PROJECT RESULTS

Separation of Wash/Spillage Water from Defecated Manure

Applicant: 

Doug Small
DGH Engineering Ltd.
St. Andrews, Manitoba  R1A 3N5  Canada

Table of Contents:

• Background and Objectives
• Procedure and Project Activities
• Results and Discussion
• Conclusions

ARDI Project:

#99-340

Project Status:

Completed March, 2002

Background and Objectives:

Odour is a concern to neighbors of hog barns. Hog barn odours emanate from the surfaces of floors, walls and pens; as well as from manure collection, storage and spreading; feed storage; dead storage and disposal; and from the hogs themselves.

Ammonia (NH₃) and hydrogen sulfide (H₂S) are two major odorous gases emitted from animal operations (Xue and Chen, 1999). These gases are generated while manure undergoes microbial degradation. Ammonia is produced by the decomposition of nitrogen-containing compounds in the excreta, especially in urine. Hydrogen sulfide is typically the result of the anaerobic decomposition of sulfur-containing amino acids in a dung/urine mixture (Overcash et al., 1983).

To reduce odour, intensive research has been undertaken on the emissions from manure storage and application. The result has been new technologies such as synthetic manure storage covers and methods of injecting manure directly into the soil, which can reduce the odour level dramatically during manure storage and application. Technologies to reduce barn odour, however, have not been readily available.

A concept to modify manure collection pits has been developed in the Netherlands. The idea is to confine the majority of the feces and urine in a customized gutter that minimizes the surface of this "strongest" portion of the total wastes. This approach can be implemented to maximum effect in a farrowing room where all the feces and urine from the sow can be collected beneath as little as 15 to 20 percent of the pen area. Similar but less dramatic reductions in the surface area of the "highest strength" wastes could be achieved in other areas of modern swine facilities. Some gutter manufactures in the Netherlands claim that their products can reduce ammonia emission up to 65 percent (IC-W, 2001).

The potential for separation to control odour is based on the principal that manure odour release is a mass transfer process occurring at the liquid-air interface. When passing over the free surface of a liquid, air tends to sweep away any gases and vapors emitted from the liquid phase. Miner (1973) and Card (1998) believed that mass transfer coefficients could be used to characterize the transfer rate of a gas through an interfacial boundary layer. The emission rate of a compound from an aqueous phase into gas phase is defined by:

R_v = K_t (C_l - C_g/H_c) A                          (1-1)

Where R_v = mass transfer rate
K_t = overall mass transfer rate
C_l = liquid-phase concentration
C_g = gas-phase concentration
H_c = henry’s law coefficient
A = surface area

The emission rate is a function the surface area of the gas/liquid interface and the concentration of the compound in the liquid and gas phases. Reducing the surface area potentially slows down the emission rate and eventually reduces the total amount of the compound emission during a certain period of time. Since manure slurry is not an ideal solution, the real emission model of this odorous material would be much more complex than expressed in the Eq. 1-1.

The objective of this study was to determine the effect that the separation of spillage water from defecated manure has on the reduction of odour, ammonia and hydrogen sulfide emissions from swine barns. The nitrogen conservation effect resulting from ammonia emissions was to be evaluated. As well the extent to which the reuse of spilled water could reduce water consumption was to be estimated.

Procedure and Project Activities:

Site Description

The study took place on Clearwater Colony Farm located in the Rural Municipality of Rockwood, Manitoba. The farm provided two farrow rooms for this study. One of the rooms was used as a test room to demonstrate the effect of waste separation, while the other was used as a control room.

The test room had an area of 887 square feet, with a holding capacity of 10 sows. A concrete divider was constructed in the manure pit to divide the pit into two channels: a spillage water (water) channel and a defecated manure (manure) channel. The surface areas of the water and manure channels were 280 and 140 square feet respectively. The test room was equipped with a 24 inch exhaust fan.

The area of the control room was 2045 square feet with a holding capacity of 28 sows. There were two identical pits (east pit and west pit) in the control room. The surface area of a single pit was 630 square feet. The room was equipped with two 24 inch exhaust fans (west and east). The west fan was in operation for the full duration of the study (April to October), while the east fan ran periodically from June to September according to the variation of the ventilation demand.

A farrow cycle in farrow room starts with filling the entire room with predeliver sows. The sows stay and deliver in the room. The sows and their offspring are held in the room for an average of 20 days after farrowing. The rooms are emptied all on the same day at the end of the farrow cycle. The room is then soaked, pressure washed, disinfected and allowed to dry before refilling with the next batch of sows.

At the beginning of a farrow cycle, the discharge hole of the manure pit was plugged. The pit is filled with two to four inches of water. During the farrow cycle, manure and urine and spillage water are stored in the pit. The manure pit was emptied and washed after the room is emptied. There was no drainage before the room was emptied. The liquid samples were collected immediately after the rooms were emptied and before the pressure washing.

Sampling and Laboratory Testing

Liquid Testing
A period of two months was allowed to acclimatize the newly installed divided pit system. Liquid samples were then collected from the pits in the control room, and the water and manure channels in the test room. These samples were collected following the end of four successive farrow-lactation cycles in each room. The initial sample set was submitted to Enviro-Test Laboratories in Winnipeg, Manitoba to evaluate total solids (TS), total Kjeldahl nitrogen (TKN), ammonia, electrical conductivity (EC), sodium, potassium, sulfur and pH. The subsequent three sample sets were only tested for TKN and ammonia.

The measurement of TKN provided the basis from which to determine the effect that pit separation had on nitrogen conservation. The TKN concentration multiplied by the volume of liquid in the pit yields the total nitrogen in the room during one farrow-lactation cycle. This value was to be used to estimate nitrogen accumulation per sow per day.

Air Sampling for Odour Testing
Originally, odour sampling was scheduled to occur on the same day that liquid sampling was conducted. In practice, however, it was found that this schedule was not practical, as weather conditions and laboratory scheduling were problematic. On days with strong winds, which can greatly influence sample quality, sampling had to be postponed. As well, the odour samples had to be analyzed within 24 hours of collection. In some cases, laboratory analysis could not be scheduled for the sampling day. As a result, odour sampling was conducted on a different day than liquid sampling.

The air samples for odour testing were collected both inside and outside of the barn rooms. The samples from inside the rooms were collected around the pits approximately four inches below the slatted floor. The exterior samples were collected at the exhaust fan’s outlet. The air flow rates were measured while air sampling took place.

The samples were collected with Tedlar bags and an AC’SCENT Vacuum Chamber. An air sampling was completed in two steps: filling the bag for conditioning and collecting a sample for testing. In the first step, a Tedlar bag was placed in AC’SCENT Vacuum Chamber. The bag was filled with air sample ¼ to ½ full and then was evacuated. This first step is also known as coating the bag. The actual sample collection was completed in the second step. In this step, the bag was filled ¾ full. The air samples were sent to the University of Manitoba where they were tested within 24 hours of their collection. In the laboratory, samples were analyzed for odour with a dynamic olfactometer. In order to observe hydrogen sulfide concentration change in the storage period (from sampling to testing), hydrogen sulfide concentration was also tested in the lab at the beginning of this study.

Hydrogen Sulfide Field Measurement
Hydrogen sulfide (H₂S) concentration was also measured in the field using a Jerome 631-X Hydrogen Sulfide Analyzer that provided a range of measurement spanning from 0.003 parts per million (ppm) to 50 ppm. The hydrogen sulfide concentration, in ppm, was displayed on a digital meter following the measurement cycle.

The hydrogen sulfide concentrations were measured at the outlet of the exhaust fans in conjunction with the measurement of air flow rate through the fans.

Ammonia Field Measurement
Ammonia (NH₃) concentration was measured with a Dräger Gas Detector providing a standard range of measurement varying from 5 ppm to 70 ppm. Dräger 5/a ammonia tubes were used. The standard number of stokes of the Dräger gas detector pump is 10. In this study, however, the number of stokes were adjusted according to the ammonia concentration to minimize the relative error caused by diffusion of the discoloration scale.

The ammonia measurement was always conducted at the same time and location as the hydrogen sulfide measurement.

Ventilation Rate Measurement
To evaluate the odour, hydrogen sulfide and ammonia emission rates, the ventilation rates were measured while sampling was conducted. The instrument employed for ventilation measurement was an ALNOR^® Electronic Balometer, with an APM 150 Meter, capable of measurements from 50 to 2000 CFM (24 to 940 L/s). The meter is able to show the instantaneous flow rate on the digital screen, store several readings during the sampling period, and give the average flow rate for the period.

Odour, Ammonia and Hydrogen Sulfide Emission Rate Calculation
The unit emission rate of the tested criteria was calculated as:

The effect of manure channel separation on emission reduction can be observed by comparing the unit emission rates between the test room and the control room.

Environmental Controls
The operating environments in the control and test rooms were monitored by members of Clearwater Colony Farm in an effort to maintain as much similarity between the two rooms as possible. The items monitored included temperature, humidity, water consumption, feed consumption as well as fill and empty dates.

Results and Discussion

Results of Liquid Sample Analysis

The concrete divider that provided the separation of wash/spillage water from defecated manure, had a substantial effect on the total solids (TS), total sulfur (S), total potassium (K), total sodium (Na), electrical conductivity (EC), pH level, ammonia and total Kjeldahl nitrogen (TKN) concentrations. The test results are listed in Table 1. The separated manure was approximately 2.6 to 15.9 times more concentrated than the separated wash/spillage water. Among them, the ratios in ionized matters, such as EC (closely related to total dissolved solids), Na, and K, 2.6, 3.0 and 5.2 respectively, were smaller than in the other matters which from 8.0 to 15.9. The reason causing this is not clear, however, the sodium chloride in the feed spilled in water channel definitely contribute to the increase of Na concentration and affect the Na ratio of manure channel to water channel.

The separated manure was approximately 1.6 to 2.1 times more concentrated than the control sample for all criteria except sodium.

Table 1 indicates that a certain amount of the impurities in the water channel can be attributed to the feces and urine production from the piglets, as well as spilled feed.

Sodium and potassium concentrations proved to be affected less by the separation technique, than were other the test criteria.

Odour, Hydrogen Sulfide and Ammonia in the Barn Rooms

The odour samples obtained inside the barn were collected at three points along each of the water channel and manure channel in the test room and six points around the manure pits in the control room, approximately four inches below the slatted floor. Hydrogen sulfide concentration and ammonia concentration were each measured 12 times.

A significant difference in odour levels above the manure pits was observed between the control room and the test room. The mean odour levels were 2705 odour units (OU) with a standard deviation (SD) of 574 in the control room and 1627 OU with a SD of 461 in the test room. The mean odour concentration measured above the test pit was 40% less than that above the control pit.

No significant difference in odour levels was detected between the samples collected above the water and manure channels. The mean odour levels were 1603 with a SD of 663 in the water channel and 1650 with a SD of 298 OU in the manure channel (Table 2). This was not expected as it was predicted that the odour concentration above the water would be less than that above the concentrated manure. A possible explanation for this phenomenon is that the concrete pit divider has little to no effect on the containment of odour. Thus, odorous molecules are free to flow over the divider from the more concentrated manure to the less concentrated water channel and elevate the odour concentration. At the same time, the air molecules flow from the water channel to the manure channel and dilute the odour concentration above the manure. Odour concentration and airflow caused by ventilation are the two driving forces behind this odour equalization. As a result, the difference in odour concentrations between the water and manure channels was very limited.

Theoretically, when the odour molecule equilibrium point is reached, the odour concentration on the manure side should be somewhat higher than that on the water side, because odour is continuously released from the manure. However, this difference in odour concentration was not significant enough to be identified by human olfactometer panelists.

Twelve hydrogen sulfide measurements were conducted in each room, with six from each of the water and manure channels in the test room, and six from each pit in the control room. The results of hydrogen sulfide measurement show that the average H₂S concentration in the control room was 2.3 times higher than that in the test room (Table 3).

Table 3. H₂S concentration in the air above the pits.

Table 3 also shows that hydrogen sulfide concentrations were lower directly above the water channel than directly above the manure channel. This difference was more readily identified than the odour tests because of the JEROME meter is more sensitive than human odour panelists. In addition, H₂S is dense molecule and likely diffuses more slowly than other constituents of odour increasing the gradient immediately above the emitting surface.

The ammonia concentrations in the test and control room were compared as shown in Table 4.

The comparison of the criteria in the rooms only partially reflects the effectiveness of the water and manure separation. Since the test room and the control room used in this study have different sizes and different holding capacities, it is necessary to investigate the emission rates of odour, hydrogen sulfide and ammonia from the rooms.

Odour, Hydrogen Sulfide and Ammonia Emission Rates

The average emission rates from the test and control rooms were 59.0 with a SD of 35.3 and 73.1 with a SD of 36.9 OU*m³ per sow per second, respectively. The average odour emission rate from the test room was approximate 19 percent lower than the control room.

The overall hydrogen sulfide emission rate from the test room was 0.92 with a SD of 0.04 litres per sow per day, approximately 28 percent lower than the control room with a value of 1.27 with a SD of 0.17 litres per sow per day.

Comparing 14 samples collected from the test room exhaust fan and 22 samples collected from the control room exhaust fans, the ammonia emission rate from the test room was approximately 25 percent lower than the control room. This ammonia reduction is lower than the 50 to 65 percent reduction obtained in the Netherlands. In the systems used in the Netherlands, the defecated manure surface for one sow is reported as low as 0.8 m² (8.6 ft²) and the water channel comprises 80 percent of the pit surface. In this study, the geometry of the installation was limited by the need to retrofit the system to an existing barn. The water channel occupied 67 percent of the pit area and each sow had 1.3 m² (14 ft²) manure channel.

The ammonia average emission rates were observed as 19.8 L/sow/day with a SD of 2.20 from the test room and 26.3 L/sow/day with a SD of 2.95 from the control room in terms of litre per sow per day. The equivalent emission rates were 5.5 and 7.3 kg ammonia (4.5 and 5.9 kg nitrogen) per sow per year from the test or the control room, respectively.

The reduction in hydrogen sulfide emission rate is very close to the reduction in ammonia emission. The reduction in odour emission rate is lower than the reduction in either H₂S and NH₃. Hydrogen sulfide and ammonia can only come from manure, but odour may result from other sources besides manure.

Nitrogen Conservation

Nitrogen levels were determined in both liquid and air samples in an effort to demonstrate the effect separation had on nitrogen conservation. This analysis, however, was clouded by some questionable laboratory test results with respect to TKN and ammonia. The laboratory reports indicated that two of the four manure samples had ammonia concentrations in excess of the TKN concentration. This data is assumed to be incorrect as ammonia is a component of TKN, and therefore cannot exceed the TKN levels. Based on previous studies, the percentage of ammonia to TKN in manure pits should be approximately 60 to 70 percent (DGH, 2001). The Farm Practice Guidelines (Manitoba Agriculture, 1998) also reported that the typical ratio is 67 percent, and range of ratios is from 40 to 78 percent. The ammonia to TKN ratio indicates the degree of mineralization of organic nitrogen in the manure. The average retention time of the manure in the collection pits was approximately 10 to 15 days. The organic nitrogen could not be thoroughly mineralized during this period.

Based on the difficulties mentioned above in the nitrogen analysis of the liquid samples, the nitrogen conservation was estimated from the difference in ammonia emission rate between the control and the test room.

Cost/Benefit Estimation

Besides the environmental benefit of odour emission reduction, some economic benefit is also provided by utilizing the separation technique. The associated nitrogen conservation provided by the reduction in ammonia emission adds to the fertilizer value of the manure. As well the manure volume can be reduced by using the spillage water for flushing other barn rooms. These savings have been estimated below:

Nitrogen in the manure is conserved lowering ammonia emission. The difference in annual ammonia emission between the control room (7.3 kg/sow/year) and the test room (5.5 kg/sow/year) is 1.8 kg ammonia (1.5 kg nitrogen)/sow/year. To purchase the same amount of fertilizer would cost $1.15 ($0.77/kg N).

The spillage water is calculated as 6 m³/sow/year. Assuming that 4 m³/sow/year of fresh water can be saved if the spillage is employed for other barn flushing, the total manure volume will be reduced by 4 m³/sow/year. The saving in manure application and transportation will be approximately $11.71/sow/year. The manure transportation cost has been estimated on the basis of a tanker hauling two miles: the unit cost was based on the first mile $1.21/m³ ($0.0055/gallon), second mile $0.22/m³ ($0.001/gallon) (Royal service, 2000). The cost of manure application has been estimated on $1.496/m³ ($0.0068/gallon) (Manitoba Agriculture, 1998).

Currently, no gutter manufacture exists in Manitoba. The costs of importing a gutter from the Netherlands will be expensive (US$250/sow). However, if the separation technology was adopted in Manitoba, local manufacturers would fabricate these gutters and the cost could be reduced.

Conclusions:

Odour levels detected in the two farrow rooms monitored in this study were much higher compared to the odour emission levels reported by Zhang et al. (2000).

The concrete divider provided substantial separation in TKN, NH₃, TS, S and P in the test room. The values of these parameters were approximately 8 to 15 times higher in the manure channel than in the water channel. The concentrations of Na and K in the manure channel were 2 and 5 times than in the water channel.

The ammonia emission rate from the test room was approximately 25 percent lower than that from the control room. The mean emission rates were 19.8 and 26.3 L/sow/day from the test room and from the control room, respectively.

The hydrogen sulfide emission rate from the test room was 28 percent lower than the control room. The mean emission rates were 0.92 and 1.27 L/sow/ from the test room and from the control room, respectively.

The odour emission rate from the test room was approximately 19 percent lower than that from the control room. The mean emission rates were 59.0 and 73.1 OU m³/sow/s from the test room and from the control room, respectively.

The nitrogen conservation obtained was 1.5 kg N/sow/year.

Approximately six cubic metres of spillage water can be collected in one sow place per year. A potential benefit of separation is to reuse this spillage water as flush water in other rooms in the barn, which will result in a reduction in water consumption and slurry production.

Application of Findings

Practical application of the results can be made to building design in several areas, as outlined below.

Segregation of the manure gutter from water spillage areas can be implemented in farrowing barns immediately, as was undertaken in this study. A practice that is followed in the design of many dry sow facilities to gain some small economies in construction is the combining of walkway and manure gutter areas. This practice should be curtailed, since the results of this study clearly confirm that increasing the surface area of the high-strength wastes increases NH₃ and odour emissions.

A large proportion of finisher facilities have been designed using totally slotted floors. Although pens are totally slotted, pigs still choose areas for dunging and do not use all areas uniformly. However, it has become common practice to open cross-over channels between the various manure gutters to allow equalization of manure accumulation. Although this seems to simplify manure handling, the results of this study would suggest that this practice is most likely to increase odour emissions significantly. Alternate manure gutter strategies need to be explored.

Similarly, with weaned pig housing systems where total slats have been utilized exclusively for several years, little regard has been given to the development of specific dunging areas. Also, a common design of manure gutters for these types of facilities has paid no regard to the potential to separate high strength wastes from other areas. It may be possible to develop pen and manure pit systems that recognize the separation between sleeping and dunging areas. Most certainly and immediately, subdividing pits into sections that can capture high strength wastes from the most common dunging areas separately will reduce NH₃ and odour emissions.

Acknowledgements:

DGH Engineering Ltd. would like to express its gratitude to Manitoba Livestock Manure Management Initiative Inc. (MLMMI) as well as the Agri-Food Research & Development Initiative (ARDI) for the financial support and co-operation provided during the course of this study. Additionally, DGH Engineering Ltd. would like to thank Clearwater Colony Farm for allowing use of and access to their hog barn and ongoing co-operation and assistance throughout the study. The advice and co-operation of Dr. Q. Zhang, University of Manitoba is also gratefully acknowledged.

References:

Card, Thomas R., 1998. Fundamentals: Chemistry and Characteristics of Odors and VOCs, Chapter 2 in Odor and VOC Control Handbook, McGraw-Hill, 1998.

DGH, 2001. DGH Engineering Ltd., The Effect of Earthen Manure Storage Covers on Nutrient Conservation and Stabilisation of Manure, Final report submitted to MLMMI.

IC-W, 2001, IC-W Mestpan, www.intercontinental.nl.

MB, 1998. Manitoba Agriculture, The Agricultural Guidelines Development Committee, Farm Practices Guidelines for Hog Producers in Manitoba.

Miner, J. R. 1973. Odour from Livestock Production. 1973. Corvallis, Ore.: Agricultural Engineering Dept., Oregon State University.

Overcash, M. R., F. J. Humenik, and J. R. Miner. 1983. Livestock Waste Management, Vol. II. Boca Raton, Fla.: CRP Press, Inc.

Xue, S. K., and Chen, S., 1999, Surface Oxidation for Reducing Ammonia and Hydrogen Sulfide Emissions from Dairy Manure Storage, Transactions of ASAE, Vol. 42, No. 5, 1401-1408.

Zhang, Q., G. Plohman, and J. Zhou. 2000. Measurement of Odour Emissions from Hog Operations in Manitoba, Final Report Submitted to MLMMI.

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