Dear Tomaž,

Yes, it is possible. Please read the following text:

The Chemical Oxygen Demand (COD) is used to quantify the amount of organic matter in waste streams and predict the potential for biogas production.

The oxygen equivalent of organic matter that can be oxidized, is measured using a strong chemical oxidizing agent in an acidic medium. During anaerobic digestion the biodegradable COD present in organic material is preserved in the end products, namely methane and the newly formed bacterial mass. In case an organic compound (CnHaObNd) is completely biodegradable and would be completely

converted by the anaerobic organism (sludge yield is assumed to be zero) into CH4, CO2 and NH3, the theoretical amount of the gases produced can be calculated according to the Buswell equation (1):

CnHaObNd + (n-a/4 - b/2 +3d/4) H2O → (n/2 +a/8 -b/4 -3d/8) CH4 + (n/2-/8+b/4+3d/8) CO2 + dNH3                                                       (equation 1)

The quantity of CO2 present in the biogas generally is significantly lower than follows from the Buswell equation. This is because of a relatively high solubility of CO2 in water and part of the CO2 may become chemically bound in the water phase.

Another widely used parameter of organic pollution is the Biological Oxygen Demand (BOD). This method involves the measurement of dissolved oxygen used by aerobic microorganisms in biochemical oxidation of organic matter during

5 days at 20 °C. A very useful parameter to evaluate substrates for anaerobic digestion is the anaerobic biodegradability and hydrolysis constant. The total anaerobic biodegradability is measured by the total amount of methane produced during a retention time of at least 50 days. The gas yield depends on factors such as digestibility of the organic matter, digestion kinetics, the retention time in the digester and the digestion temperature. By controlling conditions such as

temperature, humidity, microbial activity and waste properties, the process can be optimized.

For more on this topic, please see attached file:

http://www.sswm.info/sites/default/files/reference_attachments/MES%202003%20Chapter%204.%20Methane%20production%20by%20anaerobic%20digestion%20of%20wastewater%20and%20solid%20wastes.pdf

Hoping this will be helpful,

Rafik

The reference value is 0.35 m3 methane/kg of COD which is a theoretical value (STP).

CH4 + 2O2 --> CO2 + 2H2O

m(CH4) = 16 g

m (2O2) = 64 g

COD (CH4) = 16 g CH4 / 64 g O2 = 4 g COD

As 1 mole of gas = 22.4 L (STP)

ρ(CH4) = 16g / 22.4 L = 0.71 g/L and 1 g of CH4 occupies (STP)

V(CH4) = 22.4 / 16 = 1.4 L CH4

To summarize, 1 g of CH4 is 4 g of COD and occupies 1.4 L CH4 (STP)

therefore, 1.4 L CH4/4g COD = 0.35 m3 CH4 / kg COD

The COD in this calculation is assumed biodgradable or BOD/COD ratio is equal to 1

Dear Tomaz,

Calculation principle

• The principle of the calculation is to consider that a molecule

glucose give 3 moles of methane and 3 moles of gas

carbonic

• The glucose is 192 g COD and so this gives 6

moles of gas at 50% CH4

• We apply the ideal gas equation (PV = nRT)

• This gives 0.789 liters of biogas per gram of COD

(Measured at 35 ° C)

• Here we do not consider COD (biomass).

Generally it takes 5% of the COD for growth microorganisms

 C6 H12 O6 ----3 CH4 + 3 CO2

C6 H12 O6 + 6 O2----- 6CO2 + 6 H2O

192 g COD for 180 g glucose

6 moles of biogas at 50% CH4 and CO2

PV (l.atm) = nRT (n = 6, R = 0.082, T = 308 at 35 ° C)

151.53 l Biogas for 192 g COD

Thus, 0.789 l of biogas / g COD  (At 35 ° C.)

With my best regards

Prof. Bachir ACHOUR

yes it is possible

Yes, but is important to analyse the kind of substrate.

COD and BOD are an organic carbon stimative and the result can represent different bioavabilite.

I suggest a first comparison with COD and BMP test for each substrate.

Hello, can anyone please tell me how to calculate coefficients using elements analysis result of random element in buswell equation for finding out theoretical yield of methane.