Documents, Tools and Resources
Covered Anaerobic Lagoon (Code No. 360)
Definition
A constant volume lagoon designed for methane production
and recovery in conjunction with a separate waste storage facility.
Purpose
To produce and recover methane as an energy source
while minimizing lagoon odors.
Conditions Where Practice Applies
- where methane production and recovery are components of
a planned livestock waste management system.
- where existing waste impoundment(s) can be modified to
the requirements of this standard or for new construction.
- where the total solids (TS) concentration in the influent
waste is less than 2%.
Criteria
General Criteria:
Separation of Ruminant Manure Solids.
Solids shall be separated from ruminant manures prior to entry into the lagoon.
Contaminated Rainfall Runoff.
Manurecontaminated runoff shall bypass the covered methane production lagoon
to the waste storage facility. Uncontaminated runoff shall not enter either
the methane production lagoon or waste storage facility.
Lagoon. The lagoon shall meet the criteria
for an anaerobic lagoon contained in Practice Standard 359,
Waste Treatment Lagoon, with the following additional requirements:
(1) Design Operating Volume. The design operating volume
shall be based either on the daily volatile solids (VS) loading
rate per 1,000 ft3, or the minimum hydraulic retention time
(HRT) adequate for methane production, whichever is greater.
The maximum daily VS loading rate shall be selected from
the values listed on the map in Figure 1. The minimum HRT
shall be selected from values listed on the map in Figure
2.
(2) Length to Width Ratio. The ratio of the length to the
width of the lagoon is limited to 4:1 or less.
(3) Operating Depth. The operating depth of the lagoon shall
be 12 feet or greater.
(4) Embankment Interior Slope. The embankment interior slope
ratio (horizontal:vertical) shall be as steep as possible,
1:1 or greater as required by soil properties or construction
techniques.
(5) Location of Inlet and Outlet. The inlet and outlet devices
shall be located as far apart as practical to minimize “short
circuiting”.
(6) Inlet. Inlets shall be of any permanent type designed
to resist corrosion, plugging, and freeze damage, incorporating
erosion protection as necessary. Inlets from enclosed buildings
shall be provided with a water-sealed trap and vent or similar
devices to control gas entry into the buildings or other
confined spaces. Inlets emptying above the surface of the
lagoon shall not be covered by the methane recovery cover.
(7) Outlet. The lagoon shall be equipped with an outflow
device that will maintain the lagoon water surface at its
operating level and release directly to the waste storage
facility.
(8) Embankments and disturbed areas surrounding the facility
shall be treated to control erosion.
Waste Storage Facility. The waste storage
facility shall meet the requirements of Practice Standard XXX,
Waste Storage Facility. No storage credit shall be attributed
to the lagoon in meeting both minimum storage requirements
and Practice Standard XXX.
Lagoon Cover. The cover materials and all
appurtenances such as weights, floats, and attachments shall
be designed to capture and convey the methane to a designed
outlet. The cover shall also collect and direct precipitation
to a designed gas outlet while exposed to site climatic conditions
for its design life.
Safety. If the lagoons or methane recovery
system will create a safety hazard they shall be fenced and
warning signs posted to prevent children and others from using
it for purposes other than intended.
Regulatory. Local, state, and federal laws
shall be reviewed and complied with; there may be regulations
that affect animal population, distance separations, storage
volumes, storage periods, land requirements for nutrient application,
fencing, or visual screening in excess of recommendations contained
herein.
Considerations
Location. Location of the waste storage facility
should consider elevation and distance from the lagoon to take
advantage of gravity flow.
The covered lagoon should be located as near the source of
manure as practicable and as far from neighboring dwellings
or public areas (minimum distance of 91 m (300 ft)) as possible;
proper location should consider slope, distance of manure transmission,
vehicle access, wind direction, neighboring dwellings, proximity
of streams and floodplains, and visibility.
The covered lagoon should be located near a suitable site
for energy utilization equipment. Short distances for the transmission
of methane through buried pipe are preferable.
Visual Screening. Vegetative screens or
other methods should be used to shield the lagoons from public
view and to improve conditions.
Rainfall and Runoff. Uncontaminated runoff
should not be introduced into the covered lagoon. Contaminated
runoff should bypass the covered lagoon to the storage facility.
Incident rainfall on the covered lagoon may be drained into
the lagoon or pumped off the lagoon cover to a drainage structure.
Lagoon Depth. The lagoon shall be as deep
as possible to maximize methane production and minimize the
lagoon cover size.
Cover Material. Capital cost, repair technique,
and warranty life should be considered when selecting a cover.
Cover Design. A variety of lagoon cover designs
can be considered to meet the needs of the farm to collect
and store incident rainwater or to exclude rainfall accumulation
from the lagoons. The cover can either direct rainfall to one
edge of the lagoon, drain rainfall into the lagoon, or prevent
rainfall from entering the lagoon by accumulating rainfall
and pumping it to rainfall discharge structures.
Cover Attachment. The cover can be attached
to one or all embankments or float tethered to the embankments
depending upon the cover design.
Plans and Specifications:
Plans and specifications shall be prepared in accordance with
the criteria of this standard and shall describe the requirements
for applying this practice to achieve its intended use.
Cover. The cover manufacturer shall warrant
the cover for the intended use and design life, provide maintenance
instructions, and certify that the cover is properly installed.
Operation and Maintenance:
An operation and maintenance plan shall be developed that
is consistent with the purposes of the practice, its intended
life, safety requirements, and the criteria for its design.
The plan shall contain operation and maintenance requirements
including but not limited to:
- Proper loading rate of the lagoon.
- Proper operating level of the lagoon.
- Estimates of methane production and recovery.
- Identification of a plan for safe use or flaring of biogas.
- Cover and other component maintenance.
Figure 1: Covered Anaerobic Lagoon
Maximum Loading Rate (lb VS/1000ft3/day)
Figure 2: Covered Anaerobic Lagoon
Minimum Hydralic Retention Times
(MINHRT)
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