In the digester example, what is the percent volatile solids (VS) used?

In the digester example, what is the percent volatile solids (VS) used?

• A. 74%
• B. 50%
• C. 85%
• D. 60%

Answer: (A)

Volatile solids tell you how much of the incoming solids are organic and degradable in the digester. When you do digestion calculations, you convert total solids (TS) to volatile solids (VS) by using the VS percentage. In the digester example, the feed has 74% volatile solids, so the amount of volatile solids entering the digester is TS_feed × 0.74. This VS amount is what drives digestion and methane production, because only that portion is biodegradable. The other numbers would imply different sludge composition and would change the calculated substrate available for digestion, which is why 74% is the value used in this example.

Volatile solids tell you how much of the incoming solids are organic and degradable in the digester. When you do digestion calculations, you convert total solids (TS) to volatile solids (VS) by using the VS percentage. In the digester example, the feed has 74% volatile solids, so the amount of volatile solids entering the digester is TS_feed × 0.74. This VS amount is what drives digestion and methane production, because only that portion is biodegradable. The other numbers would imply different sludge composition and would change the calculated substrate available for digestion, which is why 74% is the value used in this example.