Precipitation

[AQ_ARQUA]

Hi All

We're seeing a rise in volume of about 10% prior to bubbles precipitating.  We figure that there must be surface tension between the gas and the microbes and that before bubbles form, the gas needs to progressively bind with like before becoming buoyant. Hydro-static pressure would further reduce bubble volume and buoyancy, so trapping gas and increasing volume.  

Agitation has been explained in terms of mixing food with microbes, yet are there any guides on agitation to release gas and reducing volume expansion?

Do ya best.  

Richard Brew

0433 633 712

[Dylan Thorpe]

You might try gas agitation by pumping some biogas through the reactor working volume. What works best will likely depend on the characteristics of your system, can you give a few more details on your setup?

Thanks,

Dylan

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[AQ_ARQUA]

Hi Daryl

It's a micro scale reactor. Static without the benefit of energy input.  We're looking for a study that identifies something that must be true of all digestions i.e. Volume at start up is x, after one week it is x +% when compared to agitation with bubbles; XXX and siring with an impeller  DC motor; XXX  and in centrifuge: XXXX....our study finds that digestion processes increases volume by x varying with in-fluent type Z and stirring decreases volume by X%/m3.   We conclude that a healthy diet and exercise reduces abdominal bloating.  

Do ya best!

Rich brew

[Paul Harris]

G'day Rich,

You must be a scientist! As an engineer I suspect that the main volume change may be thermal expansion (unless you are adding material) as the mass transfer is negative (gas leaves the digester - only a small mass though!). It is true that some microbes are growing, but that is at the expense of other organic material and any density change would be only small (except for gas micro-bubbles) as the main constituent is water. I think you are really trying to measure "second/third order" events.

I like your conclusion! Please post the reply you are replying to if it does not come through the list.

All the best,
HOOROO

Mr Paul Harris BEng (Ag) (Melbourne)
Visitor at The University of Adelaide

On 12/02/2013 9:23 AM, AQ_ARQUA wrote:

[ric...@arqua.com.au]

Thanks Paul

I think that explains it.  I’m still seeing levels fall as stirring starts. How’s my conclusion this time?

 

As temperature increases so does the tank fluid level and tank pressure, and in an unstirred tank the temperature gradient in the tank varies with depth meaning that warmer swimming layers at the top may be expanding while the lower layers remain constant.  

 

The thermal expansion coefficient is curved, increasing with temperature, so stirring harmonises the thermal layers, averages temperatures and reduces volume. The total average volume increase is less than that of the same fluid column with thermal layers. 

 

Under average operating conditions levels may be seen to drop as agitation starts.

 

Pressure at the base of the tank reduces marginally in line with falling levels, and some bubbles are observed, other than those explained by direct agitation, yet having negligible net effect on volume.

 

Conclusion: Stirring the ocean may lower sea levels.

 

Enjoy!

 

  Richard Brew       Director  AQ I  B.Arch Dip. Q.A. Accredited ACAA 173  I  M. 0433 633 712 

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