title: The development and applications of a micro-gap perforated electrode flow through cell

authors: Nath, Hilary

subjects: Electrochemistry

abstract: Electrochemical techniques provide convenient and environmentally compatible ways of bringing about chemical transformations. However they generally lose their economic viability when used with low conducting electrolyte systems. This has limited their usefulness in the treatment of water and wastewater. Increasing the electrolyte concentration of these systems is not an option as it is with industrial processes such as the chlor-alkali process. Cell resistance is the major limiting factor. Cell resistance can be reduced by reducing the inter-electrode gap. A novel micro gap perforated electrode flow through (PEFT) cell has been developed for efficient and cost effective treatment of aqueous systems of low ionic strength. The PEFT cell is an undivided flow through design which encompasses both parallel plate and porous electrode features. It consists of plate electrodes and flow is both through the electrodes and parallel to the surfaces of the two electrodes. The perforations in the electrodes and the short flow distance between the electrodes allow the inter-electrode gap to be reduced to 50 microns and less without causing excessive resistance to hydraulic flow. With reduced electrical resistance, effective electrochemical treatment of natural water and other low electrolyte systems is possible. The PEFT cell was first applied to overcome a local water supply problem, the Waikato region’s iron and manganese contaminated bore waters. These waters form stable colloidal suspensions during slow air oxidation. The problem can be overcome by rapid electrochemical oxidation using the PEFT cell. Electrochemical oxidation was found to be more effective and efficient than chemical oxidation allowing removal of iron and manganese to meet drinking water standards with minimal formation of disinfection by-products (DBP). Electrochemical oxidation of water and wastewater systems is brought about principally by chlorine mediated indirect oxidation processes. A 240 µm gap PEFT cell, with a graphite anode was used for chlorine generation. It produced chlorine at current efficiencies above 60% with an energy consumption of 4.83 kWh/kg of chlorine from a 0.5 mol/L NaCl solution. This result compares well with industrial hypochlorite production using an undivided cell. Chlorine mediated electro-oxidation of effluents was successfully demonstrated by the degradation of textile dyes in water. Complete single pass electrochemical decolourisation of indigo carmine (IC) dye effluent containing 0.35 mol/L NaCl was achieved using a graphite anode PEFT cell. Energy consumption was 0.8 kWh/m3 or 8.3 kWh/kg of dye. This is an order of magnitude less than the energy consumption reported for colour removal using graphite anodes. It is comparable or lower than most colour removal work carried out using metal oxide coated dimensionally stable anodes (DSAs) and boron doped diamond (BDD) anodes. Reduction of pH from 7 to 3 reduced the energy consumption for decolourisation of IC dye by 50% and also increased the TOC removal by 20%. When NaSO4 was used as the electrolyte rather than sodium chloride, colour removal was much less effective. A single pass through a 50 µm gap PEFT cell with a stainless steel cathode and a graphite anode operated at 5.5 V achieved a 6 log inactivation of Escherichia coli bacteria in a water sample containing only 1.7 mmol/L of chloride ions. The power consumption was 0.5 kWh/m3 of water. The narrow inter-electrode gap allows high electric fields to be produced from low applied voltages. When the cell was operated at above 5.0 volts, a synergistic electric field effect was observed. Specific lethality of the chlorine was increased to at least 50 L/(mgmin), approximately two orders of magnitude higher than in the absence of the field. Increased specific lethality means that disinfection can be achieved at much lower free available chlorine levels than previously possible. This reduces the risk of DBP formation. Improved current efficiencies and reduced energy consumption for electrolysis at low electrolyte concentrations were achieved by partial insulation of the active anode surface of a 50 µm gap PEFT cell. This electro-catalytic effect was consistent with enhanced transport of the electroactive species to the active part of the electrode, reducing concentration and resistance overpotentials. In the electrochemical production of chlorine from 0.85 mmol/L NaCl at a current density of 2 mA/cm2, current efficiency was tripled and power consumption was reduced by a factor of two, relative to the cell without the anode modification. The reduction in the inter-electrode gap to 50 µm and less has allowed the production of electric field strengths greater than 10 kV/cm from applied voltages of less than a 100V. Field strengths between 1and 10 kV/cm are known to cause reversible electroporation whereas irreversible electroporation occurs above 10 kV/cm. Evidence for irreversible electroporation was provided by the 6 log inactivation of Escherichia coli (in the absence of chlorine) at an applied electric field of 22.5 kV/cm generated in a 40 µm gap PEFT cell by a 90 V DC supply. The energy consumption was 430 J/mL and without cooling, the temperature remained below 42oC. Inactivation was achieved by 20 hydrodynamically generated DC pulses. The low applied voltage, the elimination of the need for pulsed electric fields, avoidance of external cooling and the simplicity of the experiment bring commercial non thermal electro-pasteurisation one step closer.

text: The development and applications of a micro-gap perforated electrode flow through cell Electrochemical techniques provide convenient and environmentally compatible ways of bringing about chemical transformations. However they generally lose their economic viability when used with low conducting electrolyte systems. This has limited their usefulness in the treatment of water and wastewater. Increasing the electrolyte concentration of these systems is not an option as it is with industrial processes such as the chlor-alkali process. Cell resistance is the major limiting factor. Cell resistance can be reduced by reducing the inter-electrode gap. A novel micro gap perforated electrode flow through (PEFT) cell has been developed for efficient and cost effective treatment of aqueous systems of low ionic strength. The PEFT cell is an undivided flow through design which encompasses both parallel plate and porous electrode features. It consists of plate electrodes and flow is both through the electrodes and parallel to the surfaces of the two electrodes. The perforations in the electrodes and the short flow distance between the electrodes allow the inter-electrode gap to be reduced to 50 microns and less without causing excessive resistance to hydraulic flow. With reduced electrical resistance, effective electrochemical treatment of natural water and other low electrolyte systems is possible. The PEFT cell was first applied to overcome a local water supply problem, the Waikato region’s iron and manganese contaminated bore waters. These waters form stable colloidal suspensions during slow air oxidation. The problem can be overcome by rapid electrochemical oxidation using the PEFT cell. Electrochemical oxidation was found to be more effective and efficient than chemical oxidation allowing removal of iron and manganese to meet drinking water standards with minimal formation of disinfection by-products (DBP). Electrochemical oxidation of water and wastewater systems is brought about principally by chlorine mediated indirect oxidation processes. A 240 µm gap PEFT cell, with a graphite anode was used for chlorine generation. It produced chlorine at current efficiencies above 60% with an energy consumption of 4.83 kWh/kg of chlorine from a 0.5 mol/L NaCl solution. This result compares well with industrial hypochlorite production using an undivided cell. Chlorine mediated electro-oxidation of effluents was successfully demonstrated by the degradation of textile dyes in water. Complete single pass electrochemical decolourisation of indigo carmine (IC) dye effluent containing 0.35 mol/L NaCl was achieved using a graphite anode PEFT cell. Energy consumption was 0.8 kWh/m3 or 8.3 kWh/kg of dye. This is an order of magnitude less than the energy consumption reported for colour removal using graphite anodes. It is comparable or lower than most colour removal work carried out using metal oxide coated dimensionally stable anodes (DSAs) and boron doped diamond (BDD) anodes. Reduction of pH from 7 to 3 reduced the energy consumption for decolourisation of IC dye by 50% and also increased the TOC removal by 20%. When NaSO4 was used as the electrolyte rather than sodium chloride, colour removal was much less effective. A single pass through a 50 µm gap PEFT cell with a stainless steel cathode and a graphite anode operated at 5.5 V achieved a 6 log inactivation of Escherichia coli bacteria in a water sample containing only 1.7 mmol/L of chloride ions. The power consumption was 0.5 kWh/m3 of water. The narrow inter-electrode gap allows high electric fields to be produced from low applied voltages. When the cell was operated at above 5.0 volts, a synergistic electric field effect was observed. Specific lethality of the chlorine was increased to at least 50 L/(mgmin), approximately two orders of magnitude higher than in the absence of the field. Increased specific lethality means that disinfection can be achieved at much lower free available chlorine levels than previously possible. This reduces the risk of DBP formation. Improved current efficiencies and reduced energy consumption for electrolysis at low electrolyte concentrations were achieved by partial insulation of the active anode surface of a 50 µm gap PEFT cell. This electro-catalytic effect was consistent with enhanced transport of the electroactive species to the active part of the electrode, reducing concentration and resistance overpotentials. In the electrochemical production of chlorine from 0.85 mmol/L NaCl at a current density of 2 mA/cm2, current efficiency was tripled and power consumption was reduced by a factor of two, relative to the cell without the anode modification. The reduction in the inter-electrode gap to 50 µm and less has allowed the production of electric field strengths greater than 10 kV/cm from applied voltages of less than a 100V. Field strengths between 1and 10 kV/cm are known to cause reversible electroporation whereas irreversible electroporation occurs above 10 kV/cm. Evidence for irreversible electroporation was provided by the 6 log inactivation of Escherichia coli (in the absence of chlorine) at an applied electric field of 22.5 kV/cm generated in a 40 µm gap PEFT cell by a 90 V DC supply. The energy consumption was 430 J/mL and without cooling, the temperature remained below 42oC. Inactivation was achieved by 20 hydrodynamically generated DC pulses. The low applied voltage, the elimination of the need for pulsed electric fields, avoidance of external cooling and the simplicity of the experiment bring commercial non thermal electro-pasteurisation one step closer.

year: 2011

title: Moderating effects of perceived control and need for clarity on the relationship between role stressors and employee affective reactions.

authors: O’Driscoll, Michael P.

subjects: psychology

abstract: The authors examined the salience of perceived control and need for clarity as “buffers” of the adverse consequences of role stressors by using hierarchical regressions on role ambiguity and role conflict, with job satisfaction and psychological strain as the criterion variables. In a sample of U.S. and New Zealand employees, perceived control was directly associated with higher satisfaction and reduced strain but displayed no moderating effect on stressor-outcome relationships. Need for clarity, on the other hand, was a significant moderator of the relationship of role ambiguity and conflict to both satisfaction and strain; that finding suggests that researchers could give more attention to dispositional variables in examining the correlates of role stressors.

text: Moderating effects of perceived control and need for clarity on the relationship between role stressors and employee affective reactions. The authors examined the salience of perceived control and need for clarity as “buffers” of the adverse consequences of role stressors by using hierarchical regressions on role ambiguity and role conflict, with job satisfaction and psychological strain as the criterion variables. In a sample of U.S. and New Zealand employees, perceived control was directly associated with higher satisfaction and reduced strain but displayed no moderating effect on stressor-outcome relationships. Need for clarity, on the other hand, was a significant moderator of the relationship of role ambiguity and conflict to both satisfaction and strain; that finding suggests that researchers could give more attention to dispositional variables in examining the correlates of role stressors.

year: 2000

title: Radiocarbon dates on desiccated moa (Dinornithiformes) flesh from Inland Otago, New Zealand

authors: Anderson, Atholl

subjects: New Zealand

abstract: Remains of soft tissues from extinct moa (Dinornithiformes), mainly desiccated sinew, muscle, skin, and feathers have been recovered rather seldom but their distribution is distinctive. Of 22 records of such finds accumulated between 1864 and 1987, 15 came from inland Otago (Anderson 1989: 67–68, Table 5.2), west of Dunedin in the southern South Island. Most were found in the late nineteenth century (13 records) in rockshelters, clefts or alluvial sediments and were regarded at the time as evidence of the survival of moa up to about AD 1800 (Hutton and Coughtrey 1874a). Improbable as this latter point is, it has not been tested by radiocarbon dating until now. Our particular impetus to do so, however, arises in another way. It is from research, again largely within inland Otago, on Maori artefacts which have also been made from various other kinds of soft tissues (flax, grasses, dog skin, bird skin, feathers etc.). A series of accelerator mass spectrometry (AMS) radiocarbon dates on these (Anderson et al., n.d.) shows that they are exclusively late, post-AD 1650, which begs the question of why the age range does not extend across the full prehistoric period, beginning about AD 1300.

text: Radiocarbon dates on desiccated moa (Dinornithiformes) flesh from Inland Otago, New Zealand Remains of soft tissues from extinct moa (Dinornithiformes), mainly desiccated sinew, muscle, skin, and feathers have been recovered rather seldom but their distribution is distinctive. Of 22 records of such finds accumulated between 1864 and 1987, 15 came from inland Otago (Anderson 1989: 67–68, Table 5.2), west of Dunedin in the southern South Island. Most were found in the late nineteenth century (13 records) in rockshelters, clefts or alluvial sediments and were regarded at the time as evidence of the survival of moa up to about AD 1800 (Hutton and Coughtrey 1874a). Improbable as this latter point is, it has not been tested by radiocarbon dating until now. Our particular impetus to do so, however, arises in another way. It is from research, again largely within inland Otago, on Maori artefacts which have also been made from various other kinds of soft tissues (flax, grasses, dog skin, bird skin, feathers etc.). A series of accelerator mass spectrometry (AMS) radiocarbon dates on these (Anderson et al., n.d.) shows that they are exclusively late, post-AD 1650, which begs the question of why the age range does not extend across the full prehistoric period, beginning about AD 1300.

year: 2010