WASTE MANAGEMENT PIH-95
PURDUE UNIVERSITY. COOPERATIVE EXTENSION SERVICE.
WEST LAFAYETTE, INDIANA
Gravity Drain Gutter Systems
Author:
Daniel J. Meyer, The Pennsylvania State University
Reviewers:
Phil Goodrich, University of Minnesota
Gerry and Lucille Luke, Conception Junction, Missouri
Jim Moore, Oregon State University
A gravity drain gutter is a manure handling system which has
no mechanical parts and requires little or no dilution water to
remove manure from a building. The liquids and solids are held in
a gutter until sufficient depth of manure is available for drain-
ing manure out through removable tightly sealed plugs. The
drainage interval may vary from one day in narrow gutters for big
pigs to a month in wide and deep gutters.
Manure can be removed from a swine barn by: (1) manual or
mechanical scraping, (2) flushing with dump tanks, siphons or
pumping systems with automatic or manually controlled valves, (3)
continuous flushing, and (4) gravity draining. Flushing often
requires large amounts of water (over 50 gal./ft. of gutter width
per day). Flushing with recirculation from treatment lagoons is
not practical in all areas because of odor nuisance potential
from associated lagoons and/or soil types which don't seal ade-
quately.
Gravity drain gutter systems can be utilized for handling
liquid manure from swine of all ages. Some gutter shapes are a
modification of the deep, narrow gutter developed in the early
1960's (Figure 1). Modifications to the original 6-inch-wide
gutters include wider top widths, rounded bottoms, flatter slopes
to the bottom, and shorter lengths. A new option on gravity drain
gutters is a reversing hairpin gutter. This is an 18 in. to 36
in. deep gutter with a divider wall and two plugs which are
alternately pulled. It has drastically changed swine manure han-
dling systems.
The ``Y'' and ``V'' gutter gravity drain systems have disad-
vantages when compared to slotted floors over manure storages in
that they are more complicated to build, and result in higher
total manure system costs.
Research has shown and field experience has verified that
corrosive gas production increases with storage time and storage
temperature. To minimize gas production, a gravity drain gutter
should be sized to fill and be emptied within four days. If
manure will remain in the gutter for more than one week, some
form of perforated pit pipe ventilation should be considered
unless adequate airflow is available to dilute the concentration.
This would be the case with bigger pigs (i.e., 30 lb. plus).
Design of Gravity Drain Gutters
Designing a gravity drain system involves its shape, slope,
length, and outlet.
Gutter shapes may vary considerably (Figure 1), with a trend
toward a flat bottom hairpin gutter. Some shapes have in common a
narrow section at the bottom of the gutter which receives all the
liquids and part of the solids. A minimum accumulated manure
depth of 12 in. is adequate to allow the manure to flow toward
the outlet when the plug is pulled. The total depth of Y and V
gutters varies from 12 in. to 36 in. A common feature in these
modified gutters is the bottom section which is narrowed to 6-8
in. This limits the number of days of storage needed to attain
the minimum 12-in. draining depth.
Another type of gutter which is quite different is the rev-
ersing hairpin gutter. Its depth can vary from 16 in. to 36 in.,
but the most common depth is 24 in. The width can vary from 2
ft. to 12 ft. Farrowing and nursery gutters should have per-
forated 6 in. to 8 in. diameter pit ventilation ducts above the
divider wall or a central plenum under the service alley which is
connected to high RPM (2800) exhaust fans to reduce pit gas lev-
els in farrowing and nursery buildings (see PIH 60 ``Mechanical
Ventilation of Swine Buildings''). The primary advantage of the
hairpin over Y or V gutters is the reduced construction costs.
Two types of side slopes to the Y and V gutter are used. The
first is a self-cleaning slope with a minimum of 1 in. rise per 1
in. run for farrowing and 1 in. rise per 3/4 in. run for nursery.
These steep slopes work well for nursery pens (4 ft.) housing
single litters. However, steep slopes require excavation that is
too deep for farrowing crates and long nursery pens with totally
slotted floors. The second type has flatter slopes to decrease
construction difficulty and cost. Slopes being used in this case
are up to 2 in. per foot for farrowing and up to 4 in. per foot
for nurseries. Because flatter slopes accumulate manure solids
and feed, they should be hosed or scraped off every 1-2 weeks to
reduce ammonia levels and fly populations. A combination of the
first and second type of slope can be used beneath elevated
totally slotted farrowing crates and nursery pens. The self-
cleaning steep slopes are placed under the slotted floor sections
where manure concentrates the heaviest. The flatter slopes are
placed under the remainder of the pens. Gutters should be at
least 3-in. below slats so the manure can fall free of the slot-
ted floor.
Gutter length of the Y and V gutters should not exceed 40
ft. for farrowing or nursery barns and 70 ft. for grower and fin-
isher barns. The exception is the hairpin gutter which can be up
to 200 ft. long for growing-finishing buildings. The preferred
building length is about 100 ft. If center plugs are used, the
length can be doubled since the gutters drain from both ends to
the middle. The depth should be increased from 2 to 3 ft. to
build up more flush force if longer gutters are used. A minimum
of one to two inches of water should cover the entire bottom of
the gutter before using it the first time. This initial water
also helps longer gutters to drain cleaner and helps hold down
ammonia levels longer.
The longitudinal slope of the gutter should be about 1 in.
of drop in 20-40 ft. for Y or V gutters. The bottom of hairpin
gutters should not be sloped. If the gutter slope is steeper,
solids remain on the upper end when the liquids flow out. Expect
a small deposit of solids on the upper end of the gutter.
The preferred slat type over the Y and V gutters is one with
a high percentage open area, such as woven wire. The high percen-
tage open area allows for easy visual checking to see how full
the gutter is, and how much manure has built up on the slope
above the gutter. This type of slotted floor also allows easier
slope cleaning with a hose or a high-pressure washer.
The outlet from the gutter must be equipped with an easy-
to-remove water tight plug. Three types are shown in Figure 2.
Fit the plugs into a 90-degree elbow or tee (regular or saddle
type). It is better to have an overflow as part of the plug, in
case a waterer leaks or breaks, especially where hairpin gutters
are placed on top of concrete slats (i.e., in an existing build-
ing with concrete slats, a thin concrete cap would be poured
before adding the gutters). The ones shown have a built-in gas
trap to prevent backdrafting of pit gases when the barn has nega-
tive pressure ventilation. Locate the plug outside the pen or
crate to keep pigs from falling into the gutter unless a per-
manent guard is used. For a multiple room facility, consider
locating the plugs in a common alley outside the rooms (Figure
3). However, the access to the drain must seal tightly to keep
air from entering the room over the gutter, and interfering with
ventilation system performance. The main sewer line can be buried
outside the perimeter of the barn in case access is needed for
maintenance. If the rooms are drained individually, a 6-in. diam-
eter main sewer pipe is adequate. This depends somewhat on room
size, pit or gutter size. If the barn has 4 or more rooms, and
all gutter plugs will be pulled in a short interval, use an 8-in.
pipe. A perspective view of the reversing hairpin gutters with
two plugs is shown in Figure 4. All plugs should be at least 8
in. in diameter.
Floor Cross Sections of Gravity
Drain Gutters
Farrowing
Nine cross-sections for farrowing crates are shown in Fig-
ures 5A through 5J. Figures 5A, 5B, and 5J are examples that can
be used in remodeling situations to build above an existing
floor. The other cross sections require new sites or the removal
of portions of existing floors. Only Figure 5F shows the steep
slopes which are self-cleaning; the others require periodic
cleaning.
The example in Figure 5A utilizes the reversing hairpin
gutter under the entire crate. The divider wall must be anchored
to the gutter floor as shown with reinforcing to prevent tipping
over. Gutter depth can vary from 16 in. to 24 in. The alleys can
be raised higher than the gutter bottom to reduce leakage under
the wall into the alley or a keyway (1 in. x 1 in.) can be used
to tie the floor and wall together for a better seal. The walls
can be 6" concrete block or 4" of poured concrete with reinforc-
ing.
The example in Figure 5B utilizes a formed plastic pan
(100-150 mm thick) under the slotted floor. A 3-6 in. clearance
is needed between the flooring and the start of the front slope
for access to wash down feed and manure solids. Adequate clear-
ance is especially critical if the flooring has only a small per-
centage of slotted or open area. The alternative of washing the
slope directly through the slotted flooring may splash too much
water on the pigs unless they are moved out. The crates in Fig-
ures 5A, 5B, and 5J generally are raised at least 16 in. if the
existing floor is to be left undisturbed. Crates elevated more
than 12 in. normally require a portable ramp for the sow to get
in and out.
Figure 5C shows the bottom of the rear slope starting about
18 in. from the rear of the crate. Manure solids accumulate
mostly in the rear 24 in. of the crate. The steeper 1-in. rise
per 1 in. run slope helps in washing the solids into the gutter.
The rear section of the gutter shown in Figure 5D is half of
a large PVC pipe (generally 24-in. diameter) which collects most
of the manure solids. The minimum slope of the front section
toward the half pipe is 1 in. per foot, but 2 in. per foot is
preferred. Some manure solids will accumulate on the slope to the
pipe.
The gutter shown in Figure 5E is similar to those in Figure
5F but easier to construct. Generally the bottom of the V is 6
in. wide and the top 2 to 2 1/2 ft. The depth is about 12 in. A
disadvantage of the V-shape is that it takes about three times as
long as the Y-shape for the manure level to reach the 12-in.
depth needed for good drainage.
Figure 5F shows two precast concrete gutters side by side.
The slope of the sides is about 1 in. rise per 1 in. run which is
needed for self-cleaning. These 30-in. deep gutters have a bot-
tom section 6 in. wide and 12 in. deep plus they need to rest on
a flat slab as sketched. The high cost disadvantage of the
gutters is somewhat offset by their accurate fabrication and by a
shorter installation time.
Both cast-in-place gutters in Figures 5G and 5H have a
square bottom to simplify construction. Figure 5H requires a
minimum of 1 in. per foot slope toward the gutter.
In Figure 5J concrete blocks are used to elevate the crate
in order to install a gutter. The deep gutter is a 6- or 8-in.
PVC pipe cut in half. A disadvantage of this gutter and Figure 5A
is that it takes much more time to fill to the needed depth for
good drainage than any of the other options.
Gutters shown in Figures 5B and 5F can be purchased commer-
cially whereas all the others must be cast in place.
Nursery Pen Gravity Gutter Design
Five cross-sections for nursery pens are shown in Figure 6.
Figures 6A, 6B, and 6E adapt well for remodeling barns where it
is desirable to build above an existing floor. The slope toward
the gutter should be a minimum of 1 in. per foot, but 3 to 4 in.
per foot is preferred. The gutter in Figure 6A is constructed
using two 8-in. blocks to form its bottom. It could also be con-
structed with a round instead of a square bottom for slightly
better cleaning. The legs of the pen frame should be 3 in. above
the concrete block stands to allow access for cleaning the
slopes. The nipple waterers should be located over the gutter to
encourage pigs to drop manure there. The sides of the pen toward
the alleys should be solid up to 16 in. high to keep manure
inside the pen. Prefabricated plastic is shown for the gutter and
the sloping area next to it. The plastic should be supported with
2 x 4's unless sand fill is used under the plastic for support
(check manufacturer's recommendations).
Figure 6C shows a narrow pen (4 ft.) with a Y-shaped gutter
underneath. For self-cleaning, the slope should be 1 in. rise per
3/4 in. run. This would require a 3 1/2 ft. depth to the bottom
of the gutter, assuming it has a 12-in. deep bottom section. It
is critical that the pen flooring have ample open area when the
pen is not elevated above the existing alley floor (for cleaning
reasons).
The gutter shown in Figure 6D can be cast in place more
easily than the Y- shaped gutter in Figure 6C. A portion of the
area nearest the gutter is sloped more steeply because most of
the manure solids will fall through the floor at this end of the
pen (usually the end opposite the feeder). The 6-in. square bot-
tom is also easier to construct than the rounded bottom Y- shaped
gutter in Figure 6C.
The example shown in Figure 6E is similar to the farrowing
cross section in Figure 5A. The design and construction are simi-
lar. It is a simpler design than the other cross sections to con-
struct and cheaper to build.
Growing-Finishing Barn
Figure 7 shows a sloped solid floor pen with 1 or 2 gutters
at the lower end of the pen. Floor slopes, pen partitions, and
air flow patterns are critical considerations for keeping pigs
resting on the upper end and dunging near the lower end. Dunging
generally occurs in the open partition areas where the floor
slope is steep ( 1 in. per foot recommended). It is important to
have a 2-4 in. stepdown from the resting area to the dunging
area. The dunging section should be a minimum of one-third of the
pen length. The depth of the gutter in Figures 7A and 7B should
be 24 in. A pipe grating or guard over the gutter in Figures 7A
and 7B should be installed to protect small pigs. Square gutters
work as well as semicircular gutters in finishing units.
In Figure 7C, the floor between the gutters has a steep
slope (1 in. per foot) for self-cleaning. This increases the
effective slotted floor area.
Another option is shown in Figure 7D. The manure is held in
2-ft.-deep gutters, which are drained after the manure reaches a
12-in. depth. These gutters are the reversing hairpin type. They
can work best in partially slatted pens. The maximum gutter width
is 12 ft. This requires a divider wall unless the gutters are
recharged with extra water from a two stage lagoon. The recom-
mended maximum length is 100 ft. (200 ft. of draining length).
High moisture cracked corn feed can cause these gutters to drain
poorly. Wet feeders and gravity gutters do not work well together
due to the reduced waterer spillage or dilution water. Grower-
finisher gutters fill faster than farrowing-nursery gutters and
can be drained more frequently so pit pipe or duct ventilation is
not as necessary.
Reversing hairpin gutters can be sealed tighter between
rooms than buildings with scraper systems. This is especially
important in naturally ventilated buildings. A pressure treated
hinged door works well below room divider walls to minimize air
exchange between rooms.
Manure Storage
Manure can be stored in a concrete or glass-clad steel tank,
earthen structure, or an earthen treatment lagoon (the latter two
should be properly sealed). Note: Storages are overloaded
lagoons and smell much worse in warm weather than cool weather.
At least 60 days of storage time (180 days is preferred) is
recommended. Check state regulations for minimum storage criteria
and odor stipulations. Refer to PIH-67, ``Swine Waste Management
Alternatives,'' for manure production per day and storage alter-
natives.
Caution should be exercised when draining or pumping into a
storage under another building or in the existing building if the
pit is capped since this will agitate that manure and release
gases. One of those gases is methane. If the drain plugs are left
out during cleaning and if the manure in shallow pits above a
deep pit is drained out and if manure in the deep pit is being
emptied, the possibility of fire exists from methane gas since
most heaters are unvented or have open flames. A negative venti-
lation system is essential in the pit to reduce gasses released
into the building or room connected to the storage via a drain
plug or drain pipe.
Manure Transfer Systems
If possible, design the system so that manure flows to the
storage by gravity. The drain pipes for the plugs should be at
least 6 in. for farrowing and nursery buildings to prevent plug-
ging, with the exception being the reversing hairpin gutters
which should have a minimum 8 in. diameter pipes. Eight-inch
drain pipes are suggested for finishing barns and
gestation/breeding buildings. Slope the 6-inch and 8-inch pipe
at least 1% (1/8 in./ft.) to 2% (1/4 in./ft.) to achieve good
cleaning velocities. The maximum distance between cleanouts in
the drain pipe should not exceed 300 ft. The storage inlet should
be at least 3 ft. above the bottom since solids tend to settle
out at the point where the manure enters the storage.
To obtain sufficient slope for gravity transfer of manure,
it may be necessary to construct the barn floor on extra fill;
otherwise, storage capacity is lost by not using all of the
available height. Another alternative is a collection sump with a
pump to lift the manure into the storage (for sump information,
see PIH-91, ``Pumping Liquid Manure from Swine Lagoons and Hold-
ing Ponds''). Use a pump large enough to handle 1 1/2 in. diame-
ter solids.
Gutter Construction
The gutters can be (1) assembled from commercially available
prefabricated plastic, fiberglass, or precast concrete sections;
(2) cast-in-place concrete or (3) a combination. The Y and V
gutters are more costly to construct than the reversing hairpin
gutters because of the steeper slope involved.
Prefabricated and Precast
The plastic gutter sections are joined together with a seal-
ing tape or caulking compound and bolts or channel brackets at
the joints. Installation of below-floor plastic gutters requires
inner bracing to prevent the sand backfill or fresh concrete from
pushing in the form, and weights or temporary bracing to keep the
gutter in place.
Precast concrete gutters also are used in below-floor appli-
cations. Minimal excavation is needed with the precast concrete
sections. They are set on a sloped footing and are stable without
bracing or anchoring. The sections are mortared together to
prevent leaks.
Cast-in-Place
Commercial steel forms, which are available for Y-gutters,
can be set in excavated trenches and anchored to the surrounding
concrete floor with lag bolts or weighted with sandbags. Concrete
for the alleys is placed before the trench is excavated with a
small backhoe. Commercial plywood forms can also be set in exca-
vated trenches. They are temporarily braced to the roof trusses
to prevent uplift. When gutter forms are used, the concrete is
generally poured in one step and should be well vibrated to
ensure a smooth finish without voids.
Generally, the bottom of cast-in-place concrete gutters is
constructed first, using the excavated soil as the outside form
(Figure 8). An inner frame with short spacer blocks will form the
inner wall. The wood grain should run vertically so that blocks
can be split and removed. Fresh concrete should be vibrated to
fill the space beneath the inner frame, to prevent water leakage
from the gutter, and to provide a smooth surface. A semicircular
bottom can be constructed by cutting a 6- or 8-in. PVC pipe in
half lengthwise and nailing the half-pipe in the bottom of the
inner frame.
Two methods have been used to form the steep slope in the V-
or Y-shaped gutters (3 in. to 12 in. per foot). The first method
utilizes reinforcing bars (3/8 in.) placed vertically every 4 ft.
in the gutter and extended up the sideslope. The soil forms the
sideslope for the underside of the concrete form. If the concrete
is very stiff and reinforcing mesh is placed over the rebars
(above the soil), then the concrete sideslope can be troweled in
place. This is a time-consuming method, but it requires no forms.
The second method for the steep slope construction is to use
existing soil or fill for the underside form. Stakes are driven
as shown in Figure 8. A piece of wood is nailed to the top of the
stakes to form a slat ledge ( make it the same as the depth of
the slats). Then, plywood is nailed to this piece of wood. The
plywood is braced to the roof trusses or weighted to prevent
uplift. After the concrete has set 1-2 hours, the plywood is
taken off and the concrete steel troweled. Another way to give a
quick, smooth finish with little troweling is to line the plywood
with 4-6 mil polyethylene plastic or its equivalent.
Remodeling
When remodeling requires new concrete on top of existing
concrete, the minimum thickness of the new concrete should be 2
1/2 in. if reinforcing wire mesh is used or 3 1/2 in. without
reinforcement. Use seven bags of cement per cubic yard, and pea
gravel (1 in. maximum) for the thinner concrete.
Foundation Insulation
When gutters are placed next to an outside wall foundation,
insulation is needed to minimize freezing in the gutters in cold
climate areas. At least 2 in. of a water-resistant foam insula-
tion along side the foundation or in the foundation wall is
recommended (see PIH-65 on ``Insulation for Swine Housing'').
Management of the Gravity Gutter
Start-Up
A biological slime must form on the Y and V gutter sides and
bottom to get good cleaning action when the gutter contents are
emptied. This will naturally occur in 3-4 weeks. If solids remain
in the upper end of the gutter during this initial period, they
should be removed manually or hosed down.
Draining Gutter
It is important to have the gutter filled to at least an 8
in. to 12 in. depth before emptying the contents in order to
scour solids from the upper end. When replacing the plug or gate,
wiggle it in the slot or seat to be sure the outlet is tightly
closed. The Y and V gutters should be drained at least every week
to ensure lower barn odor levels and good bottom scouring action
in the gutter. The hairpin gutters which are drained at 2-4
weeks will have more odor than Y and V gutters unless pit ducts
are used above or on the side of the gutters. With adequate air-
flow in larger pig buildings (grower and finisher) the odor is
very minimal especially with partial slat building where insu-
lated sidewall ventilation doors or insulated curtains are used.
The reversing action of pulling alternate plugs keeps solids
buildup minimal. If the producer wants to completely clean the
gutter of manure, he will need to be able to add water on the end
opposite the plugs. There should not be a lip at the plug.
Water in Gutter
Adding one inch or more of water to the gutter after drain-
ing will facilitate better drainage of the gutter next time, par-
ticularly if it is greater than 40 ft. long. A nipple waterer
over each gutter ensures having extra dilution water in the
gutter. This is especially critical in reversing hairpin gutters.
This can be done by staggering the waterers in the dividers
between pens. ``Wet'' feeders where nipple waterers are over the
feed trough minimize waterer spillage. Wet feeders and gravity
manure systems do not mix! The manure will be too thick to flow
unless extra water is always added initially.
____________________________________________________________________
| |
| |
|Safety |
| |
| Do not enter collection sumps, manure storages, or hauling |
|tanks, unless they have been and are being well-ventilated. Also, |
|do not enter these structures without a self-contained breathing |
|apparatus or an air line. In addition, a body harness with a |
|lifeline should be used, with two people standing by who are |
|capable of lifting a person from the storage. |
|__________________________________________________________________|
References
Meyer, D. J. and J. C. Converse. Gas Production vs. Storage Time
on Swine Nursery Manure. ASAE Paper 81-4512.
Avery, G. L., G. E. Merva, J. B. Gerrish. Hydrogen Sulfide Pro-
duction in Swine Confinement Units. Trans. ASAE 1975. p. 149-151.
Figure 1. Typical gravity drain gutters.
Figure 2. Alternative watertight plugs for gutter outlets.
Figure 3. Detail of main sewer line connection to gutter plugs.
Figure 4. Perspective view of reversing hairpin gutter.
Figure 5. Alternative farrowing crate floor cross-sections using
gravity drain gutters.
Figure 6. Alternative nursery pen floor cross-sections using
gravity drain gutters.
Figure 7. Alternative finishing pen floor cross-section using
gravity drain gutters.
Figure 8. Cross-section 0f a Y-gutter form for cast-in-place (two
stage process)
NEW 12/90 (5M)
______________________________________________
Cooperative Extension Work in Agriculture and Home Economics,
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culture Cooperating. H.A. Wadsworth, Director, West Lafayette,
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