If you can take out liquid sample from the batch reactor in VFA measuring syringe, You can perform its VFA profile analysis in a GC machine equipped with Flame ionized detector (FID) column on a regular interval.

Alternatively, u may perform titration of your sample after filtering it through cheese cloth on alternate days.

In this way u can monitor the VFA

1. Monitor the pH

2. Analysis of VFA can be done by the HPLC-UV method.

Thanks for your valuable suggestions.

Titration with a basic solution followed by distillation is the conventional way to measure total VFA found in your sample. However, you will not have a chance to identify the components of VFAs. Besides, from my experience, it is a bit tricky to get consistent resulst with the conventional distillation method. However, in case of you have only this option, you should check the APHA Standard Methods for the Examination of Water and Wastewater book. There is a section about that method.

As previosly mentioned above, you can detect by GC-FID or HPLC-UV systems. If you don't have an access to those systems, but have a GC-MS with polar column. There is also a solvent extraction method for VFA measurement by GC-MS.

Look at this in case if you are interested in: "M. Ghidotti, D. Fabbri, C. Torri, and S. Piccinini, “Determination of volatile fatty acids in digestate by solvent extraction with dimethyl carbonate and gas chromatography-mass spectrometry,” Anal. Chim. Acta, vol. 1034, pp. 92–101, Nov. 2018, doi: 10.1016/j.aca.2018.06.082."

Thanks for your kind suggestions.