You (can) measure how much feed you put into your reactor in terms of VS and COD. You (can) also measure how much methane you produce.

Thus you can calculate / know how much methane you produce per gVS or per g COD.

We know that 1 gram of COD can theoretically produce 350 mL methane (or to put it differently: the COD of methane is 64 gram oxygen per mol of methane, which is 22.4 L at standard temperature and pressure). Using this value you can calculate the efficiency with which the COD in the feed is converted into methane.

I am not sure what you are feeding your reactors, but if you additionally measure the concentration of volatile fatty acids (VFAs) in your reactors you can additionally calculate the fraction of the feed that is degraded/converted into VFAs (make sure that you take the VFAs in the feed into account when you do this). Using the theoretical COD of VFAs, you can now additionally calculate the fraction of COD in the feed that is hydrolysed (remember to also take methane into account in this calculation). Indeed, adding the COD of the VFAs formed and the COD of the methane formed, you can calculate the efficiency with which the COD in the substrate is degraded.

And by comparing the methane formed in the system with the methane formed in the BMP tests you evaluate how efficient your continuous system is in terms of methane recovery.

Doing all this you should be aware that some of the methane will leave your system via the water phase, so you should take this methane (production) also into account.

It goes without saying that all measurements and subsequent calculations are ultimately expressed per reactor and day; (feed in on a daily basis, methane and VFAs out on a daily basis).

Hope this helps.

Jan Dolfing Thank you for the detailed response. its quite clear and understandable. Could you kindly advise on how best to calculate the biodegradabilty/COD conversion per week instead of on daily basis? Do i use the average [gVS] fed in my reactor over the week, and subtract the average effluent [VS], i.e. ([VS]in - [VS]out)/[VS]in (all averages of a week)? [VS]out = particulate [VS] + soluble [VS]. I am measuring the effluent VS twice a week, but feeding every other day for 5 days.

Jan Dolfing

Thanks Pankaj Kumar