Saadia Meraj: According to my opiniojn the best would be determination of volatile soilids before an afterd anaerobic digestion. If you substrct the concentration of volatile solids afte anaerobic digestion from the concentration of volatile solids before anaerobic digestion, you will obtain reduction duirng anaerobic digestion.

Best regards Vit

Solids remaining after evaporation or filtration are dried, weighed, and then ignited. The loss of weight by ignition at 600°C is a measure of the volatile solids, which are classed as organic material. The remaining solids are the fixed solids, which are considered as inorganic (mineral) matter.

%volatile solids reduction = {(in - out)/ (in- [in-out])}*100%, where in, initial weight of VS; out, final weight of VS after anaerobic digestion.

Its quite simple process. Kindly follow the youtube video below and the standard methods provided in the pdf file attached

https://www.youtube.com/watch?v=OKWNgaN12cc

St. Methods 2540 Α, Β, C, D (22nd Ed.2012)

this is another related question.

Total Volatile Solids Reduction Efficiency (TVSMRE) is calculated as (find attached file). the question is how do you find Biogas Dry Factor (BDF)?