Manure Management

Manure Storage Capacity

Manure storage capacity is the #1 limiting factor for herd expansion, and a major consideration for the location and permitting of a new dairy facility. 

In the United States, general nutrient management plans are based on limits of 1 to 1.5 acres (0.4 to 0.6 hectares) per cow for nitrogen, and 2.5 to 4 acres (1 to 1.6 hectares) per cow for phosphorous, but specific regional permitting standards must be followed.

For North America, suggested minimum manure storage capacities for 12 months of storage are:

1 million gallons per 100 cows per year

3.8 million liters per 100 cows per year

For example, 1,000 cows would require 1000/100*1 = 10 million gallons

(1000/100*3.8 = 38 million liters)

Based on mean body weight, the following calculation may be used:

# cows x ((average cow weight lbs/1000) x (2 or 2.1 ft³ per day) x 365) x 7.48

For example, 1,000, 1,500-pound cows would require 1000 x (1500/1000) x 2 x 365 x 7.48 = 8.2 million gallons (31 million liters)

Use 2 ft³/day per 1000 lbs (57 cu liters/day per 454 kg) of live weight for organic bedding in freestalls and 2.1 ft³/day (59 cu liters/day) for sand bedding. For loose bedded housing, use 2.2 (chopped bedding) or 2.3 ft³/day (62 or 65 cu liters/day) for long straw bedding.

Waste Storage Facilities

There are six types of waste storage impoundments and structures that temporarily store wastes, but the type of impound or structure chosen will depend on the location of the dairy.

1. In-place clay
2. Clay lined
3. Geomembrane lined
4. Geosynthetic clay lined
5. Concrete lined
6. Structural lined

Out of these six types, in-place clay, clay lined, geomembrane lined, and geosynthetic clay lined pits may be used with most types of bedding except sand, unless these types of pits are combined with a concrete lined pit to trap sand laden manure. However, with geosynthetic clay lined pits, sand must be completely removed from the waste stream before it enters the pit. A cover over the storage structures may be considered to reduce the accumulation of additional waste such as rain water.

Below is a general overview of waste storage options and the costs associated with them according to Drew Zelle and Matt Woodrow, PE of DATCP, and Ryan Rice of Fond du Lac County LWCD. More information can be found from the Natural Resources Conservation Service Conservation Practice Standard for waste storage facilities (Code 313). Tables are from Code 313.

1. In-Place Clay Pits

In-place clay pits are the most cost effective manure pit to construct as long as clay is readily available and excess fill can be disposed of onsite. Costs are associated with the removal and excavation of clay. Concrete agitation points are required with side slopes built at 2:5:1.

2. Clay Lined Pits

Clay lined pits can be a maximum of 25 feet (7.6 m) deep with a liner thickness of 5.7 feet (1.7 m). The liner must be protected from the abrasion of sand. Wet weather makes it very difficult to maintain these pits. The excavation, importation, and compaction of clay add to the costs.

3. Geomembrane Lined Pits

Geomembrane lined pits are used when good clay is unavailable or too far to truck. They require a 0.6 cm thick membrane with a venting system to remove gases. The success of these systems depends on precise preparation work. The ability to agitate is excellent due to the smooth surface, and the pit can be easily expanded. However, repairs to the liner can be costly.

4. Geosynthetic Clay Lined Pits

Due to the extensive subgrade preparation that is needed for the liner installation, wet weather can significantly hinder the installation process. The liner consists of a bentonite clay product that is sewn between two geosynthetics and is placed in close contact with the soil below. Excavation, preparation, and repairs to the liner add to the costs.

5. Concrete Lined

Concrete lined pits can be designed with liquid tight concrete or concrete composite. Liquid tight concrete can be more expensive, but with limited pours, the quality is better and the specific control joints designed to control cracking are better protected with PVC seals. Cost for liquid tight concrete in Wisconsin is currently $3 USD per square foot (2015), but may rise, and the costs for water stop installations add to the costs.

Concrete composite is cheaper than liquid tight concrete by 10 to 15%, and can be poured all day, but quality suffers since the soil below is used to assist in leak protection without seals.

These pits are typically 5 to 6 inches (13 to 15 cm) thick. Both options are great with sand and allow for unlimited access for machinery.

6. Structural Concrete

Above ground concrete storage is a good option for places with limited space or as part of the overall facility. Vertical walls can be no more that 10 feet (3 m) high, but round structures may go higher. The average cost for an 8-foot (2.4 m) wall is about $140 USD per linear foot (2015). This type of structure is difficult to expand, but can be applied in multi-staged systems.

Moving Manure Out of the Barn

Lactating cows produce around 150 lbs (68 kg) or about 18 gallons (68 liters) of manure per day or more, and it must be safely stored and handled according to state and federal government regulations.

Organic Bedding

With organic bedding material, manure transfer and storage options are relatively simple. Gravity flow channels and a simple clay-lined lagoon, correctly sized, will often suffice.

Inorganic (Sand) Bedding

Gravity flow channels often fail with sand laden manure and are therefore not recommended.

There are four viable options to move sand laden manure out of the barn:

1. Vacuum
2. Scraper
3. Auger
4. Flume

Vacuum Tanks

In larger herds, vacuum tank trucks have been used to collect the manure directly from the alleys and discharge it into a centrally located manure handling system.

This option requires higher grade concrete in the pen alleys to compensate for the weight of the truck, and avoids the risk of blockage in transfer channels.

Scraper

This involves scraping into a channel and the use of a wire mounted scraper to move the manure out of the channel into a collection pit. These scrapers typically run the width of the barn (about 100 to 120 feet or 30.5 to 36.6 m wide).

Blockage can occur with these systems, and breakage of the scraper wire has been reported. The reception pit is also a place where sand can settle, requiring the regular use and maintenance of an agitator in the bottom of the pit.

 Auger

Scraping into a trough fitted with a horizontal screw auger is a common option. Single augers are now available at a length of 168 feet (51.2 m), and multiple augers can be combined to achieve any desired flow path.

Augers may fail, especially at the joints, but many have been installed without issue.

Flumes

Flumes use a sloped channel to move fast moving water into the barn. Manure is scraped or flushed from the alley either manually or with an automatic scraper or alley flush system into the channel, and is carried away from the barn along the channel. Flumes are usually used in association with a sand settling lane system.

Construction of the flume should follow these guidelines:

1. The flume pipe should be an 18 to 36-inch (46 to 91 cm) diameter pipe (wider pipes are needed with flush alleys; narrower ones are compatible with scrape systems). Reinforce the openings where the manure is scraped/flushed to ensure that the pipe does not collapse.
2. The flume pipe must always slope down from the barn at a slope of at least 0.5-0.75% (a 0.25% slope may be sufficient for manure solids).
3. For settling lane systems, the flume water should start with less than 2% of organic solids, usually coming from a floating pump located 2 feet (0.6 m) below the lagoon surface. Multiple lagoons in sequence deliver the cleanest water in the last lagoon, and weep walls in between can retain up to 60% of the organic solids in the previous lagoon. Clean flush water has less odor!
4. Flume water needs to enter the flume at >5 feet per second (1.5 m/s), preferably 7 to 8 ft/sec (2.1 to 2.4 m/sec), requiring the delivery of more than 600 gallons per min (2,271 liters per min) at the exit from the flume.

Flume operation is dependent on the supply of clean water. They are therefore very susceptible to lagoon inversions (where the organic solids float to the top of the lagoon), leading to a loss of available flush water. Use of organic polymers may help prevent inversions and resolve them when they occur (e.g. BEI Polymer Hydration Unit from Trident Separators).

Alley Flush Systems

Flush alleys greatly reduce labor and may be used with a flume and sand settling lane system to recycle sand. Such systems are in operation in herds as small as 120 cows.

Poured alleys must have a minimum of a 2% slope to avoid sand accumulation, and the feed alley must be sloped 3/4 inch (2 cm) from the feed rail to the stall curb to get high speed flush by the stalls, and to avoid piling of sand. The stall curb can be ‘notched’ with a 2-inch (5 cm) board to allow flush water to flow tight against the curb.

A flush tank is required to store sufficient flush water held under pressure by a flush head fitted with an air brake. When air is released, the flush head opens and water rushes down the alley.

Slatted Floors

Slatted floor systems are not compatible with sand bedded facilities. The slats are wide and traumatic to the cow’s hoof, and are not recommended for cattle facilities.

Sand Reclamation Systems

Sand is held in manure’s gel-like mucosal (sticky) structure, and sand is about 2.5 times denser than manure. All separation systems require sand laden manure to be mixed with water at a 1:1 mix of manure and water; the manure viscosity is broken and sand begins to settle at a 1:1 mix. 5:1 dilutions are created with flush systems.

Options for separation are broadly categorized into two types of systems: settling lane and mechanical systems. However, hybrid systems that mix the two systems are common.

Both systems should strive to separate more than 90 to 95% of the sand from the manure with less than 4% of organic solids, which can be done with both types of system. Fine sand types should be avoided as these are difficult to separate so a mason or concrete type sand is usually recommended.

The ASTM standards for mason and concrete sand sieve analysis is as follows (either one of these, or somewhere in between, are acceptable sand particle sizes for mechanical separation systems):

A comparison of the two broad categories of sand separation systems is provided below:

Mechanical Systems

Mechanical systems rely on the mixing of sand laden manure with water in a collection vat so that the sand settles to the bottom of the vat where it may be augured out into a pile while the manure liquid phase goes through an organic solids separation phase and is then pumped to the lagoon. It is increasingly common to see the separated sand go through a mechanical dewatering cycle before being piled.

There are several commercial mechanical systems available including, but not limited to:

• McLanahan Corporation
• Trident Separators
• Daritech

Flumes may be used with mechanical separation systems by emptying the flume into an augured trench. The trench is typically 60 feet (18.3 meters) long, 4 feet (1.2 meters) wide and varies in depth, with a reverse auger in the bottom pulling the sand toward the mechanical separator in a reverse direction to the manure flow.

Settling Lanes

Keys to successful sand settling lane construction and operation are as follows:

• Move sand laden manure along a flume at >5 ft/sec (1.5 m/sec) and discharge it into a mixing tube that is 40 to 60 feet (12.2 m to 18.3 m) long before delivering it to the sand lane. Avoid pumping from a collection pit as the sand will eventually settle at the bottom.
• Pour concrete lanes, usually two side by side, 10 to 12 feet (3 to 3.7 m) wide (depending on the width of the equipment used) and 150 to 300 feet (7 to 91.4 m) long (longer is better).
• Pour with a 0.25% slope and avoid hairpin bends unless necessary
• Create a dewatering floor on either side of the lanes where the sand can be piled with drainage back into the lane and capacity for 6 to 8 weeks.
• Minimum 10-inch (25 cm) depth, but can be up to 4 feet (1.2 m) deep. Deeper lanes can be operated at lower temperatures in the winter.
• Flume discharge at >600 gallons per min (2,271 liters per min) with a gate to moderate discharge speed. Discharge perpendicular into the lane is preferable, and make lane 30 to 50% wider to start with so that the manure stream spreads out quickly.
• Aim for a speed of 1.5 ft/sec (0.5 m/sec) at the start of the lane and maintain a speed of >1 ft/sec (0.3 m/sec) at the end of the lane to avoid organic matter settling out. In a correctly designed lane, most of the sand will settle out over the first ~80 feet (24.4 m).
• Remove sand from lane to maintain speeds as needed.

Example of a twin settling lane with a dewatering area

Options Without Sand Reclamation

If the dairy decides not to recycle sand, consider:

1. Reducing the amount of sand used

Typically, the use of a Pack Mat system will halve the amount of sand used per day to about 20 lbs (9.1 kg) sand per stall per day.

2. Ensuring that sand can be removed from the lagoon

A 2-stage lagoon can be built so that sand settles in the first stage of the lagoon while manure seeps over a weep wall into the second stage of the lagoon. The first stage of the lagoon should have a concrete floor with a sloped access point for machinery to remove sand.

Use of an agitation boat or salamander to stir up solids on the bottom of the lagoon has also been a recent improvement to the removal of sand from lagoon systems.