I have performed anaerobic digestion in a batch reactor and I want to calculate food to microorganism ratio for the same. Reactor has working volume of 100 ml.
There is a biomass yied, YXS (kg/kg) or yXS (Cmol/Cmol). Its value for given microorganism and nutrient (substrate) is usually determined experimentally. You can also look in the scientific iterature. The type of bioreactor does not affect its. Regards,
Dear Nishat,
There is a rich consortium of anaerobic bacteria which decompose the organic matter, but the methabolic ways that bacteria use for making methane are not totally elucidated, neither in full agreement amongst scientists. Different bacteria use different organic compounds as energy source (formate, acetate, methanol, methylamine, etc.). Hence it is not possible to calculate food to microorganisms ratio but it is assumed (based on many experimental works) that an optimal biogas yield could be obtained for an organic substrate to inoculum (food to microorganisms) ratio of 1:2 to 1:4. This means in average that 1 kg of dry organic matter generates ca. 250 l biogas but a precise calculation based on individual bacteria metabolic activity can not be achieved. Certainly a higher inoculum part will lead to a better methane production but this is a good solution only for lab research while it is not economic in case of industrial applications, rising a lot the investment and operational costs.
For your lab experiments in 100 ml working volume you may try to find the optimal ratio for your substrate by carrying out experiments for ratio 2, 1, 0.5, 0.25 etc. The substrate to inoculum ratio depends very much on the feedstock.
Your question can also be understood differently, for example, that you mean changes in time. Then mass balances for biomass and substrate should be used, but then the equation of specific growth rate is necessary. Regards,
Dear Nishat,
I have a difficulty to interpret your question, because there is an ambiguity in it. Therefore, I would guess what you mean.
Food (substrate) to microbes (inoculum) ratio is obtained from comparing the amount of food (substrate) to the amount of microbes (inoculum). The comparison can be done in volume (ml), total solid mass (g TS), volatile solid mass (g VS), or other measures, depend on parameters of interest.
The most easy ratio to be made is 1:1, although the choice highly depends on your research objectives.
In food-to-microbes ratio of 1:1 by volume, then you need to put 50 ml of microbes and 50 ml of food or = 100 ml/(1+1).
If you choose food-to-microbes ratio of a:b then you need to put a/(a+b) x 100 ml of food, and b/(a+b) × 100 ml of microbes.
Hope this is helpful. Good luck!
Dear Nishat,
Mass balance and kinetic equations can be used for this purpose.
Regards
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