Calculate digester volatile solids reduction two ways.
Volatile Solids Reduction (Van Kleeck)
Formula
VSR = (VS in - VS out) / (VS in - VS in x VS out) x 100 (VS as fractions)
Inputs used
- Feed volatile solids (%)
- Digested volatile solids (%)
Worked example (White River WRRF, fictional)
- VSR = (0.791 - 0.630) / (0.791 - 0.791 x 0.630) x 100 = 55.0%
Volatile Solids Reduction (mass balance)
Formula
VSR = (VS in, lb/d - VS out, lb/d) / VS in, lb/d x 100
Inputs used
- Volatile solids fed (lb/d)
- Volatile solids leaving (lb/d)
Worked example (White River WRRF, fictional)
- Destroyed = 12,257 - 5,513 = 6,744 lb/d
- VSR = 6,744 / 12,257 x 100 = 55.0%
Tips
- Van Kleeck assumes fixed solids are conserved; grit and struvite can distort it.
Results are estimates for operator use. Check units and inputs, and confirm decisions with plant data and procedures.
This calculator also appears on ActivatedSludge.com, our consulting site. Results are for training and operator use; always follow your plant’s procedures.