title: Carbon dosing of denitrifying bioreactors to remove nitrate from agricultural drainage

authors: Moghaddam, Reza

subjects: Woodchip bioreactors

abstract: Several studies have demonstrated that denitrifying woodchips bioreactors effectively remove nitrate from a broad spectrum of wastewater. Even though bioreactors have a comparatively small spatial footprint and are straightforward to construct, the low long-term nitrate removal efficiency they provide compared to other mitigation options, such as constructed wetlands, may limit their utilization by catchment managers and landowners. This thesis investigated the use of external carbon dosing in bioreactors to improve nitrate removal and quantified some potential adverse effects of carbon dosing on bioreactors and downstream aquatic environments. Through observations ranging from field to mesocosm experiments, this thesis sought to (1) determine whether and to what extent external carbon dosing could improve nitrate removal in bioreactors and (2) assess the potential adverse effects of carbon dosing, such as reduced hydraulic performance and pollution swapping. 
The first component of the study evaluated the carbon dosing of a pilot-scale (58 m³) bioreactor treating drainage waters from a 0.65 ha paddock on a dairy farm. The effects of carbon dosing on the bioreactor's nitrate removal rates were assessed following a constant dosage of 8% (v/v) methanol solution at 10 mL min⁻¹ to the bioreactor's inlet distributor. Sulfate reduction and losses of added methanol from the bioreactor’s outlet were quantified as the potential adverse effects of external carbon dosing. Methanol dosing increased seasonal nitrate removal rates to 8 g N m⁻³ day⁻¹ in 2020 and 5 g N m⁻³ day⁻¹ in 2021 (with a halved dosing rate), compared to 1 g N m⁻³ day⁻¹ in the undosed bioreactor in 2018. Even under nitrate-limiting conditions, the added methanol was effectively removed in the bioreactor, with a mean removal rate of 106 g CH₃OH-C m⁻³ day⁻¹
. Methanol concentrations decreased by order of magnitude along the bioreactor (lengthwise) and never exceeded 50 mg CH₃OH-C L⁻¹ at the outflow. The added carbon caused sulfate reduction with a mean removal rate of 8.5 g SO4²⁻-S m⁻³ day⁻¹ in 2020 (higher dosing rate) and 0.5 g SO4²⁻-S m⁻³ day⁻¹ in 2021 (halved dosing rate). Carbon dosage at a continuous rate was shown to be a viable method for increasing nitrate removal while minimizing capital and operational costs. The simplicity of this approach is a significant advantage, and it could be used by a variety of industries, including farmers.
While field observations showed that carbon dosage could improve nitrate removal, the very variable flows and nitrate concentrations made determining nitrate, sulfate, and methanol removal rates difficult. Therefore, the second component of the thesis was to assess nitrate, sulfate and added carbon removal rates more accurately using mesocosms. An empirical model was also developed to calculate the amount of methanol required to remove specific loads of nitrate. Mesocosm bioreactors were designed to share some characteristics with the field bioreactor (for example, added carbon component and dosage ratio) but diverged in that they were hydrologically regulated to eliminate the impact of transient operating circumstances on bioreactor performance. Carbon dosing increased nitrate removal rates from 7 g N m⁻³ day⁻¹ in the control treatment bioreactors (without methanol addition) to 27 g N m⁻³ day⁻¹ in the methanol-dosed treatment bioreactors. Added methanol was removed in either the absence or presence of nitrate, with mean methanol removal rates of 23 g CH₃OH-C m⁻³ day⁻¹ in nitrate prevailing conditions and 17 g CH₃OH-C m⁻³ day⁻¹ in nitrate limiting conditions. The empirical model suggested that a methanol to nitrate ratio of 0.7 resulted in complete nitrate removal. 
In the third component of this thesis research, observations from both mesocosm and full-scale bioreactors were used to assess the hydraulic characteristics of bioreactors under various carbon dosage regimes. Field measurements revealed a decrease in hydraulic conductivity from 4601 m day⁻¹ in 2018 (season without carbon dosing) to 1600 m day⁻¹ in 2021 (second year of dosing). Based on tracer tests of the mesocosm bioreactors, I investigated the effects of added carbon on the internal hydraulic performance of bioreactors. The results of the tracer tests revealed that carbon dosing had no significant effect on the hydraulic parameters of the mesocosm bioreactors (p-value > 0.05). 
The findings of this thesis have implications for improving the performance of existing bioreactors or for developing new, externally dosed bioreactors with smaller spatial footprints. The constant dosage strategy, demonstrated in the full-scale bioreactor, was effective in increasing nitrate removal rates while also being safe regarding added carbon losses to the receiving environments. The ease of implementation of the constant dosage strategy could increase take-up from landowners and managers. The thesis also provides an understanding of whether and to what extent carbon dosing affects the hydrology of bioreactors, which can be used to develop new bioreactor designs with less backflow and bypass.

text: Carbon dosing of denitrifying bioreactors to remove nitrate from agricultural drainage Several studies have demonstrated that denitrifying woodchips bioreactors effectively remove nitrate from a broad spectrum of wastewater. Even though bioreactors have a comparatively small spatial footprint and are straightforward to construct, the low long-term nitrate removal efficiency they provide compared to other mitigation options, such as constructed wetlands, may limit their utilization by catchment managers and landowners. This thesis investigated the use of external carbon dosing in bioreactors to improve nitrate removal and quantified some potential adverse effects of carbon dosing on bioreactors and downstream aquatic environments. Through observations ranging from field to mesocosm experiments, this thesis sought to (1) determine whether and to what extent external carbon dosing could improve nitrate removal in bioreactors and (2) assess the potential adverse effects of carbon dosing, such as reduced hydraulic performance and pollution swapping. 
The first component of the study evaluated the carbon dosing of a pilot-scale (58 m³) bioreactor treating drainage waters from a 0.65 ha paddock on a dairy farm. The effects of carbon dosing on the bioreactor's nitrate removal rates were assessed following a constant dosage of 8% (v/v) methanol solution at 10 mL min⁻¹ to the bioreactor's inlet distributor. Sulfate reduction and losses of added methanol from the bioreactor’s outlet were quantified as the potential adverse effects of external carbon dosing. Methanol dosing increased seasonal nitrate removal rates to 8 g N m⁻³ day⁻¹ in 2020 and 5 g N m⁻³ day⁻¹ in 2021 (with a halved dosing rate), compared to 1 g N m⁻³ day⁻¹ in the undosed bioreactor in 2018. Even under nitrate-limiting conditions, the added methanol was effectively removed in the bioreactor, with a mean removal rate of 106 g CH₃OH-C m⁻³ day⁻¹
. Methanol concentrations decreased by order of magnitude along the bioreactor (lengthwise) and never exceeded 50 mg CH₃OH-C L⁻¹ at the outflow. The added carbon caused sulfate reduction with a mean removal rate of 8.5 g SO4²⁻-S m⁻³ day⁻¹ in 2020 (higher dosing rate) and 0.5 g SO4²⁻-S m⁻³ day⁻¹ in 2021 (halved dosing rate). Carbon dosage at a continuous rate was shown to be a viable method for increasing nitrate removal while minimizing capital and operational costs. The simplicity of this approach is a significant advantage, and it could be used by a variety of industries, including farmers.
While field observations showed that carbon dosage could improve nitrate removal, the very variable flows and nitrate concentrations made determining nitrate, sulfate, and methanol removal rates difficult. Therefore, the second component of the thesis was to assess nitrate, sulfate and added carbon removal rates more accurately using mesocosms. An empirical model was also developed to calculate the amount of methanol required to remove specific loads of nitrate. Mesocosm bioreactors were designed to share some characteristics with the field bioreactor (for example, added carbon component and dosage ratio) but diverged in that they were hydrologically regulated to eliminate the impact of transient operating circumstances on bioreactor performance. Carbon dosing increased nitrate removal rates from 7 g N m⁻³ day⁻¹ in the control treatment bioreactors (without methanol addition) to 27 g N m⁻³ day⁻¹ in the methanol-dosed treatment bioreactors. Added methanol was removed in either the absence or presence of nitrate, with mean methanol removal rates of 23 g CH₃OH-C m⁻³ day⁻¹ in nitrate prevailing conditions and 17 g CH₃OH-C m⁻³ day⁻¹ in nitrate limiting conditions. The empirical model suggested that a methanol to nitrate ratio of 0.7 resulted in complete nitrate removal. 
In the third component of this thesis research, observations from both mesocosm and full-scale bioreactors were used to assess the hydraulic characteristics of bioreactors under various carbon dosage regimes. Field measurements revealed a decrease in hydraulic conductivity from 4601 m day⁻¹ in 2018 (season without carbon dosing) to 1600 m day⁻¹ in 2021 (second year of dosing). Based on tracer tests of the mesocosm bioreactors, I investigated the effects of added carbon on the internal hydraulic performance of bioreactors. The results of the tracer tests revealed that carbon dosing had no significant effect on the hydraulic parameters of the mesocosm bioreactors (p-value > 0.05). 
The findings of this thesis have implications for improving the performance of existing bioreactors or for developing new, externally dosed bioreactors with smaller spatial footprints. The constant dosage strategy, demonstrated in the full-scale bioreactor, was effective in increasing nitrate removal rates while also being safe regarding added carbon losses to the receiving environments. The ease of implementation of the constant dosage strategy could increase take-up from landowners and managers. The thesis also provides an understanding of whether and to what extent carbon dosing affects the hydrology of bioreactors, which can be used to develop new bioreactor designs with less backflow and bypass.

year: 2022

title: Andisols of New Zealand and Australia.

authors: Lowe, David J.

subjects: Vitrands

abstract: During the Quaternary, much of central North Island, New Zealand, was repeatedly overwhelmed or modified by emplacement of ignimbrites and especially by multiple rhyolitic and andesitic tephra fallout deposits, and reworked derivatives, that successively mantled landsurfaces forming buried paleosols in multisequal profiles. Relatively thick proximal deposits buried and isolated antecedent soils, forming compound soil profiles, whereas relatively thin tephra fallout at medial and distal sites resulted in composite or aggrading profiles, their character determined by the interplay of upbuilding and topdown pedogenesis. Scoriaceous basaltic tephras erupted in northern North Island were locally distributed. Andisols, of the 'allophanic' type with andic soil properties dominated by short-range-order (SRO) clays rather than Al-humus complexes, cover ~32, 100 km²  and comprise about 12.5% of New Zealand soils. They consist of three groups : (1) 'Entic' Udands or Cryands occur on mainly andesitic eruptives <1000 years old near recently active volcanoes>(Tephric Recent Soils in New Zealand Soil Classification ; ~1200 km² , ~0.5%) ; (2) Vitrands occur in central-eastern North Island on glassy, rhyolitic pumiceous deposits mainly from the Taupo eruption c. 232 AD and the Kaharoa eruption c. 1314 AD (Pumice Soils ; ~17, 200 km² , ~6.5%) ; and (3) Udands occur typically on composite, multiple tephra deposits of varying ages in Taranaki (mainly andesitic tephras), King Country-western Waikato (mixed andesitic-rhyolitic), eastern Waikato-western Bay of Plenty-Coromandel (mainly rhyolitic), and Auckland-Northland (basaltic), the age span of sola increasing towards distal sites as constituent tephra layers become thinner and shallower (Allophanic Soils ; ~13, 700 km² , ~5.5%). Moisture and temperature regimes are mainly udic and mesic, thermic, or cryic. Udands are pre-eminent among New Zealand's most versatile, high-quality soils because they provide valuable soil ecosystem services including sorption, water storage and supply, natural fertility, and foundation support. Andisols are currently known only in the Mt Gambier area of southeast South Australia, and comprise ~85 km² (~0.001%) of Australian soils. Intraplate basaltic volcanoes at Mts Gambier and Schank erupted c. 5000 years ago and the resultant localised tephras contain both exotic crystalline material, derived from underlying limestone and calcareous dunes, and juvenile basaltic material. Sand fractions at Mt Gambier are dominated by exotic, silicic crystalline material (≥80%) and relatively little glass (<20%) but at Mt Schank unaltered Al-rich glass predominates (≥50%). Vitrixerands and Haploxerands with pHs 6.4-8.0 have been formed under xeric moisture and mesic temperature regimes (Andic, Chernic Tenosols in Australian Soil Classification). The parent mineralogies have influenced clay mineral formation : SRO clays at Mt Schank (up to 20% allophane, 7% ferrihydrite, fine-earth basis) are more abundant than at Mt Gambier (≤12% allophane, 4% ferrihydrite) because the glass at Mt Schank weathers more rapidly than the Al-poor crystalline material at Mt Gambier, releasing Al. Seasonal Si-leaching has also been influential: where leaching is sufficient to remove silica, and CaCO3 content is low (in upper soil horizons at Mt Gambier; in most horizons at Mt Schank), Al-rich allophane has formed ; where leaching is weak (intermediate horizons), Si-rich allophane and layer silicate minerals (but not halloysite) have formed; and where leaching barely occurs (in lowest horizons), smectite has formed. The Xerands are versatile soils.

text: Andisols of New Zealand and Australia. During the Quaternary, much of central North Island, New Zealand, was repeatedly overwhelmed or modified by emplacement of ignimbrites and especially by multiple rhyolitic and andesitic tephra fallout deposits, and reworked derivatives, that successively mantled landsurfaces forming buried paleosols in multisequal profiles. Relatively thick proximal deposits buried and isolated antecedent soils, forming compound soil profiles, whereas relatively thin tephra fallout at medial and distal sites resulted in composite or aggrading profiles, their character determined by the interplay of upbuilding and topdown pedogenesis. Scoriaceous basaltic tephras erupted in northern North Island were locally distributed. Andisols, of the 'allophanic' type with andic soil properties dominated by short-range-order (SRO) clays rather than Al-humus complexes, cover ~32, 100 km²  and comprise about 12.5% of New Zealand soils. They consist of three groups : (1) 'Entic' Udands or Cryands occur on mainly andesitic eruptives <1000 years old near recently active volcanoes>(Tephric Recent Soils in New Zealand Soil Classification ; ~1200 km² , ~0.5%) ; (2) Vitrands occur in central-eastern North Island on glassy, rhyolitic pumiceous deposits mainly from the Taupo eruption c. 232 AD and the Kaharoa eruption c. 1314 AD (Pumice Soils ; ~17, 200 km² , ~6.5%) ; and (3) Udands occur typically on composite, multiple tephra deposits of varying ages in Taranaki (mainly andesitic tephras), King Country-western Waikato (mixed andesitic-rhyolitic), eastern Waikato-western Bay of Plenty-Coromandel (mainly rhyolitic), and Auckland-Northland (basaltic), the age span of sola increasing towards distal sites as constituent tephra layers become thinner and shallower (Allophanic Soils ; ~13, 700 km² , ~5.5%). Moisture and temperature regimes are mainly udic and mesic, thermic, or cryic. Udands are pre-eminent among New Zealand's most versatile, high-quality soils because they provide valuable soil ecosystem services including sorption, water storage and supply, natural fertility, and foundation support. Andisols are currently known only in the Mt Gambier area of southeast South Australia, and comprise ~85 km² (~0.001%) of Australian soils. Intraplate basaltic volcanoes at Mts Gambier and Schank erupted c. 5000 years ago and the resultant localised tephras contain both exotic crystalline material, derived from underlying limestone and calcareous dunes, and juvenile basaltic material. Sand fractions at Mt Gambier are dominated by exotic, silicic crystalline material (≥80%) and relatively little glass (<20%) but at Mt Schank unaltered Al-rich glass predominates (≥50%). Vitrixerands and Haploxerands with pHs 6.4-8.0 have been formed under xeric moisture and mesic temperature regimes (Andic, Chernic Tenosols in Australian Soil Classification). The parent mineralogies have influenced clay mineral formation : SRO clays at Mt Schank (up to 20% allophane, 7% ferrihydrite, fine-earth basis) are more abundant than at Mt Gambier (≤12% allophane, 4% ferrihydrite) because the glass at Mt Schank weathers more rapidly than the Al-poor crystalline material at Mt Gambier, releasing Al. Seasonal Si-leaching has also been influential: where leaching is sufficient to remove silica, and CaCO3 content is low (in upper soil horizons at Mt Gambier; in most horizons at Mt Schank), Al-rich allophane has formed ; where leaching is weak (intermediate horizons), Si-rich allophane and layer silicate minerals (but not halloysite) have formed; and where leaching barely occurs (in lowest horizons), smectite has formed. The Xerands are versatile soils.

year: 2005-01-01

title: Colouring in the White Spaces: Reclaiming Cultural Identity in Whitestream Schools

authors: Milne, Beverley Ann

subjects: Maori education

abstract: If we look at a child’s colouring book, before it has any colour added to it, we think of the page as blank.  It’s actually not blank, it’s white.  That white background is just “there” and we don’t think much about it.  Not only is the background uniformly white, the lines are already in place and they dictate where the colour is allowed to go.  When children are young, they don’t care where they put the colours, but as they get older they colour in more and more cautiously. They learn about the place of colour and the importance of staying within the pre-determined boundaries and expectations. 

This thesis argues that this is the setting for our mainstream, or what I have called, whitestream New Zealand schools — that white background is the norm.   When we talk about multiculturalism and diversity what we are really referring to is the colour of the children, or their difference from that white norm, and how they don’t fit perfectly inside our lines.  If the colour of the space doesn’t change schools are still in the business of assimilation, relegating non-white children to the margins, no matter how many school reform initiatives, new curricula, strategic plans, or mandated standards we implement.  What the schools in this study have tried to do is change the colour of the space – so that the space fits the children and they don’t have to constantly adjust to fit in.  

New Zealand’s education system has been largely silent on the topic of whiteness and the Eurocentric nature of our schooling policy and practice. However, when I talk to senior Māori and Pasifika ‘warrior-scholars” in Te Whānau o Tupuranga and Clover Park Middle School about “white spaces” they have encountered in their schooling experience they can identify them all too easily.  “White spaces,” they explain, are anything you accept as “normal” for Māori – when it’s really not,  any situation that prevents, or works against you “being Māori” or who you are, and that requires you to “be” someone else and leave your beliefs behind. White spaces are spaces that allow you to require less of yourself and that reinforce stereotypes and negative ideas about Māori.  Most telling of all was the comment from a Māori student that goes straight to the root of the problem, “White spaces are everywhere,” she said, “even in your head.”

This thesis describes the 25 year journey of two schools and their community’s determination to resist and reject alienating school environments in favour of a relevant culturally-located, bilingual learning model based in a secure cultural identity, stable positive relationships, and aroha (authentic caring and love).  While the research design is a case study, in terms of western, “white space” academic tradition, it is also a story in terms of kaupapa Māori and critical race methodology. More importantly, it is a counter-story that chronicles the efforts of these two schools to step outside education’s “white spaces” to create new space.  This counter-story is juxtaposed against pervasive, deficit-driven whitestream explanations of “achievement gaps” and the “long tail” of Māori and Pasifika “under-achievement” in New Zealand schools.  In the process of this research the focus shifted from how could Māori and Pasifika learners develop secure cultural identities in mainstream schools, to examining what barriers exist in schools that prevent this from happening already?  As these issues became clear the language of the thesis shifted accordingly; “developing” a cultural identity was reframed as a reclamation of educational sovereignty — the absolute right to “be Māori” or “be Pasifika” in school — and “mainstream” schooling became better understood as the “whitestream.” 

The study hopes to contribute to the journey other schools might take to identify and name their own white spaces, and to make learning equitable for indigenous and minoritised learners.

text: Colouring in the White Spaces: Reclaiming Cultural Identity in Whitestream Schools If we look at a child’s colouring book, before it has any colour added to it, we think of the page as blank.  It’s actually not blank, it’s white.  That white background is just “there” and we don’t think much about it.  Not only is the background uniformly white, the lines are already in place and they dictate where the colour is allowed to go.  When children are young, they don’t care where they put the colours, but as they get older they colour in more and more cautiously. They learn about the place of colour and the importance of staying within the pre-determined boundaries and expectations. 

This thesis argues that this is the setting for our mainstream, or what I have called, whitestream New Zealand schools — that white background is the norm.   When we talk about multiculturalism and diversity what we are really referring to is the colour of the children, or their difference from that white norm, and how they don’t fit perfectly inside our lines.  If the colour of the space doesn’t change schools are still in the business of assimilation, relegating non-white children to the margins, no matter how many school reform initiatives, new curricula, strategic plans, or mandated standards we implement.  What the schools in this study have tried to do is change the colour of the space – so that the space fits the children and they don’t have to constantly adjust to fit in.  

New Zealand’s education system has been largely silent on the topic of whiteness and the Eurocentric nature of our schooling policy and practice. However, when I talk to senior Māori and Pasifika ‘warrior-scholars” in Te Whānau o Tupuranga and Clover Park Middle School about “white spaces” they have encountered in their schooling experience they can identify them all too easily.  “White spaces,” they explain, are anything you accept as “normal” for Māori – when it’s really not,  any situation that prevents, or works against you “being Māori” or who you are, and that requires you to “be” someone else and leave your beliefs behind. White spaces are spaces that allow you to require less of yourself and that reinforce stereotypes and negative ideas about Māori.  Most telling of all was the comment from a Māori student that goes straight to the root of the problem, “White spaces are everywhere,” she said, “even in your head.”

This thesis describes the 25 year journey of two schools and their community’s determination to resist and reject alienating school environments in favour of a relevant culturally-located, bilingual learning model based in a secure cultural identity, stable positive relationships, and aroha (authentic caring and love).  While the research design is a case study, in terms of western, “white space” academic tradition, it is also a story in terms of kaupapa Māori and critical race methodology. More importantly, it is a counter-story that chronicles the efforts of these two schools to step outside education’s “white spaces” to create new space.  This counter-story is juxtaposed against pervasive, deficit-driven whitestream explanations of “achievement gaps” and the “long tail” of Māori and Pasifika “under-achievement” in New Zealand schools.  In the process of this research the focus shifted from how could Māori and Pasifika learners develop secure cultural identities in mainstream schools, to examining what barriers exist in schools that prevent this from happening already?  As these issues became clear the language of the thesis shifted accordingly; “developing” a cultural identity was reframed as a reclamation of educational sovereignty — the absolute right to “be Māori” or “be Pasifika” in school — and “mainstream” schooling became better understood as the “whitestream.” 

The study hopes to contribute to the journey other schools might take to identify and name their own white spaces, and to make learning equitable for indigenous and minoritised learners.

year: 2013