Abstract
Modern intensive confinement systems for livestock and poultry production have allowed farmers to greatly increase production efficiency and economic profitability, but this has inevitably resulted in significant environmental challenges, including generation of large volumes of manure in very small areas without sufficient nearby farm land for application. In addition to significant impacts on climate due to emissions of greenhouse gases (GHG) and ammonia (NH3) from manure management, losses of nitrogen to the environment reduce the fertiliser value of manure and have negative effects on human health and ecosystem health. Thus, alternative technologies for recycling manure and utilising it as a nutrient source for crop production, while minimising the environmental costs, are important for the sustainability of the livestock and poultry sectors.
Composting of animal manure and other organic wastes has been proposed as a potential strategy to reduce gaseous emissions, and is increasingly being used to handle large volumes of surplus manure in areas of intensive livestock production. Composting appears to have the potential for minimising gaseous emissions from organic wastes, but information on its effect on GHG emissions, especially nitrous oxide (N2O), is still limited. This thesis investigated the main processes and factors affecting the physicochemical composition of the compost and emissions of GHG and NH3 during composting of animal manure and other organic waste products.
Laboratory studies showed that differences in the initial physical properties (moisture, bulk density, particle density and air-filled porosity) of separated animal slurry solid fractions (SSF) had a considerable impact on the development of compost maximum temperatures (40-70 o C) and the time required (2-7 days) to reach maximum temperature. The time-temperature-CO2 profile showed that evolution of CO2 during composting could serve as a good proxy for assessing O2 uptake rates. The dynamics of physical change in composting also influenced the biodegradation of volatile solids, as described by a first-order kinetic equation. Relative losses of volatile solids varied from 21.3% to 27.5%, depending on SSF.
Considerable differences in measured and calculated particle density of SSF were observed. Particle density of SSF can be calculated fairly accurately from loss of ignition data using an estimated component particle density of 1441 kg m -3 for volatile solids and 2625 kg m -3 for fixed solids. Using these density values also improved estimated air-filled porosity of SSF within the range tested.
Depending on treatment, cumulative C losses via CO2 and CH4 emissions during composting accounted for 8.4-22.5% and 0.001-0.17% of initial Tot-C, respectively, while N losses as 2O and x NH3 emissions comprised 0.05-0.10% and 0.81-26.5% of initial Tot-N, respectively. There was strong evidence that high emissions of CH4-C and N2O-N gases can occur simultaneously, even during the thermophilic phase of composting, within the range of flow rates and composting mixtures tested. This indicates that temperature is an important factor influencing GHG emissions during composting.
Composting of nitrogen-rich manure materials with carbon-rich bulking agents proved to be an effective means of conserving nitrogen in manures, while also reducing GHG emissions. Barley straw was as effective as bio-char in conserving N in digested manure solids. owever, the results suggested that to minimise CH4-C emissions, farmers should avoid using highly biodegradable carbon sources as bulking materials when composting manure.
The studies provided further evidence that doubling the amount of bulking agent in a mixture of digested solids and bulking agent can decrease losses of CH4-C and N2O-N from compost, both GHG of high importance, without any accompanying increase in NH3-N losses.
Cumulative CH4-C emissions decreased significantly with increasing flow rate from low to high during composting of cattle slurry with barley straw. Based on the high and low eration flow rates tested, it was concluded that low flow could be an alternative strategy for educing NH3-N losses without any significant change in N2O-N emissions, indicating the otential benefits of wellcontrolled composting in reducing overall gas emissions.
There has been little research to date on the potential use of bio-char as a bulking agent in conserving nitrogen and reducing GHG emissions during manure composting. Laboratory tudies showed that adding bio-char when composting manure materials can conserve nitrogen while reducing N2O-N and CH4-C emissions to the atmosphere and that adding bio-char alone or together with barley straw to composting manure can be a potential tool for mitigating total GHG emissions in terms of CO2-equivalents.
This thesis provides insights into the underlying composting processes that lead to production and emission of GHG and NH3 during composting, allowing us to progress towards the goal of properly mitigating GHG and NH3 emissions from composting operations. In focusing on composting treatment effects on gaseous emissions within the manure management continuum, this work also falls within the larger context of environmental life cycle assessment.
Composting of animal manure and other organic wastes has been proposed as a potential strategy to reduce gaseous emissions, and is increasingly being used to handle large volumes of surplus manure in areas of intensive livestock production. Composting appears to have the potential for minimising gaseous emissions from organic wastes, but information on its effect on GHG emissions, especially nitrous oxide (N2O), is still limited. This thesis investigated the main processes and factors affecting the physicochemical composition of the compost and emissions of GHG and NH3 during composting of animal manure and other organic waste products.
Laboratory studies showed that differences in the initial physical properties (moisture, bulk density, particle density and air-filled porosity) of separated animal slurry solid fractions (SSF) had a considerable impact on the development of compost maximum temperatures (40-70 o C) and the time required (2-7 days) to reach maximum temperature. The time-temperature-CO2 profile showed that evolution of CO2 during composting could serve as a good proxy for assessing O2 uptake rates. The dynamics of physical change in composting also influenced the biodegradation of volatile solids, as described by a first-order kinetic equation. Relative losses of volatile solids varied from 21.3% to 27.5%, depending on SSF.
Considerable differences in measured and calculated particle density of SSF were observed. Particle density of SSF can be calculated fairly accurately from loss of ignition data using an estimated component particle density of 1441 kg m -3 for volatile solids and 2625 kg m -3 for fixed solids. Using these density values also improved estimated air-filled porosity of SSF within the range tested.
Depending on treatment, cumulative C losses via CO2 and CH4 emissions during composting accounted for 8.4-22.5% and 0.001-0.17% of initial Tot-C, respectively, while N losses as 2O and x NH3 emissions comprised 0.05-0.10% and 0.81-26.5% of initial Tot-N, respectively. There was strong evidence that high emissions of CH4-C and N2O-N gases can occur simultaneously, even during the thermophilic phase of composting, within the range of flow rates and composting mixtures tested. This indicates that temperature is an important factor influencing GHG emissions during composting.
Composting of nitrogen-rich manure materials with carbon-rich bulking agents proved to be an effective means of conserving nitrogen in manures, while also reducing GHG emissions. Barley straw was as effective as bio-char in conserving N in digested manure solids. owever, the results suggested that to minimise CH4-C emissions, farmers should avoid using highly biodegradable carbon sources as bulking materials when composting manure.
The studies provided further evidence that doubling the amount of bulking agent in a mixture of digested solids and bulking agent can decrease losses of CH4-C and N2O-N from compost, both GHG of high importance, without any accompanying increase in NH3-N losses.
Cumulative CH4-C emissions decreased significantly with increasing flow rate from low to high during composting of cattle slurry with barley straw. Based on the high and low eration flow rates tested, it was concluded that low flow could be an alternative strategy for educing NH3-N losses without any significant change in N2O-N emissions, indicating the otential benefits of wellcontrolled composting in reducing overall gas emissions.
There has been little research to date on the potential use of bio-char as a bulking agent in conserving nitrogen and reducing GHG emissions during manure composting. Laboratory tudies showed that adding bio-char when composting manure materials can conserve nitrogen while reducing N2O-N and CH4-C emissions to the atmosphere and that adding bio-char alone or together with barley straw to composting manure can be a potential tool for mitigating total GHG emissions in terms of CO2-equivalents.
This thesis provides insights into the underlying composting processes that lead to production and emission of GHG and NH3 during composting, allowing us to progress towards the goal of properly mitigating GHG and NH3 emissions from composting operations. In focusing on composting treatment effects on gaseous emissions within the manure management continuum, this work also falls within the larger context of environmental life cycle assessment.
| Originalsprog | Engelsk |
|---|
| Forlag | Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen |
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| Antal sider | 230 |
| Status | Udgivet - 2013 |