|
 |
|
Documents, Tools and Resources
Agstar Charter Farm Program: Experience With Five Floating
Lagoon Covers
K.F. Roos
U.S. EPA
401 M St., SW (6202-J)
Washington, DC 20001
M.A. Moser
RCM, Inc.
P.O. Box 4715
Berkeley, CA 94704
A.G. Martin
ICF, Inc
14724 Ventura Blvd., Suite 1100
Sherman Oaks, CA 91403
Presented at: Fourth Biomass Conference
of the Americas, Oakland, CA., Aug. 29-Sept. 2, 1999
Abstract
The AgSTAR Program is a voluntary program jointly administered
by U.S. EPA (Environmental Protection Agency) and the USDA-NRCS
(Natural Resources Conservation Service). The AgSTAR Program
encourages the use of methane recovery technologies at confined
animal feeding operations (CAFO) that manage manure as liquids
or slurries to reduce greenhouse gas (methane) concentrations
while achieving other environmental benefits. The Charter Farm
Program is designed to develop a broader understanding of the
benefits, costs, and applications of biogas technology by developing
commercial scale demonstration systems at livestock facilities
in various regions in the U.S. Since 1996, 10 AgSTAR Charter
Farms have been completed utilizing a variety of anaerobic
digester systems.
This paper summarizes the developmental experience of five
Charter Farms that installed floating covers on lagoons to
realize benefits including methane recovery, energy production,
odor control and exclusion of uncontaminated rainwater. Two
designs of floating cover are compared - bank to bank and modular.
Gas transfer and rainfall management are key to the success
of a biogas cover. Critical issues in cover selection include:
design, material warranty, and fabrication warranty. Types
of suitable material such as HDPE and polypropylene are discussed
along with cover performance criteria. Prices based on materials,
warranties, and installation are summarized. Costs ranged from
$0.37/ft2 to $5.81/ ft2.
Long term monitoring data (Cheng et. al., 1998) indicates >90%
reduction in Chemical Oxygen Demand (COD), 65% reduction in
total nitrogen, and 85% reduction on total phosphorus. This
environmental performance is achieved under USDA-NRCS Interim
Standard No. 360 - Covered Anaerobic Lagoon.
Keywords: anaerobic digester, anaerobic digestion,
biogas, floating cover, lagoon cover, manure management, methane,
methane recovery, odor control, pond cover
Introduction
The AgSTAR Program is a voluntary program jointly administered
by U.S. EPA (Environmental Protection Agency) and the USDA-NRCS
(Natural Resources Conservation Service). The AgSTAR Program
encourages the use of methane recovery technologies at confined
animal feeding operations (CAFO) that manage manure as liquids
or slurries to reduce greenhouse gas (methane) concentrations
while achieving other environmental benefits. The AgSTAR, Charter
Farm Program is designed to develop a broader understanding
of the benefits, costs, and applications biogas technologies
provide by developing commercial scale demonstration systems
at livestock facilities in various regions in the U.S.
Since 1996, about 10 AgSTAR Charter Farms have been completed
utilizing a variety of anaerobic digester systems including
covered anaerobic lagoons, plug flow, and complete mix systems.
This paper discusses important issues that need to be considered
when developing a covered anaerobic lagoon waste management
system for farm scale application. This paper is based on the
experience of 5 Charter Farms currently operating covered anaerobic
lagoons.
Covered Anaerobic Lagoons
Covered anaerobic lagoons for odor control and energy production
typically consist of two lagoons operating in series. The first
lagoon, for primary waste treatment consists of a dedicated
volume with a fixed operating depth to biologically stabilize
waste. Biogas production is a by product of this biological
(anaerobic) process as evidenced by volatile solids destruction
and reduction in Chemical Oxygen Demand (COD). A second lagoon
is required in back of the primary treatment lagoon for adequate
waste storage during non-cropping periods.
Long term monitoring data (Cheng et. al., 1998) indicates >90%
reduction in Chemical Oxygen Demand (COD), 65% reduction in
total nitrogen, and 85% reduction on total phosphorus from
this type of lagoon configuration. This environmental performance
is achieved utilizing lagoon sizing guidelines established
under USDA-NRCS Interim Standard No. 360 - Covered Anaerobic
Lagoon.
The goal of a lagoon cover is to collect and transmit lagoon-generated
biogas to a dedicated gas take-off point for transmission to
some type of gas use device. Gas use devices include, flares,
boilers, absorption coolers, and engine generators. All AgSTAR
Charter Farms are equipped with low cost auto-sparking flares
to ensure combustion of greenhouse gases and consistent odor
control. Other gas use equipment is selected on a farm by farm
basis dependent upon the goals of the farm owner i.e, odor
control, electrical energy, heat, co-generation.
Under all applications the cover must function to continuously
move biogas to the gas takeoff point. The cover must simultaneously
be capable of receiving and managing precipitation without
interfering with gas collection. The standard of care in fabrication,
assembly and installation must be very high to limit air intrusion
because the lagoon cover is at times operated under vacuum
for various energy end uses. The standard for a cover solely
to direct biogas to a flare is much lower because air infiltration
is less of a concern. There are three critical areas that need
to be considered in all lagoon cover gas utilization applications.
These are:
Fabrication: Workmanship related to cover assembly
and installation is critical. Quality, non-leaking seams are
a key requirement for all lagoon covers that combust biogas.
If seams open or holes develop air intrusion will result when
the cover is under vacuum, or gas will escape when the cover
is under pressure. Air intrusion contaminates gas quality and
causes failure of gas combustion equipment. Gas loss through
leaks will reduce energy equipment efficiency and erode energy
based revenue streams to the farm.
Materials: Materials need to be used that resist sun,
wind, extremes in temperature and other climate variables.
Material resistance to capillary action (wicking) should also
be considered. Material concerns include resistance to tearing,
blistering, and de-laminating. These types of material related
problems can lead to cover failure due to air intrusion and
increased point load stresses that can occur as a result.
Design: Stresses caused by wind, rain and other naturally
occurring events, if not properly designed for, can cause cover
performance problems. For example, design deficiencies can
significantly impede or completely cut-off gas flow, cause
air intrusion, and in the most extreme cases can cause complete
cover failure i.e., tearing and sinking. Design deficiencies
can also cause material and fabrication related problems due
to increased stress loading on the cover.
Lagoon Cover Design Options
Two basic options of lagoon cover design can be considered.
These are bank to bank, and modular designs. Both designs can
be effective with regard to biogas collection and odor reduction.
Bank to Bank Covers: These types of covers completely
span the lagoon surface with a fabricated floating cover. The
edges of the cover are secured to the lagoon bank by burial
in perimeter trenches. Burying the cover edges accomplishes
3 things:
1. A completely anaerobic environment is created;
2. All of gases produced are captured; and
3. A barrier to rainfall addition to the lagoon
is created.
To ensure effective cover function, proper cover flotation
and water pumping mechanisms must be incorporated in the cover
design. Rainwater management needs to be adequately addressed
in the design process to avoid longer term cover performance
problems.
Modular Covers: These types of covers use smaller cover
sections, or modules, as opposed to a single large cover used
in the bank to bank design. Modular lagoon covers typically
cover 50-90 per cent of a lagoon's surface. These covers can
be secured either with bank trenching or tether ropes. Flotation
must be included in the design for the removal of accumulated
precipitation or may not be required based on design. This
design is used where the owner or supplier decide to build
the modules offsite and assemble (rather than fabricate) the
cover on site. The modular cover design also allows for a lagoon
to be covered in stages, thus reducing any one-time capital
outlay.
Considerations in Selecting a Lagoon Cover Supplier
Recognizing that there are a variety of lagoon cover materials,
fabrication methods, and design approaches available, a set
of recommended cover performance criteria were developed for
Charter Farm participants on which to evaluate lagoon cover
suppliers prior to making a final selection. Recommended criteria
included:
-
Experience in providing lagoon covers at commercial livestock
farms for purposes of gas collection and transfer to some
gas use device.
-
Material specification and fabrication methods such as
seam technique and seam testing as related to accepted
practices and standards of the industry.
-
Method of warrantying or bonding cover performance as
related to material, fabrication, installation, and design
of the cover. Criteria defining acceptable cover performance
are:
a) Less than 10% air intrusion (2% oxygen) at negative
2" water column pressure over a 24 hour period; and
b) Continous and unrestricted gas movement at 2" water
column pressure due to design, material, and fabrication
defects.
-
Total cost of supplying and/or installing the cover.
Cover suppliers should not be requested to provide gas production
estimates nor be responsible for gas production levels as these
are separate developmental processes required in the overall
covered lagoon waste management system design.
Summary of Responses
Experience: Eight suppliers listed experience with
floating covers. Most suppliers had experience with multiple
covers and one had 9 years of experience with more than 25
installations. Floating cover experience was distributed across
rendering plant, food processing, and other waste lagoons and
not necessarily livestock lagoons. Additionally, some of the
lagoon cover experiences were not based on lagoon covers that
collect, transmit, and combust lagoon off-gases.
Services and Materials: Suppliers varied in the services
and material offered. Several suppliers work as lagoon material
installers, providing turn key services and have traveling
crews with equipment. Some suppliers asked the farm to perform
relatively inexpensive tasks such as digging a trench or supplying
a couple of man days of farm laborers to reduce costs. Material
choices included: High Density Polyethylene (HDPE); Polypropylene;
XR-5, and X-210. Each material possesses different ranges for
tensile strength, UV resistance and other properties.Warranties
and Performance Bonds: Warranties were offered for varying
lengths of time. Warranties are generally limited to a per
cent of the original cost, reduced by product age. Materials
are warranted by their manufacturer for a period of 2 to 10
years, though some accompanying literature cited 20 year warranties.
Fabrication was generally warranted 1 to 2 years. Several suppliers
warranted cover design for a period of 1 year based on the
recommended criteria for cover performance.
Some suppliers also provided performance bonds for the cover
at an additional cost. Some Charter Farm participants have
added the lagoon cover into the farms overall insurance policy
for damage coverage. This approach however does not provide
coverage for a lagoon cover in case of non-performance.
Costs: Lagoon covers included itemized costs of cover
components, including installation, labor and shipping. Costs
ranged from $0.37/ft2 to $5.81/ ft2.
Table 1 summarizes the warranty types and costs for 5 floating
lagoon covers. In general, the owners selected the cover supplier
based on cost and experience.
Summary of Experiences at Five Farms
Apex Pork
APEX Pork is an 8,900 head swine finishing operation located
in Rio, IL. Manure is collected in under-barn pull plug pits.
To address odor issues associated with the farm's current manure
storage basin, a heated and mixed covered lagoon digester,
was installed in June 1998. A modular, reinforced X-210 cover
was used to collect the biogas from the 120 ft. x 160 ft x
14 ft digester, which was then combusted in a hot water boiler
to provide the digester's heat. Once digester start-up was
completed, biological activity in the heated mixed digester
leveled off to produce approximately 36,000 ft3/day
(Moser et al., 1998). However, a micro burst windstorm damaged
the cover while blowing down a nearby building, compromising
its gas collection capabilities. As a result, the installation
of a replacement cover was deemed necessary. The owners selected
a bank to bank 40 mil HDPE to install over the existing cover
based on the price and experience of the installer. The replacement
installation includes a rainfall pumpoff and has performed
within the required tolerances since.
Barham Farm
Barham Farm, located in Zebulon, NC, is a 4,000-sow farrow
to wean pig farm that utilizes a pit recharge manure management
system in its barns. The pits empty into an earthen covered
anaerobic treatment lagoon. The lagoon, designed by USDA-NRCS,
was constructed in July 1996. The farm owner was looking to
offset farm energy requirements by collecting and utilizing
biogas generated in the lagoon to generate hot water and electricity.
A modular (4 section), 20 mil X-210 cover was installed on
the 300' x 300'lagoon. A 400,000 Btu boiler and 120 kW engine
generator were installed in December 1996 to utilize the gas.
Digester operation began in January 1997 (Moser et al., 1998).
However, several weeks into the digester operation, major fabrication
and material defects in the cover were detected, which significantly
compromised the cover's ability to collect undiluted biogas
using a vacuum pump. The manufacturer replaced the cover under
warranty, however, the same types of problems re-occurred.
The manufacturer subsequently refunded the farm's cover expenditure.
The owner selected a bank to bank 40 mil HDPE based on the
price and experience of the installer. In early 1998 the cover,
with rainfall pumpoff, was installed and has been delivering
air-free biogas to the engine/boiler system since.
Boland Farm
Boland Farm is a 2,400-head pig nursery located in Williamsburg,
IA, that prior to installing a cover was enduring storage pond
odor problems. Pull plug pits in the nursery barns are emptied
into a 140' x 160' earthen storage pond on-site. In May 1998,
a bank to bank odor control X-210 cover was installed over
the storage basin (Moser et al., 1998). The owner selected
the cover based on price and installed the cover with local
labor in about 16 hours. The biogas collected is combusted
by a flare.
Cal Poly Dairy
The Cal Poly Dairy covered lagoon project is an ongoing project
on the campus of California Polytechnic State University, San
Luis Obispo. The 300 milk-cow drylot dairy flushes manure from
its feedlanes into a newly constructed two stage anaerobic
treatment lagoon system, which was constructed July 1998. The
purpose of the installation was to curtail the significant
odor generated by the previous single lagoon, and to demonstrate
methane recovery and utilization technologies. A partially
bank buried polypropylene biogas collection cover was installed
on the primary anaerobic lagoon (260' x 260'), along with a
waste gas flare in December 1998. The cover was selected based
on local presence and experience of the installer with price
as a secondary factor. Early in 1999, a 40 kW micro turbine/generator
is considered for installation to combust the biogas and generate
electricity, as part of the demonstration project.
Piney Woods School Farm
Piney Woods School Farm is a 12-sow farrow to finish swine
operation on the campus of Piney Woods School (Piney Woods,
MS). The farm flushes manure from its farrow and finishing
barns once a day into a 115' x 125' two stage anaerobic lagoon
system. The school installed a cover on the farm's primary
anaerobic lagoon, through a project jointly funded by the Mississippi
Department of Economic and Community Development (DECD) and
the Tennessee Valley Authority (TVA). The primary purpose of
the project was to demonstrate the applicability of methane
recovery technologies to swine farms in the Southeast. The
school administrators selected the cover based on price. This
was the first installation of a floating cover by this lagoon
lining company. The buried bank to bank HDPE cover was installed
in August 1998 and has been working well. A low volume flare
was also installed to combust the collected gas.
Summary
Five AgSTAR Charter Farms installed floating covers on lagoons
in 1998. For Apex Pork, Boland Farm and Cal Poly Dairy odor
control was the primary motivation for the installation of
a lagoon cover. Barham Farm wanted to utilize and the realize
environmental and energy benefits through methane recovery,
and Piney Woods looked primarily to demonstrate the applicability
of methane recovery technologies to area farms. Two designs
of floating cover are currently available, bank to bank and
modular. Although bank to bank covers were the predominant
choice, both bank to bank and modular designs are feasible
to provide effective methane recovery and odor reduction. In
both cases however, gas transfer and rainfall management are
design elements that are key to the success of a biogas cover.
Other critical issues in cover selection are: design, material
and fabrication warranty, and cost. Materials suitable for
biogas covers include HDPE, Polypropylene and materials such
as XR-5 and X-210. The majority of suppliers include a manufacturers
warranty on the cover material for 10-20 years. Warranties
on workmanship were typically one to two years. Several cover
suppliers provided a warranty on recommended air intrusion
criteria. Costs for covers ranged from $0.37/ft2 to
$5.81/ ft2.
References
Moser, M.A., Dr. S.W. Gettier, R.P. Mattocks, and K.F. Roos, "Benefits,
Costs and Operating Experience At Seven New Agricultural Anaerobic
Digester", BioEnergy '98, Expanding Bioenergy Partnerships,
Madison, WI, October 4-8, 1998.
Cheng J., K.F. Roos, and L.M. Saele, "Evaluation of covered
Anaerobic lagoon System for Swine Waste Treatment and Energy
Recovery", North Carolina Waste Management Symposium,
North Carolina State University, January 1999.
TABLE 1. Lagoon Cover Summary |
