Dear Waleed,

Stoichiometric model parameters such as yield Y depend on the kind of microbes, on the kind of substrate and on the microbial conversion process but are not dependent on temperature. Typical values for activated sludge in municipal sewage at neutral pH on soluble substrate are 0.67/d for YH (heterotrophs) and 0.24/d for YH (autotrotrophs ), (d = day = 24 h).

Instead, kinetic parameters such as growth rate and decay rate Kd (referred in ASM1-3 as bH for heterotrophs and bA for autotrophs) are strongly depend on temperature. This temperature dependency can be modeled by the modified Arrhenius equation. Typical values for bH in municipal sewage at neutral pH are 0.62/d at 20 °C and 0.2/d at 10 °C.

Bruno is right, as yield coefficients are a stoichiometric constants that are not affected by temperature. Numbers given by Bruno are expressed as gCODbiomass/gCODremoved, and you may convert them into gVSS/gCODremoved by dividing by 1.42 gCOD/gVSS (valid for conventional activated sludge).

As for the decay coefficients for heterotrophs (bH) and autotrphic nitrifiers (bA), Metcalf & Eddy (ISBN-13: 978-0073401188, Md Graw Hill publishers) suggest an Arrhenius-type dependency that is the same for both bH and ba:

b(T)/b(20°C) = KT^(T-20)  with KT varying in the range 1,03 to 1,08 and a typical value of 1,04 (dimensionless).

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Roberto, Thank you for your further elaboration as well as for correcting my mistake in the Y (yield) unit. Yield coefficients YH and YA are of course expressed in mass/mass (as COD).

Dear Bruno

Dear Roberto

Thank you for your useful comments

I agree with you in all that you said on the subject

But I see the subject from other point of view

In activated sludge units that I mentioned, which contain a mixture of microorganisms that work within intermediate temperatures (mesophilic microorganisms), and as you know that the microorganisms increase its activity with increasing temperature within a certain range, So my question on this point, is there are studies to determine the effect of increasing the activity of microorganisms with increasing temperature within this certain range on the value of the production plants?

Dear Waleed,

I am not aware of specific studies focusing only on the effect of temperature on the biological treatment.

However we include this temperature influence in our model based design and operation of both advanced activated sludge (AAS) based and high-rate anaerobic digestion (HRAD, mesophilic and thermophilic) based biological wastewater treatment plants. For AS and AAS, a higher wastewater temperature results in smaller basins (HRT) and less waste sludge (WAS) due to the faster kinetics (growth and decay) but also in a higher fraction of recalcitrant natural organic matter (NOM) in the clarified effluent resulting from this increased microbial decay.

I fully agree with Roberto

Dear Waleed

I did some experiments on a denitrifying biofilm in a dynasand bed, and on nitryfying biomass in moving-bed biofilm reactors, and I also found some Arrhenius-like relationships between activity and temperature.

Howewer, you should distinguish between short-term temperature effects  (which are stronger, as there is a shock on the enzymatic system of bacteria) from long-term dependency (e.g.: summer/winter) as it allows adaptation and acclimation of the biomass consortium and where the balance between mesophilic/psycrophilic organisms adapt according to the environmental conditions.

I hope these hints can help you.

Pastorelli G., Andreottola G., Canziani R., Darriulat C, E. de Fraja Frangipane, Rozzi A. (1997). Organic Carbon and Nitrogen removal in moving-bed biofilm reactors, Water Science and Technology, vol. 35, n. 6, pp. 91 - 99.

Pastorelli G., Andreottola G., Canziani R., de Fraja Frangipane E., De Pascalis F., Gurrieri G., Rozzi A. (1997). Pilot-Plant Experiences with Moving-Bed Biofilm Reactors, Water Science and Technology, vol. 36, n. 1, pp. 43-50.

Bonomo L., Canziani R. (1998). Denitrification of a textile effluent in a dynamic sand-bed filter. Water Science and Technology, vol. 38, n. 1, pp. 123 -132.

Canziani R., Vismara R., Basilico D., Zinni L. (1999). Nitrogen removal in fixed-bed submerged biofilters without back-washing, Water Science and Technology, vol. 40, n. 5-6, pp.145-152.

Thank you for all,  this discussion is valuable and very helpful to me.

best regards

Randa

The growth yield is indirectly dependent on temperature through the maximum uptake rate which is temperature dependent, so is there any explanation on this? Most of you are saying it is independent of temperature how is that ?

Dear Kulthoum Ismail,

There seems to be some confusion. As already discussed, yield Y is a stoechiometric coefficient expressed as mass/mass and hence independent of temperature.

Maximum specific growth rate µmax and decay rate b are RATE coefficients expressed as 1/time which strongly depend on temperature.

The maximum (substrate) uptake rate which equals µmax/Y when b = 0, is then in the same way as µmax depending on temperature.

I hope this clarifies this issue.

Further to my previous reply, I would like to add that often the yield Y as used in the Monod model is confused with the "observed yield" Yobs as used in practice. This Yobs depends also on the temperature dependent decay rate kd [1/d] and on the solids residence time SRT [d] as follows: Yobs = Y / (1 + kd * SRT).

Waleed M. Sh. Alabdraba when we are talkking about the temperature effect and yeidl I can say that Increased temperatures from 10 C to 30 C result in a decrease in specific resistance to filtration, as well as an increase in sludge production and the removal of phosphate. At higher temperatures and lower loadings, the sludges are more resistant to bulking.