B. Kaspers, J. Koger, and T. van Kempen

Introduction

Environmental concerns with concentrated, intensively managed swine facilities have necessitated the re-evaluation of management practices for waste disposal. With the trend towards more intensive swine production, focus has been placed on manure storage and utilization. Current waste management practices in the swine industry are a slatted floor with either liquid storage under the slats (slurry system) or a flush system with lagoon storage (Keener et al., 1999). These waste systems yield a waste that usually ranges between 1-10 % dry matter, which limits the flexibility of its application primarily due to transportation costs. Solid–liquid separation techniques like tangential flow separation, settling basins, and screen separators have all been used for the improvement of manure handling because the reduction of solids in the liquid bulk facilitates pumping and handling. However, since all these technologies separate waste after it has been mixed and stored, they do nothing to mitigate odor and ammonia emissions within the hog house or at the storage facility. They also demonstrate a low efficiency of solids recovery from the swine waste.

Figure 1. Conveyor belt design for a partially slatted hog house

The belt system is an established technology that has been successfully used in the poultry industry for the past 30 years. In our belt design for swine, the belt is placed at an angle under the slatted portion of the pens (Figure 1). Its lower edge feeds into a pipe that collects the urine and transports it to the end of the building, thus allowing the separate collection of urine and feces within the hog house. Due to the rapid separation of the waste streams, bacterial urease, present in feces, has limited opportunity to metabolize urinary urea to ammonia and CO₂. This allows for a drier waste while significantly reducing odor and ammonia emissions by reportedly 90% from other belt research with swine in The Netherlands (Wim Brunnekreef, Nutreco) and 91% from poultry buildings fitted with belts (Keener et al., 2001). The harvesting of such a dry waste allows for easier and cheaper transport of the material, ultimately permitting greater flexibility in its application. This waste can be easily composted, gasified for energy production, or transported to areas where it may be land applied.

An experiment with the large-scale belt housing unit was performed 1) to evaluate the belt design; 2) to determine the pig’s growth potential using the chosen partially slatted housing design; 3) to determine the best residence time of feces on the belt to maximize drying; 4) to examine the drying efficiency of a transfer belt as a post-collection drying strategy; and 5) to quantify ammonia and methane emissions from the belt housing system.

Materials and Methods

100 pigs with an entering average body weight of 23.1 kg were housed 20 pigs per pen at 5.6 sq. ft./ pig for seven weeks. The pigs were allowed to habituate to the pens for the initial week. Body weights, feed intake, and manure production were measured weekly. There were three series of randomized collection periods off the belt over the course of the experiment. During the each series, feces was harvested off the belt after 3, 6, 9, 12, 24, 36, and 48 h residence time on the belt. The dry matter (DM) contents of the manure at 60 and 72 hour were both 29% which is lower than the dry matter content of fresh swine feces (30%) and were indicative that these time intervals were too long, preventing adequate urine flow off the belt at these times. Feces collected off the belt were then put on a transfer belt which were sampled after 6, 12, 24, 36, and 48 h. DM of feces collected off the belt and transfer belt were measured. Ammonia and methane emissions from the housing facility were analyzed at collection times off the belt using a Fourier Transform Infrared Spectroscopy (FTIR). The housing facility’s air flow was held constant at 4855 m³/h. DM and gas emission data were analyzed using SPSS (Version 10).

Results and Discussion

The data shows that residence time of feces on the belt did not significantly influence the dry matter of feces collected off the belt (Figure 2). Numerically, the optimal residence time was 15 hours on the belt. However, the time of day on which the collections were performed did have a significant effect on fecal dry matter content (P<.05) (Figure 3). The data suggest that early morning collections are favored since possibly little urine contamination on the belt occurs overnight since the pigs are sleeping.

Figure 2. Effect of fecal residence time on the belt on fecal dry matter using a fitted quadratic model

Figure 3. The sigmoidal effect of collection time of day on dry matter content of feces on the belt

Data off the transfer belt show that it is an effective means of post-collection drying. The dry matter contents were significantly higher as the residence time on the transfer belt was extended (P<.01) (Figure 4). The transfer belt effectively dried the feces .11% per hour. From these results, the transfer belt’s drying efficiency would not make this a practical drying mechanism of the feces on the swine farm.

Figure 4. Effect of post-collection drying of feces on a transfer belt

The gas emission data suggested that methane emission was constant within the room regardless of the quantity of manure on the belt which coincides with a previous trial that showed that methane production comes from the pigs alone and not from the manure pit. However, ammonia emission was significantly correlated with residence time of feces on the belt (r²=.73) (Figure 5). The belt housing system showed up to a 65% reduction in ammonia emission coming from the hog house in comparison with literature values of 2.5 kg ammonia/pig/year (Arogo et al., 2001; Aarnink, 1995).

Figure 5. Ammonia emission versus retention time of feces on the belt

The current belt design proved successful in separating the two waste streams produced. There were however a few structural kinks that are being worked out prior to future experiments with the belt. But, the future looks promising for use of a belt system for swine to eliminate ammonia and odor emissions and to effectively dry the feces within the hog house.

References

Aarnink, A., A. Keen, J. Metz, L. Speelman, and M. Verstegen. 1995. Ammonia emission

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Arogo, J., P. Westerman, A. Heber, W. Robarge, and J. Classen. 2001. Ammonia in animal

production- A review. ASAE Paper No. 01-4089. St. Joseph, MI:ASAE.

Keener, H.M., D.L. Elwell, and D. Grande. ‘Atmospheric NH₃ Emissions and N-Balances for a

1.6 Million Caged Layer Facility- Manure Belt/Composting System vs. Deep Pit Operation”. Paper presented at the 2001 International Waste Symposium Conference. Raleigh, NC.

Keener, H.M., D.L. Elwell, T. Menke, and R. Stowell. ‘Design and Management of a High-Rise

Hog Facility Manure Drying Bed’ Presented July 1999 at 1999 ASAE/CSAE-SCGR Annual International Meeting, Paper No. 994108. ASAE, 2950 Nile Rd., St. Joseph, MI 49085-9659 USA.