Dinitrogen and methane gas production during the anaerobic/anoxic decomposition of animal manure

Abstract

Trace-gas emissions from animal feeding operations (AFOs) can contribute to air quality and global change gases. Previous and current estimated gas emissions from AFOs vary widely and many do not consider all forms of carbon (C) and nitrogen (N) emissions. Studies have found that as methanogenesis in the lagoons increased, conversion of ammonium (NH 4 ? ) to dinitrogen (N 2 ) also increased. The purpose of this research was to measure N 2 and CH 4 emissions from swine AFOs in three locations of the U.S. and to evaluate the possible universal relationship between lagoon methanogenesis and the conversion of NH 4 ? to N 2 gas. This relationship was tested by measuring N 2 and CH 4 emissions in two climates at 22 different farms. Methanogenesis was correlated with NH 4 ? -to-N 2 conversion by a nearconstant N 2 to CH 4 emissions ratio of 0.20, regardless of C loading and climatic effects. The process is shown to be thermodynamically favored when there is competition between NH 4? oxidizing reactions. Under methanogenic conditions (redox potentials of methanogenesis) N 2 production is favorable and nitrification/denitrification is not. Thus, N 2 production is stimulated in methanogenic conditions. Evaluation of NH 3 gas emissions from AFOs must consider other N emissions than NH 3 . Finally, a statistical model was developed to estimate methane and N 2 emissions (kg gas ha -1 ) given feed input per lagoon surface area (kg feed ha -1 ) and local air temperature. Further studies are needed to investigate the mechanisms involved in manure processing and isolate the favorable mechanisms into engineering improved manure processing.

Effect of mechanical separation on emissions during storage of two anaerobically codigested animal slurries

“…Considering that the emissions of NH 3 had average values >200 mg m À2 h À1 of NH 3 -N, it is evident that, of those measured (NH 3 + N 2 O) the predominant N emission was in the form of NH 3 , representing on average more than 99%. As discussed above, based on the model of Harper et al (2014), we would not expect high N 2 emissions. According to Harper et al (2014), the expected N 2 would represent less than 5% of total N emissions.…”

“…As discussed above, based on the model of Harper et al (2014), we would not expect high N 2 emissions. According to Harper et al (2014), the expected N 2 would represent less than 5% of total N emissions. The absent or very small N 2 O fluxes from both C and P digestates in the first weeks of storage can be explained by the absence of a crust during the storage period (Berg et al, 2006;Sommer et al, 2000).…”

“…The combined nitrogen losses from the separated fractions were significantly greater than those from the respective unseparated digestates. Nitrogen losses in the form of N 2 are expected to be low: using the model developed by Harper et al (2014), which relates N 2 emissions to CH 4 emissions, the N 2 emissions would be 2.8-2.6 g t À1 d À1 . During the storage period, P_TR and C_TR lost 41% and 43%, respectively, of their initial TAN content while P_UN and C_UN lost 35% and 20%, respectively ( Table 2).…”

The effect of biogas ebullition on ammonia emissions from animal manure–processing lagoons

“…Although biological decomposition of animal manure in treatment lagoons results in CH 4 and CO 2 emissions (and small amounts of other gases), studies have shown significant amounts of chemical (thermodynamic) conversion of NH 4 + to dinitrogen (N 2 ) gas in lagoons in the U.S. southeastern Coastal Plains and in the Central Great Basin of Utah (Harper et al, 2000(Harper et al, , 2004(Harper et al, , 2014Weaver et al, 2012). All of these gases are emitted from the sediment layer and rise to the surface either as small gas bubbles or as an occasional large gas "breakthrough" bubble from the sediment layer where a large single emission may occur.…”

“…The effect of ebullition on each process needs to be understood to be able to integrate or discount biogas ebullition in NH 3 emission models. Bubble transport can be understood by taking advantage of earlier work (Harper et al, 2000(Harper et al, , 2004(Harper et al, , 2014Weaver et al, 2012) done to characterize biological decomposition gas emissions occurring in lagoons. These earlier studies determined not only the composition of the gases but also the daily ebullition rates averaged on a monthly basis.…”