Hi Simon and Nathan,
Thanks for your attention.
The article inspired me to test a more general idea of using temperature to monitor biological processes and use this information to quantify (biodegradable) organic load in wastewater.
Whitout to pump heat away from the sample.
A standard method for measuring the organic load in effluent is BOD (Biochemical Oxygen Demand) and is basically a measure cell respiration.
I did some work to automate respirometry measurement with Arduino and a commercial DO sensor. (http://www.c2o.pro.br/en/automation/x73.html)
My idea now is try to measure the heat dissipated by bacterial metabolic processes in an adiabatic environment using thermistors, and use this technique to estimate the organic load in wastewater.
Imagine keeping an aerated bioreactor containing bacteria fed by domestic effluents.
To make a measurement I take a sample of sludge from bioreactor and let some time only with aeration but no effluent to go into starvation state.
Imagine also two adiabatic cells (vial) (A and B), each with two thermistors mounted in a Wheatstone bridge.
_V+_
| |
R1 R2
| |
p1 p2
| |
R3 R4
| |
Gnd
R2 and R3 are installed in the reference cell B, and R1 and R4 in measurement cell A.
In compartment A I add a sample of starved sludge diluted with the effluent to be analyzed.
In compartment B (reference) I put the same starved sludge volume but diluted only with water.
Note: It is important that the sludge, the test effluent and water, are all at the same initial temperature.
It would be possible to amplify, with an OpAmp circuit, the voltage difference between p1 and p2, and measure this value with an Arduino?
The measurement time interval should be standardized and temperature variations should be initially calibrated with samples of known nutrient concentration.
Would bo possible detect temperature variations under these conditions with conventional thermistors?
What do you think about this idea?
At the moment I am dedicating to a project with LEDs. But I intend to explore the possibilities of (bio)thermal measurements in the future.
Thanks for the comments.
Markos
The article inspired me to test a more general idea of using temperature to monitor biological processes and use this information to quantify (biodegradable) organic load in wastewater.
Whitout to pump heat away from the sample.
A standard method for measuring the organic load in effluent is BOD (Biochemical Oxygen Demand) and is basically a measure cell respiration.
I did some work to automate respirometry measurement with Arduino and a commercial DO sensor. (http://www.c2o.pro.br/en/automation/x73.html)
My idea now is try to measure the heat dissipated by bacterial metabolic processes in an adiabatic environment using thermistors, and use this technique to estimate the organic load in wastewater.
Imagine keeping an aerated bioreactor containing bacteria fed by domestic effluents.
To make a measurement I take a sample of sludge from bioreactor and let some time only with aeration but no effluent to go into starvation state.
Imagine also two adiabatic cells (vial) (A and B), each with two thermistors mounted in a Wheatstone bridge.
_V+_
| |
R1 R2
| |
p1 p2
| |
R3 R4
| |
Gnd
R2 and R3 are installed in the reference cell B, and R1 and R4 in measurement cell A.
In compartment A I add a sample of starved sludge diluted with the effluent to be analyzed.
In compartment B (reference) I put the same starved sludge volume but diluted only with water.
Note: It is important that the sludge, the test effluent and water, are all at the same initial temperature.
It would be possible to amplify, with an OpAmp circuit, the voltage difference between p1 and p2, and measure this value with an Arduino?
The measurement time interval should be standardized and temperature variations should be initially calibrated with samples of known nutrient concentration.
Would bo possible detect temperature variations under these conditions with conventional thermistors?
What do you think about this idea?
At the moment I am dedicating to a project with LEDs. But I intend to explore the possibilities of (bio)thermal measurements in the future.
Thanks for the comments.
Markos
On 14-04-2015 17:03, Simon Quellen Field wrote:
The instrument they use is described here:
The specs are pretty impressive to a DIY hacker: The TAM48 keeps the temperature constant to within 0.0001 degrees Celsius. That might be a little hard to do with a thermistor and an Arduino.
They use thermoelectric modules (that sounds like the Peltier coolers used for cooling CPU chips, but presumably much smaller. Maybe we could take apart a CPU cooler and remove just one of the dozens of Peltier junctions in it and reconnect the junction to new leads.)
One side of the thermoelectric module is attached to a heat sink in a thermostat (a water bath? Mercury bath?) that has that 0.0001 degree Celsius spec. But because they expect the thermostat to have some variation, they use two thermoelectric modules -- one for the sample ampoule, and a second for a reference (say pure water or sand, to match the heat capacity of the sample) ampoule. Then they monitor the difference between the two.
The "isothermal" part of the name comes from the way they use the thermoelectric modules to pump heat away from the sample to keep the temperature constant. They measure the heat flow by monitoring how much power is required to keep the temperature constant.
Building a DIY version sounds like great project. You could tell if you were on the right track by using the same potassium carbonate / hydrochloric acid reaction they use to characterize the professional devices. Operational amplifiers can be used to amplify the tiny voltage differences between the sensors. The results could then be sent to a 16 bit A/D converter for monitoring by the microcontroller, which could then use a DAC going to the thermoelectric modules to offset the heat flow.
--
On Tue, Apr 14, 2015 at 12:02 PM, Markos <markos@c2o.pro.br> wrote:
Hi,
I've been thinking to experiment common temperature sensors (Eg: NTC) to measure microbial activity.
And today I found this paper:
http://blogs.nature.com/spoonful/2011/08/researchers_measure_bacterias.html
Would be possible to use a NTC thermistor, and Arduino for data acquisition, for detecting temperature changes in a medium containing bacteria and nutrients in a DIY approach?
Has anyone had any practical experience with this technique?
Thanks,
Markos
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