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ASAE Conference Proceeding

This is not a peer-reviewed article.

Sizing and Management Considerations for Settling Basins Receiving Sand-Laden Flushed Dairy Manure

C. D. Fulhage

Pp. 456-462 in the Animal, Agricultural and Food Processing Wastes, Proceedings of the Ninth International Symposium, 11-14 October 2003 (Raleigh, North Carolina, USA), ed. Robert Burns. ,11 October 2003 . ASAE Pub #701P1203

Abstract

In order to comply with nutrient management requirements, Missouri dairy producers are interested in settling as a means of partitioning nutrients and recovering sand used for bedding. Separation of solids also results in easier management of liquid storage facilities. This paper summarizes management requirements and performance of a manure management system utilizing flushing, sand bedding and a “porous-wall” settling basin based on a study of the Echelmier Dairy near Fulton, Missouri.

Two types of bedding sand were studied. “Classified” sand contained a significant percentage of smaller sand and clay particles. “Concrete” sand was a coarser, graded material containing few fine particles. The coarser sand was more expensive ($5.25/ton vs. $4.25/ton), resulted in cleaner cows, was more difficult to flush, settled more readily, and harbored fewer bacteria colonies in limited bacteriological studies.

The flush system provides a flow velocity of 5.2 ft/s(1.6 m/s) in the widest alley, which results in acceptable sand removal. Records of sand purchased, and sand used to bed freestalls indicate that about 75% of the sand flushed from the freestall barn is recovered from the settling basin for re-use as bedding. The rate of sand use is estimated at about 65 lb(30 kg) sand/freestall-day.

The two-chambered settling basin provides about 45 days storage in each chamber for the sand-laden flushed manure from 450 cows (1,400 lb(636 kg) Holstein cows). Settled solids accumulate in the basin at the calculated rate of 2.14 ft 3 (0.06 m 3 )/cow-day, and represent volume fractions of about 0.55 ft 3 (0.016 m 3 )/cow-day for sand, and about 1.6 ft 3 (0.045 m 3 )/cow-day for manure. Sand accounts for a significant fraction of basin volume, and should be considered in basin sizing.

Sand recovered from the settling basin is stockpiled for a “conditioning” period before re-use as bedding. Most ideal results were obtained by allowing sand to “condition” for one month, followed by a moving/mixing operation and an additional 1 week conditioning before re-use as bedding. Limited bacteriological studies indicated similar bacteria profiles in “fresh” and re-cycled sand when these procedures were followed.

KEYWORDS. Manure, Settling, Sand

Introduction

In order to comply with nutrient management requirements, Missouri dairy producers are interested in settling as a means of partitioning nutrients. A study by Burcham, 1995 showed that settling can also be effective in recovering sand for use as bedding. The amount of sand used as bedding is quite variable (Stowell, 1995), and contributes significantly to management considerations and settling basin size. Separation of solids also results in easier management of liquid storage facilities. An evaluation of the performance of the manure management system at the Echelmier Dairy near Fulton, Missouri was conducted from September, 2000 to September 2002 (Echelmier, 2002). The objectives of the study were to develop guidelines for sizing settling basins receiving sand-laden dairy manure, develop recommendations for managing sand for recycling in sand-bedded systems, and evaluate the relative bacteria profiles in “fresh” vs. re-cycled sand used for bedding.

Manure system components

Primary system components involved in this study included the freestall barn, flush system, and settling basin. These components were evaluated for management requirements and performance characteristics as affected by the use of sand for bedding in the freestall barn.

Freestall barn

The freestall barn at the Echelmier Dairy is a conventional 4-row design with 4 flush alleys and a center feed driveway. Two flush alleys are 14 ft(4.3 m) wide, and two are 10 ft(3.1m) wide. The barn is 480 ft(148 m) long, and is built with a 2% slope for flushing. The barn contains 400 freestalls, and has an average occupancy of 450 lactating Holstein cows weighing approximately 1,400 lbs(636 kg) each.

Flush system

The flush system is a tower-tank pipeline system (Fulhage, 1993) utilizing 12 in(30 cm) pipe and butterfly valves to release recycled lagoon water into the flush alleys. The two tower-tanks are 12 ft(3.7 m) in diameter and 40 ft(12.3 m) in height. Figure 1 shows the manner in which water is released into the flush alleys.

456-462isaafpw_files/image1.jpg

Figure 1. Water is released into the flush alley through a butterfly valve and 12 in steel pipe.

Flush velocity recommendations range from 5 to 10 ft/s(1.5 to 3.1 m/s) (Harner, 1998).

Settling basin

The settling basin is constructed with alternating solid and porous wall sections on either side of a center alley into which excess water drains. The center alley is also used as an access lane for the hauling vehicle when loading out solids from the settling basin. Solids are retained in basins on either side of the center alley walls. Figure 2 shows basin details.

456-462isaafpw_files/image2.gif

Figure 2. Cross-section of settling basin.

The center alley is constructed with alternating sections of solid and porous wall. The alternating sections are each 8 ft(2.5 m) in length. The porous sections are “tri-bar” flooring panels commonly used in swine nursery units and are shown in Figure 3.

456-462isaafpw_files/image3.jpg

Figure 3. Bar spacing is about 3/8 in for the swine flooring used in the porous wall sections.

The length of the settling basin is 350 ft(108 m). This length along with the cross section dimensions shown in Figure 2 provides a volume of 43,400 ft 3 (1228 m 3 ) settled solids in each chamber of the basin.

Methods

Evaluations and measurements were made to determine the effectiveness of flushing in removing sand from the freestall barn, the rate of “new” sand use and recovered sand in the system, the volume rate of accumulation of manure and sand in the settling basin, and management procedures for recovering and re-using sand for bedding.

Requirements for sand removal by flushing

Experience has shown that sand is considerably more difficult to remove from freestall alleys by flushing than is manure. In this evaluation, different rates of flush water flow in the flush alleys were used to determine the minimum velocity acceptable to the producer for sand removal. Flush water flow rates were varied by changing the degree of opening of the butterfly valve on the discharge pipe, and changing the head pressure (water level) in the tower-tanks). Flushing frequency was also investigated as a means of enhancing sand removal from freestall alleys.

Sand use and recovery

Sand requirements were determined by tracking “new” sand purchases over a two-year period. The ratio of recovered and recycled sand to total sand use was determined by comparing the time period that recovered sand was available for freestall maintenance to the time period that freestall maintenance had to be maintained with “new” sand.

Sand/manure accumulation rates

The rate of sand and manure accumulation in the settling basin was determined simply by tracking the time period required for each side of the basin to fill to capacity. This accumulated volume was then divided by the number of cows contributing manure and the number of days in the accumulation period.

Sand recovery management procedures

Recovering sand differentially from manure in a settling basin is an additional step in overall management of settled solids, and one which may require a “learning curve” for the producer. Observations were made of the operations used at the Echelmier Dairy over a two-year period as routine procedures were developed to recover and re-use sand for bedding freestalls. These observations are outlined in the results section of this paper.

The use of recycled sand for freestall bedding raises the concern that organisms detrimental to animal health and milk production may reside or proliferate in the sand at problem levels. To evaluate this hazard, “total colony forming” bacterial tests were conducted on fresh and recycled sand for comparison purposes.

Results and Discussion

Flushing requirements

Flush velocities were determined by timing the movement of the leading edge wave of a flush over the last 200 ft(61.5 m) of freestall barn length in the 14 ft(4.3 m) wide alleys. Height of water in the flush tower tank for these trials averaged 38 ft(11.7 m). Butterfly valve settings of 0, 25, and 40 degrees from wide open (wide open = 0 degrees) were used to vary flow rate and hence the velocity. The producer was asked to rate the cleanliness of the alley on a scale of 1 to 5 with 5 being most desirable. Table 1 summarizes the results of these trials.

Table 1. Flow velocities and cleanliness rating for various flush valve openings.

Valve setting from wide open, deg

Flow velocity in alley, ft/s(m/s)

Cleanliness rating

0

5.2(1.6)

4 – 5

25

4.5(1.4)

3

40

3.7(1.1)

2

Flow velocities of 5 ft/s(1.5 m/s) were effective in removing manure and most of the sand. The small amount of remaining sand was concentrated in the area next to the curb of the freestalls. Occasional input with a mechanical device (scraper or loader bucket) is necessary, but this producer considers this level of flush performance acceptable. Flush velocities obtained at the partially-closed valve settings were largely effective in removing manure from the alleys, but significantly more sand remained. Harner (1998) suggests flush velocities of 5 ft/s(1.5 m/s) or greater for flushing sand-bedded systems.

Normal procedures for this producer are to flush three times per day. A few trials were made at a higher flushing frequency (every 3-4 hours) to observe the effect of frequency on sand removal. The increased frequency enhanced sand removal at all valve settings, but the advantages gained were not significant enough in the view of this producer to change his normal procedures. The producer normally uses a wide-open valve setting for all flushes, and flushes the wider alleys “off the top” of the tower tanks, and then flushes the narrower alleys with the reduced water level in the tanks and thus obtains similar flush velocities in all alleys.

Sand use and recovery

Sand use and recovery rates were determined from the amount of “new” sand purchased over a two year period, and the fraction of time during that period when sufficient recycled sand was available to bed the freestalls. This producer’s operating plan calls for re-bedding freestalls every 7 to 9 days. Table 2 shows details of sand purchase, use patterns, and estimated recovery.

Table 2. Sand purchased, fraction of time “fresh” vs. recycled sand is used in freestalls, and estimated recovery rate of sand for the Echelmier Dairy.

Time period

Sand purchased, tons(Mg)/month

Average weeks recycled sand used

Average weeks “new” sand used

Approximate percent sand recovered

Year 1

115(104)

37

15

71

Year 2

100(91)

39

13

75

These records of new sand purchased, and recovery rates indicate that sand use in the freestall barn is about 66 lb(30 kg)/freestall-day.

Sand/manure accumulation rates

The rate of sand and manure accumulation in a settling basin directly impacts the storage period and sizing considerations for the settling basin. Table 3 outlines details describing sand/manure accumulation rate, and the estimated partitioning of sand and manure. Full-pool storage volume of one side of the two-chambered settling basin is calculated at 43,400 ft 3 (1228 m 3 ).

Table 3. Sand/manure accumulation rates and estimated volume fractions for one side of the settling basin.

Time period

Average # days to fill one side

Volume of sand/manure mixture, ft 3 (m 3 )/cow-day

Estimated volume of sand, ft 3 /freestall-day (lb/freestall-day)

Estimated volume of manure, ft 3 (m 3 )/cow-day

Year 1

43

2.30(0.065)

0.55 (66)

1.75(0.05)

Year 2

45

2.14(0.061)

0.55 (66)

1.59(0.045)

Although manure accounts for about three fourths of the volume accumulation in the settling basin, the volume of sand is significant, and should be taken into account in sizing the storage basin. Using the values in the table, a guideline for sizing settling basins is suggested as follows.

Basin volume, ft 3 = FS x SP (S/120 + 1.76)

FS = number of freestalls in barn SP = desired storage period, days S = Average sand use rate, lb/freestall-day

This guideline assumes a cow/freestall ratio of 1.1 in the freestall barn. It should be recognized that many factors impact the amount of manure and other material, which might enter a settling basin. Caution should be exercised in using this guideline under conditions significantly different than those described for this dairy. It should be recognized that the amount of sand used to bed freestalls is highly dependent upon the producer’s perception of freestall condition and acceptability. There is much variability in the sand volume (weight) parameter noted in the table above (Stowell, 1995).

Sand recovery and management procedures

In this operation, sand is recovered from the settling basin using front-end and skid-steer loaders. The sand tends to settle differentially from the manure with most sand accumulating at the “fill” end of the settling basin. Careful operation of the sand removal equipment results in a high percentage of sand recovery. However, attempts to recover too much sand can lead to excessive amounts of organic matter in the recovered sand, which could result in disease problems. Figure 4 shows characteristics of the settled sand and manure.

Figure 4. Sand settles first at the "fill" end of the basin while manure is carried to the far end.

456-462isaafpw_files/image4.jpg

Sand is removed from the settling basin and stockpiled adjacent to the facility. See Figure 5.

Figure 5. Sand is stockpiled between the settling basin and the lagoon.

456-462isaafpw_files/image5.jpg

The stockpile is located in a well-drained area, and any runoff from the stockpiled sand drains to the lagoon. The sand management protocol developed by this producer calls for a 30-day conditioning period for stockpiled sand before it is recycled as bedding in the freestall barn. Bacteria (total colony) tests on “new” and recovered sand suggest that bacterial profiles are similar for the two sources if the recovered sand has conditioned in the stockpile for 30 days. This producer has considered an additional step involving “turning” a portion of the stockpile after 30 days, allowing an additional week’s rest, and then placing the sand in the freestall barn. The producer believes this step would further enhance the sand’s bedding qualities, but as yet, has not implemented the procedure.

In the two-year period, the producer purchased two different grades of sand. “Classified” sand contained a significant fraction of finer particles and clay. “Concrete” sand was a graded material with coarser particles and few fines. Table 4 outlines some characteristics of coarse and fine sand as related to its use as freestall bedding.

Table 4. Characteristics of coarse and fine sand.

Fine sand

Flushes easier

Cheaper, $4.25/ton

Cows dirtier

Settles less readily

More bacteria

Coarse sand

Flushes harder

More expensive, $5.25/ton

Cows cleaner

Settles more readily

Less bacteria

With a recovery rate of about 75%, this producer purchases about 1,200 tons(1090Mg) of sand per year. With this recovery rate, the difference in annual cost of coarse vs. fine sand is not enough, in the producer’s judgment, to use the finer sand. Although the coarse sand is more expensive the producer feels the advantages outweigh the increased cost.

Sand, which is not recovered for bedding, is either taken out with manure, or carried through to the lagoon via the effluent drain. No attempt was made to evaluate these pathways. Attention should be given to the possibility of sand accumulation and buildup in the lagoon so that needed treatment and storage volume is not displaced.

Conclusions

Several conclusions can be drawn from this study.

REFERENCES

Burcham, T., S. Gill, and R. Moore. 1997. Comparison of dairy manure separation technologies. ASAE Paper No. 974050. St. Joseph, Mich.: ASAE.

Echelmier, T. 2002. Personal communication. Fulton, MO.

Fulhage, C., and D. Pfost. 1993. Pipeline/valve systems for flushing dairies. Extension bulletin WQ317. University of Missouri, Columbia, MO.

Harner, J., P. Murphy, and J. Smith. 1998. Tower tank valve (ttv) systems for dairy facilities. ASAE Paper No. MC98-105. St. Joseph, Mich.: ASAE.

Stowell, R., and W. Bickert. 1995. Storing and handling sand-laden dairy manure. Extension bulletin E-2561. Michigan State University, East Lansing, MI.