Hi Mustapha,
You can calculate it theoretically. But first, you need to know the BOD concentration in the influent, or the BOD/COD ratio.. Because bacteria can only convert biological substrate to the biogas.
Our first reaction is: C6H12O6 + 6O2---> 6CO2 + 6H2O.. in this equation we can see that 180 g sugar (substrate) requires 192 g of O2 to be oxidized. This O2 is our theoretical COD(in your case BOD)..
The second reaction is: C6H12O6 ---> 3CH4 + 3CO2 (anaerobic rxn). Here we can see the same amount of substrate can produce 134.4 L biogas (or 67.2 L methane).. Therefore, we can say that; by the consumption of 192 grams of COD of the anaerobic system we can produce 134.4 L of biogas.. Which means each gram of COD you removed from the system, you can produce 0.7 L of biogas.
This is a theoretical and the MAXIMUMvalue you can reach under the normal pressure and temperature. The amount of (gram) biogas is the same under different temperatures and pressures. But its volume changes, and some people thinks they produced more :) Best of luck..
As Ms. Gorkem said, The theoretical estimation will give you how much maximum biogas you can produce from the influent BOD. You can also go for empirical relationships which have been developed either by pilot scale studies or by Plant scale studies. Good Luck
Based on CH4 only, the maximum theoretical production is 0,35L CH4/g COD at 0°C. It is difficult to estimate biogas (CH4+CO2) production because CO2 is soluble and converted to HCO3-, depending on the pH, which means that the CH4/CO2 ratio in the biogas is variable.
As Nicolas said, the best estimate is based on CH4 alone. Theoretical yield for methane on COD is well established. You can always confirm it using simple experimental apparatus with anaerobic sludge, substrate, thermal provision, some mixing and some time. If you want to measure simple CH4 you can intercept the gas line with a CO2 sorbent (e.g. a bubbler containing NaOH plus phenolphthalein)
Thank you very much for your answers. For Nicolas, I don't understand why measuring it at 0°C. There's an equation to estimate production of methane by Buswell and Muellepi (1952) : CnHaOb + (n − a/4 − b/2)H2O→ (n/2 + a/8 − b/4)CH4 + (n/2 − a/8 + b/4)CO2. and I calculate the BOD/COD ratio as Gorkem Akinci said. My question is this method possible to estimate CH4 produced?
You should not measure at 0°C but express the result, if you give a volume of biogas or methane, at 0°C because for a same mass of methane, the volume will depend on the temperature. The Buswell equation will give you a very optimistic methane estimation. It will tell you the maximum theoretical methane production you can get but the actual methane production can be much lower, including in a BMP test.
given a sample how do we know the BOD and COD data ?.....are there any specific experimental methods ?
what is the maximum percentage content of methane in biogas from anaerobic reactors..theoretical as well as experimental??
Jaswanth Chowdary you can check https://archive.epa.gov/water/archive/web/html/vms52.html for an explanation about measuring procedures.
Can we estimate the amount of biogas produced during AD process of cow manure from VS of cow manure?
- Badges
- Science topic
- Similar topics
- Correction