The methodology for assessing “volatile solids” is easy, fast and cheap compared to options such as COD (chemical oxygen demand) and BOD (biological…). Therefore, it is a very convenient approach to assess organics in a sample.  If this organics comes from the “feed” or “influent” you will assume that it refers to “substrate”. However, if you sample comes from inside of the reactor, you will assume that the SV values will reflect “microbial density”.

Is it true? Nope, but it is a very good reactor operating tool.

If you really want to asses susbrate and microorganisms you would need more specific methodology, which, apart from being very expensive, they have longer delay for producing the needed result…

thank you sir. it is really useful information.

I concur with the above answer. Note that using volatile solids avoids the confounding effects of variable ash content (fixed solids) in the substrate and/or reactor inoculum.