Robert
E. Graves, Professor of Agricultural Engineering
A dairy manure handling system is a cost item that must
meet many requirements. The ultimate goal of a manure
handling system should be to improve management, provide
positive
environmental protection, and allow maximum utilization
of manure nutrients. The best manure
handling systems are usually developed as part of an
overall plan for new construction, inovation or expansion.
A well-planned system will be compatible with the type
of housing and will include manure and wastewater from
outside animal areas, the milking center, youngstock
facilities, and silage effluent. It should also be compatible
with anticipated changes in housing and management over
the next 8-10 years. An integral part of an effective
manure handling system is having adequate cropland available
to utilize the manure nutrients or an alternative outlet
for extra nutrients. Dairy expansions that include large
increases in purchased feed and no increase in cropland
often result in over application of manure nutrients.
Manure handling systems, especially storages holding
large amounts of manure, are a threat to the environment.
Any good manure handling system will include backup
plans to allow continuous operation even if key components
malfunction. Advanced thought should be given to how
a large manure spill, resulting from a damaged storage
or broken pipe, can be contained before large quantities
of manure reach nearby streams or lakes.
Hazards
Manure
systems present hazards from asphyxiation, poisoning,
drowning, and machinery entanglement and entrapment.
Pumps pits and tanks can easily contain poisonous gases
that will not be apparent until someone enters the tank
and is overcome. Multiple deaths have occurred as a
result of failure to follow appropriate procedures for
working in these confined spaces. Do not enter
manure sumps, pits or storage tanks without appropriate
safety apparatus and procedures. No tool, pump
part, or farm chore is equivalent in value to the cost
of a human life! Another common hazard is failure to
provide adequate guarding at manure tank openings and
push off ramps to prevent entry by people, tractor scrapers,
or cows. All open storages or openings into storages
must have adequate fencing, guards, or covers to prevent
visitors, including small children, from gaining entry. Everyone has an obligation to design, supply,
buy, operate, and maintain manure storage and handling
systems that are safe for workers and visitors.
Handling
Systems
A
complete system allows for collection and removal of
manure from the animal housing areas, treatment if necessary,
transport to storage system, short and long term holding
or storage, transport to cropland, and land application.
Collection systems include gutter cleaners and gravity
flow channels in tie stall dairy barns and tractor scrapers,
automatic alley scrapers, flushing, and slotted floors
in freestall dairy barns. Outside yards, lots, and feeding
areas can be cleaned with scrapers or in some instances
flushing. Bedded pack and pen areas should be designed
to allow cleaning with tractor loaders. New and major
renovated pack areas should have sufficient access and
clearance to allow use of large front end loaders for
pack removal. Scrapers with rubber edges or made from
sections of large rubber tires provide less wear and
polishing of
concrete and tend to squeegee the floor. Metal blades
or buckets with down pressure are more effective under
freezing conditions. Manure may be pushed off an elevated
lip directly into a spreader or pushed into a storage
or collection gutter. In some cases it is pushed to
an area with a buck wall for loading with a bucket loader.
Automatic freestall alley scrapers are often cost and
labor savers on large farms and frequent operation provides
cleaner alleys and cows. The cost and time required
for maintenance of alley scrapers is often less than
the total cost (labor, machinery, maintenance, injured
animals) of daily tractor scraping. Unattended operation
of alley scrapers where very small or new born calves
could be dragged away by the slow moving blade is not
recommended. Alley scrapers must discharge through a
hole, over a collection channel, or off the edge of
a storage. The drop off point for the manure must be
located and protected to assure that
people, animals or equipment will not inadvertently
fall in. Flush cleaning is a low labor method that allows
for frequent cleaning and results in drier alleys and
cleaner cows. Important components of flush systems
are adequate water supply, water disposal system, elevations,
slopes, pumps and pipes. Systems can successfully operate
much of the year, even in cold climates, if adequate
facilities are available to take care of storage of
extra water. The most common problems with flushing
systems are the quantity of water required and separating
solids for reusing water. Farmers are often overwhelmed
by the amount of water that must be handled and the
need for more dilution water in recirculating systems
than expected. Criteria for satisfactory flushing include
water volume per flush, flow rate, duration of flush,
velocity of water, and depth of water. In general, a
3 inch depth of water and 5 feet per second velocity
are recommended. A 3% alley slope is often considered
ideal. Steeper slopes will require more water and a
higher flow rate, shallower slopes will require a high
rate of water to maintain velocity. Water can be supplied
from tip tanks, reservoirs with large gates that open
or delivered through large pipes from high volume pumps
or elevated holding tanks or ponds. Slotted floors provide
a method for immediate removal of manure from the animal
area. Once beneath the floor, manure may be stored in
an underfloor tank or removed by an automatic scraper,
flushing, or a gravity flow channel. Manure stored under
slats can result in gas, odor and moisture problems
in enclosed barns and should be avoided. Keep animals
and people out of enclosed barns and provide maximum
ventilation during agitation and clean out if a manure
tank is located under the slats. Floors may be configured
with long parallel slats and slots, or oblong holes
in a so
called waffle pattern. Field observations indicate that
animals seem to walk more surely on waffle slats but
no research is available concerning either configuration.
Slatted floors allow urine to drain quickly away and
manure is pushed through the slots by animal traffic.
The result is a drier environment for the cows’
hoofs. If used in extremely cold situations manure will
eventually freeze and not go through the slots. Provide
access for a tractor scraper to remove manure during
cold weather. Removal systems move manure from the barn
to the field for immediate application or to storage.
For immediate field application the manure may be loaded
directly into a manure spreader from a gutter cleaner
discharge or push off lip, or loaded with a front end
loader. More liquid manure may be pumped from a collection
channel, sump, or small tank that holds a day or two
manure accumulation. If manure is to be pumped into
a liquid spreader,
wastewater from the milking center is usually included
to make agitation and pumping easier. Manure can be
conveyed to a storage located at the barn by the gutter
cleaner, tractor scraper, large piston pump, centrifugal
pump, gravity flow pipe or gravity flow channel. Manure
can be transported to satellite storages located away
from the barn by trucks, large spreaders or pipelines.
Manure storage systems may be located at the barn or
near the cropland that will receive the manure. If manure
must be transported long distances, it is often more
effective to provide satellite storages near the cropland.
This allows the manure to be hauled to the storage during
low labor periods and makes for more efficient spreading.
Liquid manure, especially if solids have been removed,
can be pumped long distances to satellite storages.
The storage must be compatible with the form manure
is removed from the barn. Heavily bedded manure can
be easily stacked in three sided bunker type storages
or on simple hard surfaced or packed gravel pads. Storages
should be designed to prevent clean water from running
into them and to direct any leachate or runoff water
from the storage away from streams to vegetative filter
areas or holding ponds. Liquid manure can be stored
in properly designed concrete or steel tanks, concrete
or membrane lined in ground storages and in some cases
earth storages. It is critical that storages be located
and constructed to assure that manure will not seep
through storage walls or bottom to ground or surface
water. Consult the USDA Soil Conservation Service or
a qualified soils engineer regarding location and design
of in ground manure storages. An annual inspection and
maintenance program should be in place to assure continued
safe operation of any type manure storage.
Liquid
storages require appropriate signs, guards and fences
to protect workers and visitors from unintended entry
and possible loss of life.
Treatment
Systems
Solids
separation will allow easier handling of liquid
material, allows for recycling of water for flushing,
and can provide a useful by-product. Separation systems
can be categorized as gravity,
screens, extruders, and cyclones. Settling tanks or
basins use gravity and time to allow larger particles
of liquid manure to settle or float out. Screens normally
require some method to prevent particles from plugging
or blinding the screen. This may be accomplished by
sloping the face of the screen so material slides off
or with mechanical scraping or vibration. Screens require
a dilute material similar to that obtained with flushing
systems. Extruders use screws, plungers, or belts to
pack manure against a perforated cylinder, box, belt
or plate. Liquid is forced out through the holes and
the solids are discharged out the end. These devices
tend to provide a drier solid and some will work with
a less dilute, slurry consistency manure. Cyclone separators
are similar to dust collectors. A very dilute flow of
manure is introduced into a conical chamber that encourages
large particles to move to the outside and allows liquid
to pass through the middle. These separators are not
common in dairy manure handling systems. Anaerobic
digestion or biogas production has been used
by some large farms as a method to extract energy from
manure and reduce odor that results from long term liquid
storage. The biogas process converts complex organic
material such as manure into biogas and low odor effluent.
A heated digester with a 15- 5 day detention time is
normally required. The primary constituents in biogas
are methane (natural gas), carbon dioxide and trace
gases. Originally the primary interest was in energy
production, usually electricity. Economics tended to
favor farms with more than 200-400 cows. Even at this
size most farmers chose not to bother with the extra
expense and management requirements. Recently there
has been interest is biogas digesters as a method to
solve odor and nuisance problems associated with storing
and handling large quantities of dairy manure. The process
does not significantly reduce the amount of manure or
the nutrient content, but does alter the form of the
nitrogen. The effluent will be more liquid and homogeneous
as a result of the digestion process. Composting is
another form of treatment that dairy farmers are considering
to reduce the odor and nuisance problems associated
with dairy manure. Composting is an
aerobic process that requires a material with good porosity,
40-60% moisture content and proper carbon to nitrogen
ratio. Some form of mixing and or aeration is required
to provide satisfactory composting. The process generates
its own heat, reaching temperatures of 120-140°F.
When properly done, composting will eliminate most odors
and result in a stable easily handled dry humus like
material. Most dairy manure requires some form of dry
carbonaceous material such as straw, sawdust or wood
chips to maintain the desired moisture content and carbon
nitrogen ratio. Some dairy farmers have found an additional
income source by charging municipalities or industries
to take materials such as paper, cardboard, tree trimmings,
etc. This is then mixed with the manure and after composting
either spread on land or sold as compost.
Summary
Anyone
considering major changes in manure handling or dairy
housing should give careful thought to the various components
of a complete manure handling system. A change in housing
method from a heavily bedded tie stall barn to a freestall
barn may render existing manure handing equipment useless.
Large increases in cow numbers without an increase in
land to spread manure on may result in application of
manure nutrients at levels exceeding the crop removal
rate. General guidance and requirements for handling
manure in Pennsylvania is found in the
