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Gaseous Production from Impermeable Swine Waste Storage Tanks and its Abatement Using Biofilters

G. B. Day, A. Singh, S.F. Higgins
Department of Biosystems and Agricultural Engineering

Non-Technical Summary

Animal feeding operations (AFOs) are a source of air borne contaminants including ammonia, methane, nitrous oxide, hydrogen sulfide and dust, which contribute to air and water pollution. A major source of pollutant gases on an AFO is manure storage. Structures used to store manure prior to land application include deep pits and anaerobic lagoons. However, impermeable manure storage structures are a positive alternative for Kentucky's swine operations particularly those located in hydrosensitive karst (limestone) geographical regions.

Because there is little data regarding gases produced and emitted by manure stored in impermeable structures, this project seeks to characterize gas production and apply biofiltration technology to reduce emission of noxious gases. Biofilters have not been tested for their efficiency in eliminating manure gases in ventilation air exhausted from impermeable manure storage tanks. It is expected that air pollution will be reduced if the stored swine waste is covered and ventilated and the exhaust air is treated by biofiltration prior to discharge.

A long-term goal of this project is to promote liquid manure storage in environmentally sound impermeable tanks coupled with biofilters to reduce air and water pollution. This study evaluates gaseous production rates from dilute stored swine waste, and the ability of biofilters to reduce the emission of these gases into the environment.

2010 Project Description

Experiments were conducted using small, laboratory scale, tubular reactors to determine the effects of moisture content on ammonia (NH3) removal capacity and nitrous oxide (N2O) production in compost biofilter material. Biofilters are a viable strategy in the abatement of greenhouse gases (GHG's) from enclosed liquid swine manure containment facilities. Separate moisture loss experiments were performed in addition to the gas monitoring work as a means of minimizing the impact of moisture measurement on gas activity.

The degradation of NH3 and the production of N2O were investigated for constant air flow rate and relative humidity, particle size, and initial gas concentration. Moisture conditions were varied from no moisture replacement to moisture added based on estimates of evaporation and drainage. A Drying Characteristic Curve was developed to describe relative moisture condition of the material in terms of drying rate as a function of time.

This curve was used in conjunction with developed NH3 nitrification and N2O production curves to show higher values of NH3 conversion between 35 to 65% moisture contents (w.b.). The curves also indicated high rates of N2O production for moisture contents between 45 and 65%.

The data suggests there is a (material specific) critical point just prior to the transition from constant drying rate to the first falling drying rate phase (35 to 45% w.b.) which both minimizes N2O production and maintains NH3 nitrification at suitably high levels in terms of biofilter efficiency.

These results significantly improve the focus of biofilter technology by effectively eliminating the "wetter is better" approach, and underscoring the need for a reliable moisture control system. To this end, an effective collaboration was established between the University of Kentucky, BAE Dept. and the University of Illinois at Urbana-Champaign, Agricultural and Biological Engineering Dept. in the joint development and testing of a capacitance-based sensor as part of an overall moisture control strategy.

Early tests of control boards with significantly downsized capacitance grids have demonstrated the viability of the system; however, it was observed that for moisture contents in the range(s) likely encountered, short-circuiting may be a problem. New, insulated grids were installed and tested and showed significant improvement in the reliability of the system. This sensor is currently being used in conjunction with a soaker hose delivery system to determine the effect of controlled moisture application on the degradation of NH3 and the production of N2O in quarter-scale biofilters.

The Volumetric Production Instrument was replicated to form six chambers for analyzing gas production rates from temperature controlled bioreactors. Long term data were collected for CO2 and CH4 production and are currently being analyzed. Results of these experiments will be used to determine the suitability of the bioreactors as gas sources for testing alternate materials for use in biofilters. Each of the research areas have established methodologies and standards for use in developing customized, contaminant-specific, biofilter cells.

2010 Impact

The earliest work in this project involved physical and chemical characterization of compost material. Airflow was optimized for a specific material and gradation based on NH3 removal efficiency. Moisture condition was varied as an effect on pressure drop initially, but was later found to be a critical means of controlling N2O production as well. The earlier work established the importance of particle size analysis as a first step in analyzing potential biofilter materials.

The effect of moisture condition on NH3 degradation was addressed in the initial work and further refined in a later study specifically designed to determine the effects of moisture on NH3 degradation and N2O production. The work in the later study defined critical moisture content where N2O production was minimized while maintaining suitably high conversion rates for NH3. The existence of this critical point further emphasized the need for a reliable moisture delivery/control system.

High moisture conditions, i.e., "trickling filters" have been thought to provide maximum NH3 removal, however, the results of the lab scale biofilter analyses indicate higher levels of N2O production for higher moisture conditions in the stack.

The establishment of the critical moisture condition (for the "wood chip" based compost) set constraints for the refinement of the capacitive sensor which now utilizes insulated, small form-factor plates for moisture sensing. The development of the VPI chambers allowed for longer term data collection of biogas collected directly from liquid swine manure. The production rates and chemical constituency of the gas are being analyzed to provide design information specifically for use in sizing biofilter applications.

The laboratory apparatus developed for this area of the research represents a significant opportunity to quantify other inputs to the system, i.e., temperature, changes in diet, effect of stirring, effect of aeration, dilution, solids concentration, etc., which may offer additional benefits in controlling GHG emissions. A considerable amount has been learned over the course of the work undertaken during this project. Much of the scientific method has resulted in the establishment of standards which will be used to determine the viability of alternate materials for use in compost based biofilters and installations.

It is now believed that individual, customized biofilter cells may be developed to address specific contaminants within an airstream, and that these cells may be used in series to achieve the desired air quality standards for animal housing emissions. The work in this project contributed to two M.S. degrees (Sales, 2008) and (Dutra de Melo, 2011 - anticipated), one Ph.D. degree (Maia, 2010), one Post Doctoral Study (Souza, 2010), and one undergraduate research program, (Rodrigues, 2011).

2010 Publications

Guillherme del Nero Maia, Ammonia Biofiltration and Nitrous Oxide Generation as Affected by Media Moisture Content. (Ph.D. Dissertation, University of Kentucky Graduate School, 2010).

Maia G. D. N., Gates, R. S., Day V, G. B., Taraba, J. 2010. Ammonia Biofiltration and Nitrous Oxide Generation during the Start-Up of Gas-Phase Compost Biofilters. Atmospheric Environment. Submitted on September 16, 2010 (Ref. No.:ATMENV-D-10-01139).

Maia G. D. N., R. S. Gates, G. B. Day V, J. Taraba. 2010. Method for Characterization of Sieved Media in Compost Biofilters Using Water Sorption Isotherms. Transactions of ASABE. Submitted on September 14, 2010 (Ref. No.: SE-08781-2010).

Dutra de Melo, L., G.B. Day V, J.L. Taraba, and Guilherme Del Nero Maia. 2010. Assessment of a Moisture Application System for Compost Biofilters. Paper No. 1009176. ASABE Intl Mtg. June 20th. Pittsburgh, PA. St. Joseph MI: ASABE.

Souza, C.F., G.B. Day V, J.L. Taraba, R.S. Gates, and W.P.M Ferreira. 2010. BIOG-C: Modeling the Volumetric Methane Production in the Anaerobic Digestion Process Applied to Swine Wastes. Paper No.1009181. ASABE Intl Mtg. June 20th. Pittsburgh, PA. St. Joseph MI: ASABE.