title: Sustainable Energy for New Zealand Dairy Farms by Anaerobic Digestion of Dairy Farm Effluent

authors: Yenamandra, Aparna

abstract: This study evaluated the economic feasibility and environmental impact of using a bio-digester to produce methane for energy production from a New Zealand conventional dairy farm.

Parameters effecting the bio-methanation process are examined. Analytical procedures have been carried out to determine favorable conditions for enhanced biogas production. These were: 1) pH, 2) Temperature, 3) Total solids and Total Volatile solids, 4) Gas volume and 5) Gas analysis.

Using locally supplied dairy shed effluent, it was found that 1 L reactors had peak gas production over 15 days, after which pH dropped and gas production dropped.  Optimal pH was 7 and maximum gas production was 1.25 L/L reactor.

A three stage digester was set up and run for 62 days with a maximum cumulative gas production of 21.3 L, 11.7 L and 6.6 L in the three reactors. Total volumetric methane production was 0.09 m3/kgVS/day 0.06 m3/kgVS/day and 0.07 m3/kgVS/day respectively from reactors 7, 8 and 9. The reactors produced biogas with an average composition of 74 % methane (CH4) and 25% carbon-dioxide (CO2).  A typical digester would produce 65-70% CH4.

1 kg of methane produces 4.66 kWh electricity and 5.72 kWh of heat, a typical farm of 250 cows would produce 548 kWh/day electricity and 665 kWh/day heat from using methane captured in the anaerobic digesters using dairy shed effluent.  A typical 250 cow farm consumes 1285 kWh/day total energy 40% is from heat and rest is electricity. So by having installed plug-flow anaerobic digesters it could potentially meet 130% of total energy needs and 113% of total energy needs by using a three stage mesophilic digester.

A life cycle assessment was carried out for a typical New Zealand farm.  Methane emissions from enteric fermentation, excreta, manure and farm dairy effluent irrigation and storage ponds contribute to 60% of the total greenhouse gas (GHG) emissions of a farm.   Management of dairy shed effluent will only reduce GHG emissions by 1.8%.  In addition, spray irrigation will impact on GHG emissions due increased moisture, C and N content, increasing N2O emissions.  Hence from an environmental sustainability point of view, collecting and digesting diary shed effluent will have little significant impact on overall GHG emissions.  Therefore, collecting and digesting dairy effluent is only of value if it results in economic benefits for the farm.

An economic analysis was conducted on installing a digester system.  The anaerobic digester systems for 250 cow farm would have a capital cost of $107,745 per year, an operating cost of $134,828 per year, and generate revenue of $132,819 per year, but would not be able to pay back the capital cost. For a 250 cow farm a plug flow digester would have a capital cost of $95,658 per year, operating cost $127,018 per year, generate revenue $194,722 per year, and the resulting payback period is 2 years.  A three stage digester for a 250 cow farm would have a capital cost of $259,608 an operating cost of $215,920 per year, generate revenue of $296,389 per year, a payback period of 3 years. But for a large farm size of 600-1000 cows therefore a multi stage digester would be worthwhile. For large dairy farms, CH4 capture with energy recovery can already be cost effective based on the energy value alone.

text: Sustainable Energy for New Zealand Dairy Farms by Anaerobic Digestion of Dairy Farm Effluent This study evaluated the economic feasibility and environmental impact of using a bio-digester to produce methane for energy production from a New Zealand conventional dairy farm.

Parameters effecting the bio-methanation process are examined. Analytical procedures have been carried out to determine favorable conditions for enhanced biogas production. These were: 1) pH, 2) Temperature, 3) Total solids and Total Volatile solids, 4) Gas volume and 5) Gas analysis.

Using locally supplied dairy shed effluent, it was found that 1 L reactors had peak gas production over 15 days, after which pH dropped and gas production dropped.  Optimal pH was 7 and maximum gas production was 1.25 L/L reactor.

A three stage digester was set up and run for 62 days with a maximum cumulative gas production of 21.3 L, 11.7 L and 6.6 L in the three reactors. Total volumetric methane production was 0.09 m3/kgVS/day 0.06 m3/kgVS/day and 0.07 m3/kgVS/day respectively from reactors 7, 8 and 9. The reactors produced biogas with an average composition of 74 % methane (CH4) and 25% carbon-dioxide (CO2).  A typical digester would produce 65-70% CH4.

1 kg of methane produces 4.66 kWh electricity and 5.72 kWh of heat, a typical farm of 250 cows would produce 548 kWh/day electricity and 665 kWh/day heat from using methane captured in the anaerobic digesters using dairy shed effluent.  A typical 250 cow farm consumes 1285 kWh/day total energy 40% is from heat and rest is electricity. So by having installed plug-flow anaerobic digesters it could potentially meet 130% of total energy needs and 113% of total energy needs by using a three stage mesophilic digester.

A life cycle assessment was carried out for a typical New Zealand farm.  Methane emissions from enteric fermentation, excreta, manure and farm dairy effluent irrigation and storage ponds contribute to 60% of the total greenhouse gas (GHG) emissions of a farm.   Management of dairy shed effluent will only reduce GHG emissions by 1.8%.  In addition, spray irrigation will impact on GHG emissions due increased moisture, C and N content, increasing N2O emissions.  Hence from an environmental sustainability point of view, collecting and digesting diary shed effluent will have little significant impact on overall GHG emissions.  Therefore, collecting and digesting dairy effluent is only of value if it results in economic benefits for the farm.

An economic analysis was conducted on installing a digester system.  The anaerobic digester systems for 250 cow farm would have a capital cost of $107,745 per year, an operating cost of $134,828 per year, and generate revenue of $132,819 per year, but would not be able to pay back the capital cost. For a 250 cow farm a plug flow digester would have a capital cost of $95,658 per year, operating cost $127,018 per year, generate revenue $194,722 per year, and the resulting payback period is 2 years.  A three stage digester for a 250 cow farm would have a capital cost of $259,608 an operating cost of $215,920 per year, generate revenue of $296,389 per year, a payback period of 3 years. But for a large farm size of 600-1000 cows therefore a multi stage digester would be worthwhile. For large dairy farms, CH4 capture with energy recovery can already be cost effective based on the energy value alone.

year: 2016

title: Accidental immersion and unintentional drowning of rural children: An investigation for the Child Accident Prevention Foundation of New Zealand

authors: Mahony, Lisa

subjects: child safety

abstract: In New Zealand drowning amongst preschoolers is one of the leading causes of death. The monetary and emotional costs to society are devastating and cannot be underestimated . The need to reduce the high number of deaths and the monetary and emotional costs prompted this research. This research presents the possibility for proactive measures to be taken in this area. In addition, it provides insightful knowledge for parents and educators alike. Ultimately, it seeks to reduce the number of child drownings that occur in the rural environment.

text: Accidental immersion and unintentional drowning of rural children: An investigation for the Child Accident Prevention Foundation of New Zealand In New Zealand drowning amongst preschoolers is one of the leading causes of death. The monetary and emotional costs to society are devastating and cannot be underestimated . The need to reduce the high number of deaths and the monetary and emotional costs prompted this research. This research presents the possibility for proactive measures to be taken in this area. In addition, it provides insightful knowledge for parents and educators alike. Ultimately, it seeks to reduce the number of child drownings that occur in the rural environment.

year: 2002

title: Donna Awatere’s Māori Sovereignty: Reflections on White Supremacy and the Racialization of Crime Control and Surveillance in Aotearoa New Zealand

authors: Dawson, Brian

abstract: Donna Awatere’s examination of whiteness within the Aotearoa New Zealand context, specifically white cultural imperialism, has largely been ignored in academic scholarship. For her, white culture, and its articulation through governance and policy, is the starting point and lens to understanding and addressing historical and contemporary Māori dispossession and ensuing strategies of racialized surveillance, control, and containment. In this essay, we argue that Awatere’s attention to past forms of genocide – mapping them to emerging forms of state confinement of Māori, which engender genocidal characteristics, and problematizing “whiteness” – situates the book Māori Sovereignty as an important text in the field of criminal justice, especially that which manifests in settler-colonial contexts.

text: Donna Awatere’s Māori Sovereignty: Reflections on White Supremacy and the Racialization of Crime Control and Surveillance in Aotearoa New Zealand Donna Awatere’s examination of whiteness within the Aotearoa New Zealand context, specifically white cultural imperialism, has largely been ignored in academic scholarship. For her, white culture, and its articulation through governance and policy, is the starting point and lens to understanding and addressing historical and contemporary Māori dispossession and ensuing strategies of racialized surveillance, control, and containment. In this essay, we argue that Awatere’s attention to past forms of genocide – mapping them to emerging forms of state confinement of Māori, which engender genocidal characteristics, and problematizing “whiteness” – situates the book Māori Sovereignty as an important text in the field of criminal justice, especially that which manifests in settler-colonial contexts.

year: 2023-07-27