You can select for VFA production almost without methane production by operating the digester at a low substrate retention time (2-5 days depending on substrate and temperature). The mechanism is that the methane producing bacteria are slow growing and some VFA producing bacteria grow fast.

Adding also recycling system to your liquid waste then avoid methan producing.

Hi there,

Check the attached article.

So basically, if you have metanogenic biofilms is difficult to prevent the methane production. The other alternative is to work in continuous, with high loading rate, in order to break the biofilms, and pH around 5. That will promote the washing of the methanogenic archea. Other approaches are the use of high temperature to kill the methanogenic archea, or use of air.

These are explained in more detail in the attached article.

Cheers,

Any organic mass/slurry to be fermented anaerobically pass four fermentation stages but all the time methane is generated in the last stage, after VFA will have been generated before. In fact it is much easier to not reach methane since methanogenic species are very sensitive to the enviornment conditions and much slowly growing than those making VFA. The simplest way to avoid methane is to keep high acidity, pH

Please refer to:-

Article Anaerobic digestion of food waste for volatile fatty acids (...

http://www.tandfonline.com/doi/abs/10.1080/09593330.2015.1041426?journalCode=tent20

Regards

I am not real clear as to why producing VFA's in an AD reactor makes any sense. While it can be done by keeping the pH below 6, the economics of extraction are just not there to make the process attractive. Please let me know what I am missing is this area. Thanks.

Dear Prof. Henrik Rasmus Andersen ,

Thank you for your valuable comment.

Dear prof. Edward Calt ,

Thank you for your answer.

which process will be good, you think aerobic process will be more beneficial for VFA production? can you clear please?

Dear Prof. Nabeel Hameed Al-Saati ,

Thank you

Dear Prof. Carmen Mateescu

Thank you for such an explanatory answer.

Dear Prof. Juan-Rodrigo Bastidas-Oyanedel

Thank you, for your detailed review article, this was very informative.

Dear Prof. Jan B. A. Arends ,

Thank you for your detail explanation and links.

VFA's are a bulk commodity readily available. What is the process you would be using to do the extraction? All of the methods (ion resin based) we tried fouled with the residual proteins.

Also, what is your feed stock? There are 3 other issues I have with AD. First, what does one do with the digestate from the process? In an urban environment the economics of transporting the digestate back to the rural farms is prohibitive. Second, is the cycle time for the process.... from an economic stand point, it is way to long. Finally, is the through put for the process.... the best numbers I have found are 6 kg per cubic meter of reactor per day.... this means a large volume is required to be efficient and a large capital expense.