Commission in the
Philippines (4). The proposal called for the application of landfill mining
in the upgrading of one of Metro Manila's disposal sites on the Island of
Balut, Tondo. However, the project was not implemented, primarily due to a
shortage of funds.
Status of landfill mining
Limited information is available on landfill mining projects that have been
carried out on a worldwide basis (5-9).. However, it has been reported that
LFMR projects have been planned or implemented at the Non Khaem Landfill in
Bangkok, Thailand, and at the Nanjido Landfill serving metropolitan Seoul,
Korea. In the United States, only six landfills have been mined. The
following brief descriptions of some US projects and their results serve to
illustrate the variety of reasons for considering and implementing LFMR
operations, and to illustrate operating experiences.
Collier County, Florida
A comprehensive field test evaluation of the Collier County landfill mining
system was conducted in 1992 under the US EPA's Municipal Innovation
Technology Evaluation (MITE) Program. The complex LFMR system was operated
by the County as a demonstration. The mined wastes were relatively well
decomposed. The soil fraction recovered from the process (ie cover material
plus fine decomposed wastes) accounted for about 60% of the infeed material.
With the exception of the soil fraction, the degree of purity of the
recovered materials was in the order of 82% or lower. Thus, the ferrous and
plastics fractions contained substantial levels of contamination that would
probably impact their marketability.
In the case of the soil fraction, the concentrations of metals were found to
be below the limits imposed by the State of Florida for unrestricted use of
As part of a permit application to expand a private sanitary landfill in
Barre, Massachusetts, a proposal was made to mine a section of the property
that had been filled between the mid-1950s and 1970. The sections to be
mined would be lined prior to any additional filling.
Test pits were dug to evaluate the material that would be processed.
Excavation showed that some of the cells had been constructed to be almost
completely impervious to the external penetration of water. The contents of
these cells showed little decomposition. The recovered soil fraction was
retained for use as cover material.
Bethlehem, New Hampshire
The Bethlehem, New Hampshire landfill site served small towns and rural
tourist areas. The soils beneath the site were generally glacial till.
Between 1979 and 1987, landfilled wastes were covered with 1 metre of
material as an interim closure measure for the fill.
In 1989, the company that owned the landfill was sold and the new enterprise
filed a permit to expand the Bethlehem landfill. The expansion would include
a double-lined landfill adjacent to the old, unlined one. The New Hampshire
Department of Environmental Services (NHDES) required that approximately 160
tonnes of material be relocated from the old, unlined portion of the
landfill to the newly lined section. As part of the relocation process,
NHDES allowed the company to mine the unlined landfill. Once the plans were
approved, the NHDES included various requirements in the permit to build the
new landfill that pertained specifically to the mining operation. Among
those requirements were stipulations regarding daily cover, leachate
management, and the testing of soil and groundwater. Due to concerns
regarding odours, the permit prohibited any mining or waste removal
operations during June, July, and August and required that odour masking
agents be applied to the wastes being processed.
Throughout the landfill mining process, the impacts on air quality and
quality of the storm water runoff were monitored. The monitoring process
also included measuring the concentrations of oxygen, hydrogen sulphide, and
volatile organics in the air. Water quality monitoring also focused on
changes in conductivity and pH. Slight increases in conductivity were noted;
no changes in pH were detected.
Equipment used consisted of two excavators, one front-end loader, four
trucks, two bulldozers, one trommel screen, and one odour control sprayer.
Edinburg, New York
In 1988, the New York State Energy Research and Development Authority
(NYSERDA) contacted more than 250 landfill owners and operators in the state
to ascertain their interest in participating in a landfill mining
demonstration project. The Town of Edinburg was subsequently selected by
NYSERDA as the host site for a one-acre demonstration project. Edinburg is a
small, rural community and has a relatively small landfill.
The objectives of NYSERDA in undertaking the Edinburg project were as follows:
Residue (ie material larger than 2.5cm) from the screening of materials
during a hand sorting phase of the project was evaluated. The evaluation
indicated that more than 50% of the rejects could be taken to a materials
recovery facility (MRF) for recycling, although the excessive concentration
of dirt in the LFMR residue could contaminate clean source-separated
recyclables. White goods and scrap metal would require cleaning to remove
soil, and then the material could be baled and sold. The assessment of
manually-separated film and HDPE plastic indicated that these materials
could also be sold.
Samples of materials were collected for analysis. No significant contaminant
concentrations were detected during tests for asbestos, compost parameters,
Toxicity Characteristic Leaching Procedure (TCLP) parameters, Target
Compound List (TCL) parameters, and pathogens. Results of analyses indicated
that the soil fraction met the State of New York standards for Class I
compost and qualified for off-site use in a variety of applications,
including clean fill in public construction projects and daily landfill
The Lancaster County Solid Waste Management Authority (LCSWMA) operates the
landfill and transfer stations in the county. The Frey Farm landfill,
located in Manor Township, was opened for waste disposal in September 1988.
Construction of a three-train, massburn facility, with a design capacity of
1,100 tonnes/day, was completed in December 1990. Since the initial delivery
of waste was less than anticipated, previously landfilled wastes were
excavated from the first 18-acre landfill cell and added to fresh MSW as
supplementary fuel for the massburn facility. Mined material is combusted
with raw MSW in a ratio of about 1:3 (weight basis). Earlier tests using
unscreened mined material required a ratio of 1:7 or 1:8 in order to
maintain design conditions for combustion, due to the relatively low heating
value of mined wastes. The facility yields about 660 kWh/tonne of raw MSW,
based on a heating value of 12,200 kJ/kg. When mined material is combined
with fresh MSW for combustion, the yield decreases to about 500 kWh/tonne of
fuel burned. Ash yield from mined material is about 35%.
Combustion of mined MSW did not have a negative impact on the permits for
either the resource recovery facility or the landfill. The Pennsylvania
Department of Environmental Resources (PADER) monitors the mining.
Concerns initially expressed by PADER included the potential for changes
storm water runoff, extra leachate generation, and gas releases from the
mining operation. However, none of the concerns became a problem. The only
negative impact has been the additional traffic generated by the delivery of
mined material to the project.
The LCSWMA's objective in landfill mining has been to minimise the area
landfill in use. The energy value of the mined material is estimated to be
US $33/tonne. Material recovery is less attractive economically and,
therefore, it is not a component of the operation.
In 1986, the municipal landfill was due to close in the Town of Thompson,
Connecticut. The Town initiated a landfill mining project with the objective
of recapturing landfill volume and extending the life of the landfill
temporarily while a permanent disposal alternative could be selected.
A local excavation contractor conducted the project, using a bulldozer, a
pay loader, a truck, and a screen. The contractor first excavated about 20
test pits in the landfill. The area mined was a combination of the residuals
from an old dump (which was set on fire periodically) and bulky wastes. No
odours were detected as a result of the mining program. Waste decomposition
was relatively incomplete in material that was 15 years old or less. This
younger waste probably occupies areas where daily cover was initiated after
the period of open burning. At the time of the mining project, the available
disposal alternatives represented costs in the range of US$66 to
US$88/tonne, plus transportation. The cost of the mining project was
US$117,000, including grading the base of the mined area to receive new MSW.
Representatives from the town estimated that the town saved US$1m in tip
fees over an 18-month period.
Technology design centers on the attainment of the following two goals:
excavate the landfilled material
process the excavated material such that target material can be separated
from the excavated mass and further processed to fit its intended use or
A third goal is introduced if the mining is intended to reclaim landfill
capacity or to upgrade the landfill. In such a case, the portion of the
landfill destined to be upgraded is excavated and processed as needed.
The technology involved in the excavation of landfilled waste has not
changed much since the Tel Aviv project in the 1950s. Generally, excavation
is conducted using techniques similar to those used for open face mining.
Equipment involved may be a front-end loader, a clamshell, a backhoe, a
hydraulic excavator, or a combination of these. Excavated material either
may be directly processed on-site or be stockpiled for later processing,
either on-site or at a processing facility.
Processing begins with the segregation of the excavated mass into discrete
streams. The number and composition of the streams depends upon the desire
and extent of resource recovery. Excavated material is discharged into a
coarse screen; and oversize, non-processible wastes are removed by the
screen. The remaining fraction is transferred to another screen having
relatively small openings. Material that passes through the screen openings
(ie the undersize stream) constitutes the soil fraction. A trommel screen
is an efficient unit process for separation of soil fraction from excavated
waste. Material retained in the screen is removed and is exposed to a magnet
to recover ferrous metals. The non-ferrous fraction is processed through an
air classifier that separates light organic materials from heavy organics.
As shown, air classification could be used to recover a waste-derived fuel.
At present, processing at the landfill site is typically accomplished by
means of equipment mounted on trailers. The equipment usually consists of
conveyor belts, a coarse screen, a fine screen, and a magnet. Useful
products are soil which may contain stable organic matter and a low-quality
ferrous fraction. The number of separated streams and the degree of
processing involved depend upon several factors, not least of which is
whether the separated material is to serve as a resource or is to be
rendered innocuous (landfill remediation or upgrading). Other factors
include those which determine economic feasibility and advisability, and
market demand for the recovered materials.
Amounts and characteristics of products recovered from a landfill are
functions of the landfilled wastes. Those few values reported in the
literature or cited herein must be regarded as being related to single
instances, and may or may not be representative.
The percentage recovery of a landfilled resource depends upon:
the physical and chemical properties of the resource
the effectiveness of the type of mining technology
the efficiency with which the technology is applied.
Judging from available information and mechanical processing efficiencies,
recovery of soil could be expected to fluctuate between 85% and 95%, ferrous
metals from 70% to 90%, and plastic from 50% to 75%. Purity of these
materials could be expected to be 90% to 95% for soil, 80% to 95% for
ferrous metals, and 70% to 90% for plastic. The higher percentage of purity
for each material category would generally be attributed to relatively
complex processing designs.
The types of materials recovered from an LFMR project are determined by the
goals of the project, the characteristics of the landfilled wastes, and the
process design. In a typical LFMR operation, once the oversize
non-processibles, the dirt fraction, and the ferrous metals are removed, the
remaining material may be recovered as fuel for a waste-to-energy facility,
processed for recovery of other recyclables, or landfilled as residue.
The soil fraction recovered by mining typical landfilled MSW will probably
comprise the largest percentage by weight of all materials; a range of 50%
to 60% can be expected, although values from 30% to 70% have been reported.
The ratio of soil to other materials depends upon the type of waste
landfilled, landfill operating procedures, and the extent of degradation of
the landfilled wastes. As mentioned earlier, in the Collier County, Florida
demonstration project, about 60% (by weight) of all mined materials was
recovered as a soil fraction.
The major difficulty in
marketing mined materials is in producing the
necessary high quality. Another obstacle is the limited number of
waste-to-energy facilities in some areas to serve as a market for
Key conditions include: