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: Characterization and adsorption performance of New Zealand biochar for the removal of paracetamol and ibuprofen from synthetic solutions in batch and column systems

authors: Shein, Shun Lei Shwe Yee

abstract: Pharmaceuticals are a significant class of emerging organic contaminants that have been increasingly detected in aquatic environments. Their persistence and limited removal by conventional treatment methods poses considerable risks to both flora and fauna. The study investigates the adsorption performance of New Zealand-sourced biochar both raw and surface-modified for the removal of two widely used pharmaceuticals, paracetamol and ibuprofen, from aqueous solutions. With its local availability and carbon-rich structure, biochar was evaluated as an innovative solution to address the growing challenge of emerging pharmaceutical pollutants in aquatic environments. The research aimed to characterize the physicochemical properties of biochar and evaluate its adsorption capacity under batch and column configurations, addressing removal efficiency, equilibrium behaviour, kinetic mechanisms, and dynamic breakthrough performance. The biochar was instrumentally analysed by BET surface area analysis, Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX) to examine the biochar’s surface structure and functional groups. Premium Biochar demonstrated the highest BET surface area (308.3 m²/g), which further increased to 354 m²/g after 30% KOH activation, indicating enhanced porosity and improved availability of adsorption sites. Batch adsorption experiments revealed that paracetamol achieved higher removal efficiencies and adsorption capacities (up to 8.5 mg/g) compared to ibuprofen (maximum of 2.8 mg/g), largely due to its smaller molecular size and greater polarity. The non-linear technique using isotherm and kinetic model was used to validate the process efficiency of pharmaceuticals removal. Kinetic modelling indicated pseudo-second order and Elovich models best described the adsorption mechanisms (R² > 0.997), confirming chemisorption on heterogeneous surfaces as the dominant process. Isotherm analysis showed multilayer Freundlich adsorption for paracetamol and monolayer Langmuir adsorption for ibuprofen reflecting differences in multilayer versus monolayer adsorption behaviour. Column experiments were conducted under single-pass, closed-loop recirculation, and semi-continuous dosing modes. Single-pass continuous flow showed in rapid breakthrough at short empty bed contact times (1.6–4.5 minutes) due to hydraulic limitations. In contrast, closed-loop recirculation columns achieved up to 90% paracetamol removal and 58% ibuprofen removal under extended operation, specifically, the optimal condition when using 1 mm particle size KOH-activated biochar (1 mm KOH-modified biochar, 15 L/min flow, 500 min runtime). Semi-continuous dosing experiments demonstrated gradual adsorbent saturation with final adsorption capacities of approximately 0.43–0.57 mg/g, supporting the need for regeneration strategies in long-term applications.

text: Characterization and adsorption performance of New Zealand biochar for the removal of paracetamol and ibuprofen from synthetic solutions in batch and column systems Pharmaceuticals are a significant class of emerging organic contaminants that have been increasingly detected in aquatic environments. Their persistence and limited removal by conventional treatment methods poses considerable risks to both flora and fauna. The study investigates the adsorption performance of New Zealand-sourced biochar both raw and surface-modified for the removal of two widely used pharmaceuticals, paracetamol and ibuprofen, from aqueous solutions. With its local availability and carbon-rich structure, biochar was evaluated as an innovative solution to address the growing challenge of emerging pharmaceutical pollutants in aquatic environments. The research aimed to characterize the physicochemical properties of biochar and evaluate its adsorption capacity under batch and column configurations, addressing removal efficiency, equilibrium behaviour, kinetic mechanisms, and dynamic breakthrough performance. The biochar was instrumentally analysed by BET surface area analysis, Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM–EDX) to examine the biochar’s surface structure and functional groups. Premium Biochar demonstrated the highest BET surface area (308.3 m²/g), which further increased to 354 m²/g after 30% KOH activation, indicating enhanced porosity and improved availability of adsorption sites. Batch adsorption experiments revealed that paracetamol achieved higher removal efficiencies and adsorption capacities (up to 8.5 mg/g) compared to ibuprofen (maximum of 2.8 mg/g), largely due to its smaller molecular size and greater polarity. The non-linear technique using isotherm and kinetic model was used to validate the process efficiency of pharmaceuticals removal. Kinetic modelling indicated pseudo-second order and Elovich models best described the adsorption mechanisms (R² > 0.997), confirming chemisorption on heterogeneous surfaces as the dominant process. Isotherm analysis showed multilayer Freundlich adsorption for paracetamol and monolayer Langmuir adsorption for ibuprofen reflecting differences in multilayer versus monolayer adsorption behaviour. Column experiments were conducted under single-pass, closed-loop recirculation, and semi-continuous dosing modes. Single-pass continuous flow showed in rapid breakthrough at short empty bed contact times (1.6–4.5 minutes) due to hydraulic limitations. In contrast, closed-loop recirculation columns achieved up to 90% paracetamol removal and 58% ibuprofen removal under extended operation, specifically, the optimal condition when using 1 mm particle size KOH-activated biochar (1 mm KOH-modified biochar, 15 L/min flow, 500 min runtime). Semi-continuous dosing experiments demonstrated gradual adsorbent saturation with final adsorption capacities of approximately 0.43–0.57 mg/g, supporting the need for regeneration strategies in long-term applications.

year: 2025-07-06

title: Indigenous fertility in Aotearoa New Zealand: How does ethnic identity affect birth spacing and timing?

authors: Rarere, Moana

abstract: The survival of Indigenous peoples in the CANZUS states of Canada, Australia, Aotearoa New Zealand, and the United States is nothing short of remarkable. Not only have Indigenous peoples thwarted colonial tropes of the vanishing native but, for decades, Indigenous population growth rates have significantly outpaced those of the dominant settler populations. The future survival of Indigenous peoples fundamentally rests on continued natural increase, and understanding the causes and consequences of fertility behaviour is critical. While total fertility rates for Indigenous women in CANZUS countries are relatively low, childbearing tends to be concentrated at younger ages in contrast to the dominant white populations. The fertility transitions of both settler and Indigenous populations in the CANZUS states are well documented, however, a significant gap remains: how cultural factors shape contemporary Indigenous fertility behaviours. Using Aotearoa as a case study, we explore the relationship between Māori cultural identity, birth timing, and the duration of birth intervals. We use the 1995 New Zealand Women: Family, Employment and Education survey data to further test the impact of cultural identity on birth transition rates using the piecewise exponential model and Kaplan-Meier estimates. We find that women who identify Mainly Māori (exclusively or primarily) are at greater risk of bearing much earlier to first birth but not necessarily subsequent births. However, because of the earlier start, Māori have a longer reproductive window to bear more children, and at higher birth orders still bear earlier than non-Māori. The empirical evidence strengthens our case to suggest that cultural orientation has some influence on Indigenous fertility and contributes to the development of Indigenous-centred theories of fertility and demography more broadly.

text: Indigenous fertility in Aotearoa New Zealand: How does ethnic identity affect birth spacing and timing? The survival of Indigenous peoples in the CANZUS states of Canada, Australia, Aotearoa New Zealand, and the United States is nothing short of remarkable. Not only have Indigenous peoples thwarted colonial tropes of the vanishing native but, for decades, Indigenous population growth rates have significantly outpaced those of the dominant settler populations. The future survival of Indigenous peoples fundamentally rests on continued natural increase, and understanding the causes and consequences of fertility behaviour is critical. While total fertility rates for Indigenous women in CANZUS countries are relatively low, childbearing tends to be concentrated at younger ages in contrast to the dominant white populations. The fertility transitions of both settler and Indigenous populations in the CANZUS states are well documented, however, a significant gap remains: how cultural factors shape contemporary Indigenous fertility behaviours. Using Aotearoa as a case study, we explore the relationship between Māori cultural identity, birth timing, and the duration of birth intervals. We use the 1995 New Zealand Women: Family, Employment and Education survey data to further test the impact of cultural identity on birth transition rates using the piecewise exponential model and Kaplan-Meier estimates. We find that women who identify Mainly Māori (exclusively or primarily) are at greater risk of bearing much earlier to first birth but not necessarily subsequent births. However, because of the earlier start, Māori have a longer reproductive window to bear more children, and at higher birth orders still bear earlier than non-Māori. The empirical evidence strengthens our case to suggest that cultural orientation has some influence on Indigenous fertility and contributes to the development of Indigenous-centred theories of fertility and demography more broadly.

year: 2023