Project : USDA ARS

ARS Home » Midwest Area » Bowling Green, Kentucky » Food Animal Environmental Systems Research » Research » Research Project #431282

Research Project: Developing Safe, Efficient and Environmentally Sound Management Practices for the Use of Animal Manure

Location: Food Animal Environmental Systems Research

2021 Annual Report

Accomplishments
1. In situ sonification of anaerobic digestion: Extended evaluation of performance in a temperate climate. Increasing the efficiency of wastewater treatment and improving sludge breakdown is vital to reducing the cost of biogas production and reducing environmental costs of sludge disposal. ARS researchers at Bowling Green, Kentucky, compared two unheated wastewater treatment systems, one using sound supplied by waterproofed speakers and one with no sound, for over a year. The wastewater was treated in an air free environment and discharged wastewater was mixed with feed and fed back to the system. Wastewater is typically saturated with gases due to the digestion and these gases form bubbles that vibrate in response to sound. These vibrations can be used to speed up the breakdown of wastewater. Exposure of the gas saturated wastewater to a low frequency sound induced bubbles to produce harmonics up to, and beyond, the range of human hearing. This result shows that bubbles can be used to treat the wastewater more effectively to sound than is the case with ultrasonic treatment which is absorbed at very short distances. Through the summer, the sound-treated system produced 27% more gas than the control system, and 74 times more during the winter when gas production by the control system stopped. Afterwards, the control system produced more gas due to depletion of feed in the sound-treated digester. Results show that sound can be used for faster digester startup and substitute for a share of heating requirements during cool months. This will impact and benefit livestock producers and farmers.

2. Evaluation of microaeration and sound to increase biogas production from poultry litter. Small amounts of air introduced into otherwise airless wastewater, has been shown to enhance methane production. This occurs by promoting the growth of bacteria that tolerate small amounts of oxygen and that can digest substances that oxygen sensitive bacteria cannot. The treatment of wastewater with sound has also been shown to increase methane gas production. Air treatment and treatment with sound as well as combined air and sound were compared by ARS researchers at Bowling Green, Kentucky, to an untreated digester for the production of gas and if they could improve wastewater quality. Chicken waste from a farm using wood chips as floor covering was used. At first, the digesters were fed 400 grams per week, and this was slowly increased to 2400 grams per week. Compared to untreated wastewater, sound treatment, air, and sound/air together produced more gas. The air only treatment may have worked better than combined air and sound due to the sound causing escape of air from the digesters. Digesters treated with sound had the highest amounts of particles, likely due to air bubbles attaching to the particles and lifting them. This will impact and benefit livestock producers and farmers.

3. Optimization of nanoparticles formation from plant extracts and their effectiveness on agricultural pathogens. Antibiotic resistant microorganisms are on the rise in the environment due to the increasing use and/or inappropriate use of antibiotics in human medicine and livestock production. It is necessary to find a simple and economical way to reduce the proliferation of these antibiotic resistant microorganisms. Nanoparticles with antimicrobial properties along with medicinal plants hold a great promise in this arena, especially nanoparticles that can be synthesized from eco-friendly methods. ARS scientists from Bowling Green, Kentucky, along with researchers from universities in South Korea and Mexico carried out the optimization of nanoparticle synthesis mediated from plant extracts as a model to utilize. These nanoparticle formations were optimized based on the right ratios of extracts and metallic concentrations. The results show that the maximum formation concentrations were obtained at almost equal ratios of extract and metallic concentrations. These nanoparticles are also effective against agricultural pathogens such as Escherichia coli. Synthesized nanoparticles have increased potency against E. coli in optimum culture media in comparison to metallic ions alone. For example, silver nanoparticles treated microcosms achieved 100% killed in less incubation time and lower dosage than bulk silver ion. Based on these findings, the current method can be suitable for the scale-up production of nanoparticles from a commonly available plants in a fight against agricultural pathogens that could harbor antibiotic resistance genes.

4. Governing microbial transport through biochar-amended sand filters. Animal manure is often applied to agricultural fields to add nutrients and organic matter to the soil to enhance soil quality and fertility. Manure, however, can also be a source of pathogenic microorganisms that pose a threat to humans. Because tile drainage significantly alters field hydrology, when manure is applied to tile-drained fields the movement of pathogens from agricultural fields to drinking water can be greatly enhanced. An ARS research at Bowling Green, Kentucky, investigated the potential of using biochar – a charcoal-like material generated during the pyrolysis of biomass – as an amendment to sand filters as a management strategy for removing pathogenic and indicator microorganisms from tile-drainage waters. Laboratory experiments were conducted to determine the best combination of biochar concentration and sand grain size for maximizing both retention capacity of bacteria and water flow. Results indicate that the addition of the biochar reduces the transport of E. coli and Salmonella through laboratory-scale biofilters and that the amount of retention is strongly dependent on biochar application rate. Results also show that sand size is a strong determinant on the ability of the biochar to retain bacteria, with retention decreasing with increasing grain size. Research also showed that treating biochar with Fe-hydroxides can modestly increase retention of bacteria while also drastically increasing retention of phosphorus, a nutrient that can lead to water quality problems and is often found to be elevated in tile-drainage waters. Results from this research can help guide the development and application of using biochar-amended sand filters for treating tile-drainage waters prior to release into the environment.

5. Modeling of sulfur emissions from animal operations. Sulfur is emitted from animal operations as reduced sulfur compounds and can react in the atmosphere to produce sulfur dioxide and particulate matter. As sulfur emissions from coal power plants continues to decline, agriculture-related sulfur is expected to elicit more scrutiny, but modeling of agriculture-emitted sulfur compounds has not typically been performed to understand the impact. Sulfur emissions and its dispersion over the southeastern U.S. were simulated by ARS researchers at Bowling Green, Kentucky, using the Weather Research and Forecasting-Chemistry model. Simulations were performed for dry periods and precipitation events. Spatial coverage of sulfur dispersion was reduced during precipitation events and expanded during dry periods. The highest concentrations of sulfur remained within close range of the emission locations for the majority of the simulations, except for when local surface wind speeds were high. Most emissions from the locations remained limited to the surface and lower levels of the atmosphere. This has impact on the scientific community and regulatory bodies to correctly model and assess the effects of agricultural emissions to air quality.

6. Antibiotic and metal resistance genes increased following anaerobic digestion of tetracycline containing animal manure. Antibiotics are used for the treatment of diseases in food producing animals. Metals such as copper and zinc are essential in animal nutrition. Antibiotics, metals, and bacteria including resistant ones are excreted through feces and urine resulting in environmental pollution. Once excreted, antibiotics exert selection pressure on native soil bacteria leading to propagation and spread of antibiotic resistant bacteria contaminating surface waters through run-offs from animal manure amended soils. Microbial digestion of animal manure in the absence of oxygen, while also producing renewable energy, is a promising technology for the management of animal manure. ARS scientists in Bowling Green, Kentucky, in collaboration with researchers from Western Kentucky University, investigated the effect of anaerobic digestion on the removal of antibiotic and metal resistance genes, and bacteria in cattle, poultry and swine manure. Manure samples were spiked with tetracycline antibiotics and digested for 64 days. While anaerobic digestion decreased the concentration of tetracyclines but not completely removed, it increased the concentrations of tetracycline and methicillin resistance genes, total bacterial population including Escherichia coli, enterococci, and Staphylococcus aureus species. Anaerobic digestion did not have any impact on the concentrations of metals themselves, and concentrations of metal resistance genes either increased or remained unaffected depending on the animal species. This study showed the need for post-digestion treatments of animal manure to remove bacteria, antibiotic resistance genes, heavy metals, and their resistance genes to reduce environmental and public health impacts. This has impact on the scientific community, farmers, and local and federal government regulators.

7. Atmospheric chemistry and secondary product analysis of reduced sulfur emissions. Several sulfur compounds emitted from animal operations are known precursors to particulate matter formation in the atmosphere from previous studies of the same compounds in the marine atmosphere due to ocean emissions. Laboratory experiments in a Teflon environmental chamber were conducted by ARS researchers at Bowling Green, Kentucky, to study oxidation and particulate forming potential of several sulfur compounds. Experiments were conducted with both the presence and absence of other urban pollutants to observe interactions. One expected product, methanesulfonic acid, was never observed during the study in the presence of other emissions. The absence of methanesulfonic acid when in the presence of other emissions has not been reported in previous studies and indicates a lack of understanding of the atmospheric chemistry. It implies that chemistry observed over the continent in agriculture regions may diverge from what has been observed in ocean regions. This information is important for the scientific and public health communities to help them correctly estimate impacts of agricultural activities to the atmosphere.

U.S. DEPARTMENT OF AGRICULTURE

Food Animal Environmental Systems Research: Bowling Green, KY