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: A combinatorial-like probe on the reactivity of the {Pt₂S₂} core of Pt₂(PPh₃)₄(μ-S)₂ by electrospray mass spectrometry. Synthesis and structures of novel heterometallic sulfide aggregates of gold(III), mercury(II), and tin(IV) with platinum(II)

authors: Fong, S.W. Audi

subjects: chemistry

abstract: Electrospray mass spectrometry (ESMS) provides a rapid and convenient technique for probing the nucleophilicity of the {Pt₂S₂} butterfly  core. Positive-ion electrospray mass spectra have been recorded for a wide array of aggregates incorporating various metallo-fragments into the Pt₂(PPh₃)₄(μ-S)₂ 1 moiety. Such combinatorial-like screening allowed a large number of different metal–sulfur interactions to be studied and the resultant heterometallic aggregates postulated. Such postulations were subsequently confirmed by synthetic studies and single-crystal X-ray crystallographic analyses. This approach helped to minimize the  wastage  by focusing on the synthesis of aggregates that were supported by the ESMS evidence. It has resulted in the isolation of a series of novel aggregates such as {AuIIIPt₂S₂}, {HgIIPt₂S₂}, and {SnIVPt₂S₂} in good lab-scale yields. It also led to the trapping and characterization of the monoprotonated product of 1, which has eluded isolation.

text: A combinatorial-like probe on the reactivity of the {Pt₂S₂} core of Pt₂(PPh₃)₄(μ-S)₂ by electrospray mass spectrometry. Synthesis and structures of novel heterometallic sulfide aggregates of gold(III), mercury(II), and tin(IV) with platinum(II) Electrospray mass spectrometry (ESMS) provides a rapid and convenient technique for probing the nucleophilicity of the {Pt₂S₂} butterfly  core. Positive-ion electrospray mass spectra have been recorded for a wide array of aggregates incorporating various metallo-fragments into the Pt₂(PPh₃)₄(μ-S)₂ 1 moiety. Such combinatorial-like screening allowed a large number of different metal–sulfur interactions to be studied and the resultant heterometallic aggregates postulated. Such postulations were subsequently confirmed by synthetic studies and single-crystal X-ray crystallographic analyses. This approach helped to minimize the  wastage  by focusing on the synthesis of aggregates that were supported by the ESMS evidence. It has resulted in the isolation of a series of novel aggregates such as {AuIIIPt₂S₂}, {HgIIPt₂S₂}, and {SnIVPt₂S₂} in good lab-scale yields. It also led to the trapping and characterization of the monoprotonated product of 1, which has eluded isolation.

year: 2001

title: Boat electrofishing survey of fish abundance in the Ohau Channel, Rotorua, in 2017

authors: Hicks, Brendan J.

abstract: The aim of the survey was to provide on-going monitoring of the fish communities and abundance by boat electrofishing in the Ohau Channel, especially fish species that are taonga to Maori (tuna, or eels, morihana, or goldfish, and kōura, or freshwater crayfish). In the current study, we present the findings from the eleventh year of sampling (2017) and a summary of previous surveys.
We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 1,110 fish and 3 kōura (18.2 kg in total) from 11 sites on 5 December 2017. The sites comprised 2,909 lineal m and 11,636 m2 in area. Kōura (freshwater crayfish) and 6 fish species were present, with common bully the most abundant species (up to 29.6 fish 100 m⁻² at the site 8, edge habitat). Goldfish (up to 14.2 100 m⁻²) was the next most abundant species, with most goldfish at sites 8 and 11 in and around the side channel. Common smelt were next the most abundant species (up to 11.4 fish 100 m⁻²). Mean density of bullies (7.8 fish 100 m⁻²) was much higher than for smelt (1.69 fish 100 m⁻²). Kōura had a patchy distribution with only 3 individuals were caught at two sites.
Comparing catches over the 11 years of sampling, the mean abundance of common bullies in 2017 was consistent with densities in most post-wall years (after 2007), but lower than in 2007 before wall closure (Newman-Keuls multiple range test, P = 0.034). The cause of fluctuating bully abundance is not known, and was not accounted for by changes in water clarity expressed as black disc distance (BDD), water temperature, or water conductivity. Poor water clarity can reduce the efficiency of electrofishing, but low BDD did not correspond with low common bully densities. In 2017, smelt abundance had recovered somewhat from the low catches from 2014 to 2016.
Goldfish biomass increased initially (2009-2010) because of targeted fishing in the side channel (site 11), which has dense macrophytes and offers good habitat for goldfish with no flow. However, the continued rise in goldfish density from 2012 on suggests a real increase in goldfish numbers. In contrast to most previous years, no eels were caught in 2017.
Analysis of fish densities before and after wall closure is hampered by the single data point before closure. However, we now have 10 years of post-wall data, and comparisons of means and standard deviations suggest that the number of bullies have been lower since 2008 with the exception of 2015, when bully densities were the same as 2007, i.e., before wall closure. The large number of small juvenile bullies (<30 mm) suggests that recruitment is taking place in the channel, so fluctuating bully abundance is likely to be controlled by factors other than wall closure.

text: Boat electrofishing survey of fish abundance in the Ohau Channel, Rotorua, in 2017 The aim of the survey was to provide on-going monitoring of the fish communities and abundance by boat electrofishing in the Ohau Channel, especially fish species that are taonga to Maori (tuna, or eels, morihana, or goldfish, and kōura, or freshwater crayfish). In the current study, we present the findings from the eleventh year of sampling (2017) and a summary of previous surveys.
We used the University of Waikato’s 4.5 m-long, aluminium-hulled electrofishing boat to catch a total of 1,110 fish and 3 kōura (18.2 kg in total) from 11 sites on 5 December 2017. The sites comprised 2,909 lineal m and 11,636 m2 in area. Kōura (freshwater crayfish) and 6 fish species were present, with common bully the most abundant species (up to 29.6 fish 100 m⁻² at the site 8, edge habitat). Goldfish (up to 14.2 100 m⁻²) was the next most abundant species, with most goldfish at sites 8 and 11 in and around the side channel. Common smelt were next the most abundant species (up to 11.4 fish 100 m⁻²). Mean density of bullies (7.8 fish 100 m⁻²) was much higher than for smelt (1.69 fish 100 m⁻²). Kōura had a patchy distribution with only 3 individuals were caught at two sites.
Comparing catches over the 11 years of sampling, the mean abundance of common bullies in 2017 was consistent with densities in most post-wall years (after 2007), but lower than in 2007 before wall closure (Newman-Keuls multiple range test, P = 0.034). The cause of fluctuating bully abundance is not known, and was not accounted for by changes in water clarity expressed as black disc distance (BDD), water temperature, or water conductivity. Poor water clarity can reduce the efficiency of electrofishing, but low BDD did not correspond with low common bully densities. In 2017, smelt abundance had recovered somewhat from the low catches from 2014 to 2016.
Goldfish biomass increased initially (2009-2010) because of targeted fishing in the side channel (site 11), which has dense macrophytes and offers good habitat for goldfish with no flow. However, the continued rise in goldfish density from 2012 on suggests a real increase in goldfish numbers. In contrast to most previous years, no eels were caught in 2017.
Analysis of fish densities before and after wall closure is hampered by the single data point before closure. However, we now have 10 years of post-wall data, and comparisons of means and standard deviations suggest that the number of bullies have been lower since 2008 with the exception of 2015, when bully densities were the same as 2007, i.e., before wall closure. The large number of small juvenile bullies (<30 mm) suggests that recruitment is taking place in the channel, so fluctuating bully abundance is likely to be controlled by factors other than wall closure.

year: 2018