Title: Greenhouse gas emission and groundwater pollution potentials of soils amended with raw and carbonized swine solids Authors
Submitted to: U.S. Biochar Initiative Conference
Publication Type: Abstract Only
Publication Acceptance Date: March 2, 2010
Publication Date: June 22, 2010
Citation: Ro, K.S., Novak, J.M., Berge, N. 2010. Greenhouse gas emission and groundwater pollution potentials of soils amended with raw and carbonized swine solids [abstract]. In: Proceedings of the U.S. Biochar Initiative Conference, June 27-30, 2010, Ames, Iowa. Technical Abstract: The objective of this research is to study the greenhouse gas emission and groundwater pollution potentials of the soils amended with raw swine solids and swine biochars made from different thermochemical conditions. Triplicate sets of small pots were designed: 1) control soil with a 50/50 mixture of Norfolk Ap and E horizon; 2) soil amended with raw swine solid to provide 200 lb-N/ac; 3) soil amended with high-temperature swine biochar at a rate of 20 g/kg; and 4) soil amended with hydrothermally carbonized swine biochar (hereafter it will be called hydrochar) at a rate of 20 g/kg. Hydrochar was made using hydrothermal carbonization processes from swine solids at 80% moisture content under mild temperature (200°C) and autogenic pressure of about 2.7 MPa for 20 hours. High temperature swine biochar was made using a skid-mounted batch pyrolysis system ? pyrolyzingd dried swine solids at 620°C and atmospheric pressure for two hours. The biochar structural properties were characterized using 13CNMR spectroscopy. The soil moisture was maintained gravimetrically at 10% (w/w) by replenishing with D.I. Water. After 18 days of incubation, the pots were leached with between 1.2 to 1.3 pore volumes of deionized H2O to simulate flushing. The leachates were collected and analyzed for oxygen-demanding water quality parameters (BOD, COD), nutrients (N, P, K, Na), and heavy metals (Cd, Cr, Cu, Ni, Zn). Soil samples from the initial set up along with samples at the end of the 54-day study were analyzed for fertility. During the incubation period, greenhouse gas (CO2 and N2O) concentrations from each soil pot headspace were measured with respect to time using a photoacoustic multi-gas analyzer. Nonlinear multiparameter regression method was used to estimate instantaneous gas flux rates from these time-series gas concentration data. Throughout the incubation period, the control soils did not produce any significant CO2 nor N2O fluxes. Swine hydrochar-amended soil, however, 5 days after the incubation started emitted the highest CO2 flux of about 7.1 g CO2 m/2d. The CO2 fluxes from the hydrochar amended soil decreased exponentially with incubation time to less then 0.2 g CO2 m/2d on day 54. We speculate that the high CO2 fluxes were attributable to oxidation of aliphatic compounds in the hydrothermally carbonized biochar. For the entire incubation period, the hydrochar-amended soil produced a small N2O flux of 0.13 mg N2O m/2d only on day 20 (2 days after leaching test). Similarly on that day, control soils produced about 0.06 mg N2O m/2d, suggesting that anaerobic condition may be the driving force for N2O emission. Additional data on water quality of leachates and GHG emission from the soils pots will be presented at the meeting.