It is crucial to explore new methods to deal with ammonia pollution in hog barns. In this experiment, ammonia gas generated from the decomposition of nitrogenous organic matter, such as feed and manure in hog barns, was studied. Growing environmental parameters monitored included temperature, humidity, and ammonia nitrogen concentration. For 92 days between March and May, ammonia emissions were characterized by monitoring and collecting the ammonia concentration during the selected time. The results showed that the average temperature in the hog house was 18.2 ± 2.7°C, the humidity was 62.7 ± 0.3%, and the average ammonia concentration range was 17.7∼23.1 mg m−3. The collected ammonia-nitrogen-containing wastewater that entered the denitrification device showed 173, 232, 201, and 280 mgNH4-N/L, respectively. An integrated denitrification device with anaerobic ammonia-oxidizing bacteria as a functional strain was used for denitrification treatment. Through the change of ion concentration in the incoming and outgoing water, an 85.5% average denitrification efficiency was calculated according to the denitrification reaction chemical formula. Thus, the results presented here provide data support for the future use of microbial denitrification equipment to treat ammonia in hog houses.
The breeding environment of hogs is directly related to herd health. A good livestock house environment ensures livestock and poultry health, fully utilizes its production performance, and complies with animal welfare requirements. However, due to the rapid development of the large-scale breeding industry, the increasing density of hog farms and the harsh breeding environment have become fundamental problems restricting the development of the large-scale swine industry. The livestock productivity depends 20% on genetics, 40%∼50% on nutrition, and 30%∼40% on environmental conditions [
There are three aspects in controlling and treating ammonia pollution in animal husbandry: source prevention and control, emission reduction in the breeding process, and end treatment. More well-established research on controlling nitrogen emissions at the feed source can be adjusted through the entire diet stage, and standards have been established. Various feed additives that meet the production needs have been developed, yet the research continues on cost-effective and nonresistant additives. Emission reduction in the feeding process is closely related to feeding management, and it is difficult to unify standards and requirements for all farms. The end treatment of ammonia has excellent potential in the environmental protection of aquaculture, and the emission reduction effect is also rather satisfactory, which is the general trend of ammonia emission reduction in the future. The main technical challenge of ammonia end treatment is maintaining the emission reduction effect at a higher load rate, increasing the biofilter medium’s service life, and increasing the abundance and number of microorganisms in the biofilter medium.
The Labfors fermenter in this experiment is an integrated denitrification device, which occupies a small area and contains a probe that can be flexibly configured according to the required measurement data. The open-air path makes it suitable for microbial cultivation, high-density cultivation, and anaerobic culture. It has also been used in nitrogen and phosphorus removal research and tailgas collection and analysis, but no research has been performed on the ammonia removal in swine houses. This study selected the temperature, humidity, and ammonia concentration of the pig growing environment as the main environmental parameters for monitoring. Ammonia concentration monitoring was conducted for 100 days, ammonia emission characteristics were analyzed, and the main environmental factors affecting ammonia emissions were comprehensively evaluated. Based on the performance of the integrated denitrification unit to effectively remove ammonia nitrogen wastewater, the ammonia gas collected in the hog house was passed to the integrated denitrification unit. The reactor parameters and
An experimental hog house in Changchun City was selected as the test site. The hog house was a double-slope windowed structure 40 m in length, 12 m in width, and 3 m in height. The columns were arranged in two rows and a single walkway in the middle of the hog house. The test hog house was equipped with a storage room, a feeding area, and a tower. Figure
Schematic layout of the fattening swine barn.
The fattening hog house used mechanical ventilation with an automatic temperature sensor controlling the fan operation. Temperature and humidity data collectors (RS-YS-GPRS-B) placed at both ends and along the middle aisle of the longitudinal axis of the hog house automatically collected the temperature and relative air humidity at 10 min intervals.
A Labfors bench fermentation tank composed of a tank body and a host served as the experimental reaction device (Figure
Schematic diagram of the integrated denitrification device.
Determination of ammonia nitrogen was performed according to the “Ambient Air and Exhaust Gas-Determination of Ammonia-Nessler’s Reagent Spectrophotometry” Standard (HJ 533-2009). Briefly, 10 mL of 0.01 mol·L−1 sulfuric acid absorption solution was prepared in the lab and added into the absorption tube. The mouth of the tube was sealed and sent to the experimental pig farm. The air in the hog house was collected at a flow rate of 100 L h−1 for 1 h. After sampling, the nozzle was sealed and returned to the laboratory. The sample analysis was completed on the same day. Simultaneously, blank parallel samples were tested throughout the process.
Combining the sampling time point and the fan running time, in this experiment, the hog house management activity time (7:00-17:00) was divided into 5 sampling periods (7:00-9:00, 9:00-11:00, 11:00-13:00, 13:00-15:00, and 15:00-17:00). The total amount of ventilation per period was multiplied by the corresponding ammonia concentration averages at 8:30, 10:30, 12:30, 14:30, and 16:30. The sum of the ammonia concentration averages represents the ammonia emissions during the day. On this basis, the ammonia emission at night was calculated by the night ventilation and ammonia concentration at 8:30, and the ammonia emission factor in the hog house was further calculated (
During the 92 days of the experiment, ammonia gas was collected every half a month a total of 4 times, and each sampling lasted for 7 days. Ammonia has a high solubility in water; thus, it was collected with a stock solution lacking only
An ion-selective electrode (Labfors 3.6 L) measured the NH4-N and NO3-N concentrations in the incoming and outgoing water. The data were recorded online, and the specific data in operation in the IRIS online data acquisition system were selected. The NH4-N and NO3-N concentrations were also measured offline three times a week on average, and the online measured values were compared and calibrated. Throughout the experiment, the NO2-N concentration was only measured offline with a colorimetric detection kit (BesetBio-470571). The chemical reaction would change the color intensity based on the concentration, and an ultraviolet spectrophotometer (722G-Jingke Shangfen) measured the concentration value. The denitrification efficiency was calculated using the measured changes in the inflow and outflow water concentration according to the stoichiometry equation (
The livestock house environmental conditions mainly refer to the environmental temperature, relative humidity, light intensity, airflow speed, and air quality. Environmental temperature is an important factor affecting the normal production and life of pigs. Pigs are thermostatic animals that maintain body temperature within a specific range through heat production and heat dissipation [
Daily change of temperature and humidity in the hog house.
Season | Parameters | 7:00 | 9:00 | 11:00 | 13:00 | 15:00 | 17:00 | 22:00 | Standard error |
---|---|---|---|---|---|---|---|---|---|
Spring | Temperature (°C) | 17.8A | 18.2A | 18.6A | 19.3A | 19.1A | 18.5B | 18.0 | 0.33 |
Humidity (%) | 63.5B | 63.4A | 62.4A | 61.7A | 62.5B | 63.1A | 63.2 | 0.25 |
The humidity in the hog house changes regularly every day, and the range of humidity changes is within the comfort range of pigs, consistent with previous studies [
Figure
Daily temperature and humidity in the hog house during the experiment.
Measurement statistics show that, in most small- and medium-sized pig farms in China, especially in closed barns, ammonia concentrations range from as low as 6–35 mg-m−3 to as high as 150–500 mg-m−3, far exceeding the permissible concentration of ammonia in pig farms in China (25 mg-m−3) [
Monthly changes in ammonia concentration.
The average daily ammonia concentration in the hog house is 17.7–23.1 mg m−3, which does not exceed the GB/T 17824.3-2008 (25 mg m−3). As shown in Figure
Studies showed that ammonia volatilization in feces and urine increases with temperature. When the environmental temperature increased from 4 to 20°C, ammonia volatilization increased by 3.6∼5.8-fold [
As shown in Figure
The emission rate of ammonia in different months.
In this test, ammonia was collected from the house for seven consecutive days after obtaining the ammonia concentration and emission rate to ensure the influent concentration of the integrated unit in the future. The functional microorganism in the integrated denitrification device was anaerobic ammonia-oxidizing bacteria. The device maintained a pH of 7.5 ± 0.5 and a temperature of 28 ± 2°C. For intermittent aeration, a mechanical agitator in the fermentation tank was used for the disturbance at a speed of 70 rpm with an airflow of 0.7–1.2 L/min during the aeration stage. The solution in the gas collection device gas passed into the device for denitrification treatment. The influent concentrations of the four samples were 173, 232, 201, and 280 mg NH4-N/L, respectively. Online monitoring and offline experiments were used, and a sampling test was performed every 15 min. During the operation, the various parameter indicators of the integrated device were controlled based on the denitrification reaction equation (
As shown in Figure
In this experiment, the temperature, humidity, ammonia concentration, and emission rate in the hog house were monitored to study the monthly changes in the environmental indicators. The results showed that the average temperature and humidity in the test house were18.2 ± 2.7°C and 62.7 ± 0.3%, respectively. The possible reason for the positive correlation between ammonia concentration and humidity is that ammonia is readily soluble in water, and with high humidity, the air retained much ammonia; hence, ammonia concentration was relatively high. The hog house ammonia concentration during the daytime management activities was 17.7–23.1 mg m−3, which did not exceed the GB/T 17824.3–2008 (25 mg m−3) limit, and the ammonia emission rate was 1.92∼2.72 g h−1 m−2. Ammonia in the house was collected and passed to the integrated denitrification device with influent concentrations of 173, 232, 201, and 280 mgNH4-N/L, respectively. After running for 375–495 min, the final average denitrification efficiency reached 85.5%. The ammonia removal from swine barns with an integrated denitrification unit showed positive lab test results, providing data to support ammonia microbial denitrification devices for ammonia removal in swine barns. Future research directions should aim at the collection and processing of ammonia in swine houses. Jilin Province is an agricultural province, and it can promote the removal of ammonia in other livestock breeding houses within this province, which is conducive to the growth, development, and reproduction of livestock and poultry and improve the breeding efficiency.
The experimental data used to support the findings of this study are included within the article.
The authors declare no conflicts of interest.
C.L. and N.L conceptualized the study and prepared the original draft of the manuscript; C.L. and M.L. formulated the methodology; M.L. and S.Z. varied out validation; C.L. M.L., and S.Z. conducted investigation; Y.L. and M.L. curated data; S.Z. reviewed and edited the manuscript; N.L. performed visualization; M.L. supervised the work; Z.L. was involved in project administration;and C.L. acquired funding. All authors have read and agreed to the published version of the manuscript.
This research was funded by the Open Project Program of Key Laboratory of Groundwater Resources and Environment (Jilin University, Ministry of Education).