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.
History
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
approximately 2.5cm.
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
process.
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
systems.
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
waste-derived compost.
Barre, Massachusetts
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
the
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
dump
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:
- determine equipment needs and develop optimal procedures for the excavation,
- separation, handling, and storage of landfilled materials
- determine appropriate uses for the reclaimed material
- identify available markets for the materials
- develop required processing needs for the reclaimed materials
- develop recommendations regarding health and safety requirements
- conduct contingency planning for future landfill reclamation projects in New York.
employed during the Edinburg LFMR project. Approximately 25% of the mined
materials passed through a screen surface with 7.6cm openings and was
retained on a screen surface with 2.5cm openings. This fraction consisted
primarily of cans and bottles. The material larger than 7.6cm included
plastics, textiles, paper, wood, and metal.
A test burn of a sample of residue from the LFMR process was conducted at
the Pittsfield, Massachusetts waste combustion facility. The results of the
tests indicated that the higher heating values for the residue varied
between 4,700 and 5,800 kJ/kg.
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
cover.
Lancaster, Pennsylvania
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
to
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
of
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.
Thompson, Connecticut
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.
The discussion on technology is prefaced by a paragraph on accelerated
decomposition, because stability of buried organic wastes is essential to
landfill mining and reclamation. Mining insufficiently decomposed wastes
would result in an unacceptable generation of nuisances and negative impacts
with regard to health and safety and the environment. Landfill mining should
not be attempted before the landfilled wastes are sufficiently stabilised.
This prerequisite and other factors related to management of a completed
landfill have led to an increase in studies on accelerating decomposition of
organic matter in landfills (10).
Technology design
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
disposition.
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.
Excavation
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
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 under size 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.
Product characteristics
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.
Recovery efficiency
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.
Feasibility
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
combustible materials.
Site-specific conditions will determine whether or not LFMR is feasible for a given location.
Key conditions include:
- composition of the waste initially put in place in the landfill
- historic operating procedures
- extent of degradation of the waste
- types of markets and uses for the recovered materials.
following:
- use of recovered soil fraction as landfill cover material;
- recovery of secondary materials;
- reduction of landfill footprint and, therefore, reduction in costs of
- closure and post-closure; and
- reclamation of landfill volume for reuse.
Landfill mining and reclamation is a developing technology and method of
waste management. Given its developmental status, only tentative conclusions
can be drawn regarding LFMR potential, and prospects for fulfilling that
potential.
The technology of LFMR can be effective in recovering landfill capacity for
reuse for land-filling or for use as reclaimed land for other applications.
It can also be employed to recover landfilled resources such as a soil
fraction for reuse on-site as cover material and for use as a soil
amendment. Based on the few analyses reported thus far, the heavy metal
content and other characteristics of the recovered soil fraction indicate
that the fraction can be suitable for landfill cover material. However, it
should be emphasised that the characteristics of the recovered materials are
substantially a function of the composition of the buried waste - including
concentrations of heavy metals and of other toxic compounds. Some organic
materials may be recovered that may have a use as a refuse-derived fuel.
Low-quality ferrous scrap is readily recovered, but its utility has only
been demonstrated to a limited degree. The percentage of recovered materials
and their characteristics and properties are functions of the composition of
the landfilled material and the configuration and operating conditions of
the landfill mining process. The concept of landfill mining and reclamation
and related technology merits serious consideration. It may be relevant to
consider the incorporation of the concept into landfill design so that the
landfilled waste can be readily accessible for mining.