Summary

Controlled experiments were conducted to evaluate various types of nanoparticles and deployment techniques for their effectiveness in controlling emissions from swine manure. Nanoparticles were deployed by mixing with the slurry, spraying into the head-space above the manure slurry, and acting as a filtering medium for the manure gases. Among the 12 types of nanoparticles tested, zinc oxide (ZnO) was able to reduce hydrogen sulphide (H₂S) concentration by up to 99 per cent using the mixing and filtration methods in laboratory-scale tests. Up to 86 per cent reduction in ammonia (NH₃) concentration and up to 79 per cent reduction in odour concentrations were achieved by filtration and mixing with ZnO nanoparticles. About 55 per cent reduction in methane was achieved from the mixing method using ZnO, but no other application of the treatments had significant impact on other greenhouse gases (GHG; nitrous oxide and carbon dioxide) and on manure nutrient properties.

Introduction

Nanoparticles are materials with at least one dimension in the 1-100 nanometer scale. At this scale, nanoscale materials exhibit unique quantum properties that may be radically different from the properties of the same material at macro-scale. Recent advances in the ability to manipulate and build at the atomic and molecular levels led to creation of nanomaterials with specific properties desired in a wide range of applications. A variety of nanoparticles had been used for treatment and remediation of environmental pollutants. Their small size, large surface area, unusual crystal shape and lattice order can make specific nanoparticles highly reactive and very flexible in terms of deployment, while remaining non-toxic to humans and environmentally benign. The goal of this study was to examine the application of nanoparticles as an effective, safe, and viable means for reducing odour and gas levels in swine barns.

Experimental Procedures

The overall approach for this work was to conduct a systematic evaluation of the effectiveness of various types of nanoparticles and deployment techniques that can be potentially implemented in swine barns to reduce odour and gas levels. Initial tests were conducted to develop the experimental test protocols and the test parameters that will be applied in subsequent experiments. The deployment techniques tested included: filtration – which involved passing the target gas through a packed-bed filter with the test powder; head-space spraying – which involved spraying the nanoparticles into the head-space above the manure slurry; and mixing – which involved adding the nanoparticles to manure slurry.

For all tests with the various deployment methods, the effect of the treatments on the concentrations of ammonia, hydrogen sulphide (H₂S), odour concentration, and greenhouse gases (GHGs) such as methane, nitrous oxide and carbon dioxide, as well as on manure physical and chemical properties were monitored. Direct reading instruments for ammonia and hydrogen sulphide were used to measure the concentrations of these gases before and after treatment. Gas samples for odour measurement were collected using 10-L Tedlar® bags and sent for olfactometry analysis. Prior to sending the sample bags, a 10-mL gas sample was transferred from each bag to an evacuated gas tube and sent to a gas chromatography laboratory for analysis of GHG concentrations. Manure samples collected from the untreated and treated slurry were sent to a commercial laboratory for analysis of manure characteristics and properties.

Results and Discussion

Filtration method

* “Zinc oxide (ZnO) nanoparticles have the potential to significantly reduce ammonia and hydrogen sulphide levels.”

Figure 1 shows a comparison of the effectiveness of various nanoparticles, a common powder (AC – activated carbon), and a blank filter and pad cassette, in reducing the levels of ammonia and hydrogen sulphide. The plots are expressed in normalized concentrations (derived by dividing the concentration of the gas in the filtered sample by the initial concentration of the gas), indicating that values much lower than 1.0 signify better effectiveness in reducing the gas levels. From these tests, ZnO was significantly (p<0.05) better than the other materials as it was able to reduce hydrogen sulphide to levels below the detection limit (<1 ppm) of the hydrogen sulphide monitor used. For ammonia, ZnO showed the highest reduction (46%) although it was not significantly different (p>0.05) from the other materials. Additional tests showed that increasing the amount of ZnO nanoparticles applied resulted to increased capacity to reduce hydrogen sulphide.

Mixing method

The top four nanoparticles (namely, Fe3O4, MgO, MnO and ZnO) were subjected to verification tests and the results shown in Table 1. Untreated samples showed 15 per cent increase in ammonia and all samples treated with nanoparticles resulted in 16 to 33 per cent increase in ammonia levels one day after treatment application; the effect of the treatment on ammonia was not significant (p=0.64) but it did cause an undesirable increase in ammonia levels. For hydrogen sulphide, treated samples showed 22 to 53 per cent decrease in concentration while untreated samples showed 26 per cent increase; the effect of the treatment on hydrogen sulphide was significant (p=0.02). From this test, the biggest reduction in hydrogen sulphide concentration was achieved using ZnO nanoparticles, which was used in subsequent tests.

Figure 2 shows the actual gas concentrations after mixing ZnO at various application rates. The hydrogen sulphide concentration of the sample treated with 1.5 g/L was significantly different (p<0.05) from the control and the samples treated with 0.1 g/L and 0.25 g/L. At 1.5 g/L application rate, 75 per cent of hydrogen sulphide was removed 1 hour after treatment application, and was further decreased to 95% relative to the initial value 1 day after treatment. Hydrogen sulphide concentration was observed to continuously decrease until the end of the treatment period. The decrease in hydrogen sulphide concentration was probably due to precipitation of hydrogen sulphide when directly in contact with ZnO.

Head-space spraying method

The 12 different types of nanoparticles were tested using the head-space spraying method at an application rate of 0.01 g per liter of head-space volume. Similar to the results from the mixing method, head-space spraying did not result in desirable impact on ammonia levels; either the gas levels were reduced minimally or the levels actually increased 1 day after treatment application. From the results of the tests, tungsten oxide (WO₃) nanoparticles was able to reduce ammonia levels by about 16 per cent one day after treatment. For hydrogen sulphide, all treatments resulted to almost negligible hydrogen sulphide levels one day after treatment application, but this can not be fully attributed to being the effect of the nanoparticles because the control (untreated) samples showed a similar trend. From these observations, it was evident that the treatment did not result in the expected beneficial outcome for these tests.

Effect on odour, greenhouse gases, and manure properties summarised in Table 2 are the average gas concentrations from the different tests for each deployment method as well as the results from the analysis of odour and greenhouse gases. In general, no treatment had significant impact (p>0.05) on nitrous oxide and carbon dioxide concentrations although the methane from slurry treated by mixing ZnO nanoparticles had almost 55 per cent lower concentration (p=0.014) compared with untreated samples.

Manure analysis showed that the treatments had no significant effect on manure physical and chemical properties, except for the mixing method which resulted to a slight increase in pH (by 0.02 pH value) and the Zn content (which was 1.2 kg per cubic metre higher than the untreated samples). These results were expected because ZnO nanoparticles were mixed directly with the slurry samples.

Conclusions

Based on the results of the study, using filtration and mixing methods with zinc oxide (ZnO) nanoparticle were effective in reducing the concentrations of ammonia, hydrogen sulphide and odour in the manure gases generated from swine manure slurry. Methane was reduced by mixing ZnO with the manure slurry, but the other greenhouse gases monitored were not affected.

Direct mixing and spraying of other nanoparticles into the head-space above the manure slurry showed no significant desirable effect on gas and odour concentrations. These methods need further evaluation using possibly higher application rates and other types of nanoparticles.

This exploratory study confirmed that nanoparticles can be effective in controlling gas and odour emissions from swine manure. Further tests are needed to evaluate other types of nanomaterials and other possible deployment methods. The economic, environmental, and health aspects of this application should be assessed to determine its feasibility and overall impact on the swine industry.

Acknowledgement

Strategic program funds were provided by Saskatchewan Pork Development Board, Alberta Pork, Manitoba Pork Council, and Saskatchewan Agriculture. Project funding provided by the Saskatchewan Agriculture Development Fund and the National Science and Engineering Research Council.

March 2010