Confined Animal Feeding Operations (CAFO’s), such as freestall
dairy barns, are becoming closely regulated by federal and state environmental
agencies. Development and implementation of appropriate management plans
for utilization of CAFO animal wastes are important to minimizing contamination
of surface and underground water resources and insuring long-range sustainability
of the agricultural enterprise.
Composting is an acceptable and recommended means of recycling
organic wastes and is gaining acceptance in the U.S. The success of the
composting process depends on several basic conditions including moisture
content of the raw material, the ability to aerate the compost mass and
the degradability of the organic material. The optimal material for aerobic
composting should contain approximately 50% water, be of high porosity,
and have a C/N ratio of 15 to 30. These conditions can be achieved for
animal wastes collected from freestall dairy barns via hydraulic flush
and solids separation techniques.
Waste Collection from a Freestall Barn
While feeding, animals stand in a recessed flush
lane where most animal waste products are deposited. Periodically,
recycled lagoon water is released into the flush lane
to remove wastes from the barn.
Composting of animal wastes utilizes biological procedures similar to those
used in municipal sewage treatment plants, although the mechanics of operation
are different. The composting process produces an environmentally stable
product which is typically free of disease causing organisms, offensive
odors, insects, and weed seeds. Composting provides microorganisms the
opportunity to utilize many of the nutrients present in animal manure and
convert them into more stable organic compounds. These compounds release
nutrients at a slower, more controlled rate. This slow release rate allows
plants an opportunity to maximize nutrient uptake and use before excessive
leaching into the watershed occurs.
Composting of Solid Waste
Freshly separated solids from a freestall dairy facility averages between
70 and 75% moisture. Based upon developmental research in prototype
mechanical in-vessel composters, this moisture level should be reduced
to 60-65% or less to achieve rapid aerobic composting. Either partial drying
prior to composting or bulking agents such as hay or
sawdust should be added. Temperatures should be monitored
to assure thermophilic composting at temperatures above
130 deg. F for at least three days. Under these conditions, weed seeds
and most pathogenic microorganisms will be destroyed.
Based upon preliminary work with prototype composters, a commercial
sized composter measuring 8 ft. in diameter and 24.5 ft. long was manufactured
and installed on a 400-cow freestall dairy in northeast Texas by B
W Organics. This composter is sized to handle all of the solid waste
produced by 400 cows. When temperatures begin to decline after approximately
three days of composting, the compost can be unloaded
and a new batch can be loaded.
Advantages of In-Vessel Composting
Although composting can be achieved using a number of different processes
including windrow techniques, in-vessel composting
offers a number of potential advantages:
Waste is retained on-farm until composted, eliminating the need to transport
raw waste on highways to a centralized composting yard.
Composting can be completed rapidly, resulting in product stabilization/sanitation
in 3-6 days.
While in the composter, raw wastes are isolated from the environment
until the composting process is complete.
The site manager has precise control of moisture, temperature and aeration
during the composting process.
The raw waste looses all offensive odors within 24 hours of composter
start-up.
In-vessel composting can maintain a rapid decomposition process year-round
regardless of external ambient conditions.
This composting process utilizing separated solids from a freestall
barn produces a high quality organic material resembling peat moss.
Utilization as a Peat Moss Substitute
Production trials in TAMU-C greenhouses have shown that plants grown in
media containing 50% composted dairy cattle waste
are comparable to plants grown in media containing 50%
peat moss. However, uncomposted waste is unacceptable
as a growing media component.
The nutritional components of composted solid waste from a freestall
barn and peat moss are compared below:
Component
Peat Moss
Composted Waste
pH
4.1
6.7
Nitrate (ppm)
16.0
269.0
Ammonium (ppm)
22.7
48.9
Phosphorous (ppm)
7.4
46.2
Potassium (ppm)
21.0
682.0
Calcium (ppm)
65.9
75.4
Magnesium (ppm)
27.1
61.2
Boron (ppm)
0.1
0.3
Iron (ppm)
0.1
0.1
Manganese (ppm)
0.6
0.3
Sodium (ppm)
13.9
256.0
Salts (mmhos/cm)
0.8
3.9
Mutual Benefits to the Dairyman and the Environment
Through in-vessel composting techniques, the dairyman can convert a waste
product with potential liability into a marketable, value-added material
suitable for wholesale/retail marketing with profit potential. If the compost
from a 400-cow freestall dairy is marketed outside the "at risk" watershed,
approximately 8000 lbs. of nitrogen and 3000 lbs. each of phosphorous and
potassium will be relocated annually and placed in non-threatened areas.
Compost Utilization
The product from in-vessel composting of dairy cattle
solid waste collected by hydraulic flush and solids separation techniques
is uniform and exceptionally high quality.
The product can be used:
For improvement of organic matter content and fertility of soil.
As a peat moss substitute in greenhouse and landscape applications.
The product can be marketed:
Bulk for field, landscape, or nursery utilization.
Bagged for retail sales to the homeowner market.
Summation of Conclusions To-Date
Properly composted dairy cattle manure, whether collected by hydraulic
flush or dry-scrape techniques, can be substituted for peat moss in a soilless
growing media for marigold production without a loss of plant quality.
Due to the texture of composted dairy manure collected by hydraulic flush
techniques, plants were successfully grown in 100% compost without the
addition of vermiculite and/or perlite typically used in a peat-lite blend
with peat moss. Composted poultry litter may have limited utility as a
peat moss substitute for bedding plant production due to high nitrogen
and high total salt concentration. However, use of a compost blend containing
between 12.5 or 25% poultry litter may be acceptable for some applications.
Addition of 12.5 to 25% poultry litter with dairy manure increased the
rate of composting as indicated by composting temperature. Sewage sludge
did not generate the temperatures experienced during composting of either
dairy or poultry waste, but appears (data not yet analyzed) to produce
excellent quality plants in a greenhouse situation.
Fresh dairy manure collected by hydraulic flush techniques
from a confined animal facility averages between 70 and 75% moisture. This
moisture level was found to be too high to achieve aerobic composting due
to a lack of porosity and oxygen availability. Either partial drying of
the animal waste prior to composting or use of bulking agents to absorb
excess moisture and improve porosity were necessary to achieve adequate
composting. The use of bulking agents with wet dairy manure was detrimental
to subsequent plant growth. However, supplemental nitrogen applied at the
rate of 0.37% actual N (dry wt. basis) overcame the detrimental effects
of bulking agent addition. Use of a bulking agent of high carbon content
such as sawdust or hay in conjunction with a low nitrogen containing manure
from a hydraulic flush collection system probably restricts nitrogen availability
to plants. Co-composting of a high-carbon bulking agent with poultry litter
was beneficial to plant growth due to the high nitrogen content of poultry
litter.
A 24 cubic yard in-vessel aerobic composter modeled from the
prototype composters used in this project has been manufactured and installed
on a 400-cow dairy near Como, Texas. The economics of operating this composting
facility has been determined using actual installation costs and estimated
annual fixed and variable costs. For this project, annual fixed costs included
depreciation, insurance, taxes and value of land used for the composting
site. Variable costs included electricity, fuel, labor, repairs, and maintenance.
Annualized fixed and variable costs total $18,780.45.
A 400-cow freestall dairy will produce 6 cubic yards of solid
waste per day for composting. At a market value of $20.00 per cubic yard
(FOB compost facility), the composter would net an estimated $14,972.00
annually while removing a waste product liability from a targeted watershed.
More detailed economic data will be available during the next year as variable
costs are substantiated and markets are developed and tested.
