title: The temperature response of nitrate removal in denitrification beds

authors: Carter, Anna Marie

subjects: nitrate removal

abstract: The addition of reactive nitrogen (Nᵣ) to agricultural systems has helped crop production match human population growth. However, the addition of Nᵣ comes at a cost to environment in the form of ozone destruction, habitat degradation and biodiversity loss. Denitrification beds represent an effective method for the removal of Nᵣ from a range of wastewaters and groundwater with high nitrate (NO₃¯) concentrations. Beds are lined containers filled with a carbon (C) source to enhance denitrification: the conversion of NO₃¯ to unreactive dinitrogen (N₂). 

In general, the rate of NO₃¯ removal in denitrification beds increases with increasing temperature. However, the temperature response of NO₃¯ removal in beds is poorly constrained as other controlling factors (e.g. NO₃¯ concentration and C source availability) can obscure the effect of temperature. The objective of this study was to measure the rates of NO₃¯ removal in three denitrification beds as temperature changed seasonally. The beds were located in the North Island of New Zealand and were loaded with NO₃¯ from wastewater from a hydroponic glasshouse (Karaka), domestic effluent from a campground (Motutere) and wastewater and domestic effluent from a research station (Newstead). Water samples were collected from wells installed along the length of each bed every month and were analysed for NO₃¯ concentration by ion chromatography. Rates of NO₃¯ removal were calculated using the change in NO₃¯ concentration and the flow rate. The temperatures of the beds were also measured at each sampling. 

Nitrate concentrations declined along the length of each denitrification bed and rates of NO₃¯ removal were calculated to average 3.6, 4.3 and 1.7 g N m¯³ day¯¹ for Karaka, Motutere and Newstead, respectively. The rates of removal increased with increasing temperature at Karaka and Motutere and the Q₁₀ values (the factor by which the rate of removal increased for a 10 °C increase in temperature) were calculated as 4.1 and 2.2 for Karaka and Motutere, respectively. The rates of NO₃¯ removal and Q₁₀ values were similar to those reported in previous studies of denitrification beds both in New Zealand and overseas. However, the rate of NO₃¯ removal at Karaka was less than the rate of removal of 7.6 g N m¯³ day¯¹ previously measured at Karaka in a study 5 years ago. Similarly, the temperature response at Karaka was higher than the Q₁₀ of 2 reported in this previous study at Karaka. The decrease in removal and increase in Q₁₀ may have been due to a decline in C source quality. 

There was no evidence of an increase in the rate of NO₃¯ removal with temperature at Newstead, with a Q₁₀ calculated as 1.0. The denitrification bed had been recently installed and was in a start-up phase. It was likely that the pretreatment system, in particular the nitrifying component responsible for converting ammonium (NH4+) in the effluent to NO₃¯, was not functioning effectively which resulted in low NO₃¯ concentrations entering the bed at Newstead. Nitrate was depleted within the beds at Motutere and Newstead which indicated that the rates of removal were NO₃¯ limited and that the temperature response may not have been adequately measured. 

This study confirmed that the rate of NO₃¯ removal increased with increasing temperature in the denitrification beds at Karaka and Motutere. The temperature response of NO₃¯ removal was similar to the response reported in previous studies of denitrification beds. However, additional research is required to further constrain the range of Q₁₀ values from which future denitrification beds can be designed to optimise NO₃¯ removal. Whether Q₁₀ values increase as wood chips age and C quality decreases also requires further investigation.

text: The temperature response of nitrate removal in denitrification beds The addition of reactive nitrogen (Nᵣ) to agricultural systems has helped crop production match human population growth. However, the addition of Nᵣ comes at a cost to environment in the form of ozone destruction, habitat degradation and biodiversity loss. Denitrification beds represent an effective method for the removal of Nᵣ from a range of wastewaters and groundwater with high nitrate (NO₃¯) concentrations. Beds are lined containers filled with a carbon (C) source to enhance denitrification: the conversion of NO₃¯ to unreactive dinitrogen (N₂). 

In general, the rate of NO₃¯ removal in denitrification beds increases with increasing temperature. However, the temperature response of NO₃¯ removal in beds is poorly constrained as other controlling factors (e.g. NO₃¯ concentration and C source availability) can obscure the effect of temperature. The objective of this study was to measure the rates of NO₃¯ removal in three denitrification beds as temperature changed seasonally. The beds were located in the North Island of New Zealand and were loaded with NO₃¯ from wastewater from a hydroponic glasshouse (Karaka), domestic effluent from a campground (Motutere) and wastewater and domestic effluent from a research station (Newstead). Water samples were collected from wells installed along the length of each bed every month and were analysed for NO₃¯ concentration by ion chromatography. Rates of NO₃¯ removal were calculated using the change in NO₃¯ concentration and the flow rate. The temperatures of the beds were also measured at each sampling. 

Nitrate concentrations declined along the length of each denitrification bed and rates of NO₃¯ removal were calculated to average 3.6, 4.3 and 1.7 g N m¯³ day¯¹ for Karaka, Motutere and Newstead, respectively. The rates of removal increased with increasing temperature at Karaka and Motutere and the Q₁₀ values (the factor by which the rate of removal increased for a 10 °C increase in temperature) were calculated as 4.1 and 2.2 for Karaka and Motutere, respectively. The rates of NO₃¯ removal and Q₁₀ values were similar to those reported in previous studies of denitrification beds both in New Zealand and overseas. However, the rate of NO₃¯ removal at Karaka was less than the rate of removal of 7.6 g N m¯³ day¯¹ previously measured at Karaka in a study 5 years ago. Similarly, the temperature response at Karaka was higher than the Q₁₀ of 2 reported in this previous study at Karaka. The decrease in removal and increase in Q₁₀ may have been due to a decline in C source quality. 

There was no evidence of an increase in the rate of NO₃¯ removal with temperature at Newstead, with a Q₁₀ calculated as 1.0. The denitrification bed had been recently installed and was in a start-up phase. It was likely that the pretreatment system, in particular the nitrifying component responsible for converting ammonium (NH4+) in the effluent to NO₃¯, was not functioning effectively which resulted in low NO₃¯ concentrations entering the bed at Newstead. Nitrate was depleted within the beds at Motutere and Newstead which indicated that the rates of removal were NO₃¯ limited and that the temperature response may not have been adequately measured. 

This study confirmed that the rate of NO₃¯ removal increased with increasing temperature in the denitrification beds at Karaka and Motutere. The temperature response of NO₃¯ removal was similar to the response reported in previous studies of denitrification beds. However, additional research is required to further constrain the range of Q₁₀ values from which future denitrification beds can be designed to optimise NO₃¯ removal. Whether Q₁₀ values increase as wood chips age and C quality decreases also requires further investigation.

year: 2014

title: Helping students value cultural diversity through research-based teaching

authors: Deakins, Eric

subjects: diversity (institutional)

abstract: Although international students studying in New Zealand desire and expect contact with their domestic peers, the level of cross-national interactions remains generally low. This paper describes an initiative to promote more and better intercultural understanding within a target group of students having similar needs and interests in a higher education setting. A research-based teaching approach progressively increased student engagement with higher order cognitive skills and both topic and process were aligned in such a way that training opportunities in intercultural competence were explored while also providing a process that offered further training in intercultural competence. Enduring appreciation of cultural diversity issues was achieved via deep styles of teaching and learning that raised awareness, changed attitudes and behaviour and ultimately impacted classroom culture. Initiative design, evaluation and results are described and limitations noted. The findings should be of interest to teachers of multicultural students and to academics studying cultural diversity issues.

text: Helping students value cultural diversity through research-based teaching Although international students studying in New Zealand desire and expect contact with their domestic peers, the level of cross-national interactions remains generally low. This paper describes an initiative to promote more and better intercultural understanding within a target group of students having similar needs and interests in a higher education setting. A research-based teaching approach progressively increased student engagement with higher order cognitive skills and both topic and process were aligned in such a way that training opportunities in intercultural competence were explored while also providing a process that offered further training in intercultural competence. Enduring appreciation of cultural diversity issues was achieved via deep styles of teaching and learning that raised awareness, changed attitudes and behaviour and ultimately impacted classroom culture. Initiative design, evaluation and results are described and limitations noted. The findings should be of interest to teachers of multicultural students and to academics studying cultural diversity issues.

year: 2009

title: Grounding the state of exception in New Zealand: A case study of racial segregation in Pukekohe, Whiteness and the Carceral State

authors: Martin, Jessica

subjects: State of exception

abstract: Indigenous scholars in settler-colonial contexts have highlighted the hyper-imprisonment of Indigenous people, locating it as an extension of the colonial project. Although research on this issue in New Zealand is emerging, there is a notable gap in understanding how the carceral state has developed within this particular context. This study aims to address the following research question: How does the historical context of racial segregation in Pukekohe contribute to our understanding of the mechanisms of the carceral state in New Zealand?
To thoroughly examine the hyper-imprisonment of Māori, it is essential to unpack the historical origins of state violence. Despite existing research establishing a link between Māori over-representation in prisons and the enduring effects of colonisation, there is a lack of studies exploring the complex interplay among the carceral state, whiteness, policy, policing, and law, which collectively shape the current landscape of incarceration. This study focuses on the racial segregation in Pukekohe between 1920 and 1960 and utilises reflexive thematic analysis within a case study framework, drawing on the insights offered by Robert Bartholomew's book, No Māori Allowed (2020). The analysis centres on the theoretical concept of the state of exception, shedding light on how power was wielded by the white racial polity. Thus, providing a unique perspective on the carceral state and state-sanctioned violence.
The findings highlight the interconnectedness of various systemic control mechanisms employed by the carceral state. Housing, policing, and whiteness emerge as crucial factors in the control and confinement of Māori in Pukekohe. By emphasising the role of whiteness in suppressing this history, this study underscores the need for critical examination and recognition of white cultural imperialism as a fundamental pillar of the carceral state. Overall, this research offers significant insights into the construction of a targeted population and the enduring consequences of state-sanctioned violence, emphasising the importance of a comprehensive examination of New Zealand's racialised history in discussions on the hyper-imprisonment of Māori.

text: Grounding the state of exception in New Zealand: A case study of racial segregation in Pukekohe, Whiteness and the Carceral State Indigenous scholars in settler-colonial contexts have highlighted the hyper-imprisonment of Indigenous people, locating it as an extension of the colonial project. Although research on this issue in New Zealand is emerging, there is a notable gap in understanding how the carceral state has developed within this particular context. This study aims to address the following research question: How does the historical context of racial segregation in Pukekohe contribute to our understanding of the mechanisms of the carceral state in New Zealand?
To thoroughly examine the hyper-imprisonment of Māori, it is essential to unpack the historical origins of state violence. Despite existing research establishing a link between Māori over-representation in prisons and the enduring effects of colonisation, there is a lack of studies exploring the complex interplay among the carceral state, whiteness, policy, policing, and law, which collectively shape the current landscape of incarceration. This study focuses on the racial segregation in Pukekohe between 1920 and 1960 and utilises reflexive thematic analysis within a case study framework, drawing on the insights offered by Robert Bartholomew's book, No Māori Allowed (2020). The analysis centres on the theoretical concept of the state of exception, shedding light on how power was wielded by the white racial polity. Thus, providing a unique perspective on the carceral state and state-sanctioned violence.
The findings highlight the interconnectedness of various systemic control mechanisms employed by the carceral state. Housing, policing, and whiteness emerge as crucial factors in the control and confinement of Māori in Pukekohe. By emphasising the role of whiteness in suppressing this history, this study underscores the need for critical examination and recognition of white cultural imperialism as a fundamental pillar of the carceral state. Overall, this research offers significant insights into the construction of a targeted population and the enduring consequences of state-sanctioned violence, emphasising the importance of a comprehensive examination of New Zealand's racialised history in discussions on the hyper-imprisonment of Māori.

year: 2024