title: Evaluation of passive solar heating and alternative flow regimes on nitrate removal in denitrification beds

authors: Cameron, Stewart Graham

subjects: denitrification bed

abstract: Denitrification beds are a simple and relatively inexpensive technology for removing nitrate from point source discharges. To date, operational beds have used wood media as the carbon source, as it provides a sustained nitrate removal rate (2–10 g N m⁻³ of media d⁻¹) while maintaining permeability. In pilot-scale (2.9 m⁻³) denitrification beds receiving municipal wastewater effluent dosed with KNO₃, we looked at improving nitrate removal by using alternative carbon media (maize cobs) and increasing bed temperature through passive solar heating. The influence of flow regime (horizontal-point, horizontal-diffuse, downflow and upflow) on short-circuit flow was also investigated.
The long-term nitrate removal rate (21.8 g N m⁻³ d⁻¹) of the maize cob beds over the 15-month period of the trial was 2–11-fold higher than sustained removal rates reported by other researchers for wood-based beds. While passive solar heating raised the mean bed temperature by 3.4 °C, it did not cause a measurable increase in the nitrate removal rate due to the variability in the removal rate exceeding the expected increase due to temperature.
Horizontal flow had more short-circuiting than vertical flow. Short-circuiting in the horizontal flow was attributed to flow being concentrated near the top surface due to the buoyancy effect of warmer water. Greater short-circuiting in the solar heated horizontal and upflow beds than in the corresponding unheated beds was attributed to the buoyancy effect being more pronounced in the solar heated beds.
Overall, downflow was deemed the most effective of the four tested flow regimes. It provided the highest increase in bed temperature due to solar heating, had the highest nitrate removal rate in the latter part of the trial and had more plug-flow characteristics. While passive solar heating raised bed temperature, we were unable to demonstrate a significant difference (at 95% CL) in nitrate removal rate between the unheated and solar heated beds because of the high variability in nitrate removal rate and the increase in short-circuiting in the solar heated horizontal and upflow beds.

text: Evaluation of passive solar heating and alternative flow regimes on nitrate removal in denitrification beds Denitrification beds are a simple and relatively inexpensive technology for removing nitrate from point source discharges. To date, operational beds have used wood media as the carbon source, as it provides a sustained nitrate removal rate (2–10 g N m⁻³ of media d⁻¹) while maintaining permeability. In pilot-scale (2.9 m⁻³) denitrification beds receiving municipal wastewater effluent dosed with KNO₃, we looked at improving nitrate removal by using alternative carbon media (maize cobs) and increasing bed temperature through passive solar heating. The influence of flow regime (horizontal-point, horizontal-diffuse, downflow and upflow) on short-circuit flow was also investigated.
The long-term nitrate removal rate (21.8 g N m⁻³ d⁻¹) of the maize cob beds over the 15-month period of the trial was 2–11-fold higher than sustained removal rates reported by other researchers for wood-based beds. While passive solar heating raised the mean bed temperature by 3.4 °C, it did not cause a measurable increase in the nitrate removal rate due to the variability in the removal rate exceeding the expected increase due to temperature.
Horizontal flow had more short-circuiting than vertical flow. Short-circuiting in the horizontal flow was attributed to flow being concentrated near the top surface due to the buoyancy effect of warmer water. Greater short-circuiting in the solar heated horizontal and upflow beds than in the corresponding unheated beds was attributed to the buoyancy effect being more pronounced in the solar heated beds.
Overall, downflow was deemed the most effective of the four tested flow regimes. It provided the highest increase in bed temperature due to solar heating, had the highest nitrate removal rate in the latter part of the trial and had more plug-flow characteristics. While passive solar heating raised bed temperature, we were unable to demonstrate a significant difference (at 95% CL) in nitrate removal rate between the unheated and solar heated beds because of the high variability in nitrate removal rate and the increase in short-circuiting in the solar heated horizontal and upflow beds.

year: 2011

title: The contribution of lakes to greenhouse gas emissions – fact sheet

authors: Santoso, A

abstract: Greenhouse gases such as carbon dioxide (C0₂) , methane (CH₄)  and nitrous oxide (N₂0) trap heat in the atmosphere. Lakes can play an important role in regulating these gases at global scales. Total carbon uptake by lakes is of the same magnitude as that of oceans or forests, despite lakes occupying <1% of the Earth's area. In lakes, GHGs are mostly produced in the bottom sediment as products of organic matter decomposition. Geothermal activities - of importance to some Rotorua lakes - may also contribute substantial amounts of C0₂ and CH₄.

text: The contribution of lakes to greenhouse gas emissions – fact sheet Greenhouse gases such as carbon dioxide (C0₂) , methane (CH₄)  and nitrous oxide (N₂0) trap heat in the atmosphere. Lakes can play an important role in regulating these gases at global scales. Total carbon uptake by lakes is of the same magnitude as that of oceans or forests, despite lakes occupying <1% of the Earth's area. In lakes, GHGs are mostly produced in the bottom sediment as products of organic matter decomposition. Geothermal activities - of importance to some Rotorua lakes - may also contribute substantial amounts of C0₂ and CH₄.

year: 2015

title: Evidence of swarm intelligence in collective cultures: Identifying the use of the swarm goal directive of productivity in Pacific organisation systems as well as getween genders

authors: Arun, Natalie M.

subjects: Maori

abstract: Intrigued by the existence of societies outside that of the human population, scientists have ventured to study social aggregations within insects to seek insights on effective colonizing. The most popular of these social aggregations are colonies of ants and bees. In studying these groups of social insects researchers have developed algorithms loosely termed swarm intelligence that increase work efficiency within businesses and other social organizations (Bonabeau & Meyer, 2001). A subsequent proliferation of research in surrounding fields has allowed for investigation of key variables that improve work on a global scale (Bonabeau & Meyer, 2001). James Kennedy (1999), an initiator of swarm research, has suggested that there is a high correlation between systems that rely on each other for information and greater task accomplishment.

text: Evidence of swarm intelligence in collective cultures: Identifying the use of the swarm goal directive of productivity in Pacific organisation systems as well as getween genders Intrigued by the existence of societies outside that of the human population, scientists have ventured to study social aggregations within insects to seek insights on effective colonizing. The most popular of these social aggregations are colonies of ants and bees. In studying these groups of social insects researchers have developed algorithms loosely termed swarm intelligence that increase work efficiency within businesses and other social organizations (Bonabeau & Meyer, 2001). A subsequent proliferation of research in surrounding fields has allowed for investigation of key variables that improve work on a global scale (Bonabeau & Meyer, 2001). James Kennedy (1999), an initiator of swarm research, has suggested that there is a high correlation between systems that rely on each other for information and greater task accomplishment.

year: 2008