# What is the purpose of measuring both VS (volatile solid) and TS (total solid)?

In the biogas process you often measure Volatile solid and Total solids. Can any one explain these concepts more accurately and why it is interesting to look at these properties.

The biogas process I refer to is a process of fermenting waste food materials and slaugther house waste in to bio fuels, consisting largely of methane. The fermentation is conducted in anaerobic milieu in large plants.

Total solids and Volatile solid are measurements on the sludge the currently fermented waste,(the gooey stuff that is in the bio-reactor).

• Can you elaborate on what the "biogas process" is? – jonsca Oct 22 '12 at 23:03

## 3 Answers

Total solids (TS): The part of the sludge that remain after drying at 105$^{\circ}$C for 20 hours:

$$TS(\%) = \frac{\textrm{weight dried at } 105^{\circ}C}{\textrm{wet weight} }\times 100$$

Volatile solids (VS): The part of the sludge that is combusted at 550$^{\circ}$C after 2 hours:

$$VS(\% \textrm{ of TS}) = \frac{\textrm{dried weight at }105^{\circ}C - \textrm{dried weight at }550^{\circ}C}{\textrm{dried weight at }105^{\circ}C}\times100$$

For the definition, see Pelle's answer. For the reasons, both are easy and cheap to measure and can tell you a lot about your material if you have similiar mterial to compare. TS is often used to asses howa material can be handled (pumpable, stackable) In agricultural biogas applications for example, a sometimes used assumption is 1g COD = 1,6 g VS

In AD, VS is broadly associated with digestible biomass, and depending on input one third to one half of VS will be converted to gas. In fact, gas yields are often given per mass of VS because of this.

Note that solutes that are actually volatile, like alcohol, will be evaporated when testing for TS. Laso note that the points give na bove only work if you compare similiar materials.

VS and TS are very important parameter when it comes to Biogas production, in the following ways.

VS = Represent organic matter of the feedstock (excluding the inorganic salts, ash). Having in mind that bacterial action is on Organic mater and not Inorganic. meanwhile,

TS = Denote all the organic as well as inorganic matter in the feedstock.

Finally, VS/TS for different feedstocks can be model to give the biogas production.