title: Development of a real-time technique for in-sditu measurement of pH in capacitive deionisation

authors: Tharman, Mathavan

abstract: Capacitive Deionisation (CDI) as a desalination technique proves to be one of the most promising technologies owing to its simplicity and ease of manufacturability. The longevity of CDI depends on a number of factors, such as the ability of carbon to withstand Faradaic reactions to CO2. Furthermore,
like other technologies such as (reverse osmosis) RO and (electrodialysis reversal) EDR, scale formation is known to affect its hydraulic efficiency. The slow mineral deposition of magnesium and calcium carbonate is responsible for such phenomena. The extent of the problem is one where the
hydraulic efficiency of the device drops well below 10%, a state where the device is considered to be at the end-of-life as it is too difficult to pump water through it. In the preliminary study we examined the performance of an industrial scale (membrane capacitive deionisation) MCDI module that has
been in operation intermittently for 5 years to establish familiarity with the performance of a used module.
In the main study, we described a new technique for observing the chemical state within the spacer channel of a CDI cell, the part of the electrode that is prone to blockage. This new technique for the direct measurement of pH is based on colourimetric analysis of a novel synthetic formulation of a
pH-sensitive dye dissolved in the electrolyte phase. The basis for this novel technique combined a simple optical microscope integrated with a microfluidic device. This microfluidic device containing a microreactor cell of 750 picolitres in size was fabricated to host the electrochemical reaction (electrode and electrolyte phases) demonstrated in this study that recreates the “CDI effect” of an industrial cell.
The pH indicator formulations were synthesised from a 1:1:2 ratio of phenolphthalein, bromothymol blue and methyl red in an ethanol solution. The pH indicator, which we denote as the standard formulation (SF), had a density of 0.93 kg/L and pH of 2.74. This was the formulation that was subsequently used in the main part of the study. The dye was characterised by visible range
spectroscopy and subsequent conversion to (hue saturation value) HSV colourmap coordinates using the 1976 CIE (International Commission on Illumination) chromaticity model. This enabled the development of a range of pH-Hue relationships using best approximated by sigmoid functions. In
the analysis of these functions, we investigated the sensitivity of the pH-Hue relationship to variation in the SF formulation due to selective electrosorption of the dye. It was shown that the variation in functions produced was not significant and that the general pH-Hue relationship did not break down
into a non-usable form.

Application of the novel technique was initially performed on a membraneless cell configuration. The pH profile was investigated from a starting range of interest of pH 8 to 9 where scale formation occurs. In the second series of reactions, we demonstrated microreactor CDI configurations with varying degrees of membrane coverage from 12.5% to 100%. It was found that the pH variation in the spacer channel was minimal or non-existent across the full charge cycle from adsorption through to desorption. This indicates that obscuration of the carbon surface blocks the protons diffusing from the surface of the carbon where it is generated by way of the standard faradaic reaction in CDI or blocking co-ions from being expelled from the membrane that may result in speciation that affects the pH.
We recommend longer in-situ observation type studies be performed to confirm the speciation chemistry present in the spacer channel typical of many situations where electrodes are reducing in performance by way of fouling and scale formation.

text: Development of a real-time technique for in-sditu measurement of pH in capacitive deionisation Capacitive Deionisation (CDI) as a desalination technique proves to be one of the most promising technologies owing to its simplicity and ease of manufacturability. The longevity of CDI depends on a number of factors, such as the ability of carbon to withstand Faradaic reactions to CO2. Furthermore,
like other technologies such as (reverse osmosis) RO and (electrodialysis reversal) EDR, scale formation is known to affect its hydraulic efficiency. The slow mineral deposition of magnesium and calcium carbonate is responsible for such phenomena. The extent of the problem is one where the
hydraulic efficiency of the device drops well below 10%, a state where the device is considered to be at the end-of-life as it is too difficult to pump water through it. In the preliminary study we examined the performance of an industrial scale (membrane capacitive deionisation) MCDI module that has
been in operation intermittently for 5 years to establish familiarity with the performance of a used module.
In the main study, we described a new technique for observing the chemical state within the spacer channel of a CDI cell, the part of the electrode that is prone to blockage. This new technique for the direct measurement of pH is based on colourimetric analysis of a novel synthetic formulation of a
pH-sensitive dye dissolved in the electrolyte phase. The basis for this novel technique combined a simple optical microscope integrated with a microfluidic device. This microfluidic device containing a microreactor cell of 750 picolitres in size was fabricated to host the electrochemical reaction (electrode and electrolyte phases) demonstrated in this study that recreates the “CDI effect” of an industrial cell.
The pH indicator formulations were synthesised from a 1:1:2 ratio of phenolphthalein, bromothymol blue and methyl red in an ethanol solution. The pH indicator, which we denote as the standard formulation (SF), had a density of 0.93 kg/L and pH of 2.74. This was the formulation that was subsequently used in the main part of the study. The dye was characterised by visible range
spectroscopy and subsequent conversion to (hue saturation value) HSV colourmap coordinates using the 1976 CIE (International Commission on Illumination) chromaticity model. This enabled the development of a range of pH-Hue relationships using best approximated by sigmoid functions. In
the analysis of these functions, we investigated the sensitivity of the pH-Hue relationship to variation in the SF formulation due to selective electrosorption of the dye. It was shown that the variation in functions produced was not significant and that the general pH-Hue relationship did not break down
into a non-usable form.

Application of the novel technique was initially performed on a membraneless cell configuration. The pH profile was investigated from a starting range of interest of pH 8 to 9 where scale formation occurs. In the second series of reactions, we demonstrated microreactor CDI configurations with varying degrees of membrane coverage from 12.5% to 100%. It was found that the pH variation in the spacer channel was minimal or non-existent across the full charge cycle from adsorption through to desorption. This indicates that obscuration of the carbon surface blocks the protons diffusing from the surface of the carbon where it is generated by way of the standard faradaic reaction in CDI or blocking co-ions from being expelled from the membrane that may result in speciation that affects the pH.
We recommend longer in-situ observation type studies be performed to confirm the speciation chemistry present in the spacer channel typical of many situations where electrodes are reducing in performance by way of fouling and scale formation.

year: 2025

title: Volcanic History and Eruption Processes of Blue Lake Crater, Tongariro

authors: Simons, Benjamin Clifford

subjects: Volcanology

abstract: Blue Lake Crater (BLC) is a volcanic crater lake situated on the northern end of the Tongariro Volcanic Centre (TgVC) and is one of at least 11 vents that have been active since c. 25 ka. The stratigraphy of the proximal-to-vent deposits and associated eruption history of BLC has been poorly constrained compared to many of the other young TgVC vents. The resurgence of volcanic activity on the northern end of the TgVC in 2012 prompted research into other young northern vents to determine if any relationships exist, and whether these vents are capable of future eruptions.
The stratigraphy, geomorphological and facies characteristics have been compiled from detailed field mapping and stratigraphic logs around the BLC pyroclastic rim and the Mangahouhounui Valley. BLC is surrounded by a rim of agglutinates and pyroclastic fall deposits that drape over older Tongariro landforms. The northern rim is comprised of Rotopaunga peak (~130 m above Blue Lake) which includes a series of four thick, welded agglutinate units (the Rotopaunga Agglutinates) which are considered to pre-date BLC, overlain by a succession of scoria and spatter beds (the Rotopaunga Scorias) which are sourced, at least in part, from BLC. A discontinuous exposure of agglutinate, up to 8 m thick, mantles the western and southern rim. A ~4 m thick, ~700 m long a'a lava flow derived from BLC extends over the eastern rim into the Mangahouhounui valley. The proximal-vent-forming deposits are comprised of non to intensely welded and agglutinated spatter and scoria and have all been produced by explosive Hawaiian-and Strombolian-style fire-fountaining. These deposits do not represent the original crater-forming event however, which based on geomorphology, is suggested to have been pheatomagmatic.
Petrography, electron microprobe and x-ray fluorescence analyses were carried out on a selection of samples. The deposits are all plagioclase-dominated porphyritic pyroxene andesites and basaltic andesites, some of which contain rare olivine. A lack of phenocryst and whole rock geochemical trends through the stratigraphic sequence indicates that there is no progression or evolution of the magmas through time, and that multiple magma batches mingled prior to eruption.
The hazards associated with BLC include: phreatomagmatic pyroclastic density currents, ballistic blocks and bombs and fire-fountaining, and lahars caused either by a future eruption or from the failure of the BLC rim.
The northern vents of the TgVC (North Crater, Te Maari craters and BLC) are closely spaced and of a similar age and similar geochemical composition. BLC and Te Maari are likely to share a similar subsurface hydrothermal system and a spatial distribution of seismicity, although these alone do not imply a link in subsurface magma plumbing between the two vents.

text: Volcanic History and Eruption Processes of Blue Lake Crater, Tongariro Blue Lake Crater (BLC) is a volcanic crater lake situated on the northern end of the Tongariro Volcanic Centre (TgVC) and is one of at least 11 vents that have been active since c. 25 ka. The stratigraphy of the proximal-to-vent deposits and associated eruption history of BLC has been poorly constrained compared to many of the other young TgVC vents. The resurgence of volcanic activity on the northern end of the TgVC in 2012 prompted research into other young northern vents to determine if any relationships exist, and whether these vents are capable of future eruptions.
The stratigraphy, geomorphological and facies characteristics have been compiled from detailed field mapping and stratigraphic logs around the BLC pyroclastic rim and the Mangahouhounui Valley. BLC is surrounded by a rim of agglutinates and pyroclastic fall deposits that drape over older Tongariro landforms. The northern rim is comprised of Rotopaunga peak (~130 m above Blue Lake) which includes a series of four thick, welded agglutinate units (the Rotopaunga Agglutinates) which are considered to pre-date BLC, overlain by a succession of scoria and spatter beds (the Rotopaunga Scorias) which are sourced, at least in part, from BLC. A discontinuous exposure of agglutinate, up to 8 m thick, mantles the western and southern rim. A ~4 m thick, ~700 m long a'a lava flow derived from BLC extends over the eastern rim into the Mangahouhounui valley. The proximal-vent-forming deposits are comprised of non to intensely welded and agglutinated spatter and scoria and have all been produced by explosive Hawaiian-and Strombolian-style fire-fountaining. These deposits do not represent the original crater-forming event however, which based on geomorphology, is suggested to have been pheatomagmatic.
Petrography, electron microprobe and x-ray fluorescence analyses were carried out on a selection of samples. The deposits are all plagioclase-dominated porphyritic pyroxene andesites and basaltic andesites, some of which contain rare olivine. A lack of phenocryst and whole rock geochemical trends through the stratigraphic sequence indicates that there is no progression or evolution of the magmas through time, and that multiple magma batches mingled prior to eruption.
The hazards associated with BLC include: phreatomagmatic pyroclastic density currents, ballistic blocks and bombs and fire-fountaining, and lahars caused either by a future eruption or from the failure of the BLC rim.
The northern vents of the TgVC (North Crater, Te Maari craters and BLC) are closely spaced and of a similar age and similar geochemical composition. BLC and Te Maari are likely to share a similar subsurface hydrothermal system and a spatial distribution of seismicity, although these alone do not imply a link in subsurface magma plumbing between the two vents.

year: 2014

title: Nga taonga o Te Urewera

authors: Te Awekotuku, Ngahuia

subjects: Maori

abstract: This report sets out to establish that Te Urewera and Tuhoe - the place, the people -
are synonymous. It is argued by two discrete approaches - cultural property and the
significance of place. These are both enmeshed in the Tuhoe concept of
matemateaone, which is defined and demonstrated throughout the text. Issues of
Tuhoe heritage and cultural property are positioned within the international
indigenous context, and considered in detail with reference to the United Nations
Report on the Protection of the Heritage of Indigenous Peoples tabled in June 1995.
A Tuhoe response to the nine sections of this document form the basis of this
submission, as they clearly reflect the intentions and principles that configure the
articles of the Treaty of Waitangi.

text: Nga taonga o Te Urewera This report sets out to establish that Te Urewera and Tuhoe - the place, the people -
are synonymous. It is argued by two discrete approaches - cultural property and the
significance of place. These are both enmeshed in the Tuhoe concept of
matemateaone, which is defined and demonstrated throughout the text. Issues of
Tuhoe heritage and cultural property are positioned within the international
indigenous context, and considered in detail with reference to the United Nations
Report on the Protection of the Heritage of Indigenous Peoples tabled in June 1995.
A Tuhoe response to the nine sections of this document form the basis of this
submission, as they clearly reflect the intentions and principles that configure the
articles of the Treaty of Waitangi.

year: 2003-08